PDF, 1.1 Mb, File published: Apr 1, 1985
The AN13 is an extensive discussion of the causes and cures of problems in very high speed comparator circuits. A separate applications section presents circuits, including a 0.025% accurate 1Hz to 30MHz V/F converter, a 200ns 0.01% sample-hold and a 10MHz fiber-optic receiver. Five appendices covering related topics complete this note.
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Application Note 13
April 1985
High Speed Comparator Techniques
Jim Williams
INTRODUCTION
Comparators may be the most underrated and underutilized monolithic linear component. This is unfortunate
because comparators are one of the most flexible and
universally applicable components available. In large
measure the lack of recognition is due to the IC op amp,
whose versatility allows it to dominate the analog design
world. Comparators are frequently perceived as devices,
which crudely express analog signals in digital form—a
1-bit A/D converter. Strictly speaking, this viewpoint is
correct. It is also wastefully constrictive in its outlook.
Comparators don’t “just compare” in the same way that
op amps don’t “just amplify”.
Comparators, in particular high speed comparators, can
be used to implement linear circuit functions which are
as sophisticated as any op amp-based circuit. Judiciously
combining a fast comparator with op amps is a key to
achieving high performance results. In general, op ampbased circuits capitalize on their ability to close a feedback
loop with precision. Ideally, such loops are maintained
continuously over time. Conversely, comparator circuits …
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, 641 Kb, File published: Dec 1, 1985
A tutorial on SAR type A/D converters, this note contains detailed information on several 12-bit circuits. Comparator, clocking, and preamplifier designs are discussed. A final circuit gives a 12-bit conversion in 1.8µs. Appended sections explain the basic SAR technique and explore D/A considerations.
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Application Note 17
December 1985
Considerations for Successive Approximation
A→D Converters
Jim Williams
conversion speeds below 2Ојs, although they are quite
expensive. Because of these factors, it is often desirable to
build, rather than buy, a high speed 12-bit SAR converter.
Even in cases where high speed is not required, lower cost
may still mandate building the circuit instead of using a
monolithic device. The most popular A→D method employed today is the
successive approximation register (SAR) converter (see
Box, “The Successive Approximation Technique”). Numerous monolithic, hybrid and modular devices embodying
the successive approximation technique are available, and
monolithic devices are slowly gaining in performance.
Nevertheless, hybrid and modular SAR types feature
the best performance. In particular, at the 12-bit level,
the fastest monolithic devices currently available require
about 10Ојs to convert. Modular and hybrid units achieve LT1021
R1
15V
7V
1k …
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, 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, 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, 349 Kb, File published: Oct 1, 1994
This application note presents a wide variety of data acquisition circuits. The detailed circuit schematics cover 8-, 10-, and 12- bit ADC and DAC applications, serial and parallel digital interfaces, battery monitoring, temperature sensing, isolated interfaces, and connections to various popular microprocessors and microcontrollers. An appendix covers suggested voltage references.
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Application Note 62
October 1994
Data Acquisition Circuit Collection
Kevin R. Hoskins
INTRODUCTION
This application note features 8-, 10-, and 12-bit data
acquisition components in various circuit configurations.
The circuits include battery monitoring, temperature sensing, isolated serial interfaces, and microprocessor and
microcontroller serial and parallel interfaces. Also included are voltage reference circuits (Application Note 42
contains more voltage reference circuits). Additional circuit information is located in the information
references listed in the Circuit Index. Each information
reference refers to either an application note (example:
AN42 = Application Note 42), a data sheet (example:
LTCВ®1292 DS = LTC1292 Data Sheet), or a design note
(example: DN66 = Design Note 66).
and LTC are registered trademarks and LT is a trademark of Linear Technology Corporation. CIRCUIT INDEX
FIGURE TITLE
FIGURE NO.
General Analog-to-Digital Application Circuits
Two-Quadrant 150kHz Bandwidth Analog Multiplier . Figure 1 .
Infinite Hold-Time Sample-and-Hold (tACQ = 240ns) . Figure 2 .
Four-Quadrant 250kHz Bandwidth Analog Multiplier . Figure 3 .
Demodulating a Signal Using Undersampling . Figure 4 . …
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, 980 Kb, File published: Jul 1, 1998
DAC DC specifications are relatively easy to verify. AC specifications require more sophisticated approaches to produce reliable information. In particular, the settling time of the DAC and its output amplifier is extraordinarily difficult to determine to 16-bit resolution. This application note presents methods for 16-bit DAC settling time measurement and compares results. Appendices discuss oscilloscope overdrive, frequency compensation, circuit and optimization techniques, layout, power stages and a historical perspective of precision DACs.
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Application Note 74
July 1998
Component and Measurement Advances Ensure
16-Bit DAC Settling Time
The art of timely accuracy
Jim Williams
Introduction
Instrumentation, waveform generation, data acquisition,
feedback control systems and other application areas are
beginning to utilize 16-bit data converters. More specifically, 16-bit digital-to-analog converters (DACs) have
seen increasing use. New components (see Components
for 16-Bit Digital-to-Analog Conversion, page 2) have
made 16-bit DACs a practical design alternative1. These
ICs provide 16-bit performance at reasonable cost compared to previous modular and hybrid technologies. The
DC and AC specifications of the monolithic DAC’s
approach or equal previous converters at significantly
lower cost.
DAC Settling Time
DAC DC specifications are relatively easy to verify. Measurement techniques are well understood, albeit often
tedious. AC specifications require more sophisticated
approaches to produce reliable information. In particular,
the settling time of the DAC and its output amplifier is
extraordinarily difficult to determine to 16-bit resolution. …
PDF, 172 Kb, File published: Nov 1, 1999
Just how do bandgaps and buried Zeners stack up against Weston cells? Did you know your circuit board may induce more drift in a reference than time and temperature? Learn the answers to these and other commonly asked reference questions ranging from burn-in recommendations to ΔVBE generation in this Application Note.
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Application Note 82
November 1999
Understanding and Applying Voltage References 30
2 4 20
8 3
10 –20
16
32 4
–30 5 Today’s IC reference technology is divided along two
lines: bandgap references, which balance the temperature coefficient of a forward-biased diode junction against
that of a ∆VBE (see Appendix B); and buried Zeners (see
Appendix A), which use subsurface breakdown to achieve
outstanding long-term stability and low noise. With few
exceptions, both reference types use additional on-chip
circuitry to further minimize temperature drift and trim
output voltage to an exact value. Bandgap references are
generally used in systems of up to 12 bits; buried Zeners
take over from there in higher accuracy systems.
, LTC and LT are registered trademarks of Linear Technology Corporation. –1 5
3
2 64 6
1 –40 As with other specialized electronic fields, the field of
monolithic references has its own vocabulary. We’ve …
PDF, 540 Kb, File published: Jan 1, 2001
This publication details a true 1ppm D-to-A converter. Total DC error of this processor corrected DAC remains within 1ppm from 18-32°C, including reference drift. DAC error exclusive of reference drift is substantially better. Construction details and performance verification techniques are included, along with a complete software listing.
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Application Note 86
January 2001
A Standards Lab Grade 20-Bit DAC with 0.1ppm/В°C Drift
The Dedicated Art of Digitizing One Part Per Million
Jim Williams
J. Brubaker
P. Copley
J. Guerrero
F. Oprescu INTRODUCTION
Significant progress in high precision, instrumentation
grade D-to-A conversion has recently occurred. Ten years
ago 12-bit D-to-A converters (DACs) were considered
premium devices. Today, 16-bit DACs are available and
increasingly common in system design. These are true
precision devices with less than 1LSB linearity error and
1ppm/В°C drift.1 Nonetheless, there are DAC applications
that require even higher performance. Automatic test
equipment, instruments, calibration apparatus, laser trimmers, medical electronics and other applications often
require DAC accuracy beyond 16 bits. 18-bit DACs have
been produced in circuit assembly form, although they are
expensive and require frequent calibration. 20 and even
23+ (0.1ppm!) bit DACs are represented by manually
switched Kelvin-Varley dividers. These devices, although …
PDF, 73 Kb, File published: May 1, 1988
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Electrically Isolating Data Acquisition Systems
Design Note 10
Guy Hoover and William Rempfer
Introduction
In data acquisition systems it is often necessary to
electrically isolate the measurement points from the
system controller. Reasons for the electrical isolation
include the following: to allow floating measurements
at high voltages; for safety, to reduce the danger of
electrical shock, as might occur in medical applications;
and to eliminate ground loops between measurement
points and the system controller which can cause errors.
The data transmitted over the isolated lines can be
either analog or digital. Analog signals have poor noise
immunity and one isolator is required for each signal
point. Traditionally, the highly noise immune, digitally
encoded signals required many isolated lines for each
channel. Now, with the LTCВ®1090 family of serial data
acquisition systems, it is possible to transmit eight
channels of data with only four isolated lines. Each
additional eight channels requires only one additional
isolated line.
Both opto isolators and pulse transformers could be …
PDF, 78 Kb, File published: Sep 3, 1996
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Micropower ADC and DAC in SO-8 Give PCs
a 12-Bit Analog Interface – Design Note 138
Kevin R. Hoskins
Introduction
Adding two channels of analog input/output to a PC
computer is simple, inexpensive, low powered and
compact when using the LTC В®1298 ADC and LTC1446
DAC. The LTC1298 and the LTC1446 are the п¬Ѓrst SO-8
packaged 2-channel devices of their kind. While the
application shown is for PC data acquisition, the two
converters provide the smallest, lowest power solutions
for many other analog I/O applications. PC 2-Channel Analog I/O Interface
The circuit shown in Figure 1 connects to a PC’s serial
interface using four interface lines: DTR, RTS, CTS and
TX. DTR is used to transmit the serial clock signal, RTS
is used to transfer data to the DAC and ADC, CTS is
used to receive conversion results from the LTC1298,
and the signal on TX selects either the LTC1446 or
the LTC1298 to receive input data. The LTC1298’s and
LTC1446’s low power dissipation allow the circuit to
be powered from the serial port. The TX and RTS lines
charge capacitor C4 through diodes D5 and D6. An
LTВ®1021-5 regulates the voltage to 5V. Returning the …
PDF, 81 Kb, File published: Jan 1, 1989
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A Two Wire Isolated and Powered 10-Bit Data Acquisition Sytem
Design Note 19
Guy Hoover and William Rempfer
Introduction
For reasons of safety or to eliminate error producing
ground loops, it is often necessary to provide electrical
isolation between measurement points and the microprocessor. Unfortunately, the isolated side of this measurement system must still be provided with power. One
alternative is to power the isolated side of the circuit with
batteries. This solution works if power consumption is
low, environmental conditions are mild and the batteries
are easily accessible. If these conditions are not met a
separate isolated supply may be constructed. This can be
both difficult and expensive. This design note describes
a transformer isolated system in which one small pulse
transformer provides both power and a data path.
The circuit of Figure 1 is a 10-bit data acquisition system
with 700V of isolation. The circuit takes advantage of the
serial architecture of the LTC В®1092 which allows data
and power to be transmitted using only one transformer.
A 10-bit conversion can be completed and the data transferred to the microprocessor in 100Ојs. Using standard
ribbon cable the isolated side of this circuit has been remotely located as much as 50 feet from the transformer
without affecting circuit performance.
Circuit Description …
PDF, 455 Kb, File published: Dec 1, 1989
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A Single Supply RS232 Interface for Bipolar A to D Converters
Design Note 29
Sean Gold
system. Construction also requires close attention to the
layout of the system grounds and other aspects of circuit
board design to avoid noise problems.2 Designing circuitry for single supply operation is often an
attractive simplification for reducing production costs. Yet
many applications call for just a few additional supplies to
solve simple interface problems. The example presented
here describes how an advanced RS232 interface can simplify an A to D converter which processes bipolar signals. To accommodate bipolar inputs (–5 < VIN < 5), the
LTC1094’s negative rail must be biased beyond the extreme
signal swing, but below absolute maximum ratings for
supplies. A 5.6V Zener diode, D1, provides a sufficient
bias because the V– pin draws very little current. The LT®1180 RS232 transceiver includes a charge pump
which produces low ripple supplies with sufficient surplus
current to drive a CMOS A to D converter and precision
voltage reference. The circuit in Figure 1 operates from
a single 5V supply, and draws a total quiescent current
of only 37mA. These features make the circuit ideal for
applications which must process bipolar signals with
minimal support electronics. The A to D converter communicates with a remote controller via three wires, which carry the clock, the configuration
word, and the output data. The chip select signal, CS, is
generated from the incoming clock with a peak detector, …
PDF, 54 Kb, File published: Sep 2, 2002
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advertisement 250ksps, 16-Bit Micropower ADC Offers an Excellent
Combination of Size, Power and Speed – Design Note 294
Guy Hoover MSOP Package for Portable Applications
Available in the MSOP package, the LTC1864 is well suited
for portable applications where space is limited. As seen
in Figure 1, the MSOP package provides considerable
space savings over other serial parts available in 20-lead
SW or 28-lead SSOP packages. 20-LEAD SW 28-LEAD SSOP MSOP
DN294 F01 Figure 1. This 16-Bit ADC—Available in the Tiny MSOP
Package—is an Obvious Space Saver Over Other Serial
ADCs Low ADC Supply Current for
Battery-Operated Applications
With a typical supply current of only 850ВµA at the
maximum sample rate of 250ksps, the LTC1864 already
has one of the lowest power consumptions of any 16-bit
ADC available. After a conversion, the LTC1864 goes into
a low power SLEEP mode (ICC = 1nA typ, ICC = 3ВµA max)
further reducing supply current. The LTC1864 can therefore run at true micropower levels in applications that do
not require the maximum LTC1864 sampling rate. At
1ksps, the supply current is typically only 2ВµA as shown
in Figure 2. The part’s low power consumption combined with the ability to go into sleep mode after a
09/02/294 1000 100 SUPPLY CURRENT (ВµA) Introduction
The demand for ever smaller portable devices is increasing. In addition, there is a corresponding demand for …
PDF, 101 Kb, File published: Jun 1, 1990
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12-Bit 8-Channel Data Acquisition System Interfaces to IBM PC
Serial Port – Design Note 35
Guy Hoover and William Rempfer
IBM PCs Collect Analog Data
IBM PC compatibles can be found just about everywhere.
In those instances where a PC is not already in place,
battery operated portables are readily available. This
makes the PC a good choice for controlling a data acquisition system. Typically, such data acquisition systems
have been expensive. Using dedicated A/D cards or
IEEE-488 controllers and instruments, these systems
tie up slots in the PC and are not readily transportable
from one machine to another. As an alternative, the
schematic of Figure 1 shows a 12-bit, 8-channel data
acquisition system that connects to the serial port of
the PC. This system uses an LTC В®1290, a reference,
a handful of other low cost components and requires
12 lines of BASIC to transfer data into the PC. If only
ten bits of resolution are required the LTC1290 can be
replaced with an LTC1090. Additionally, if the LTC1090
is used, the system can be powered directly from the
PC serial port with the option shown. Two Glue Chips Provide the Interface
The control and status lines of the PC serial port are
used to send data to and receive data from the LTC1290. …
