Abstract: An analog demodulator used in a low IF receiver to down-convert a pair of quadratureIF signals and to perform image-rejection operations. The analog demodulator includes at least one first calibration apparatus and/or at least one second calibration apparatus so that the analog demodulator can reduce DC offset that would cause LO leakage in the low IF receiver by using the first calibration apparatus and/or the second calibration apparatus. The analog demodulator further includes a filtering device connected to a LO generator for removing the 3rd and 5th order harmonic components.

Abstract: An optical receiver preamplifier provides a transimpedance feedback path between the output node and the input node that comprises a feedback resister and the two diodes are coupled ("paralleled") in opposite direction. While the input current signal is too large, and the voltage reach the diode's threshold voltage. The preamplifier can provide current path passing the signal to solve the problem that charge-discharge time is not uniform and changed over duty-cycle. Further, the two diodes are coupled ("paralleled") in opposite direction make photo-diode working under the large-signal current by anode or cathode input. Thus, increase the dynamic range of the transimpedance preamplifier. Besides, the low impedance of series resistance connects with input node and feedback network. The influence of bandwidth and stability that the aforementioned two paralleled diodes resulted in diode junction capacitor will reduce due to the low impedance of series resistance.