Comparison of a bipolar and a CMOS front end in broadband optical transimpedance amplifiers

Abstract

In this paper, first a new configuration for a preamplifier circuit used in broadband optical communication networks is presented. Secondly this dcfferential transimpedance amplifier has been implemented in both a bipolar and a CMOS process. Simple formulas for the main characteristics are derived for both implementations. Measurements show the good pe$ormance of the configuration used, and highlight the differences between both implementations.

A 3-V CMOS optical preamplifier with DC photocurrent rejection

“…The circuit has a balanced structure consisting of an input differential pair followed by a pair of common-source second stages that utilize shunt feedback. Although, the basic structure follows the design reported by Coppoolse et al [3], significant changes were made to adapt their original 5-V design for 3-V operation. Specifically, we reduced the number of stages from three to two, replaced all biasing resistors with active current sources, and introduced a p-type input stage to create a complementary structure.…”

“…A low output impedance allows us to eliminate the output source follower stage used in [3] to achieve an improved phase response. The output common-mode voltage is naturally set to .…”

“…Small-signal analysis reveals that the second stage has a transimpedance of . (2) The overall gain is the product of the two gain stages: (3) which is typically in the range of 10 to a few hundred.…”

“…Consequently, bulk CMOS is the preferred technology. Recent papers on CMOS optical preamplifiers [1][2][3] have highlighted some of the design challenges of single-chip receivers, specifically that of obtaining sufficient speed and sensitivity given low supply voltages, small transconductances, and noisy power supplies.…”

“…Although inverter-based transimpedance amplifiers have shown good speed and sensitivity [2], they generally have poor power supply rejection because of the capacitive coupling of the supplies to the signal path [5]. A more robust approach is to use a differential structure with shunt feedback [3]. However, this approach has only been realized using bipolar and NMOS devices.…”