A bias generation method or apparatus defined by any one or any practical combination of numerous features that contribute to
low noise and / or high efficiency biasing, including: having a
charge pump control
clock output with a waveform having limited
harmonic content or
distortion compared to a
sine wave; having a
ring oscillator to generating a
charge pump clock that includes inverters current limited by
cascode devices and achieves substantially rail-to-rail output amplitude; having a differential
ring oscillator with optional startup and / or
phase locking features to produce two phase outputs suitably matched and in adequate phase opposition; having a
ring oscillator of less than five stages generating a
charge pump clock; capacitively
coupling the clock output(s) to some or all of the charge transfer
capacitor switches; biasing an FET, which is capacitively coupled to a drive
signal, to a bias
voltage via an “active bias
resistor” circuit that conducts between output terminals only during portions of a waveform appearing between the terminals, and / or wherein the bias
voltage is generated by switching a small
capacitance at cycles of said waveform. A charge pump for the bias generation may include a regulating feed back loop including an OTA that is also suitable for other uses, the OTA having a ratio-control input that controls a
current mirror ratio in a
differential amplifier over a continuous range, and optionally has differential outputs including an inverting output produced by a second
differential amplifier that optionally includes a
variable ratio current mirror controlled by the same ratio-control input. The ratio-control input may therefore control a common mode
voltage of the differential outputs of the OTA. A control loop around the OTA may be configured to control the ratio of one or more
variable ratio current mirrors, which may particularly control the output common mode voltage, and may control it such that the inverting output level tracks the non-inverting output level to cause the
amplifier to function as a high-
gain integrator.