Monolithically Integrated Silicon Photodiode-Based FIR Filter in 65 nm CMOS Technology

This letter presents a finite impulse response (FIR) filter utilizing segmented silicon (Si) photodiodes as a part of the filter for equalization. The filter utilizes an integrated Si photodiode divided into three segments which serve as current sources and capacitors, and realizes a high-pass FIR that partially compensates for the frequency-dependent gain loss due to the physical and the electrical bandwidths of Si photodiode. This technique is well-suited for low-power applications since it uses only passive components. The photodiode-based FIR filter is implemented in a standard 65-nm CMOS technology utilizing an n-well to p-substrate junction photodiode with 12 fingers. The photodiode has a measured physical bandwidth of 15 MHz and a simulated electrical bandwidth of 5.9 GHz. The filter compensates for the photodiode gain loss by 8.7 dB in the frequency range from 1 to 5 GHz.