Variable gain amplifier

Claim 2

A variable gain amplifier, comprising: an input stage transistor for amplifying an input signal; a resistive network including a plurality of resistors connected in series between potential sources; a plurality of switching transistors for supplying the collector current of said input stage transistor to each node of said resistive network; and control means for selectively enabling either one of said switching transistors; wherein an output signal of predetermined different gains is derived from at least one of the resistors of said resistive network.

Claim 3

A variable gain amplifier in accordance with claim 1, wherein said input stage transistor and said switching transistors constitute a cascode amplifier.

Claim 4

A variable gain amplifier in accordance with claim 2, wherein said control means is a logic circuit to provide a logic signal to the base electrodes of said switching transistors.

Claim 5

A variable gain amplifier in accordance with claim 1, wherein the resistors of said resistive network have programmed resistance to provide predetermined gains.

Claim 6

A variable gain amplifier in accordance with claim 1 wherein said input stage transistor is a differential amplifier and said switching transistors include a plurality of transistor pairs.

Claim 7

A variable gain amplifier in accordance with claim 5 wherein the base electrodes of each transistor pair of said switching transistor pairs are coupled together to receive a control signal from said control means.

Claim 8

A selection amplifier including first and second variable gain differential amplifiers each amplifying a respective input signal and the outputs thereof coupled together to a common output section having a plurality of resistors connected in series between potential sources, each of said variable gain differential amplifiers comprising: a differential transistor pair; a plurality of switching transistor pairs connected between the collector electrode of each of said differential transistor pair and node of said plurality of resistors in said common output section; and control means for selectively enabling either one pair of said plurality of switching transistor pairs; wherein the collector electrodes of one pair of said switching transistor pairs are coupled together to the mid point of said resistors.

Claim 9

A selection amplifier including first and second variable gain differential amplifiers each amplifying a respective input signal and the outputs thereof coupled together to a common output section having a plurality of resistors connected in series between potential sources, each of said variable gain differential amplifiers comprising: a differential transistor pair; a plurality of switching transistor pairs connected between the collector electrode of each of said differential transistor pair and node of said plurality of resistors in said common output section; and control means for selectively enabling either one pair of said plurality of switching transistor pairs; wherein the collector electrodes of one pair of said switching transistor pairs are coupled together to the mid point of said resistors.

Claim 10

A selection amplifier in accordance with claim 7 further including a polarity switching circuit in at least one of said first and second variable gain differential amplifiers.