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Variable gain amplifier

  • US 5,331,290 A
  • Filed: 09/08/1992
  • Issued: 07/19/1994
  • Est. Priority Date: 09/08/1992
  • Status: Expired due to Term
First Claim
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1. A gain-controlled amplifier stage comprising:

  • first and second transistors having respective emitter electrodes, respective base electrodes, and respective collector electrodes;

    means for connecting said first and second transistors in emitter-coupled differential amplifier configuration, which means includesmeans for applying a direct base bias voltage to the base electrode of said first transistor,means for applying said direct base bias voltage to the base electrode of said second transistor,means for applying an input signal voltage between the base electrodes of said first and second transistors,means for coupling the emitter electrodes of said first and second transistors together, andmeans for causing similar direct emitter current flows through said first and second transistors;

    a first resistance, having a first end connected to conduct the entirety of a direct current flowing through the collector electrode of said first transistor responsive to its said direct emitter current flow, and having a second end;

    a second resistance, having a first end connected to conduct the entirety of a direct current flowing through the collector electrode of said second transistor responsive its said direct emitter current flow, and having a second end;

    means for receiving a direct operating voltage for application to the second ends of said first and said second resistances;

    means for taking an output signal voltage from at least one of the first ends of said first and said second resistances; and

    means for providing a controllable conductance between the first ends of said first and said second resistances, which said means for providing a controllable conductance includes;

    first and second diodes of unilaterally conductive type, having respective first electrodes respectively connecting to the first end of said first resistance and to the first end of said second resistance, and having respective second electrodes connecting together at a control node; and

    means for supplying a direct control current to said control node for controlling the unilateral conduction of said first and second diodes which direct control current has a value regulated responsive to an electric control signal, said electric control signal being applied to said means for supplying a direct control current through connections other than at the second ends of said first and said second resistances.

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