High gain, high bandwidth CMOS transimpedance amplifier

Details High gain, high bandwidth CMOS transimpedance amplifier High gain, high bandwidth CMOS transimpedance amplifier

2002-12-11

2004-12-07

Nguyen, Patricia (Department: 2817)

Amplifiers

With semiconductor amplifying device

Including push-pull amplifier

C330S308000, C330S271000

Reexamination Certificate

active

06828857

ABSTRACT:

FIELD
The present invention relates to analog circuits, and more particularly, to amplifiers.
BACKGROUND
With increasing data rates in electronic systems, it is expected that optical interconnects (optical fibers) may in the near future replace wire interconnects at the board-to-board and chip-to-chip level. For example, a computer system such as that illustrated in
FIG. 1
may comprise one or more boards
102
and memory hierarchy
104
that exchange data packets over optical interconnects
106
. These packets may be routed via switch
108
, or perhaps the various integrated circuits may be directly connected to one another. In the example of
FIG. 1
, each board
102
comprises I/O circuit or board
110
, and comprises one or more microprocessors, e.g., microprocessor
112
, in communication with its corresponding I/O circuit.
An I/O circuit utilizes an optical transceiver, comprising an optical transmitter for up-converting an electrical signal to an optical signal, and an optical receiver for down-converting an optical signal to an electrical signal. An optical receiver usually comprises a photodetector to provide an electrical signal indicative of a received optical signal. A typical small-signal model for a photodetector is provided in
FIG. 2
, comprising small-signal current source
202
and parasitic capacitor
204
. The small-signal current provided by current source
202
is representative of the received optical signal. The output current signal is provided at output port
206
.
The output signal provided by the photodetector is amplified to a logical voltage level before utilized by a CDR (Clock and Data Recovery) circuit to recover both the original clock signal and the optically transferred data. A multi-stage amplifier is often employed to amplify the small signal output of the photodetector to a logical voltage level. The front end of the multi-stage amplifier usually a transimpedance amplifier. A transimpedance amplifier provides a small-signal output voltage signal in response to a small-signal input current signal. As one example, the output voltage signal of a transimpedance amplifier may have an amplitude in the range of 100 mV. Because this voltage swing is usually inadequate to drive a CDR circuit, further amplification is usually provided by a limiting and saturating post-amplifier.
Currently, high speed optical communication links involve data rates high than 10 Gb/s (bits-per-second). The bandwidth of a transimpedance amplifier is typically chosen to be equal to about 0.7 times the bit-rate, which is a compromise between the total integrated noise and the intersymbol interference resulting from the limited bandwidth. For example, a 14 GHz bandwidth transimpedance amplifier may be desirable for a 20 Gb/s optical link. Furthermore, the number of photons integrated in the photo detector during one clock cycle and the resulting number of electrons generated by the photodetector is relatively low. As a result, there is a need for high gain, high bandwidth transimpedance amplifiers. In the past, such transimpedance amplifiers have often been realized by expensive and high power consumption Si-bipolar or III-V semiconductor technologies. But for a low cost solution, it would be desirable to realize high gain, high bandwidth transimpedance amplifiers utilizing CMOS (Complementary Metal Oxide Semiconductor) technology.


REFERENCES:
patent: 4100502 (1978-07-01), Yamashiro
patent: 4535233 (1985-08-01), Abraham
patent: 5745010 (1998-04-01), Miyamoto et al.
patent: 5963094 (1999-10-01), Linder et al.

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