Analysis and Design of Wideband CMOS Transimpedance Amplifiers Using Inductive Feedback

摘要

Optical receivers have an important role in high data rate wireline data communication systems. Nowadays, these receivers have data rates of multi Gb/s. To achieve such high data rate in the design of optical receivers, all the amplifiers in the signal path need to be wideband and at the same time have minimum gain variations in the passband. As a rule of thumb, the bandwidth of amplifiers in the optical receivers should be 70% of the data rate. ududThe first component of the optical receiver is photodiode which converts photons received from optical fiber to current signals. The small current received from the photodiode is amplified using the transimpedance amplifier (TIA) which is one of the main building blocks in the receiver frontend. Due to high data rate of fiber optic communication systems the bandwidth of TIAs should be high and it should satisfy gain requirements.ududIt has been shown that inductive feedback technique is capable of extending the bandwidth of CMOS TIAs amplifiers effectively. However, no mathematical analysis is available in the literature explaining this phenomenon. The main focus of this thesis is to explain mathematically the mechanism of bandwidth extension of CMOS TIAs with inductive feedback. ududIn this thesis, it is shown mathematically that the bandwidth extension of inverter based CMOS TIAs with inductive feedback is due to either zero-pole cancellation or change in the characteristics of complex conjugate poles. It is shown that for large photodiode capacitance for example 150fF the phenomenon for the bandwidth extension is zero pole cancellation. In the case of small photodiode capacitance for example 50fF, the bandwidth extension happens due to change in the characteristics of complex conjugate poles. ududFinally, the zero pole cancellation using inductive feedback method for common source based transimpednace amplifier with resistive load using different values of photodiode capacitances has been analyzed. In addition to that a new 3-stage common source based transimpedance amplifier using inductive feedback technique is designed. The process of bandwidth extension is shown analytically and is confirmed with simulation results using well-known tools and technologies. To show the system level motivation, an eye diagram simulation is performed for all topologies and it is verified that bandwidth extension does not disturb the performance. Moreover, the concept is verified based on a frequency scaled down discrete implementation. ududIn this thesis, for inverter based CMOS TIA using photodiode capacitances of 150fF and 50fF bandwidths of 16.7GHz and 29.7GHz are achieved. In the case of common source based TIAs, considering 50fF, 100fF, 150fF photodiode capacitances, -3dB bandwidths of 32.1GHz, 21.8GHz, and 15.8GHz are achieved. A new three-stage TIA is proposed which achieves bandwidths of 42.8GHz, 35.5GHz, and 28.5GHz for 50fF, 100fF, 150fF photodiode capacitances. Based on comparative analysis, it is shown that, inductive feedback is the most effective method to extend the bandwidth of TIAs in terms of number of inductors. ud