CMOS optical preamplifier design using graphical circuit analysis

grantor: University of TorontoNew requirements on optical receivers are being driven by the rapid expansion of optical communications beyond traditional fiber-optic links. This thesis discusses the design of transimpedance amplifiers that are used in the preamplifier stage of optical receivers. The three specific requirements that are addressed here are a wide dynamic range, ambient light rejection, and low-voltage operation. To achieve a wide dynamic range, we present a fully-differential, variable-gain CMOS transimpedance amplifier. The proposed topology is simpler than previous designs and has improved stability. The implemented design consumes 8mW at 3V, and provides 70 MHz bandwidth with a dynamic range of 77dB, a maximum transimpedance gain of 19k[Omega] and a gain range of 32dB. To reject ambient light, we place an active feedback loop around the transimpedance amplifier. This topology eliminates the need for large passive components and improves the regulation of the photodiode bias voltage. However, the lower-frequency limit of this topology is dependent on the ambient light level. We experimentally verify this technique, and analyze the stability requirements of the feedback loop. To achieve low-voltage operation, we develop a CMOS transimpedance amplifier capable of IV operation without the use of low-threshold MOS transistors. The design has a wide output swing and maximizes the available bias voltage for the photodiode. The biasing of the MOS feedback resistor is performed using a charge pump to generate a stable gate voltage--a technique called dynamic gate biasing (DGB). The proposed design was implemented as part of an optical receiver front-end which also included two post amplifiers. The resulting front-end consumes 1mW from a 1V supply and provides 210k[Omega] transimpedance gain over a 50MHz bandwidth. Also included in this thesis is the development and application of a graphical circuit analysis technique called DPI/SFG analysis that is based on driving-point impedances (DPI) and signal-flow graphs (SFG). We develop a general formulation of the technique, illustrate its use on a number of circuit examples, and apply it to the design and optimization of the low-voltage transimpedance amplifier.Ph.D