CMOS Optical Preamplifier Design Using Graphical Circuit Analysis

Information
Source
Modulator
Drive
Circuitry
LED or
Laser
Optical channel
Photodetector
Preamplifier
Figure 1.1 Block diagram of a typical optical link.
Demodulator
Transmitter Receiver
1.1 Overview 3
The expansion of optical communications into new applications has created
exciting opportunities for the research and innovation of optical receivers. While the
growth of fiber-optic networks in the last few decades has refined our understanding
of optical receivers, its primary focus has been on speed and sensitivity. With the
expansion of optical communications comes new requirements on receiver designs.
Probably the most widespread trend has been that of increased system integra-
tion and the drive to reduce system components, cost, and size. Traditionally, optical
receivers have not been subject to many system level constraints since optical
receivers for long-haul fiber-optic networks are principally designed for perfor-
mance rather than cost. As such, they have typically used advanced high-speed
semiconductor technologies such as GaAs and Si bipolar processes.
Recovered
Information
Increasingly, new optical receiver designs are being implemented in low-cost,
high-integration technologies such as CMOS. However, the desire to implement in
CMOS implies a need to design receivers that keep pace with developments in
CMOS technology. One of the dominant trends is the continual reduction of system
supply voltage as illustrated by the forecasted trend shown in Figure 1.2 from the
Semiconductor Industry Association [SIA,1997]. Upper and lower boundary lines
are drawn to highlight the fact that the ‘industry standard’ voltage is disappearing,
being replaced instead by a range of voltages encompassing different applications.
Increasingly, the supply voltage is seen as an adaptable design parameter used to