| 摘要 |
<p>A transconductor circuit, such as a gyrator filter, comprises an arrangement of balanced class AB transconductors, capacitors and floating MOS resistors formed by MOS transistors operating in their triode region. Tuning of the filter is effected by varying a common supply rail voltage (Vdda). In order to enable the resistance values of the MOS resistors to track changes in the transconductance values (-G) of the transconductors, a circuit provides the condition R = 1/G. The circuit includes a means (102) for producing a voltage (Vcm - DeltaV) offset from the common mode voltage (Vcm) of the class AB transconductors. The offset voltage is supplied to a parallel arrangement of a class AB transconductor (108) having a transconductance (-G) and the source-drain path of a MOS transistor (110) emulating a MOS resistor. The current output I = DeltaV(G -1/R) of the parallel arrangement is integrated and supplied as a control voltage (cntrl) to the gate electrode of the MOS transistor (110). By loop action the control voltage is adjusted so that the loop stabilises with I = 0 which occurs when R = 1/G, this control voltage being supplied also to the floating MOS resistors.</p> |
