Dual Precision Instrumentation Switched-Capacitor Building Block
PDF, 230 Kb, File published: Sep 1, 1985
This note covers the considerations for designing precision linear circuits which must operate from a single 5V supply. Applications include various transducer signal conditioners, instrumentation amplifiers, controllers and isolated data converters.
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Application Note 11
September 1985
Designing Linear Circuits for 5V Single Supply Operation
Jim Williams
In predominantly digital systems it is often necessary
to include linear circuit functions. Traditionally, separate
power supplies have been used to run the linear components (see Box, “Linear Power Supplies—Past, Present,
and Future”).
Recently, there has been increasing interest in powering
linear circuits directly from the 5V logic rail. The logic
rail is a difficult place for analog components to function.
The high amplitude broadband current and voltage noise
generated by logic clocking makes analog circuit operation difficult. (See Box, “Using Logic Supplies for Linear
Functions”.)
Generally speaking, analog circuitry which must achieve
very high performance levels should be driven from dedicated supplies. The difficulties encountered in maintaining
the lowest possible levels of noise and drift in an analog
system are challenging enough without contending with
a digitally corrupted power supply.
Many analog applications, however, can be successfully
implemented using the logic supply. Combining components intended to provide high performance from the 167Ω Q1 –
+ 2M 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. RATIOMETRIC …
PDF, 387 Kb, File published: Mar 1, 1986
A variety of high performance V/F circuits is presented. Included are a 1Hz to 100MHz design, a quartz-stabilized type and a 0.0007% linear unit. Other circuits feature 1.5V operation, sine wave output an nonlinear transfer functions. A separate section examines the trade-offs and advantages of various approaches to V/F conversion.
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Application Note 14
March 1986
Designs for High Performance Voltage-to-Frequency
Converters
Jim Williams
Monolithic, modular and hybrid technologies have been
used to implement voltage-to-frequency converters. A
number of types are commercially available and overall
performance is adequate to meet many requirements. In
many cases, however, very high performance or special
characteristics are required and available units will not work.
In these instances V→F circuits specifically optimized for
the desired parameters(s) are required. This application
note presents examples of circuits which offer substantially improved performance over commercially available
V→Fs. Various approaches (see Box Section, “V→F
Design Techniques”) permit improvements in speed, dynamic range, stability and linearity. Other circuits feature
low voltage operation, sine wave output and deliberate
nonlinear transfer functions.
Ultra-High Speed 1Hz to 100MHz V→F Converter
Figure 1’s circuit uses a variety of circuit methods to
achieve wider dynamic range and higher speed than any
commercial V→F. Rocketing along at 100MHz full-scale
(10% overrange to 110MHz is provided), it leaves all other …
PDF, 2.5 Mb, File published: Mar 1, 1986
This note presents output state circuits which provide power gain for monolithic amplifiers. The circuits feature voltage gain, current gain, or both. Eleven designs are shown, and performance is summarized. A generalized method for frequency compensation appears in a separate section.
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Application Note 18
March 1986
Power Gain Stages for Monolithic Amplifiers
Jim Williams
Most monolithic amplifiers cannot supply more than a few
hundred milliwatts of output power. Standard IC processing
techniques set device supply levels at 36V, limiting available output swing. Additionally, supplying currents beyond
tens of milliamperes requires large output transistors and
causes undesirable IC power dissipation.
Many applications, however, require greater output power
than most monolithic amplifiers will deliver. When voltage
or current gain (or both) is needed, a separate output
stage is necessary. The power gain stage, sometimes
called a “booster”, is usually placed within the monolithic
amplifier’s feedback loop, preserving the IC’s low drift and
stable gain characteristics. 150mA Output Stage
Figure 1a shows the LTВ®1010 monolithic 150mA current
booster placed within the feedback loop of a fast FET
amplifier. At lower frequencies, the buffer is within the
feedback loop so that its offset voltage and gain errors
are negligible. At higher frequencies, feedback is through
Cf, so that phase shift from the load capacitance acting
against the buffer output resistance does not cause loop …
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, 1.5 Mb, File published: Jul 1, 1985
This application note describes a wide range of useful applications for the LTC1043 dual precision instrumentation switched capacitor building block. Some of the applications described are ultra high performance instrumentation amplifier, lock-in amplifier, wide range digitally controlled variable gain amplifier, relative humidity sensor signal conditioner, LVDT signal conditioner, charge pump F/V and V/F converters, 12-bit A/D converter and more.
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Application Note 3
July 1985
Applications for a Switched-Capacitor Instrumentation
Building Block
Jim Williams
CMOS analog IC design is largely based on manipulation
of charge. Switches and capacitors are the elements used
to control and distribute the charge. Monolithic п¬Ѓlters, data
converters and voltage converters rely on the excellent
characteristics of IC CMOS switches. Because of the importance of switches in their circuits, CMOS designers have
developed techniques to minimize switch induced errors,
particularly those associated with stray capacitance and
switch timing. Until now, these techniques have been used
only in the internal construction of monolithic devices. A
new device, the LTCВ®1043, makes these switches available
for board-level use. Multi-pole switching and a self-driven,
non-overlapping clock allow the device to be used in circuits
which are impractical with other switches. Conceptually, the LTC1043 is simple. Figure 1 details its
features. The oscillator, free-running at 200kHz, drives a
non-overlapping clock. Placing a capacitor from Pin 16 to
ground shifts the oscillator frequency downward to any
desired point. The pin may also be driven from an external
source, synchronizing the switches to external circuitry. …
PDF, 1.7 Mb, File published: Jun 1, 1991
A wide variety of voltage reference circuits are detailed in this extensive guidebook of circuits. The detailed schematics cover simple and precision approaches at a variety of power levels. Included are 2 and 3 terminal devices in series and shunt modes for positive and negative polarities. Appended sections cover resistor and capacitor selection and trimming techniques.
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, 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, 297 Kb, File published: Feb 1, 1985
Analog-to-digital conversion circuits which directly digitize low level transducer outputs, without DC preamplification, are presented. Covered are circuits which operate with thermocouples, strain gauges, humidity sensors, level transducers and other sensors.
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Application Note 7
February 1985
Some Techniques for Direct Digitization of Transducer Outputs
Jim Williams
Almost all transducers produce low level signals. Normally,
high accuracy signal conditioning amplifiers are used to
boost these outputs to levels which can easily drive cables,
additional circuitry, or data converters. This practice raises
the signal processing range well above the error floor,
permitting high resolution over a wide dynamic range.
Some emerging trends in transducer-based systems are
causing the use of signal conditioning amplifiers to be
reevaluated. While these amplifiers will always be useful,
their utilization may not be as universal as it once was.
In particular, many industrial transducer-fed systems are
employing digital transmission of signals to eliminate
noise-induced inaccuracies in long cable runs. Additionally, the increasing digital content of systems, along with
pressures on board space and cost, make it desirable to
digitize transducer outputs as far forward in the signal chain
as possible. These trends point toward direct digitization
of transducer outputs—a difficult task.
Classical A/D conversion techniques emphasize high level
input ranges. This allows LSB step size to be as large …
PDF, 177 Kb, File published: Aug 7, 1999
This application note describes six low power differential-tosingle- ended signal conditioning circuits for the LTC2400 No Latency ΔΣTM 24-bit ADC. These circuits offer the customer a number of choices for conditioning differential input signals as low as 5mV to as high as ±2.5V, as well as operation on a single 5V or ±5V supplies. Each circuit description also covers circuit design and implementation techniques that can help preserve the LTC2400's inherently high effective resolution. AN78 concludes with two circuits for digitizing temperature when using an RTD or Type S thermocouple.
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Application Note 78
August 1999
A Collection of Differential to Single-Ended Signal Conditioning
Circuits for Use with the LTC2400, a 24-Bit No Latency ∆Σ ADC
in an SO-8
By Kevin R. Hoskins and Derek V. Redmayne
INTRODUCTION
The LTC®2400 is the industry’s first No Latency ∆ΣTM ADC
that combines automatic offset and full-scale calibration,
an internal oscillator, a sinc4 digital filter, and serial I/O to
yield a 24-bit ADC with 1.5ВµVRMS input noise and singleshot conversion time architecture. It is the ideal
A/D converter for temperature measurement and high
effective resolution instrumentation applications, such as
digital multimeters.
This application note contains six circuits that
extend the LTC2400’s capabilities using a number of low power differential-to-single-ended signal conditioning circuits. These circuits offer the customer a number of
choices for conditioning differential input signals as low as
5mV to as high as В±2.5V, as well as operation on a single
5V or В±5V supplies. In each case, careful circuit design and
implementation techniques were used to maintain or preserve the LTC2400’s inherently high effective resolution.
In some cases, circuit accuracies (uncalibrated) exceed
17 bits.
, LTC and LT are registered trademarks of Linear Technology Corporation. …
PDF, 708 Kb, File published: May 1, 1985
A variety of approaches for power conditioning batteries is given. Switching and linear regulators and converters are shown, with attention to efficiency and low power operation. 14 circuits are presented with performance data.
PDF, 625 Kb, File published: Aug 5, 1986
A discussion of circuit, layout and construction considerations for low level DC circuits includes error analysis of solder, wire and connector junctions. Applications include sub-microvolt instrumentation and isolation amplifiers, stabilized buffers and comparators and precision data converters.
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Application Note 9
August 1986
Application Considerations and Circuits for a New
Chopper-Stabilized Op Amp
Jim Williams
A great deal of progress has been made in op amp DC
characteristics. Carefully executed designs currently available provide sub-microvolt VOS О”T drift, low bias currents
and open-loop gains exceeding one million. Considerable
design and processing advances were required to achieve
these specifications. Because of this, it is interesting to
note that amplifiers with even better DC specification
were available in 1963 (Philbrick Researches Model
SP656). Although these modular amplifiers were large
and expensive (≈3" × 2" × 1.5" at $195.00 1963 dollars)
by modern standards, their DC performance anticipated
today’s best monolithic amplifiers while using relatively
primitive components. This was accomplished by employing chopper-stabilization techniques (see Box “Choppers,
Chopper-Stabilization and the LTC®1052”) instead of the
more common DC-differential stage approach.
The chopper-stabilized approach, developed by E. A.
Goldberg in 1948, uses the amplifier’s input to amplitude
modulate an AC carrier. This carrier, amplified and synchronously demodulated back to DC, furnishes the amplifier’s PARAMETER
EOS – 25В°C …
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, 1.1 Mb, File published: Feb 1, 2003
Instrumentation applications for a monolithic programmable oscillator are presented in this publication. Circuits include platinum and thermistor based thermometers, an isolated thermometer and three relative humidity signal conditioners. Bipolar and FET input chopper stabilized amplifiers with noise below 45nV (0.1Hz to 10Hz) are detailed. Two clock tunable sine wave generators with settable amplitude appear, as well as a tunable notch filter, an interval generator and an A to D converter. The oscillator's performance is contrasted against other approaches and its interval operation discussed.
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Application Note 93
February 2003
Instrumentation Applications for a Monolithic Oscillator
A Clock for All Reasons
Jim Williams INTRODUCTION Clock Types Oscillators are fundamental circuit building blocks. A
substantial percentage of electronic apparatus utilize oscillators, either as timekeeping references, clock sources,
for excitation or other tasks. The most obvious oscillator
application is a clock source in digital systems.1 A second
area is instrumentation. Transducer circuitry, carrier based
amplifiers, sine wave formation, filters, interval generators and data converters all utilize different forms of
oscillators. Although various techniques are common, a
simply applied, broadly tunable oscillator with good accuracy has not been available. Commonly employed oscillators are resonant element
based or RC types.2 Figure 1 shows two of each. Quartz
crystals and ceramic resonators offer high initial accuracy
and low drift (particularly quartz) but are essentially
untunable over any significant range. Typical RC types
have lower initial accuracy and increased drift but are
easily tuned over broad ranges. A problem with conventional RC oscillators is that considerable design effort is
required to achieve good specifications. A new device, the
LTC1799, is also an RC type but fills the need for a simply
applied, broadly tunable, accurate oscillator. Its accuracy
and drift specifications fit between resonator based types
and typical RC oscillators. Additionally, its board footprint, …
PDF, 886 Kb, File published: Nov 19, 2004
Eighteen circuits are presented in this compilation. Signal sources include a voltage controlled current source, an amplitude/frequency stabilized sine wave oscillator, a versatile, 0V to 50V wideband level shift and four sub-nanosecond pulse generators with risetimes as low as 20ps. Five signal conditioners appear; a unique, single positive rail powered amplifier with output to (and below) zero volts, a milliohmmeter, a 0.02% accurate instrumentation amplifier with 120dB CMRR at 125VCM, a 100MHz switch with 5mV control channel feedthrough and a 5V powered, 15ppm linearity quartz stabilized V→F, converter. The power circuits section features a Xenon flashlamp supply, two 5V powered, 0V to 300V DC/DC converters, a fixed 200V output circuit for APD bias, a 100W 0V to 500V, 28V powered converter and a high current paralleling scheme for linear regulators. Two appended sections consider measurement technique and connection practice in sub-nanosecond circuits.
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Application Note 98
November 2004
Signal Sources, Conditioners and Power Circuitry
Circuits of the Fall, 2004
Jim Williams
Introduction
Occasionally, we are tasked with designing circuitry for a
specific purpose. The request may have customer origins
or it may be an in-house requirement. Alternately, a circuit
may be developed because its possibility is simply too
attractive to ignore1. Over time, these circuits accumulate,
encompassing a wide and useful body of proven capabilities. They also represent substantial effort. These considerations make publication an almost obligatory proposition
and, as such, a group of circuits is presented here. This is
not the first time we have displayed such wares and, given
the encouraging reader response, it will not be the last2.
Eighteen circuits are included in this latest effort, roughly
arranged in the categories given in this publication’s title.
They appear at the next paragraph.
Voltage Controlled Current Source—Ground Referred
Input and Output
A voltage controlled current source with ground referred
input and output is difficult to achieve. Executions exist,
but are often cumbersome, involving numerous components. Figure 1’s conceptual design utilizes a differential …
