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Circuit arrangement for forming the difference and the sum of two detected signals

  • US 5,029,276 A
  • Filed: 04/10/1990
  • Issued: 07/02/1991
  • Est. Priority Date: 04/12/1989
  • Status: Expired due to Term
First Claim
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1. A circuit arrangement for forming the difference and the sum of first and second detected signals, comprising a first detector (D2) and a second detector (D3) connected to each other in back-to-back fashion for forming a junction (J), a first operational amplifier (PI) connected with its input to said junction (J) to directly form a difference signal from currents representing said first and second detected signals and flowing through said first and second detectors (D2 -D3), a second operational amplifier (OPII) connected with its input to said first detector (D2) for inverting and amplifying said first detected signal to provide an inverted and amplified signal, a third operational amplifier (OPIII) connected with its input to said second detector (D3) for supplying said second detected signal to said third operational amplifier (OPIII), said second and third operational amplifiers virtually short-circuiting said first and second detectors (D2, D3) to ground, and resistor means (R4) connecting an output of said second operational amplifier (OPII) to said input of said third operational amplifier (OPIII) for forming said sum from said inverted and amplified signal and from said second detected signal.

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