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.
Extract from the document
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, 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.
Extract from the document
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, 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, 299 Kb, File published: Oct 7, 2013
Extract from the document
Application Note 141
October 2013
Risk Assessment Advice for High Reliability Amplifiers
Tim Regan and James Mahoney Introduction
In long life, high reliability systems, supplied power is
provided only to essential circuitry. As a result many of
the unpowered circuits may have voltages applied to inputs and outputs without proper supply biasing. As part
of any diligent system safety risk assessment, a question
often arises; will the unpowered components be damaged,
degraded, or impair circuit performance under these
abnormal operating conditions?
The purpose of this article is to provide advice for what
lies within the pins of several common amplifiers used in
these applications. Most of the amplifiers of interest are the
radiation hard amplifiers so indicated with a device prefix
of RH. Another amplifier, the LT6016, is particularly robust
with over, under and reversed polarity voltage conditions
and is included for reference.
With no power applied to the amplifier, forcing a voltage
between two pins will cause a current to flow. The magnitude of this current differs from pin to pin and device to
device. A curve tracer is used to show the current vs voltage
characteristic when overdriving specific pin combinations.
Referencing these curve trace plots will provide an indication of the magnitude of current flow for a particular …
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.
Extract from the document
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, 2.8 Mb, File published: Sep 1, 1986
Discusses the principles of operation of the LTC1062 and helpful hints for its application. Various application circuits are explained in detail with focus on how to cascade two LTC1062s and how to obtain notches. Noise and distortion performance are fully illustrated.
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Application Note 20
September 1986
Application Considerations for an
Instrumentation Lowpass Filter
Nello Sevastopoulos
Description of this, the value of the (R C) product is critically related
to the filter passband flatness and to the filter stability.
The internal circuitry of the LTC1062 is driven by a clock
which also determines the п¬Ѓlter cutoff frequency. For a
maximally flat amplitude response, the clock should be
100 times the desired cutoff frequency and the (R, C)
should be chosen such as: The LTCВ®1062 is a versatile, DC accurate, instrumentation
lowpass п¬Ѓlter with gain and phase that closely approximate
a 5th order Butterworth п¬Ѓlter. The LTC1062 is quite different from presently available lowpass switched-capacitor
п¬Ѓlters because it uses an external (R, C) to isolate the
IC from the input signal DC path, thus providing DC accuracy. Figure 1 illustrates the architecture of the circuit.
The output voltage is sensed through an internal buffer,
then applied to an internal switched-capacitor network
which drives the bottom plate of an external capacitor to
form an input-to-output 5th order lowpass п¬Ѓlter. The input
and output appear across an external resistor and the IC
part of the overall п¬Ѓlter handles only the AC path of the
signal. A buffered output is also provided (Figure 1) and …
PDF, 330 Kb, File published: Jul 1, 1986
Applications often require an amplifier that has extremely high performance in several areas. For example, high speed and DC precision are often needed. If a single device cannot simultaneously achieve the desired characteristics, a composite amplifier made up of two (or more) devices can be configured to do the job. AN21 shows examples of composite approaches in designs combining speed, precision, low noise and high power.
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Application Note 21
July 1986
Composite Amplifiers
Jim Williams
Amplifier design, regardless of the technology utilized, is
a study in compromise. Device limitations make it difficult
for a particular amplifier to achieve optimal speed, drift,
bias current, noise and power output specifications. As
such, various amplifier families emphasizing one or more
of these areas have evolved. Some amplifiers are very good
attempts at doing everything well, but the best achievable
performance п¬Ѓgures are limited to dedicated designs. designed with little attention to DC biasing considerations
if a separate stabilizing stage is employed.
Figure 1 shows a composite made up of an LTВ®1012 low drift
device and an LT1022 high speed amplifier. The overall circuit is a unity-gain inverter, with the summing node located
at the junction of three 10k resistors. The LT1012 monitors
this summing node, compares it to ground and drives the
LT1022’s positive input, completing a DC stabilizing loop
around the LT1022. The 10k-300pF time constant at the
LT1012 limits its response to low frequency signals. The
LT1022 handles high frequency inputs while the LT1012
stabilizes the DC operating point. The 4.7k-220О© divider
at the LT1022 prevents excessive input overdrive during …
PDF, 3.3 Mb, File published: Sep 1, 1987
AN22 details the theoretical and application aspects of the LT1088 thermal RMS/DC converter. The basic theory behind thermal RMS/DC conversion is discussed and design details of the LT1088 are presented. Circuitry for RMS/DC converters, wideband input buffers and heater protection is shown.
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, 587 Kb, File published: Sep 1, 1987
Highlights the LTC1062 as a lowpass filter in a phase lock loop. Describes how the loop's bandwidth can be increased and the VCO output jitter reduced when the LTC1062 is the loop filter. Compares it with a passive RC loop filter. Also discussed is the use of LTC1062 as simple bandpass and bandstop filter.
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.
Extract from the document
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, 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, 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, 297 Kb, File published: Nov 8, 1991
LTC's op amp macromodels are described in detail, along with the theory behind each model and complete schematics of each topology. Extended modeling topics are discussed, such as phase/frequency response modifications and asymmetric slew rate for JFET op amp models. LTC's macromodels are optimized for accuracy and fast simulation times. Simulation times can be further reduced by using streamlining techniques found throughout AN48.
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Application Note 48
November 1991
Using the LTC Op Amp Macromodels
Getting the Most from SPICE and the LTC Library
Walt Jung INTRODUCTION This application note is an overview discussion of the
Linear Technology SPICE macromodel library. It assumes
little if any prior knowledge of this software library or its
history. However, it does assume familiarity with both the
analog simulation program SPICE (or one of its many
derivatives), and modern day op amps, including bipolar,
JFET, and MOSFET amplifier technologies.
Some Preliminary SPICE Facts of Life
In the past few years, SPICE simulations have really begun
to capture a high level of attention on the part of analog
circuit designers. Perhaps this is due to more affordable
high performance computers, or perhaps the time for
simulation is now upon us. In any event, the bottom line is
that IC vendors are now making macromodels for op amps
available to their customers.
For the analog circuit designer, there can be no better fate
for simulations, viewing this situation in terms of which
model to use. Designers no longer need worry about
whether the third party supplier’s model can really cut it. …
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, 75 Kb, File published: Jul 1, 1988
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An Op Amp SPICE Macromodel
Design Note 12
Walter G. Jung
applications library. It is hoped that eventually most
op amps in the product line will be developed as macromodels and made available to customers. With the advent of low cost and powerful desktop computers, present day op amp circuit designs can mature
more quickly with good simulation tools. One such tool
since its inception has been SPICE, the standard analog
circuit simulator. However, while PCs and workstations
may now be present on more and more desks, a potential
bottleneck towards effective simulation has been SPICE
models for the more popular parts. The LTВ®1013 and LT1014 devices are popular single
supply LTC op amps, and are thus logical candidates
for macromodels. While existing macromodels for the
generic 358 and 324 types might suffice for some applications, circuit designs which take advantage of the
unique precision and functional features of the LT1013
warrant a model which reflects those features. The
schematic diagram of the LT1013 and LT1014 macromodel is shown in Figure 1, and is applicable to one
channel of either device. The macromodel approach to simulation of an op amp
is viable for many designs, with the great asset of
simulation speeds far faster than that of a full devicelevel circuit. With this design note, Linear Technology
Corporation introduces op amp macromodels to its 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. …
PDF, 95 Kb, File published: Aug 1, 1988
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Closed Loop Control with Data Acquisition Systems
Design Note 13
Guy Hoover and William Rempfer
Introduction
The use of microprocessors in process control loops
is quite common. A processor based control loop requires special design considerations as compared to
traditional analog loops. Often a single centrally located
processor will be used to control several remotely
located processes. The outputs of the remote process
sensors can be digitized at the sensor location and then
be transmitted to the central processor. Unfortunately,
transmitting digital signals typically requires one wire
for each bit of resolution and requires expensive cabling.
Alternatively, the sensor output can be transmitted
as an analog signal to the central processor area for
digitization. However, transmitting analog signals over
distances can introduce errors because of noise and
voltage drops in the wires.
The solution to these control loop problems can be found
in the LTC В®1090 series of data acquisition systems. As
can be seen in the schematic of Figure 2, ten bits of
data can be digitized remotely and sent to the processor
with only three wires plus ground. The single supply …
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, 224 Kb, File published: Oct 1, 1987
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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, 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 …
PDF, 78 Kb, File published: Feb 1, 1992
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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
PDF, 95 Kb, File published: May 1, 1993
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A Broadband Random Noise Generator – Design Note 70
Jim Williams
Filter, audio and RF communication testing often requires a random noise source. The circuit in Figure 1
provides an RMS amplitude regulated noise source with
selectable bandwidth. The RMS output is 300mV with
a 1kHz to 5MHz bandwidth selected in decade ranges. output feeds LT1228 A4, a current feedback amplifier.
A4’s output, the circuit’s output, is sampled by the A5
based gain control configuration. This closes a gain
control loop back at A3. A3’s ISET input current controls
its gain, allowing overall output level control. The A1 amplifier, biased from the LT®1004 reference,
provides optimum drive for D1, the noise source. AC
coupled A2 takes a broadband gain of 100. The A2
output feeds a gain control stage via a simple selectable
lowpass filter. The filter’s output is applied to LT1228
A3, an operational transconductance amplifier. A3’s To adjust this circuit, place the filter in the 1kHz position
and trim the 5k potentiometer for maximum negative
bias at A3, Pin 5.
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. 1M
0.1ОјF
15V
100k 2 3 – 1kHz 8 0.01ОјF …
