|
[ Back ] [ Home ] [ Up ] [ Next ]
RECEIVER DESIGN
The simplest fiber optic receivers consist of only the optical detector and a load
resistor. However, the output signal of these simple receivers is not in a suitable form
for most types of interfacing circuitry. To produce a suitable signal, a preamplifier, a
post amplifier, and other circuitry are generally included in the receiver.
The choice of an optical detector and the design of the preamplifier help determine the
operational characteristics of the receiver. Fiber optic receivers using APDs have greater
sensitivity than those using PIN photodiodes.
In addition, trade-offs are made in preamplifier designs to increase sensitivity while
optimizing bandwidth and dynamic range. The two basic types of amplifiers used in fiber
optic receivers are the high-impedance amplifier and the transimpedance
amplifier.
The high-impedance preamplifier is generally used with a large load resistor to improve
sensitivity. The large load resistor is used to reduce thermal noise. Although the
high-impedance preamplifier achieves high sensitivity, receiver bandwidth and dynamic
range are limited. The transimpedance preamplifier uses a low-noise, high-input impedance
amplifier with negative feedback. This design provides improvements in bandwidth and
dynamic range with some degradation in sensitivity from an increase in noise. For more
information on receiver performance and design, refer to the reference material listed in
appendix 2.
Q.25 What are the two basic types of preamplifiers used in fiber optic receivers?
Q.26 Which preamplifier design (high-impedance or transimpedance) provides improvements in
bandwidth and greater dynamic range with some degradation in sensitivity from an increase
in noise?
[ Back ] [ Home ] [ Up ] [ Next ]
Order this information
in Adobe PDF Printable Format
| 