US 2003/0038677 A1 · Variable-gain amplifier

Abstract

In a conventional variable-gain amplifier, when high-frequency signals are fed in, leak current flows through the collector-emitter parasitic capacitance of transistors, making it impossible to attenuate the gain sufficiently. A variable-gain amplifier of the invention has a controller for controlling the operation of input transistors so as to reduce the leak current that flows through transistors because of their collector-emitter parasitic capacitance when high-frequency signals are fed in and thereby prevent saturation of gain attenuation. Another variable-gain amplifier of the invention has a plurality of variable-gain amplifier circuits connected in parallel, and has a current control circuit for controlling the bias current sources provided within each of the variable-gain amplifier circuits so as to reduce the leak current that flows through transistors because of their collector-emitter parasitic capacitance when high-frequency signals are fed in and thereby prevent saturation of gain attenuation.

Claims19

Dependent claims

A variable-gain amplifier comprising:

a first differential amplifier circuit having first and second transistors, a differential input voltage being applied between bases of the first and second transistors;
a second differential amplifier circuit having third and fourth transistors of which emitters are connected to a collector of the first transistor, the second differential amplifier circuit outputting a signal amplified by the first transistor after attenuating the signal according to a voltage applied between bases of the third and fourth transistors;
a third differential amplifier circuit having fifth and sixth transistors of which emitters are connected to a collector of the second transistor, the third differential amplifier circuit outputting a signal amplified by the second transistor after attenuating the signal according to a voltage applied between bases of the fifth and sixth transistors;
a first controller for controlling operation of the first transistor;
and
a second controller for controlling operation of the second transistor.

3 more elements

A variable-gain amplifier comprising:

a plurality of variable-gain amplifier circuits connected in parallel;
a voltage shift circuit for producing, from a reference control voltage fed in from outside, a first control voltage for each of the variable-gain amplifier circuits;
and
a current control circuit for controlling bias currents for each of the variable-gain amplifier circuits,
wherein the plurality of variable-gain amplifier circuits each comprise:
a first differential amplifier circuit having first and second transistors and current sources, a differential input voltage being applied between bases of the first and second transistors, the current sources outputting bias currents to supply currents to the first and second transistors;
a second differential amplifier circuit having third and fourth transistors of which emitters are connected to a collector of the first transistor, the second differential amplifier circuit outputting a signal amplified by the first transistor after attenuating the signal according to a difference between the first control voltage applied to a base of the third transistor and a bias voltage applied to a base of the fourth transistor;
a third differential amplifier circuit having fifth and sixth transistors of which emitters are connected to a collector of the second transistor, the third differential amplifier circuit outputting a signal amplified by the second transistor after attenuating the signal according to a difference between the first control voltage applied to a base of the fifth transistor and the bias voltage applied to a base of the sixth transistor.

5 more elements

Dependencies are inferred from the claim text.

Variable-gain amplifier

Life of this patent

Variable-gain amplifier

Life of this patent

Abstract

Claims19