The ADC channels are fed from an analog front end (AFE) which contains photodiodes, TIAs, fully-differential amplifiers (FDA) and analog muxes. The return pulse is collected by an optical lens which focuses the light to the corresponding photodiode. The photodiode generates a current which is converted to a voltage and amplified by a TIA. This single-ended voltage is converted to a differential voltage using a fully-differential amplifier which then drives the differential input of the ADC. The ADC common-mode voltage of 1.1V is easily interfaced to by unipolar supply FDAs for lowest cost. Analog muxing of parallel photodiode receivers can be done after the TIAs or after the FDAs depending on the chosen components.
The input network must have sufficient bandwidth to support the minimum pulse width required by the system. The required bandwidth to support a given rise time (10-90%) is given in Equation 13.
Assuming the laser has a rise and fall time of 1 ns (10-90%), then the input network bandwidth should be greater than 400 MHz to avoid excessive degradation of the pulse shape and spatial resolution.