A current-mode gain-control scheme with constant bandwidth and propagation delay for a transimpedance preamplifier

This paper presents a current-mode gain-control scheme that significantly increases the input dynamic range of a wideband optoelectronic receiver without affecting its bandwidth or delay or deteriorating its noise properties. A current buffer with variable attenuation is placed between the photodetector and the transimpedance preamplifier. In this way, the input dynamic range of the receiver can be increased, or alternatively, the signal dynamics can be reduced, by over 20 dB. A BiCMOS test circuit designed for a pulsed time-of-flight laser rangefinder has a measured bandwidth of 170 MHz and an input dynamic range of ~80 dB. The delay varies only ±5 ps when the gain is varied by 24 dB (1:15)