Variable-gain amplifier with stepwise controller

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,
• wherein the first controller controls an emitter potential of the first transistor according to a first control signal fed in from outside, and the second controller controls an emitter potential of the second transistor according to a second control signal fed in from outside.

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,
• wherein the first controller controls an emitter potential of the first transistor according to a first control signal fed in from outside, and the second controller controls an emitter potential of the second transistor according to a second control signal fed in from outside,
• wherein the first controller is composed of a seventh transistor of which an emitter is connected to an emitter of the first transistor, the seventh transistor feeding out an emitter current according to the first control signal applied to a base thereof, and
• the second controller is composed of an eighth transistor of which an emitter is connected to an emitter of the second transistor, the eighth transistor feeding out an emitter current according to the second control signal applied to a base thereof.

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,
• wherein, when a gain is equal to or higher than a predetermined value, the first and second controllers are brought into an off state.

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.