THESIS
2014
v leaves, vi-xv, 64 pages : illustrations ; 30 cm
Abstract
Optical communication is essential in industrial applications and the consumer market.
Active optical fiber has great potential to replace copper in short-distance wire line
communication. Current products and some research focus on 100-Gb/s Ethernet. This is
achieved by 10 channels, with each operating at 10-Gb/s. In our group, we have started
building each block of a 25-Gb/s optical receiver for next generation Ethernet.
In this thesis, two major areas are covered. Firstly, CMOS photodetectors, including
the n+/p-substrate, n-well/p-substrate, and n-well/Deep n-well/p-substrate photodiode and
PNP phototransistors and the Darlington pair, are presented. Currently, the common
photodetector is made of Ge, InGaAs or GaAs. Although Ge p-i-n photodiodes are proved
CMOS process comp...[
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Optical communication is essential in industrial applications and the consumer market.
Active optical fiber has great potential to replace copper in short-distance wire line
communication. Current products and some research focus on 100-Gb/s Ethernet. This is
achieved by 10 channels, with each operating at 10-Gb/s. In our group, we have started
building each block of a 25-Gb/s optical receiver for next generation Ethernet.
In this thesis, two major areas are covered. Firstly, CMOS photodetectors, including
the n+/p-substrate, n-well/p-substrate, and n-well/Deep n-well/p-substrate photodiode and
PNP phototransistors and the Darlington pair, are presented. Currently, the common
photodetector is made of Ge, InGaAs or GaAs. Although Ge p-i-n photodiodes are proved
CMOS process compatible, the standard CMOS process still cannot build these
photodetectors integrated with the circuits. The measured responsivity of the CMOS
photodetectors is extracted and built into a model for our circuit simulation. Secondly, a
limiting amplifier with high gain and large bandwidth is presented. Bipolar transistors in III-V
compound technology used to be employed in high speed front ends due to their high mobility
and low noise, but they cost much power and area. Currently, advanced CMOS technology is
more attractive in terms of integration and power consumption. In this thesis, a CMOS
limiting amplifier based on the structure of the modified Cherry-Hooper amplifier design is
presented in detail.
The CMOS photodetector and the limiting amplifier are fabricated in TSMC 65 nm CMOS
technology with f
T=185 GHz. The n-well/p-substrate has the largest bandwidth, 120 MHz,
and the Darlington pair has the highest responsivity, 1176 mA/W. Simulation results show that the CMOS photodiode is capable of achieving a 14Gb/s optical receiver. The measured
results of the 25-Gb/s optical receiver with off-chip photodiode indicate that the limiting
amplifier achieves a high gain and large bandwidth with low power consumption 23 mW.
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