VARIABLE GAIN AMPLIFYING CIRCUIT

摘要

<P>PROBLEM TO BE SOLVED: To provide a variable gain amplifying circuit which easily performs stable gain control while securing precision all over a whole variable area since a change of gain with respect to a control signal (control voltage) has a continuous and log-linear shape, and secures a sufficient dynamic range. Ž<P>SOLUTION: Value of a reference signal Va for gain control is converted into voltage Sr of a value along an index function by using a step response characteristic to be a 121 analog transitional phenomenon of a time constant circuit by a resistor R1 and a capacitor C1, a variable pulse width signal Pw whose pulse width is adjusted by comparison (131) between a sampling hold value Srh of the voltage Sr and a sawtooth wave signal Ps is obtained, and gain about an input signal Vin of a gain control circuit 140 by controlling a Duty factor related to an on period of a switch SW4 is controlled by the signal Pw to obtain a variable gain amplifying output Vout from a smoothing circuit 150 at the subsequent stage. Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž