NOISE PERFORMANCE AND CHOPPER FREQUENCY IN INTEGRATED MICROMACHINED CHOPPER-DETECTORS IN SILICON

The noise behavior of the basic transimpedance amplifier has been inve stigated in the frequency range in between 100 kHz and 1 MHz. At frequ encies below 10 kHz JFET-based operational amplifiers are preferred, b ecause of the low equivalent input current noise that dominates overal l noise performance. At frequencies beyond 10 MHz circuits with a bipo lar Input stage are generally used, because the equivalent input volta ge dominates noise performance due to the capacitive source impedance of the photodiode at such frequencies. The transitional frequency rang e indicated has become important due to the increased operating freque ncy of optical choppers. It will be shown that a transimpedance amplif ier with a bipolar input stage is preferred at intermediate frequencie s and that the noise performance limits the operating frequency in an integrated micromechanical chopper rather than its inertia.