Precision, Single Supply Op Amp
PDF, 358 Kb, Language: en, File published: Jul 16, 2005, Pages: 12
Application Note 101. Linear regulators are commonly employed to post-regulate switching regulator outputs. Benefits include improved stability, accuracy, transient response and lowered output impedance. Ideally, these performance gains would be accompanied by markedly reduced switching regulator generated ripple and spikes. In practice, all linear regulators encounter some difficulty with ripple and spikes, particularly as frequency rises. This publication explains the causes of linear regulators' dynamic limitations and presents board level techniques for improving ripple and spike rejection. A hardware based ripple/spike simulator is presented, enabling rapid breadboard testing under various conditions. Three appendices review ferrite beads, inductor based filters and probing practice for wideband, sub-millivolt signals.
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Application Note 101
July 2005
Minimizing Switching Regulator Residue
in Linear Regulator Outputs
Banishing Those Accursed Spikes
Jim Williams
INTRODUCTION
Linear regulators are commonly employed to post-regulate
switching regulator outputs. Benefits include improved
stability, accuracy, transient response and lowered output
impedance. Ideally, these performance gains would be
accompanied by markedly reduced switching regulator
generated ripple and spikes. In practice, all linear regulators
encounter some difficulty with ripple and spikes, particularly as frequency rises. This effect is magnified at small
regulator VIN to VOUT differential voltages; unfortunate,
because such small differentials are desirable to maintain
efficiency. Figure 1 shows a conceptual linear regulator
and associated components driven from a switching
regulator output.
The input filter capacitor is intended to smooth the ripple and
spikes before they reach the regulator. The output capacitor maintains low output impedance at higher frequencies,
improves load transient response and supplies frequency
compensation for some regulators. Ancillary purposes include noise reduction and minimization of residual inputderived artifacts appearing at the regulators output. It is
…
PDF, 2.6 Mb, File published: Mar 28, 2008
Photomultipliers (PMT), avalanche photodiodes (APD), ultrasonic transducers, capacitance microphones, radiation detectors and similar devices require high voltage, low current bias. Additionally, the high voltage must be pristinely free of noise; well under a millivolt is a common requirement with a few hundred microvolts sometimes necessary. Normally, switching regulator configurations cannot achieve this performance level without employing special techniques. One aid to achieving low noise is that load currents rarely exceed 5mA. This freedom permits output filtering methods that are usually impractical.
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Application Note 118
March 2008
High Voltage, Low Noise, DC/DC Converters
A Kilovolt with 100 Microvolts of Noise
Jim Williams This publication describes a variety of circuits featuring
outputs from 200V to 1000V with output noise below 100ВµV
measured in a 100MHz bandwidth. Special techniques
enable this performance, most notably power stages
optimized to minimize high frequency harmonic content.
Although sophisticated, all examples presented utilize
standard, commercially available magnetics—no custom
components are required. This provision is intended to
assist the user in quickly arriving at a produceable design.
Circuits and their descriptions are presented beginning
with the next ink.
BEFORE PROCEEDING ANY FURTHER, THE READER
IS WARNED THAT CAUTION MUST BE USED IN THE
CONSTRUCTION, TESTING AND USE OF THE TEXT’S
CIRCUITS. HIGH VOLTAGE, LETHAL POTENTIALS ARE
PRESENT IN THESE CIRCUITS. EXTREME CAUTION
MUST BE USED IN WORKING WITH, AND MAKING
CONNECTIONS TO, THESE CIRCUITS. REPEAT: THESE
CIRCUITS CONTAIN DANGEROUS, HIGH VOLTAGE …
PDF, 2.2 Mb, File published: Apr 1, 1987
Low power operation of electronic apparatus has become increasingly desirable. AN23 describes a variety of low power circuits for transducer signal conditioning. Also included are designs for data converters and switching regulators. Three appended sections discuss guidelines for micropower design, strobed power operation and effects of test equipment on micropower circuits.
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Application Note 23
April 1987
Micropower Circuits for Signal Conditioning
Jim Williams
Low power operation of electronic apparatus has become
increasingly desirable. Medical, remote data acquisition,
power monitoring and other applications are good candidates for battery driven, low power operation. Micropower
analog circuits for transducer-based signal conditioning
present a special class of problems. Although micropower
ICs are available, the interconnection of these devices to
form a functioning micropower circuit requires care. (See
Box Sections, “Some Guidelines for Micropower Design
and an Example” and “Parasitic Effects of Test Equipment
on Micropower Circuits.”) In particular, trade-offs between
signal levels and power dissipation become painful when
performance in the 10-bit to 12-bit area is desirable. Additionally, many transducers and analog signals produce +V inherently small outputs, making micropower requirements complicate an already difficult situation. Despite the
problems, design of such circuits is possible by combining
high performance micropower ICs with appropriate circuit
techniques.
Platinum RTD Signal Conditioner
Figure 1 shows a simple circuit for signal conditioning
a platinum RTD. Correction for the platinum sensor’s
nonlinear response is included. Accuracy is 0.25В°C over …
PDF, 359 Kb, File published: Sep 2, 1987
Subtitled "A Gentle Guide for the Trepidatious," this is a tutorial on switching regulator design. The text assumes no switching regulator design experience, contains no equations, and requires no inductor construction to build the circuits described. Designs detailed include flyback, isolated telecom, off-line, and others. Appended sections cover component considerations, measurement techniques and steps involved in developing a working circuit.
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Application Note 25
September 1987 Switching Regulators for Poets
A Gentle Guide for the Trepidatious
Jim Williams
The above title is not happenstance and was arrived at after
considerable deliberation. As a linear IC manufacturer, it is
our goal to encourage users to design and build switching
regulators. A problem is that while everyone agrees that
working switching regulators are a good thing, everyone
also agrees that they are difficult to get working. Switching
regulators, with their high efficiency and small size, are
increasingly desirable as overall package sizes shrink.
Unfortunately, switching regulators are also one of the
most difficult linear circuits to design. Mysterious modes,
sudden, seemingly inexplicable failures, peculiar regulation characteristics and just plain explosions are common
occurrences. Diodes conduct the wrong way. Things get
hot that shouldn’t. Capacitors act like resistors, fuses
don’t blow and transistors do. The output is at ground, and
the ground terminal shows volts of noise.
Added to this poisonous brew is the regulator’s feedback
loop, sampled in nature and replete with uncertain phase
shifts. Everything, of course, varies with line and load
conditions— and the time of day, or so it seems. In the face …
PDF, 988 Kb, File published: Feb 1, 1988
Considerations for thermocouple-based temperature measurement are discussed. A tutorial on temperature sensors summarizes performance of various types, establishing a perspective on thermocouples. Thermocouples are then focused on. Included are sections covering cold-junction compensation, amplifier selection, differential/isolation techniques, protection, and linearization. Complete schematics are given for all circuits. Processor- based linearization is also presented with the necessary software detailed.
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Application Note 28
February 1988
Thermocouple Measurement
Jim Williams
Introduction Thermocouples in Perspective In 1822, Thomas Seebeck, an Estonian physician, accidentally joined semicircular pieces of bismuth and copper
(Figure 1) while studying thermal effects on galvanic arrangements. A nearby compass indicated a magnetic disturbance. Seebeck experimented repeatedly with different
metal combinations at various temperatures, noting relative
magnetic п¬Ѓeld strengths. Curiously, he did not believe that
electric current was flowing, and preferred to describe the
effect as “thermo-magnetism.” He published his results in
a paper, “Magnetische Polarisation der Metalle und Erze
durch Temperatur-Differenz” (see references). Temperature is easily the most commonly measured
physical parameter. A number of transducers serve temperature measuring needs and each has advantages and
considerations. Before discussing thermocouple-based
measurement it is worthwhile putting these sensors in
perspective. Figure 2’s chart shows some common contact
temperature sensors and lists characteristics. Study reveals
thermocouple strengths and weaknesses compared to
other sensors. In general, thermocouples are inexpensive,
wide range sensors. Their small size makes them fast and
their low output impedance is a benefit. The inherent voltage output eliminates the need for excitation. Subsequent investigation has shown the “Seebeck Effect”
to be fundamentally electrical in nature, repeatable, and
quite useful. Thermocouples, by far the most common …
PDF, 1.2 Mb, File published: Oct 1, 1988
This note examines a wide range of DC/DC converter applications. Single inductor, transformer, and switched-capacitor converter designs are shown. Special topics like low noise, high efficiency, low quiescent current, high voltage, and wide-input voltage range converters are covered. Appended sections explain some fundamental properties of different types of converters.
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Application Note 29
October 1988
Some Thoughts on DC/DC Converters
Jim Williams and Brian Huffman
INTRODUCTION
Many systems require that the primary source of DC power
be converted to other voltages. Battery driven circuitry is
an obvious candidate. The 6V or 12V cell in a laptop computer must be converted to different potentials needed for
memory, disc drives, display and operating logic. In theory,
AC line powered systems should not need DC/DC converters
because the implied power transformer can be equipped
with multiple secondaries. In practice, economics, noise
requirements, supply bus distribution problems and other
constraints often make DC/DC conversion preferable. A
common example is logic dominated, 5V powered systems
utilizing В±15V driven analog components.
The range of applications for DC/DC converters is large,
with many variations. Interest in converters is commensurately quite high. Increased use of single supply powered
systems, stiffening performance requirements and battery
operation have increased converter usage.
Historically, efficiency and size have received heavy emphasis. In fact, these parameters can be significant, but
often are of secondary importance. A possible reason
behind the continued and overwhelming attention to size …
PDF, 606 Kb, File published: Feb 1, 1989
Switching regulators are of universal interest. Linear Technology has made a major effort to address this topic. A catalog of circuits has been compiled so that a design engineer can swiftly determine which converter type is best. This catalog serves as a visual index to be browsed through for a specific or general interest.
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Application Note 30
February 1989
Switching Regulator Circuit Collection
John Seago
Switching regulators are of universal interest. Linear
Technology has made a major effort to address this topic.
A catalog of circuits has been compiled so that a design
engineer can swiftly determine which converter type is
best. This catalog serves as a visual index to be browsed
through for a specific or general interest. The catalog is organized so that converter topologies can
be easily found. There are 12 basic circuit categories:
Battery, Boost, Buck, Buck-Boost, Flyback, Forward, High
Voltage, Multioutput, Off Line, Preregulator, Switched
Capacitor and Telecom. Additional circuit information can
be located in the references listed in the index. The
reference works as follows, i.e., AN8, Page 2 = Application
Note 8, Page 2; LTC1044 DS = LTC1044 data sheet;
DN17 = Design Note 17. DRAWING INDEX
FIGURE TITLE FIGURE # PAGE REFERENCE/SOURCE Battery
2A Converter with 150ВµA Quiescent Current (6V to 12V)
200mA Output Converter (1.5V to 5V)
Up Converter (6V to 15V)
Regulated Up Converter (5V to 10V) …
PDF, 1.5 Mb, File published: Feb 2, 1989
Subtitled "Some Affable Analogs for Digital Devotees," discusses a number of analog circuits useful in predominantly digital systems. VPP generators for flash memories receive extensive treatment. Other examples include a current loop transmitter, dropout detectors, power management circuits, and clocks.
PDF, 361 Kb, File published: Feb 1, 1990
Safe, fast charging of NiCad batteries is attractive in many applications. This note details simple, thermally-based fast charge circuitry for NiCads. Performance data is summarized and compared to other charging methods.
PDF, 3.8 Mb, File published: Jun 1, 1990
Subtitled "Marrying Gain and Balance," this note covers signal conditioning circuits for various types of bridges. Included are transducer bridges, AC bridges, Wien bridge oscillators, Schottky bridges, and others. Special attention is given to amplifier selection criteria. Appended sections cover strain gauge transducers, understanding distortion measurements, and historical perspectives on bridge readout mechanisms and Wein bridge oscillators.
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Application Note 43
June 1990
Bridge Circuits
Marrying Gain and Balance
Jim Williams
Bridge circuits are among the most elemental and powerful
electrical tools. They are found in measurement, switching, oscillator and transducer circuits. Additionally, bridge
techniques are broadband, serving from DC to bandwidths
well into the GHz range. The electrical analog of the mechanical beam balance, they are also the progenitor of all
electrical differential techniques. and stability of the basic configuration. In particular, transducer manufacturers are quite adept at adapting the bridge
to their needs (see Appendix A, “Strain Gauge Bridges”).
Careful matching of the transducer’s mechanical characteristics to the bridge’s electrical response can provide a
trimmed, calibrated output. Similarly, circuit designers
have altered performance by adding active elements (e.g.,
amplifiers) to the bridge, excitation source or both. Resistance Bridges
Figure 1 shows a basic resistor bridge. The circuit is
usually credited to Charles Wheatstone, although S. H.
Christie, who demonstrated it in 1833, almost certainly
preceded him.1 If all resistor values are equal (or the two
sides ratios are equal) the differential voltage is zero. The
excitation voltage does not alter this, as it affects both
sides equally. When the bridge is operating off null, the
excitation’s magnitude sets output sensitivity. The bridge …
PDF, 1.2 Mb, File published: Jun 5, 1991
A variety of measurement and control circuits are included in this application note. Eighteen circuits, including ultra low noise amplifiers, current sources, transducer signal conditioners, oscillators, data converters and power supplies are presented. The circuits emphasize precision specifications with relatively simple configurations.
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Application Note 45
June 1991
Measurement and Control Circuit Collection
Diapers and Designs on the Night Shift
Jim Williams
Introduction
During my wife’s pregnancy I wondered what it would
really be like when the baby was finally born. Before that
time, there just wasn’t much mothering and fathering to
do. As a consolation, we busied ourselves watching the
baby’s heartbeat (Figure 1) on a thrown-together fetal heart
monitor (see References). feedings. As such, the circuits are annotated with the
number of feedings required for their completion; e.g., a
“3-bottle circuit” took three feedings. The circuit’s degree
of difficulty, and Michael’s degree of cooperation, combined
to determine the bottle rating, which is duly recorded in
each figure.
Low Noise and Drift Chopped Bipolar Amplifier
Figure 2’s circuit combines the low noise of an LT®1028
with a chopper based carrier modulation scheme to achieve
an extraordinarily low noise, low drift DC amplifier. DC
drift and noise performance exceed any currently available
monolithic amplifier. Offset is inside 1ОјV, with drift less …
PDF, 5.3 Mb, File published: Aug 1, 1991
This application note, subtitled "A Designer's Companion for Wideband Circuitry," is intended as a reference source for designing with fast amplifiers. Approximately 150 pages and 300 figures cover frequently encountered problems and their possible causes. Circuits include a wide range of amplifiers, filters, oscillators, data converters and signal conditioners. Eleven appended sections discuss related topics including oscilloscopes, probe selection, measurement and equipment considerations, and breadboarding techniques.
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Application Note 47
August 1991
High Speed Amplifier Techniques
A Designer’s Companion for Wideband Circuitry
Jim Williams PREFACE
This publication represents the largest LTC commitment
to an application note to date. No other application note
absorbed as much effort, took so long or cost so much.
This level of activity is justified by our belief that high speed
monolithic amplifiers greatly interest users.
Historically, monolithic amplifiers have represented packets of inexpensive, precise and controllable gain. They
have partially freed engineers from the constraints and
frustrations of device level design. Monolithic operational
amplifiers have been the key to practical implementation
of high level analog functions. As good as they are, one
missing element in these devices has been speed.
Devices presently coming to market are addressing monolithic amplifiers’ lack of speed. They bring with them the
ease of use and inherent flexibility of op amps. When Philbrick Researches introduced the first mass produced
op amp in the 1950’s (K2-W) they knew it would be used.
What they couldn’t possibly know was just how widely,
and how many different types of applications there were.
As good a deal as the K2-W was (I paid $24.00 for mine or rather, my father did), monolithic devices are far better.
The combination of ease of use, economy, precision and …
PDF, 190 Kb, File published: Jan 1, 1993
This application note consolidates the circuits from the first few years of Linear Technology magazine into one publication. Presented in the note are a variety of circuits ranging from a 50W high efficiency (>90%) switching regulator to steep roll-off filter circuits with low distortion to 12-bit differential temperature measurement systems.
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Application Note 52
January 1993
Linear Technology Magazine Circuit Collection, Volume 1
Richard Markell, Editor
Introduction
Over the past several years Linear Technology, the magazine, has come of age. From nothing, the publication has
come into its own, as has its subscriber list. Many innovative circuits have seen the light of day in the pages of our
now hallowed publication. This Application Note is meant to consolidate the circuits
from the first few years of the magazine in one place.
Circuits herein range from laser diode driver circuits to
data acquisition systems to a 50W high efficiency switcher
circuit. Enough said. I’ll stand aside and let the authors
explain their circuits.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners. CIRCUIT INDEX
A-to-D Converters .2
LTC1292: 12-BIT DATA ACQUISITION CIRCUITS .2
Temperature-Measurement System .2
Floating, 12-Bit Data Acquisition System .2
Differential Temperature Measurement System .2
MICROPOWER SO8 PACKAGED ADC CIRCUITS .4
Floating 8-Bit Data Acquisition System .4
0В°C – 70В°C Thermometer .5 …
PDF, 688 Kb, File published: Aug 1, 1993
This publication details several LCD backlight circuits which feature 92% efficiency. Other benefits include low voltage operation, synchronizing capability, higher output power for color displays, and extended dimming range. Extensive coverage of practical issues includes layout problems, multi-lamp displays, safety and reliability concerns and efficiency and photometric measurements. Also included is a review of circuits which did not work along with appropriate commentary.
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Application Note 55
August 1993
Techniques for 92% Efficient LCD Illumination
Waste Not, Want Not .
Jim Williams
INTRODUCTION
In August of 1992 LTC published Application Note 49,
“Illumination Circuitry for Liquid Crystal Displays.” One
notable aspect of this event is that it generated more
response than all previous LTC application notes combined. This level of interest, along with significant performance advances since AN-49’s appearance, justifies
further discussion of LCD backlighting circuitry.
This publication includes pertinent information from the
previous effort in addition to updated sections and a large
body of new material. The partial repetition is a small
penalty compared to the benefits of text flow, completeness and time efficient communication. The most noteworthy performance advance is achievement of 92%
efficiency for the backlight power supply. Additional new
benefits include low voltage operation, synchronizing capability, higher output power for color displays, and extended dimming range.
A practical 92% efficient LCD backlight design is a classic
study of compromise in a transduced electronic system.
Every aspect of the design is interrelated, and the physical
embodiment is an integral part of the electrical circuit. The
choice and location of the lamp, wires, display housing
and other items has a major effect on electrical characteristics. The greatest care in every detail is required to …
PDF, 385 Kb, File published: Aug 2, 1996
Application Note 64 details characteristics of various battery types and appropriate charging management schemes. The LTC1325 battery management IC is highlighted along with information for applying it to any type battery. Techniques and circuitry for conditioning, charging and monitoring NiCd, NiMH, Li-Ion and Lead-Acid batteries are presented.
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Application Note 64
August 1996
Using the LTC1325 Battery Management IC
Anthony Ng, Peter Schwartz, Robert Reay,
Richard Markell
INTRODUCTION
For a variety of reasons, it is desirable to charge batteries
as rapidly as possible. At the same time, overcharging
must be limited to prolong battery life. Such limitation of
overcharging depends on factors such as the choice of
charge termination technique and the use of multi-rate/
multi-stage charging schemes. The majority of battery
charger ICs available today lock the user into one fixed
charging regimen, with at best a limited number of
customization options to suit a variety of application needs
or battery types. The LTCВ®1325 addresses these shortcomings by providing the user with all the functional
blocks needed to implement a simple but highly flexible
battery charger (see Figure 1) which not only addresses
the issue of charging batteries but also those of battery
conditioning and capacity monitoring. A microprocessor
interacts with the LTC1325 through a serial interface to
control the operation of its functional blocks, allowing
software to expand the scope and flexibility of the charger …
PDF, 1.2 Mb, File published: Sep 1, 1996
Application Note 67 is a collection of circuits for data conversion, interface and signal processing from the first five years of Linear Technology. This application note includes circuits such as fast video multiplexers for high speed video, an ultraselective bandpass filter circuit with adjustable gain, and a fully differential, 8-channel, 12-bit A/D system. The categories included in this app note are data conversion, interface, filters, instrumentation, video/op amps and miscellaneous circuits.
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Application Note 67
September 1996
Linear Technology Magazine Circuit Collection, Volume III
Data Conversion, Interface and Signal Processing
Richard Markell, Editor
INTRODUCTION
Application Note 67 is a collection of circuits from the first
five years of Linear Technology, targeting data conversion,
interface and signal processing applications. This
Application Note includes circuits such as fast video
multiplexers for high speed video, an ultraselective
bandpass filter circuit with adjustable gain and a fully differential, 8-channel, 12-bit A/D system. The categories
included herein are data conversion, interface, filters,
instrumentation, video/op amps and miscellaneous
circuits. Application Note 66, which covers power products
and circuits from Linear Technology ’s first five years, is
also available from LTC. ARTICLE INDEX
Data Conversion . 3
Fully Differential, 8-Channel, 12-Bit A/D System Using the LTCВ®1390 and LTC1410 . 3
12-Bit DAC Applications . 5
LTC1329 Micropower, 8-Bit, Current Output DAC Used for Power Supply Adjustment,
Trimmer Pot Replacement . 7
12-Bit Cold Junction Compensated, Temperature Control System with Shutdown . 8 …
PDF, 1.7 Mb, Language: en, File published: Oct 1, 1997
This publication details circuitry and applications considerations for the LT1533 low noise switching regulator. Eleven DC/DC converter circuits are presented, some offering <100µV output noise in a 100MHz bandwidth. Tutorial sections detail low noise DC/DC design, measurement, probing and layout techniques, and magnetics selection.
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Application Note 70
October 1997
A Monolithic Switching Regulator with 100ВµV Output Noise
“Silence is the perfectest herald of joy .”
Jim Williams INTRODUCTION
Size, output flexibility and efficiency advantages have
made switching regulators common in electronic apparatus. The continued emphasis on these attributes has
resulted in circuitry with 95% efficiency that requires
minimal board area. Although these advantages are welcome, they necessitate compromising other parameters. back to the driving source (“reflected” noise) and it is
radiated. The multiple transmission paths combine with
the high frequency content to make noise suppression
difficult. Unconscionable amounts of bypass capacitors,
ferrite beads, shields, Mu-metal and aspirin have been
expended in attempts to ameliorate noise-induced effects. Switching Regulator “Noise”
Something commonly referred to as “noise” is a primary
concern. The switched mode power delivery that permits
the aforementioned advantages also creates wideband
harmonic energy. This undesirable energy appears as
radiated and conducted components commonly labeled
as “noise.” Actually, switching regulator output “noise” is
not really noise at all, but coherent, high frequency residue
directly related to the regulatorвЂTMs switching.1 Figure 1
shows typical switching regulator output noise. Two distinct characteristics are present. The slow, ramping output
…
PDF, 882 Kb, File published: May 1, 1998
AN72 is an extensive discussion of the causes and cures of problems in very high speed comparator circuits. A separate applications section uses the 7ns LT1394 in V-to-F converters, crystal oscillators, clock skew generators, triggers, sampling configurations and a nanosecond pulse stretcher. Appendices cover related topics.
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Application Note 72
May 1998
A Seven-Nanosecond Comparator
for Single Supply Operation
Guidance for Putting Civilized Speed to Work
Jim Williams INTRODUCTION
In 1985 Linear Technology Corporation introduced the
LT В®1016 Comparator. This device was the first readily
usable, high speed TTL comparator. Previous ICs were
either too slow or unstable, preventing widespread
acceptance. The LT1016 was, and is, a highly successful
product.
Recent technology trends have emphasized low power,
single supply operation. The LT1016, although capable of
such operation, does not include ground in its input range.
As such, it must be biased into its operating common
mode range for practical single supply use. A new device,
the LT1394, maintains the speed and application civility of
its predecessor while including ground in its input operating range. Additionally, the new comparator is faster and
pulls significantly lower operating current than the LT1016.
This publication borrows shamelessly from earlier LTC
efforts, while introducing new material.1 It approximates,
affixes, appends, abridges, amends, abbreviates, abrogates, ameliorates and augments the previous work.2 …
PDF, 490 Kb, File published: Aug 1, 2000
Telecommunication, satellite links and set-top boxes all require tuning a high frequency oscillation. The actual tuning element, a varactor diode, requires high voltage bias for operation. The high voltage bias must be free of noise to prevent unwanted oscillator outputs. This publication details a method for generating noise free high voltage from low voltage inputs using switching regulators. Spurious oscillator outputs are below -90dBc. Suggested circuit and layout information is included. Appendices cover varactor diode theory and performance verification techniques.
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Application Note 85
August 2000
Low Noise Varactor Biasing with Switching Regulators
Vanquishing Villainous Vitiators Vis-Г -Vis Vital Varactors
Jim Williams and David Beebe
INTRODUCTION “hyperabrupt” devices. Response modification is possible,
with compromises in performance, particularly with regard
to linearity and sensitivity.2 Telecommunication, satellite links and set-top boxes all
require tuning a high frequency oscillator. The actual
tuning element is a varactor diode, a 2-terminal device that
changes capacitance as a function of reverse bias voltage.1 The oscillator is part of a frequency synthesizing
loop, as detailed in Figure 1. A phase locked loop (PLL)
compares a divided down representation of the oscillator
with a frequency reference. The PLL’s output is level
shifted to provide the high voltage necessary to bias the
varactor, which closes a feedback loop by voltage tuning
the oscillator. This loop forces the voltage controlled
oscillator (VCO) to operate at a frequency determined by
the frequency reference and the divider’s division ratio. Note 1. Theoretical considerations of varactor diodes are treated in
Appendix A, “Zetex Variable Capacitance Diodes,” guest written by Neil
Chadderton of Zetex.
Note 2. The reader is again referred to Appendix A for in-depth discussion
of varactor diodes. …
PDF, 409 Kb, File published: Apr 1, 2002
A large group of fiber optic lasers are powered by DC current. Laser drive is supplied by a current source with modulation added to the signal. The current source, although conceptually simple, constitutes an extraordinarily tricky design problem. There are a number of practical requirements for a fiber optic current source and failure to consider them can cause laser and/or optical component destruction. This application note describes ten laser current source circuits with a range of capabilities. High and low current types are presented, along with designs for grounded anode, cathode or floating operation. Each circuit also includes laser protection features. Appended sections cover laser load simulation and current source noise measurement techniques.
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Application Note 90
April 2002
Current Sources for Fiber Optic Lasers
A Compendium of Pleasant Current Events
Jim Williams, Linear Technology Corporation
INTRODUCTION
A large group of fiber optic lasers are powered by DC
current. Laser drive is supplied by a current source with
modulation added further along the signal path. The
current source, although conceptually simple, constitutes
an extraordinarily tricky design problem. There are a
number of practical requirements for a fiber optic current
source and failure to consider them can cause laser and/
or optical component destruction. Protection features must be included to prevent laser and
optical component damage. The laser, an expensive and
delicate device, must be protected under all conditions,
including supply ramp up and down, improper control
input commands, open or intermittent load connections
and “hot plugging.”
Detailed Discussion of Performance Issues Design Criteria for Fiber Optic Laser Current Sources It is useful to expand on the above cursory discussion to
clarify design goals. As such, each previously called out
issue is treated in greater detail below. Figure 1 shows a conceptual laser current source. Inputs
include a current output programming port, an output …
PDF, 1.1 Mb, File published: Nov 1, 2002
Avalanche photodiodes, used in laser based fiberoptic systems, require high voltage bias and accurate, wide range current monitoring. Bias voltage varies from 15V-90V and current ranges from 100nA to 1mA, a 10,000:1 dynamic range. This publication presents various 5 volt powered circuits which meet these requirements. Appended sections detail specific circuit techniques and cover measurement practice.
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Application Note 92
November 2002
Bias Voltage and Current Sense Circuits for
Avalanche Photodiodes
Feeding and Reading the APD
Jim Williams, Linear Technology Corporation
INTRODUCTION
Avalanche photodiodes (APDs) are widely utilized in laser
based fiberoptic systems to convert optical data into
electrical form. The APD is usually packaged with a signal
conditioning amplifier in a small module. An APD receiver
module and attendant circuitry appears in Figure 1. The
APD module (figure right) contains the APD and a transimpedance (e.g., current-to-voltage) amplifier. An optical
port permits interfacing fiberoptic cable to the APD’s
photosensitive portion. The module’s compact construction facilitates a direct, low loss connection between the
APD and the amplifier, necessary because of the extremely
high speed data rates involved.
The receiver module needs support circuitry. The APD
requires a relatively high voltage bias (figure left) to
operate, typically 20V to 90V. This voltage is set by the bias
supply’s programming port. This programming voltage
may also include corrections for the APD’s temperature
dependent response. Additionally, it is desirable to monitor the APD’s average current (figure center), which indi-cates optical signal strength. This information can be …
PDF, 495 Kb, File published: Jul 1, 1995
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C-Load Op Amps Conquer Instabilities – Design Note 107
Kevin R. Hoskins
Introduction
Linear Technology Corporation has taken advantage of
advances in process technology and circuit innovations
to create a series of C-Loadв„ў operational amplifiers that
are tolerant of capacitive loading, including the ultimate,
amplifiers that remain stable driving any capacitive load.
This series of amplifiers has a bandwidth that ranges from
160kHz to 140MHz. These amplifiers are appropriate for
a wide range of applications from coaxial cable drivers to
analog-to-digital converter (ADC) input buffer/amplifiers.
Driving ADCs
Most contemporary ADCs incorporate a sample-and-hold
(S/H). A typical S/H circuit is shown in Figure 1. The hold
capacitor’s (C1) size varies with the ADC’s resolution but
is generally in the range of 5pF to 20pF, 10pF to 30pF and
10pF to 50pF for 8-, 10-and 12-bit ADCs, respectively. gracefully and accurately drive capacitive loads, such as
Linear Technology’s C-Load line of monolithic amplifiers.
Table 1 lists Linear Technology’s unconditionally stable
voltage feedback C-Load amplifiers. Table 2 lists other
voltage feedback C-Load amplifiers that are stable with
loads up to 10,000pF. …
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advertisement Dual Regulators Power Pentium Processor or Upgrade CPU
Design Note 122
Craig Varga
Many manufacturers of Pentium processor-based
motherboards have been searching for an economical
solution to the problem of powering the present generation Pentium P54C and accommodating the upgrade
processors that will soon become available. The existing
processor uses a single supply for both the processor
core and the I/O. For the highest frequency offerings,
the supply required is 3.5V ±100mV (VRE specification).
For the lower performance end of the clock frequency
spectrum, a supply voltage of 3.3V В±5% is adequate.
Recently, Intel respecified the standard 3.3V CPUs for
operation at 3.5V. This allows designs for any clock
frequency to be operated from a single 3.5V supply. The
I/O ring and chipset should be powered by the same
voltage as the CPU core, whether that is 3.3V or 3.5V.
The P55C upgrade processor, which will soon be available, requires separate supplies for the core and the I/O.
The nominal core voltage is targeted at 2.500V В±5%,
whereas the I/O supply is still nominally 3.3V. There is
also a processor pin, VCC2DET, at location AL1, that is
bonded to ground on the P55C, but is open on the P54C.
A signiп¬Ѓcant complication is introduced by the core …
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Power Supplies for Subscriber Line Interface Circuits
Design Note 130
Eddie Beville
As the demand for world wide networking grows, so
will the need for advanced data transmission products.
In particular, ISDN services have become popular because of the recent development of the Internet. ISDN
provides higher speed data transmission than standard
modems used in PCs. Also, ISDN supports the standard
telephone interface (voice and fax), which includes the
Subscriber Line Interface Circuit. A Subscriber Line
Interface Circuit requires a negative power supply for
the interface and the ringer voltages. The power supplies
described herein are designed for these applications.
Specifically, these designs address the AMD79R79
SLIC device with on-chip ringing.
CIRCUIT DESCRIPTIONS
LT®1171 Supplies –23.8V at 50mA and
–71.5V at 60mA
Figure 1 shows a current mode flyback power supply
using the LT1171CQ device. This current mode device
has a wide input voltage range of 3V to 60V, current
limit protection and an on-chip 65V, 0.30О© bipolar
D3 …
PDF, 224 Kb, File published: Sep 1, 1988
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Noise Calculations1 in Op Amp Circuits – Design Note 15
Alan Rich
Noise calculations in op amp circuits are one of the most
confused calculations that an analog engineer must
perform.
One cannot just look at noise specifications; the total op
amp circuit including resistors and operating frequency
range must be included in calculations for circuit noise. A
“low” noise amplifier in one circuit will become a “high”
noise amplifier in another circuit.
As part of this Design Note, an IBM-PC2 or compatible
computer program, NOISE, has been written to perform
the noise calculations. This program allows the user to
calculate circuit noise using LTC op amps, determine the
best LTC op amp for a low noise application, display the
noise data for LTC op amps, calculate resistor noise, and
calculate circuit noise using noise specs for any op amp.
At the end of this Design Note there are detailed operating
instructions for the computer program NOISE.
To calculate noise for an op amp circuit, one must consider the op amp voltage and current noise density and
1/f corner frequency, the frequency range of interest, and
the resistor noise.
The most comprehensive specification for voltage or current noise is the noise density frequency response curve …
PDF, 120 Kb, File published: Nov 1, 1988
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advertisement Programming Pulse Generators for Flash Memories
Design Note 17
Jim Williams
Recently introduced “flash” memories add electrical chip-erasure and reprogramming to established
EPROM technology. These features make them a cost
effective and reliable alternative for updatable nonvolatile memory. Utilizing the electrical program-erase
capability requires linear circuitry techniques. The Intel
28F256 flash memory, built on the ETOX process,
specifies programming operation with 12V or 12.75V
(faster erase/program times) amplitude pulses. These
“VPP” amplitudes must fall within 1.6%, and excursions
beyond 14.0V will damage the device.
Providing the VPP pulse requires generating and controlling high voltages within the tightly specified limits.
Figure 1’s circuit does this. When the VPP command
pulse goes low (trace A, Figure 2) the LTВ®1072 switching
regulator drives L1, producing high voltage. DC feedback occurs via R1 and R2, with AC roll-off controlled
by C1 and R3-C2. The result is a smoothly rising VPP
pulse (trace B) which settles to the required value. The
specified R1 values allow either 12V or 12.75V outputs.
The 5.6V zener permits the output to return to 0V when
the VPP command goes high. It may be deleted in cases
where a 4.5V minimum output is acceptable (see Intel
28F256 data sheet). The 0.1% resistors combine with …
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A Single Amplifier, Precision High Voltage Instrument Amp
Design Note 25
Walt Jung and George Erdi
be relatively simple, while at the same time capable of
high performance. Whereas dual summing amplifier
setups can provide high input-voltage qualifications,
a more simple single amp solution is often sought. An
IA topology which achieves all the above objectives
is shown in Figure 1, the “Precision High Voltage IA.”
The circuit employs the virtues of two key parts in
performing its function; the resistor array and the op
amp used with it. Instrumentation amplifier (IA) circuits abound in analog
systems, in fact virtually any linear applications handbook will show many useful variations on the concept (1).
While this may be somewhat bewildering to a newcomer,
all the variations have uses which are differentiated and
valuable. A good working knowledge of the alternate
forms can be a powerful tool towards designing costeffective high performance linear circuits.
A case in point is a single amplifier precision qualified
high voltage IA. This circuit must withstand very high
common mode voltages at the input, yet it should still L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their
respective owners. R5
975k R1 …
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Extract from the document
Operational Amplifier Selection Guide for Optimum Noise
Performance – Design Note 3
George Erdi
The LTВ®1028 is the lowest noise op amp available today.
Its voltage noise is less than that of a 50О© resistor. In
other words, if the LT1028 is operated with source resistors in excess of 50О© , resistor noise will dominate. If the
application requires large source resistors, the LT1028’s
relatively high current noise will limit performance, and
other op amps will provide lower overall noise. The table below lists which op amp gives minimum total
noise for a specified equivalent source resistance. A two
step procedure should be followed to optimize noise: In general, the total noise of any op amp (referred to the
input) is given by: The table actually has two sets of devices: one for low
frequency (instrumentation), one for wideband applications. The slight differences between the two columns
occur because voltage and current noise increase at low
frequencies (below the so-called 1/f corner) while resistor
noise is flat with frequency. total noise = (voltage noise) + (resistor noise) + (current noise R )
2 2 2 eq where, (2) Enter the table to find the optimum op amp. Best Op Amp for Lowest Noise vs Source Resistance resistor noise = 0.13 Re q in nV Hz
and Req = equivalent source resistance
= R2 + R1//R3
R3
R1 – R2 + DN003 F01 Several conclusions can be reached by inspection of the
equation:
(a) To minimize noise, resistor values should be minimized to make the contribution of the second and …
PDF, 95 Kb, File published: Mar 1, 1990
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advertisement A Simple Ultra-Low Dropout Regulator – Design Note 32
Jim Williams
Linear voltage regulators with low dropout characteristics are a frequent requirement, particularly in battery powered applications. It is desirable to maintain
regulation until the battery is almost entirely depleted.
Regulator dropout limits significantly impact useful
battery life, and as such should be minimized. Figure 1
shows dropout characteristics for a monolithic regulator,
the LTВ®1085. The …
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Designing with a New Family of Instrumental Amplifiers
Design Note 40
Jim Williams
A new family of IC instrumentation amplifiers achieves
performance and cost advantages over other alternatives.
Conceptually, an instrumentation amplifier is simple.
Figure 1 shows that the device has passive, fully differential inputs, a single ended output and internally set
gain. Additionally, the output is delivered with respect to
the reference pin, which is usually grounded. Maintaining
high performance with these features is difficult, accounting for the cost-performance disadvantages previously
associated with instrumentation amplifiers.
Figure 2 summarizes specifications for the amplifier
family. The LTC В®1100 has the extremely low offset, drift,
and bias current associated with chopper stabilization
techniques. The LTВ®1101 requires only 105ВµA of supply
current while retaining excellent DC characteristics. The
FET input LT1102 features high speed while maintaining
+
– → NO FEEDBACK RESISTORS USED
в†’ GAIN FIXED INTERNALLY (TYP 10 OR 100)
OR SOMETIMES RESITOR PROGRAMMABLE
в†’ BALANCED, PASSIVE INPUTS
в†’ …
PDF, 70 Kb, File published: Dec 1, 1990
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Chopper vs Bipolar Op Amps—An Unbiased Comparison
Design Note 42
George Erdi Table 1 lists the parameters of importance. In all input
parameters (except noise) the advantage unquestionably goes to the choppers. 5ОјV maximum offset voltage, 0.5ОјV/В°C maximum drift are commonly found
Table 1. Chopper Stabilized vs Precision Bipolar Op Amps
ADVANTAGE
PARAMETER
Offset Voltage
Offset Drift
All Other DC Specs CHOPPER BIPOLAR COMMENTS
вњ“
вњ“
вњ“ No Contest Wideband, 20Hz to
1MHz вњ“ See Details in Text Noise вњ“ See Details in Text вњ“ Rail to Rail Swing
2mA Limit on
Choppers Output: Light Load
Heavy Load
Single Supply
Application вњ“ вњ“ Inherent to
Choppers Needs
Special Design
Bipolars В±15V Supply Voltage вњ“ Except LTC1150 Prejudice/Tradition вњ“ Still a Chopper
Problem Cost 08/90/86_conv вњ“ Unless DC …
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Signal Conditioning for Platinum Temperature Transducers
Design Note 45
Jim Williams
High accuracy, stability, and wide operating range make
platinum RTDs (resistance temperature detectors)
popular temperature transducers. Signal conditioning
these devices requires care to utilize their desirable
characteristics. Figure 1’s bridge-based circuit is highly
accurate and features a ground referred RTD. The ground
connection is often desirable for noise rejection. The
bridges RTD leg is driven by a current source while the
opposing bridge branch is voltage biased. The current
drive allows the voltage across the RTD to vary directly
with its temperature induced resistance shift. The difference between this potential and that of the opposing
bridge leg forms the bridges output.
A1A and instrumentation amplifier A2 form a voltage
controlled current source. A1A, biased by the LTВ®1009
reference, drives current through the 88.7О© resistor and
the RTD. A2, sensing differentially across the 88.7Ω resistor, closes a loop back to A1A. The 2k-0.1μF combination sets amplifier roll-off, and the configuration
is stable. Because A1A’s loop forces a fixed voltage
across the 88.7О© resistor, the current through Rp is
constant. A1’s operating point is primarily fixed by the
2.5V LT1009 voltage reference. …
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Gain Trimming In Instrumentation Amplifier
Based Systems – Design Note 51
Jim Williams
Gain trimming is almost always required in instrumentation amplifier based systems. Gain uncertainties, most
notable in transducers, necessitate such a trim.
Figure 1, a conceptual system, shows several points as
candidates for the trim. In practice, only one of these
must actually be used. The appropriate trim location
varies with the individual application.
Figure 2 approaches gain trimming by altering transducer excitation. The gain trim adjustment results in
changes in the LT®1010’s output. The LT1027 reference
and LT1097 ensure output stability. Transducer output varies with excitation, making this a viable approach.
It is important to consider that gain “lost” by reducing
transducer drive translates into reduced signal-to-noise
ratio. As such, gain reduction by this method is usually
limited to small trims, e.g., 5-10%. Similarly, too much
gain introduced by this method can cause excessive
transducer drive, degrading accuracy. The transducer
manufacturer’s data sheet should list the maximum
permissible drive for rated accuracy.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their
respective owners. &9$*5"5*0/ …
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3V Operation of Linear Technology Op Amps -Design Note 56
George Erdi
The latest trend in digital electronics is the introduction
of numerous ICs operating on regulated 3V or 3.3V
power supplies. This is a logical development to increase
circuit densities and to reduce power dissipation. In addition, many systems are directly powered by two AA
cells or 3V lithium batteries. Clearly, analog ICs which
work on 3V with good dynamic range to complement
these digital circuits are, and will be, in great demand.
Many Linear Technology operational amplifiers work
well on a 3V supply. The purpose of this design note
is to list these devices and their performance when
powered by 3V. The op amps can be divided into two
groups: single and dual supply devices. The single supply
op amps are optimized for, and fully specified at, a 5V
positive supply with the negative supply terminal tied
to ground. Input common mode voltage range goes
below ground, and the output swings to within a few
millivolts of ground while sinking current. Members of
the single supply family are the micropower LTВ®1077/
LT1078/LT1079 single, dual and quad op amps with
40μA supply current per amplifier, the LT1178/LT1179 dual and quad with 13μA per amplifier. The LT1006/
LT1013/LT1014 single, dual and quad have faster speed …
PDF, 137 Kb, File published: Jan 1, 1988
