VARIABLE GAIN AMPLIFIER
The present invention provides a variable gain amplifier including a plurality of initial-stage LNAs 1 to 4 connected parallel to one input terminal IN, a next-stage LNA 5 connected after the initial-stage LNAs 1 to 4 and a variable current source 20 that performs control such that a total value of initial-stage control currents IB 1 to IB 4 simultaneously flowing through the initial-stage LNAs 1 to 4 is kept constant and such that-next-stage control currents IB 13 and IB 24 of magnitude proportional to the initial-stage control currents IB 1 to IB 4 which are let flow through the initial-stage LNAs 1 to 4 are let flow through the next-stage LNA 5 , wherein the necessity for causing an excessively large fixed current to flow through the next-stage LNA 5 is eliminated and the next-stage control currents IB 13 and IB 24 are reduced to a minimum necessary magnitude so that increases of useless current consumption can be suppressed.
1 . A variable gain amplifier comprising:
a plurality of initial-stage amplifiers connected parallel to one input for performing amplification operation by initial-stage control currents which are let flow through the respective amplifiers;
level adjusters connected to input sides of the initial-stage amplifiers with respect to at least some of the plurality of initial-stage amplifiers for adjusting levels of signals inputted to the plurality of initial-stage amplifiers so as to differ from each other;
a next-stage amplifier connected after the plurality of initial-stage amplifiers for performing amplification operation by a next-stage control current, a plurality of combined output lines formed by connecting output lines of initial-stage amplifiers out of the plurality of initial-stage amplifiers through which the initial-stage control currents never flow simultaneously being connected to a plurality of input ends separately, and signals inputted from the plurality of input ends being amplified and the respective amplified signals being added up and outputted; and
a variable current source for controlling the initial-stage control currents to be let flow through the plurality of initial-stage amplifiers and the next-stage control current to be let flow through the next-stage amplifier,
wherein the variable current source performs control such that a total value of the initial-stage control currents to be let flow through the simultaneously operated initial-stage amplifiers out of the plurality of initial-stage amplifiers is kept constant and such that a next-stage control current of magnitude proportional to the initial-stage control currents to be let flow through the initial-stage amplifiers is let flow through the next-stage amplifier.
2 . The variable gain amplifier according to claim 1 , the plurality of initial-stage amplifiers each comprise:
a first amplifier for amplifying an input signal by inverting a phase thereof; and
a second amplifier for amplifying the input signal;
wherein an output signal of the first amplifier and an output signal of the second amplifier are added up and outputted.
3 . The variable gain amplifier according to claim 2 , the plurality of initial-stage amplifiers each further comprise:
switch means for turning OFF operations of the first amplifier and the second amplifier when the initial-stage control current is not supplied from the variable current source.