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, 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.
Extract from the document
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.
Extract from the document
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, 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.
Extract from the document
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.
Extract from the document
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.
Extract from the document
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, 784 Kb, File published: Jan 1, 1985
Application considerations and circuits for the LT1001 and LT1002 single and dual precision amplifiers are illustrated in a number of circuits, including strain gauge signal conditioners, linearized platinum RTD circuits, an ultra precision dead zone circuit for motor servos and other examples.
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.
Extract from the document
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, 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.
Extract from the document
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 …
