CMOS Optical Preamplifier Design Using Graphical Circuit Analysis

New 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 19kΩ, 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.