US 2002/0171489 A1 · Variable gain amplifier stage

Abstract

A variable gain amplifier stage has first and second input terminals for receiving a differential input signal and first and second emitter follower transistors having their base electrodes coupled to the input terminals and their emitter electrodes coupled to a pair of matched voltage controlled current sources. A differential pair of transistors has their base electrodes coupled to the emitter electrodes of the first and second emitter follower transistors and their emitter electrodes coupled together and to a third voltage controlled current source. The voltage controlled current sources are controlled by the same voltage source so that a decrease in the differential pair tail current increases the bandwidth and decreases the gain of the stage, but a decrease in the current through the emitter follower transistors decreases the bandwidth of the stage so that by carefully controlling the relationship between these currents, a constant bandwidth can be maintained.

Claims11

Dependent claims

A variable gain amplifier stage comprising:

first and second input terminals for receiving a differential input signal;
first and second input transistors, the first input transistor having a base electrode coupled to the first input terminal, a first current electrode coupled to a first supply rail and a second current electrode coupled to a first voltage controlled current source, and the second input transistor having a base electrode coupled to the second input terminal, a first current electrode coupled to the first supply rail and a second current electrode coupled to a second voltage controlled current source;
a differential pair of transistors having respective base electrodes coupled to the second current electrodes of the first and second input transistors, respectively, first current electrodes coupled to the first supply rail via load components and second current electrodes coupled together and to a third voltage controlled current source, wherein the gains of the first and second voltage controlled current sources are matched;
and
first and second output terminals coupled respectively to the respective first current electrodes of the differential pair of transistors.

2 more elements

Dependencies are inferred from the claim text.

Variable gain amplifier stage

Life of this patent

Variable gain amplifier stage

Life of this patent

Abstract

Claims11