Patent ID: 7468629

Claim:
A transconductance tuning circuit comprising: a transconductor cell, capable of receiving an input signal and providing a corresponding driving signal, the transconductor cell having a transconductance being changeable according to a control signal, the input signal being a square wave voltage signal having a constant frequency; a capacitor module having an input being coupled to the capacitor module for charging or discharging according to the driving signal to thereby provide a corresponding output signal; and an amplitude detecting feedback circuit having an input being coupled to the output signal of the capacitor module, the amplitude detecting feedback circuit for tuning a value of the control signal according to an amplitude level of the output signal and utilizing feedback of the control signal to the transconductor cell to lock an amplitude of the output signal within a predetermined range; wherein the amplitude detecting feedback circuit includes: a peak detector, for detecting the amplitude of the output signal and providing a corresponding pre-control signal being asserted when the amplitude of the output signal exceeds a predetermined value, the peak detector comprising: a comparison module, for detecting whether the level of the output signal is greater than a predetermined target range; and a charge pump and at least a second capacitor module, the charge pump being capable of charging or discharging the second capacitor module according to a detection result of the comparison module such that the second capacitor module is capable of providing the pre-control signal according to the detection result; and a low-pass filter being coupled directly to the pre-control signal being outputted from the peak detector, the low pass-pass filter for providing the control signal according to the pre-control signal, and providing the control signal as feedback to the transconductor cell.