Low-cost and minimal-conditioning interface for a PbSe photoconductor array

A low cost conditioning structure for PbSe photoconductor arrays with few components is described. We use a PbSe array of 64 pixels in a simultaneous atmospheric pollutant detector of several gases. The sensor system is based on infrared optical absorption spectroscopy. The authors present a second version of the sensor. From the first version they deduced: i) it is necessary to work at high chopper frequencies to reduce the effect of 1/f noise, ii) it is necessary to provide a conditioning circuit for each channel, and iii) the conditioning interface must be near the array. Therefore, they propose to amplify and mix the incoming signal to produce a signal at a fixed intermediate frequency (IF), in their case 1 Hz. The fact that the circuit has few components makes possible to place 64 conditioners in a small volume (10/spl times/4.9/spl times/7.6 cm/sup 3/) using the with SMT technique. The conditioner is divided into eight boards. Each board has eight channels and an analog multiplexor. These characteristics permit to approach the circuitry to the array. Each channel conditioner has up to 100 dB voltage gain. The low IF technique makes it possible to have high-performance circuits with low-cost components.