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Application Notes

• Download
  Instrumentation Circuitry Using RMS-to-DC Converters &mdash AN106
  PDF, 354 Kb, File published: Feb 21, 2007
  It is widely acknowledged that RMS measurement of waveforms furnishes the most accurate amplitude information. Rectify-andaverage schemes, usually calibrated to a sine wave, are only accurate for one waveshape. Departures from this waveshape result in pronounced errors. Although accurate, RMS conversion often entails limited bandwidth, restricted range, complexity and difficult to characterize dynamic and static errors. The LTC1966/67/68 RMS converter family addresses these issues, making instrument grade applications practical. A variety of instrumentation oriented applications are presented. Included are basic circuits, a fully isolated AC line monitor, a distortionless AC line voltage regulator, wideband X1000 pre-amplifiers, a quartz crystal RMS current meter, a crystal stabilized AC voltage reference, an RMS amplitude leveled random noise generator and an RMS amplitude level controller. Appended sections cover RMS theory and converter operation, AC measurement and signal handling practice, test equipment recommendations, noise theory and noise diodes.
  Extract from the document

  Application Note 106
  February 2007
  Instrumentation Circuitry Using RMS-to-DC Converters
  RMS Converters Rectify Average Results
  Jim Williams
  INTRODUCTION Isolated Power Line Monitor It is widely acknowledged that RMS (Root of the Mean
  of the Square) measurement of waveforms furnishes
  the most accurate amplitude information.1 Rectify-andaverage schemes, usually calibrated to a sine wave, are
  only accurate for one waveshape. Departures from this
  waveshape result in pronounced errors. Although accurate,
  RMS conversion often entails limited bandwidth, restricted
  range, complexity and difficult to characterize dynamic
  and static errors. Recent developments address these
  issues while simultaneously improving accuracy. Figure 1
  shows the LTCВ®1966/LTC1967/LTC1968 device family. Low
  frequency accuracy, including linearity and gain error, is
  inside 0.5% with 1% error at bandwidths extending to
  500kHz. These converters employ a sigma-delta based
  computational scheme to achieve their performance.2 BEFORE PROCEEDING ANY FURTHER, THE READER
  IS WARNED THAT CAUTION MUST BE USED IN THE
  CONSTRUCTION, TESTING AND USE OF THIS CIRCUIT.
  HIGH VOLTAGE, LETHAL POTENTIALS ARE PRESENT IN
  THIS CIRCUIT. EXTREME CAUTION MUST BE USED IN …

Design Notes

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  RMS-to-DC Conversion Just Got Easy &mdash DN288
  PDF, 82 Kb, File published: Jun 2, 2002
  Extract from the document

  RMS-to-DC Conversion Just Got Easy – Design Note 288
  Glen Brisebois and Joseph Petrofsky
  Introduction
  The LTC ®1966 is a precision, micropower, true RMSto-DC converter that utilizes an innovative patented ∆Σ
  computational technique.* The internal delta-sigma
  circuitry of the LTC1966 makes it simpler to use, more
  accurate, lower power and dramatically more flexible
  than conventional log-antilog RMS-to-DC converters.
  Unlike previously available RMS-to-DC converters, the
  superior linearity of the LTC1966 allows hassle-free
  system calibration with any input voltage, even DC.
  Ease of Use
  The flexibility of the LTC1966 is illustrated in the typical
  applications shown in Figures 1a, 1b and 1c. The LTC1966
  accepts single ended or differential input signals (for
  EMI/RFI rejection) and supports crest factors up to 4.
  Common mode input range is rail-to-rail while the differential input range is 1VPEAK. The LTC1966 also has
  a rail-to-rail output with a separate output reference
  pin providing for flexible level shifting. The LTC1966
  operates on a single power supply from 2.7V to 5.5V
  or dual supplies up to В±5.5V while drawing only 155ОјA.
  When the LTC1966 is shut down, supply current is
  reduced to just 0.1ОјA. …

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  An Autoranging True RMS Converter &mdash DN339
  PDF, 77 Kb, File published: Jun 1, 2004
  Extract from the document

  An Autoranging True RMS Converter – Design Note 339
  Philip Karantzalis and Jim Mahoney
  True RMS voltage detection is most commonly required
  to measure complex amplitude and time varying signals,
  such as machine or engine vibration monitoring and
  complex AC power line load monitoring. Sometimes
  these applications require accurate input signal measurement over an extremely wide dynamic range—even
  more than the 50dB range of the LTC1966. One solution
  is to add an autoranging function to the LTC1966, thus Introduction
  The LTC В®1966 is a true RMS-to-DC converter that uses
  a ∆Σ computational technique to make it dramatically
  simpler to use, significantly more accurate, lower in
  power consumption and more flexible than conventional log-antilog RMS-to-DC converters. The LTC1966
  RMS-to-DC converter has an input signal range from
  5mVRMS to 1.5VRMS (a 50dB dynamic range with a
  single 5V supply rail) and a 3dB bandwidth of 800kHz
  with signal crest factors up to four. 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.
  LT1783 BUFFER RMS-DC CONVERTER 5V 0.01ОјF 5V 0.1ОјF
  2 3 AGND G2 INPUT 4 IN G1 V– G0 0.1μF 1 OUTPUT 5
  0.1ОјF 6
  –5V GND VSS 8 1 4 WINDOW …

Articles

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  Delta Sigma Breakthrough: LTC1966 True RMS-to-DC Converter Uses No Diodes, Heaters or Logarithms &mdash LT Journal
  PDF, 270 Kb, File published: Mar 1, 2002
  Extract from the document

  LINEAR TECHNOLOGY
  MARCH 2002 IN THIS ISSUE…
  COVER ARTICLE
  ∆Σ Breakthrough: LTC1966 True
  RMS-to-DC Converter Uses No Diodes,
  Heaters or Logarithms . 1
  Joseph Petrofsky and Glen Brisebois Issue Highlights . 2
  LTCВ® in the News . 2
  DESIGN FEATURES
  Unique Instrumentation Amplifier
  Precisely Senses Differential Voltages
  from ВµV to V . 7
  David Hutchinson and Nello Sevastopoulos High Efficiency DDR Termination
  Power Supplies Source and Sink
  More than 10 Amps . 9
  Wei Chen A High Performance, Single-Ended, No
  RSENSEв„ў Controller for Negative
  Output Supplies . 13
  Tick Houk Rail-to-Rail Output Dual Comparator
  Resolves 150MHz Signals While
  Shifting from Analog to Digital
  Voltage Levels . 17
  John D. Morris and Glen Brisebois It Just Got Easier to Convert LithiumIon Battery Voltage to 3.3V with this …

Model Line

Manufacturer's Classification

• Signal Conditioning > RMS-DC Conversion
• Space & Harsh Environment > Extended Temperature Plastic (H & MP) > Extended Temperature (H & MP) System Monitor