Digital gain balancing technique for sensitive detection of minor gas concentrations

Ultra-sensitive detection of minor species is important in many fields. The requirement of direct online measurement of gas species in process engineering motivates fast measurements over short pathlengths. The resulting high bandwidth and low absorptions reduce the measurement Signal-to-Noise Ratio (SNR). Our target is to detect CO in engine exhaust with sensitivity of the order of 0.05 ppm-m at several kHz. In this paper, a novel electronic scheme is discussed and presented with simulation results. A generic approach is followed, to use it with either a pulsed or a continuous wave (CW) laser source. A detailed noise analysis is presented for improved understanding of the SNR of the overall scheme.