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Application Notes

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  Performance Verification of Low Noise, Low Dropout Regulators &mdash AN83
  PDF, 542 Kb, File published: Mar 1, 2000
  In an increasing trend, telecommunications, networking, audio and instrumentation require low noise power supplies. In particular, there is interest in low noise, low dropout linear regulators (LDO). Establishing and specifying LDO dropout performance is relatively easy to do. Verifying that a regulator meets dropout specification is similarly straightforward. Accomplishing the same missions for noise and noise testing is considerably more involved. The noise bandwidth of interest must be called out, along with operating conditions. Low noise performance is affected by numerous subtleties; changes in operating conditions can cause unwelcome surprises. Because of this, LDO noise must be quoted under specified operating and bandwidth conditions to be meaningful. Failure to observe this precaution results in misleading data and erroneous conclusions. This Application Note suggests a noise testing method, details its implementation and presents results.
  Extract from the document

  Application Note 83
  March 2000
  Performance Verification of Low Noise,
  Low Dropout Regulators
  Silence of the Amps
  Jim Williams and Todd Owen, Linear Technology Corporation
  Introduction
  In an increasing trend, telecommunications, networking,
  audio and instrumentation require low noise power supplies. In particular, there is interest in low noise, low
  dropout linear regulators (LDO). These components power
  noise-sensitive circuitry, circuitry that contains noisesensitive elements or both. Additionally, to conserve power,
  particularly in battery driven apparatus such as cellular
  telephones, the regulators must operate with low input-tooutput voltages.1 Devices presently becoming available
  meet these requirements (see separate section, “A Family
  of 20µVRMS Noise, Low Dropout Regulators”).
  Noise and Noise Testing
  Establishing and specifying LDO dropout performance is
  relatively easy to do. Verifying that a regulator meets
  dropout specification is similarly straightforward. Accomplishing the same missions for noise and noise testing is
  considerably more involved. The noise bandwidth of interest must be called out, along with operating conditions.
  Operating conditions can include regulator input and
  output voltage, load, assorted discrete components, etc.
  Low noise performance is effected by numerous subtleties; changes in operating conditions can cause unwelcome surprises.2 Because of this, LDO noise must be …

Design Notes

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  Get 100dB Stopband Attenuation with the LTC1562 Universal Filter Family &mdash DN195
  PDF, 333 Kb, File published: Dec 1, 1998
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  Get 100dB Stopband Attenuation with the LTC1562
  Universal Filter Family – Design Note 195
  Max W. Hauser
  The LTC ®1562 and LTC1562-2 are compact, high performance, “universal” continuous-time filter products, each
  containing four 2nd order Operational Filterв„ў blocks.
  These low noise, DC-accurate filters let you tailor their
  center frequencies (f0) over a range of roughly 10kHz
  to 150kHz (LTC1562) or 20kHz to 300kHz (LTC1562-2)
  and replace several precision capacitors, resistors and
  op amps. All frequency-setting components are internal
  and trimmed, except for one resistor per block, which is
  desensitized (1% error in this external resistor’s value
  contributes only 0.5% error to the programmed f0). Additional components program each block’s Q and gain.
  A complete application circuit using either the LTC1562
  or LTC1562-2 on a surface mount board is about the size
  of a dime (155mm2).
  Figure 1 shows one block, or 2nd order section (each
  LTC1562 contains four of these), with external resistors
  to set the standard 2nd order filter parameters f0, Q and
  gain. In this example, the section is configured so that
  the two outputs give lowpass and bandpass responses.
  Cascades of Figure 1 circuits, with appropriate resistor
  *R1 AND C ARE PRECISION …

Articles

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  Universal Continuous-Time Filter Challenges Discrete Designs &mdash LT Journal
  PDF, 291 Kb, File published: Feb 1, 1998
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  LINEAR TECHNOLOGY
  FEBRUARY 1998
  IN THIS ISSUE…
  COVER ARTICLE
  Universal Continuous-Time Filter
  Challenges Discrete Designs . 1
  Max Hauser Issue Highlights . 2
  LTCВ® in the News . 2
  DESIGN FEATURES
  An SMBus-Controlled 10-Bit, Current
  Output, 50Вµ A, Full-Scale DAC . 6
  Ricky Chow Micropower 600kHz Fixed-Frequency
  DC/DC Converters Step Up from a
  1-Cell or 2-Cell Battery . 8
  Steve Pietkiewicz New 333ksps, 16-Bit ADC Offers 90dB
  SINAD and –100dB THD . 11
  Marco Pan Ultralow Power 14-Bit ADC Samples
  at 200ksps . 14
  Dave Thomas A 10MB/s Multiple-Protocol Chip Set
  Supports Net1 and Net2 Standards
  . 17
  David Soo DESIGN IDEAS
  High Clock-to-Center Frequency Ratio …

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  How to Design High Order Filters with Stopband Notches Using the LTC1562 Operational Filter (Part 2) &mdash LT Journal
  PDF, 87 Kb, File published: Feb 1, 1999
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  DESIGN IDEAS How to Design High Order Filters with
  Stopband Notches Using the LTC1562
  Operational Filter (Part 2) by Nello Sevastopoulos
  This is the second in a series of
  articles describing applications of the
  LTC1562 connected as a lowpass,
  highpass or bandpass filter with added
  stopband notches to increase selectivity. Part 1 (Linear Technology VIII:2,
  May 1998, pp. 28–31) described one
  method of coupling the four Operational Filterв„ў building blocks of the
  LTC1562 to design an 8th order lowpass filter with two stopband notches.
  Part 2 expands the technique of Part
  1 to design an 8th order bandpass
  filter with two stopband notches.
  Throughout this series of articles,
  notches will be generated by first summing the input signal with a 180
  degree out-of-phase signal appearing
  at the output(s) of the LTC1562
  Operational Filter and second, by adjusting the summation gains to yield
  a zero sum.
  Part 1 showed one proprietary
  method of creating notches in the
  stopband of a lowpass filter. The …

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  New Universal Continuous-Time Filter with Extended Frequency Range &mdash LT Journal
  PDF, 87 Kb, File published: Feb 1, 1999
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  DESIGN FEATURES New Universal Continuous-Time Filter
  with Extended Frequency Range
  by Max W. Hauser
  Introduction
  The original LTC1562, described in
  the February 1998 issue of this magazine, is a compact, quadruple 2nd
  order, universal, continuous-time filter that is DC accurate and user
  programmable for the 10kHz–150kHz
  frequency range. The LTC1562 introduced Operational Filter building
  blocks, whose virtual-ground input,
  rail-to-rail outputs and precision
  internal R and C components satisfy
  diverse filter requirements and applications compactly.1, 2, 3
  The design of the LTC1562 entailed
  choices in the internal R and C values
  and internal amplifiers, and these
  elements were optimized to minimize
  wideband noise. The LTC1562-2 is a
  new product with the same block
  diagram, pinout and packaging, but
  optimized for higher filter frequencies: 20kHz to 300kHz. The internal
  precision R and C components and
  amplifiers are different in the …

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  How to Design High Order Filters with Stopband Notches Using the LTC1562 Quad Operational Filter (Part 1) &mdash LT Journal
  PDF, 293 Kb, File published: May 1, 1998
  Extract from the document

  DESIGN IDEAS How to Design High Order Filters
  with Stopband Notches Using the
  LTC1562 Quad Operational Filter (Part 1)
  by Nello Sevastopoulos
  This is the first in a series of articles
  describing applications of the LTC1562
  connected as a lowpass, highpass or
  bandpass filter with added stopband
  notches to increase selectivity. Part 1
  covers lowpass filters.
  Lowpass filters with stopband
  notches are useful in applications seeking steep attenuation in the vicinity of
  the cutoff frequency. When compared
  to classical all-pole realizations (such
  as Butterworth or Chebyshev) they are
  more “efficient”; that is, they meet a
  given attenuation requirement with
  the least number of poles.
  Lowpass filters with stopband
  notches (broadly referred to as
  “elliptics” or “Cauers”) can be designed
  with the aid of some literature or with
  commercially available software. The …

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  Sharp Gain Roll-Offs Using the LTC1562 Quad Operational Filter IC (Part 3) &mdash LT Journal
  PDF, 178 Kb, File published: Nov 1, 1999
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  DESIGN IDEAS Sharp Gain Roll-Offs Using the LTC1562
  Quad Operational Filter IC (Part 3)
  by Nello Sevastopoulos
  This is the third in series of articles
  describing applications of the
  LTC1562 quad Operational Filterв„ў
  IC connected as a lowpass, highpass,
  notch or bandpass filter with added
  stopband notches to increase
  selectivity.
  Parts 1 and 2 of the series (Linear
  Technology VIII: 2, May 1998, pp. 28–
  31 and IX:1, February 1999, pp.
  31–35) described two notch techniques referred to as “feedforward.”
  In these techniques, the filter topology was modified to introduce
  summing junctions in the signal path
  and passive components were carefully selected to allow summed signals
  to cancel each other at specific
  frequencies.
  Part 3 of this series describes a new
  notch technique, the RC notch, that
  can be broadly applied to create
  notches at any frequency. At the end …

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  Performance Verification of Low Noise, Low Dropout Regulators &mdash LT Journal
  PDF, 1.2 Mb, File published: Sep 1, 2000
  Extract from the document

  DESIGN IDEAS Performance Verification of
  Low Noise, Low Dropout Regulators
  by Jim Williams and Todd Owen
  Introduction
  In an increasing trend, telecommunications, networking, audio and
  instrumentation require low noise
  power supplies. In particular, there is
  interest in low noise, low dropout
  linear regulators (LDOs). These
  5Hz SINGLE ORDER
  HIGHPASS components power noise-sensitive circuitry, circuitry that contains
  noise-sensitive elements or both.
  Additionally, to conserve power, particularly in battery-driven apparatus 10Hz 2nd ORDER
  BUTTERWORTH HP GAIN = 60dB IN such as cellular telephones, the
  regulators must operate with low
  input-to-output voltage differentials.
  Devices presently becoming available
  meet these requirements. 100kHz 4th ORDER
  BUTTERWORTH LP 5Hz SINGLE ORDER
  HIGHPASS
  10Hz TO 100kHz Figure 1. Filter structure for noise testing LDOs; Butterworth sections provide the appropriate response in the desired frequency range. EXTERNAL INPUT +
  +
  INPUT 100Ω + 330ВµF 100Ω A1 …

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Manufacturer's Classification

• Signal Conditioning > Filters > Filter Building Blocks