Amplifier circuit and method for reducing voltage and current noise

摘要

An amplifier circuit with current noise reduction employs first and second variable impedance devices between a signal source and an amplifier. A modulation frequency generator establishes a modulation frequency fmod to alter the first and second impedance values out of phase from one another at the modulation frequency so that the sum of the first and second impedance values at the input of the amplifier is relatively constant. The modulation at frequency fmod shifts the signal to side bands about the modulation frequency. The output from the amplifier is passed to a bandpass filter centered on the modulation frequency in order to remove all frequencies outside the bandwidth of interest. The signal itself is recovered by demodulating the output of the bandpass filter using a synchronization signal that is derived from the modulation signal.