A low-noise nonlinear feedback technique for compensating offset in analog multipliers

We present a novel nonlinear feedback technique for canceling DC offset present in analog multipliers. This feedback method can be applied to any kind of analog multiplier, regardless of its topology or implementation technology. We use the properties of modulation and demodulation to separate signal from offset and nonlinear multiplicative feedback to cancel the offset. This scheme reduces flicker noise, and allows robust multiplier operation. Transient, DC, and frequency responses obtained from experimental chip measurements in a 1.5 μm BiCMOS process confirm the efficiency of our design. After compensation, a residual DC offset of 1-2 mV was attenuated to 20 μV. As an example application, we have employed this circuit in an ultra-low-noise analog VLSI system that allows 2.5 milli angstrom sensing of capacitance motion in a MEMS vibration sensor using a multiplicative lock-in technique.