Abstract: A reference receiver has a biased, strobed sampling system that is tuned to provide the predominant frequency response of the reference receiver allowing for the removal of the discrete reference receiver filter. The reference receiver has a photodiode optical-to-electrical converter that is configured to effectively utilize the current output of the high impedance source in that the converter is not reverse terminated to the characteristic impedance of a transmission coupled to the electrical output of the converter. The electrical output of the converter is coupled to a sampling circuit that receives biasing voltages and gating strobe pulses for producing an approximate Bessel-Thompson filter response from the sampling circuit. The combination of the unterminated optical-to-electrical converter and the tuned sampling circuit results in a reference receiver having higher gain and narrower reference receiver tolerance limits.

Abstract: An automatic output offset control circuit for a DC-coupled RF amplified optical-to-electrical converter has a photodiode for converting an optical signal to an electrical signal. The current from one side of the photodiode is coupled into the input of a bipolar RF amplifier that generates a voltage output. The current from the other side of the photodiode is sensed for generating a voltage that is compared with the output of the RF amplifier. Any mismatch between the sensed current and the RF amplifier generates an error signal that is used to control the DC bias supplies of the RF amplifier. The DC bias supplies are adjusted in unison to produce the correct offset at the amplifier output for the given photodiode current while maintaining a constant AC-gain. The circuit automatically corrects for the DC-coupled output offset drift and variations of the RF bipolar amplifier. The circuit may be implemented using either voltage or current signals to the feedback circuit.