A mixed signal which contains a noise is inputted. Then, the signal is inverted and amplified by an inverting amplifier which has a high gain, and attenuated by a attenuator in order to generate an inverted phase signal. In a mixer, the inputted signal and the inverted phase signal are added, and outputted. Since the inverted phase component of the noise is added to the noise, the noise in the mixed signal is canceled. For the voice signal, an amplified inverted signal is generated by an invert amplifier. However, an amplitude is restricted due to a high gain. Since the amplitude is restricted, a level of the inverted phase signal is lower than a level of a voice signal. Even if the voice signal and the inverted phase component are added in the mixer, the voice signal is outputted almost thoroughly.

A class AB operational amplifier has first and second intermediate differential nodes respectively driving intermediate stage inverting and non-inverting amplifiers to produce a single-ended output voltage, which are provided with a frequency compensating feedback signal at a selected one of the first and second intermediate differential nodes, derived from the single-ended output of the operational amplifier subject to frequency compensation. The frequency compensating feedback signal is generated with the feedback circuitry. The feedback circuitry includes a compensation capacitor connected to the single-ended output and a current mirror circuit connected to the selected one of the first and second intermediate differential nodes of the operational amplifier.

An amplifier circuit and method for reducing bias noise is disclosed. The amplifier circuit includes a passive biasing source for supplying a desired bias signal to the amplifier and an active biasing source for energizing the passive biasing source to supply the desired bias signal. The amplifier circuit also includes a decoupler for selectively decoupling the active biasing source from the passive biasing source when the amplifier is configured for amplifying an input signal so that the amplifier remains isolated from electronic noise produced by the active biasing source while still being supplied the desired bias signal by the passive source.

An oscillator circuit having improved long term and short term phase stability. A source follower provides a signal to a bipolar transistor. The bipolar transistor is fed with a current from a current mirror which may be selectively controlled. A piezoelectric crystal and a high resistance element are connected in parallel from the collector of the bipolar transistor to the input of the source follower. The drive voltage to the piezoelectric crystal is controlled by the current mirror to improve long term frequency stability.