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LT1789 LT1789-10

Application Notes

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  Bias Voltage and Current Sense Circuits for Avalanche Photodiodes &mdash AN92
  PDF, 1.1 Mb, File published: Nov 1, 2002
  Avalanche photodiodes, used in laser based fiberoptic systems, require high voltage bias and accurate, wide range current monitoring. Bias voltage varies from 15V-90V and current ranges from 100nA to 1mA, a 10,000:1 dynamic range. This publication presents various 5 volt powered circuits which meet these requirements. Appended sections detail specific circuit techniques and cover measurement practice.
  Extract from the document

  Application Note 92
  November 2002
  Bias Voltage and Current Sense Circuits for
  Avalanche Photodiodes
  Feeding and Reading the APD
  Jim Williams, Linear Technology Corporation
  INTRODUCTION
  Avalanche photodiodes (APDs) are widely utilized in laser
  based fiberoptic systems to convert optical data into
  electrical form. The APD is usually packaged with a signal
  conditioning amplifier in a small module. An APD receiver
  module and attendant circuitry appears in Figure 1. The
  APD module (figure right) contains the APD and a transimpedance (e.g., current-to-voltage) amplifier. An optical
  port permits interfacing fiberoptic cable to the APD’s
  photosensitive portion. The module’s compact construction facilitates a direct, low loss connection between the
  APD and the amplifier, necessary because of the extremely
  high speed data rates involved.
  The receiver module needs support circuitry. The APD
  requires a relatively high voltage bias (figure left) to
  operate, typically 20V to 90V. This voltage is set by the bias
  supply’s programming port. This programming voltage
  may also include corrections for the APD’s temperature
  dependent response. Additionally, it is desirable to monitor the APD’s average current (figure center), which indi-cates optical signal strength. This information can be …

Design Notes

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  New Instrumentation Amplifiers Maximize Output Swing on Low Voltage Supplies &mdash DN323
  PDF, 83 Kb, File published: Oct 2, 2003
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  New Instrumentation Amplifiers Maximize Output Swing
  on Low Voltage Supplies – Design Note 323
  Glen Brisebois
  INTRODUCTION
  Instrumentation amplifiers suffer from a chronic output
  swing problem, even when the input common mode
  range and output voltage swing specifications are not
  violated. This is because the first stage of an instrumentation amplifier has internal output voltages that can
  clip at unspecified levels. The clipping itself is invisible
  to the user, but it affects the output swing adversely,
  usually causing a gain reduction and thus an invalid
  result. The new LTC В®6800 and LTВ®1789-10 both solve
  this output swing problem, but in two extremely different ways. The LTC6800 incorporates a flying capacitor
  differential level shifter followed by a rail-to-rail output
  autozero amplifier. The LT1789-10 is a more classical
  three op amp instrumentation amplifier with the twist
  that it takes gain in the п¬Ѓnal stage.
  A CLEARER PICTURE OF THE PROBLEM
  Figure 1 shows the classical three op amp instrumentation amplifier (IA) topology. Assume that the op amps
  involved can common mode to VS – and have rail-to-rail
  output stages. This would normally mean that the inputs
  can be anywhere from VS – to about a volt from VS+ and
  that the output can be anywhere within the supply rails. …

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Manufacturer's Classification

• Signal Conditioning > Amplifiers > Instrumentation Amplifiers