Zero-pole modulation and demodulation for noise reduction in charge amplifiers

A novel method of noise reduction, referred to as zero-pole modulation and demodulation, is proposed for charge amplifiers in imaging and sensor systems. In this method, the input signal is passed through a zero-pole system without being modified. However, the noise at the output of the charge amplifier is reduced by the demodulation. An experimental charge amplifier for applications in x-ray crystallography with zero-pole modulation-demodulation has been designed and integrated in a 0.18-μm CMOS technology. The circuit operates at a frequency of 10 kHz and has a conversion gain of 100 mV/fC. The amount of noise reduction achieved by the proposed method is 40%, which corresponds well to the theoretically expected noise reduction. The experimental charge amplifier exhibits an input-referred noise of 100 ENC.