Patent ID: 7193465

Claim:
A variable gain amplifier comprising: a first constant current source, a second constant current source, and a third constant current source; differentially-connected first and second amplifying elements for signal amplification; differentially-connected third and fourth amplifying elements for gain control; and differentially-connected fifth and sixth amplifying elements for gain control, wherein the first constant current source and the first and second amplifying elements are composed of a PNP transistor, wherein the second and third constant current sources and the third to sixth amplifying elements are composed of an NPN transistor, wherein drains of the first and second amplifying elements are connected to each other at a node, and the node is connected to a first terminal of the first constant current source, wherein sources of the third and fourth amplifying elements are connected to each other at a node, and the node is connected to a source of the first amplifying element, wherein sources of the fifth and sixth amplifying elements are connected to each other at a node, and the node is connected to a source of the second amplifying element, wherein a second terminal of the first constant current source is connected to a high potential terminal of a power source, wherein a first terminal of the second constant current source is connected to the node of the sources of the first, third, and fourth amplifying elements, and a second terminal of the second constant current source is connected to a low potential terminal of the power source, and wherein a first terminal of the third constant current source is connected to the node of the sources of the second, fifth, and sixth amplifying elements, and a second terminal of the third constant current source is connected to the low potential terminal of the power source.