Noise performance and chopper frequency in integrated micromachined chopper-detectors in silicon

The noise behavior of the basic transimpedance amplifier has been investigated in the frequency range in between 100 kHz and 1 MHz. At frequencies below 10 kHz JFET-based operational amplifiers are preferred, because of the low equivalent input current noise that dominates overall noise performance. At frequencies beyond 10 MHz circuits with a bipolar input stage are generally used, because the equivalent input voltage dominates noise performance due to the capacitive source impedance of the photodiode at such frequencies. The transitional frequency range indicated has become important due to the increased operating frequency of optical choppers. It will be shown that a transimpedance amplifier with a bipolar input stage is preferred at intermediate frequencies and that the noise performance limits the operating frequency in an integrated micromechanical chopper rather than its inertia