Agc circuit

[0080]FIG. 1 shows a typical configuration of an AGC circuit in accordance with a first embodiment of the present invention.

[0081]In FIG. 1, symbol GCA1 represents a variable gain amplifying circuit constituted by a differential amplifying circuit Amp1, and variable resistors R1, R2, R3, and R4. Symbol Tin represents a signal input terminal into which an analog voltage, for example, an analog audio signal or the like, is inputted. Symbol Tout represents a signal output terminal from which an amplified or attenuated analog voltage is outputted, for example. Symbol Tagc represents gain control terminals into which gain control signals are inputted. Symbol Toffset represents an offset compensation terminal into which an offset compensation signal is inputted. Symbol Tbias represents a reference voltage terminal into which a reference voltage for determining an output bias voltage is inputted.

[0082]Symbol AD1 represents an A / D conversion circuit for A / D converting an output signal of t

[0136]FIG. 12 shows a configuration of an AGC circuit in accordance with a second embodiment of the present invention.

[0137]In FIG. 12, description will be omitted by giving the same symbol to the same component as that of the AGC circuit shown in FIG. 9, and only components which are newly added to the AGC circuit shown in FIG. 1 will be described.

[0138]In FIG. 12, n (n≧2) variable gain amplifying circuits GCA1, GCA2, . . . , GCAn, n gain control signal holding circuits GLatch1, GLatch2, . . . , GLatchn, n offset compensation signal holding circuits OLatch1, OLatch2, . . . , OLatchn, a selector circuit MUX1 that receives output signals Vout1, Vout2, . . . , Voutn of the variable gain amplifying circuits GCA1, GCA2, . . . , GCAn, and selects one of them to then output it to an A / D converter AD1, and a mode control circuit Ctrl3 that controls a signal selection, a gain control operation, and the offset compensation operation are arranged in this AGC circuit.

[0139]Signals Vin1, Vin2, .