A new approach for sensing and measuring the incident radiation on semiconductor mercury-cadmium-telluride (MCT) detector

In this paper a new circuit for sensing and measuring the incident radiation on a constant-voltage biased infrared semiconductor mercury-cadmium-telluride (MCT) detector is presented. The circuit is built around the current-feedback operational amplifier (CFOA). Moreover, a mathematical model for the relationship between the output voltage and incident radiation is obtained. The model, basically a sine-series function, can easily yield closed-form expressions for the harmonic and intermodulation performance of the constant-voltage biased MCT detector with large-amplitude multisinusoidal incident radiation. The special case of two-tone equal-amplitude incident radiation is considered in detail. The results show that the second-order harmonic and intermodulation products are always higher than the third-order components. Moreover, the results show that the second-order intermodulation is always dominant. Furthermore, a comparison with the harmonic and intermodulation performance of constant-current biased MCT detectors is presented. This comparison clearly shows that the nonlinear performance of the constant voltage-biased and the constant current-biased MCT is exactly the same. Thus, in terms of the nonlinear performance, both constant voltage- and constant current-biased MCT detectors are identical. This implies that the previously reported improvement in the nonlinear performance of the constant voltage-biased MCT detector is attributed to the use of proper feedback in the biasing/preamplifier circuit.