Zero-Drift Operational Amplifier
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, 421 Kb, File published: Aug 1, 1985
This note describes some of the unique IC design techniques incorporated into a fast, monolithic power buffer, the LT1010. Also, some application ideas are described such as capacitive load driving, boosting fast op amp output current and power supply circuits.
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Application Note 16
August 1985
Unique IC Buffer Enhances Op Amp Designs,
Tames Fast Amplifiers
Robert J. Widlar
Abstract: A unity gain IC power buffer that uses NPN
output transistors while avoiding the usual problems of
quasi-complementary designs is described. Free of parasitic oscillations and stable with large capacitive loads, the
buffer has a 20MHz bandwidth, a 100V/Ојs slew and can
drive В±10V into a 75О© load. Standby current is 5mA. A
number of applications using the buffer are detailed, and
it is shown that a buffer has many uses beyond driving
a heavy load.
Introduction
An output buffer can do much more than increase the
output swing of an op amp. It can also eliminate ringing
with large capacitive loads. Fast buffers can improve the
performance of high speed followers, integrators and
sample/hold circuits, while at the same time making them
much easier to work with.
Interest in buffers has been low because a reasonably
priced, high performance, general purpose part has not
been available. Ideally, a buffer should be fast, have no …
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, 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, 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, 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 …
