PDF, 150 Kb, File published: Oct 1, 1985
Circuits for clock sources are presented. Special attention is given to crystal-based designs including TXCOs and VXCOs.
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Application Note 12
October 1985
Circuit Techniques for Clock Sources
Jim Williams
Almost all digital or communication systems require some
form of clock source. Generating accurate and stable clock
signals is often a difficult design problem.
Quartz crystals are the basis for most clock sources. The
combination of high Q, stability vs time and temperature,
and wide available frequency range make crystals a
price-performance bargain. Unfortunately, relatively little
information has appeared on circuitry for crystals and
engineers often view crystal circuitry as a black art, best
left to a few skilled practitioners (see box, “About Quartz
Crystals”).
In fact, the highest performance crystal clock circuitry does
demand a variety of complex considerations and subtle
implementation techniques. Most applications, however,
don’t require this level of attention and are relatively easy
to serve. Figure 1 shows five (5) forms of simple crystal
clocks. Types 1a through 1d are commonly referred to
as gate oscillators. Although these types are popular,
they are often associated with temperamental operation, …
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, 975 Kb, File published: Aug 2, 1984
This application note describes a number of enhancement circuit techniques used with existing 3-terminal regulators which extend current capability, limit power dissipation, provide high voltage output, operate from 110VAC or 220VAC without the need to switch transformer windings, and many other usefu application ideas.
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Application Note 2
August 1984
Performance Enhancement Techniques for
Three-Terminal Regulators
Jim Williams
Three terminal regulators provide a simple, effective solution to voltage regulation requirements. In many situations
the regulator can be used with no special considerations.
Some applications, however, require special techniques
to enhance the performance of the device.
Probably the most common modification involves extending the output current of regulators. Conceptually, the
simplest way to do this is by paralleling devices. In practice,
the voltage output tolerance of the regulators can cause
problems. Figure 1 shows a way to use two regulators to
achieve an output current equal to their sum. This circuit
capitalizes on the 1% output tolerance of the specified
regulators to achieve a simple paralleled configuration.
Both regulators sense from the same divider string and
the small value resistors provide ballast to account for the
slightly differing output voltages. This added impedance
degrades total circuit regulation to about 1%. Figure 2 shows another way to extend current capability
in a regulator. Although this circuit is more complex than
Figure 1, it eliminates the ballasting resistor’s effects
and has a fast-acting logic-controlled shutdown feature. …
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, 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, 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, 1.2 Mb, File published: Sep 1, 1996
Application Note 67 is a collection of circuits for data conversion, interface and signal processing from the first five years of Linear Technology. This application note includes circuits such as fast video multiplexers for high speed video, an ultraselective bandpass filter circuit with adjustable gain, and a fully differential, 8-channel, 12-bit A/D system. The categories included in this app note are data conversion, interface, filters, instrumentation, video/op amps and miscellaneous circuits.
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Application Note 67
September 1996
Linear Technology Magazine Circuit Collection, Volume III
Data Conversion, Interface and Signal Processing
Richard Markell, Editor
INTRODUCTION
Application Note 67 is a collection of circuits from the first
five years of Linear Technology, targeting data conversion,
interface and signal processing applications. This
Application Note includes circuits such as fast video
multiplexers for high speed video, an ultraselective
bandpass filter circuit with adjustable gain and a fully differential, 8-channel, 12-bit A/D system. The categories
included herein are data conversion, interface, filters,
instrumentation, video/op amps and miscellaneous
circuits. Application Note 66, which covers power products
and circuits from Linear Technology ’s first five years, is
also available from LTC. ARTICLE INDEX
Data Conversion . 3
Fully Differential, 8-Channel, 12-Bit A/D System Using the LTCВ®1390 and LTC1410 . 3
12-Bit DAC Applications . 5
LTC1329 Micropower, 8-Bit, Current Output DAC Used for Power Supply Adjustment,
Trimmer Pot Replacement . 7
12-Bit Cold Junction Compensated, Temperature Control System with Shutdown . 8 …
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, 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 …
