HFCT-5205A Avago Technologies US Inc., HFCT-5205A Datasheet - Page 3

• Manufacturer Part Number: HFCT-5205A
• Manufacturer: Avago Technologies US Inc.

Specifications of HFCT-5205A

• Optical Fiber Type: TX/RX
• Data Transfer Rate: 155Mbps
• Optical Rise Time: 2ns
• Optical Fall Time: 2ns
• Operating Temperature Classification: Industrial
• Peak Wavelength: 1360nm
• Operating Supply Voltage (min): 4.75V
• Operating Supply Voltage (typ): 5V
• Operating Supply Voltage (max): 5.25V
• Output Current: 30mA
• Operating Temp Range: -40C to 85C
• Mounting: Through Hole
• Pin Count: 9
• Lead Free Status / RoHS Status: Compliant

Functional Description - Receiver Section
Design
The receiver section contains an InGaAs/InP photo
detector and a preamplifier within the receptacle,
coupled to a postamp/decision circuit on a separate
circuit board.
The postamplifier is ac coupled to the preampli-
fier as illustrated in Figure 1. The coupling capacitor
is large enough to pass the SONET/SDH test pattern at
155 MBd without significant distortion or performance
penalty. If a lower signal rate, or a code which has sig-
nificantly more low frequency content is used, sensitivity,
jitter and pulse distortion could be degraded.
Figure 1 also shows a filter network which limits
the bandwidth of the preamp output signal. The
filter is designed to bandlimit the preamp output
noise and thus improve the receiver sensitivity.
These components will also reduce the sensitivity of
the receiver as the signal bit rate is increased above 155
MBd.
Figure 1 - Receiver Block Diagram
Figure 2 - π Filter Network for Noise Filtering
V
3
100 nF
RECEIVER
RECEPTACLE
CC
TRANS-
IMPEDANCE
PRE-
AMPLIFIER
3.3 µH
100 nF
GND
FILTERED V
+
10 µF
FILTER
CC
to DATA LINK
LIMITING
AMPLIFIER
CIRCUIT
SIGNAL
DETECT
Noise Immunity
The receiver includes internal circuit components to filter
power supply noise. Under some conditions of EMI and
power supply noise, external power supply filtering
may be necessary. If receiver sensitivity is found to be
degraded by power supply noise, the filter network illus-
trated in Figure 2 may be used to improve performance.
The values of the filter components are general recom-
mendations and may be changed to suit a particular
system environment. Shielded inductors are recom-
mended.
Terminating the Outputs
The PECL Data outputs of the receiver may be terminated
with the standard Thevenin-equivalent 50 ohm to V
V termination. Other standard PECL terminating tech-
niques may be used.
The two outputs of the receiver should be terminated
with identical load circuits to avoid unnecessarily large
ac current in V
ac current is largely nulled. The Signal Detect output of
the receiver is PECL logic and must be loaded if it is to be
used. The Signal Detect circuit is much slower than the
data path, so the ac noise generated by an asymmetrical
load is negligible. Power consumption may be reduced
by using a higher than normal load impedance for the
Signal Detect output. Transmission line effects are not
generally a problem as the switching rate is slow.
The Signal Detect Circuit
The Signal Detect circuit works by sensing the peak
level of the received signal and comparing this level to
a reference.
CC
PECL
OUTPUT
BUFFER
PECL
OUTPUT
BUFFER
. If the outputs are loaded identically the
DATA OUT
DATA OUT
SD
CC
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