Transconductance-capacitance filter system

摘要

A gm-C filter system having low power consumption is provided. An adjusting circuit 2 is equipped with an oscillator 3 constructed of a gm amplifier 3a having the same arrangement as that of a gm amplifier 1a of a gm-C filter circuit 1. The adjusting circuit 2 generates a digital adjusting value "D gm " based upon an oscillation signal OSC outputted from this oscillation 3, and this digital adjusting value "D gm " is used to adjust a gm value of the gm amplifier 3a of the oscillator 3. This digital adjusting value "D gm " is held in a register 10. The digital adjusting value "D gm " held in this register 10 is converted into an analog adjusting value (bias current) by a D/A converter 8, and then, this analog adjusting value is supplied to the gm amplifier 1a of the gm-C filter circuit 1 so as to adjust the gm value. The adjusting circuit 2 is operated in an intermittent manner based upon, for example, a change contained in ambient temperatures of the gm-C filter system.