-12
Receiver Section
The receiver contains an InGaAs
HFBR-5208M at a BER of 1 x 10
the receiver will require an input
,
relative input optical power varies
by <0.7 dB over this full range.
This small sensitivity variation
allows the optical budget to
remain nearly constant for designs
that make use of the broad
PIN photodiode mounted together signal approximately 0.6 dB higher
with a custom, silicon bipolar
than the -26 dBm level required for
-10
transimpedance preamplifier IC in 1 x 10 operation, i.e. -25.4 dBm.
an OSA. This OSA is mated to a
An informative graph of a typical,
custom, silicon bipolar circuit
signaling rate range of the
short fiber transceiver link per-
providing post amplification and
HFBR/HFCT-5208M. The curve
has been normalized to the input
optical power level (dBm avg.) of
the receiver for 622 MBd at center
of the Baud interval with a BER of
formance can be seen in Figure 2.
quantization and optical signal
This figure is useful for designing
detection.
short reach links with time-based
The custom, silicon bipolar circuit jitter requirements. This figure
includes a Signal Detect circuit
which provides a PECL logic high
state output upon detection of a
usable input optical signal level.
This single-ended PECL output is
indicates Relative Input Optical
Power versus Sampling Time
Position within the receiver
output data eye-opening. The
-10
10 . The data patterns that can
be used at these signaling rates
should be, on average, balanced
duty factor of 50%. Momentary
excursions of less or more data
duty factor than 50% can occur,
but the overall data pattern must
remain balanced. Unbalanced data
duty factor will cause excessive
pulse-width distortion, or worse,
bit errors. The test conditions are
listed in Figure 3.
given curves are at a constant bit-
designed to drive a standard PECL error-ratio (BER) of 10 for four
-10
input through normal 50 W PECL
load.
different signaling rates, 155 MBd,
311 MBd, 622 MBd and 650 MBd.
These curves, called “tub”
Applications Information
diagrams for their shape, show
the amount of data eye-opening
time-width for various receiver
input optical power levels. A
wider data eye-opening provides
more time for the clock recovery
circuit to operate within without
creating errors. The deeper the
tub is indicates less input optical
power is needed to operate the
receiver at the same BER
condition. Generally, the wider
and deeper the tub is the better.
The Relative Input Optical Power
amount (dB) is referenced to the
absolute level (dBm avg.) given
in the Receiver Optical
Typical BER Performance of
HFBR-5208M Receiver versus Input
Optical Power Level
The HFBR/HFCT-5208M
transceiver can be operated at
Bit-Error-Ratio conditions other
Recommended Circuit Schematic
When designing the HFBR/HFCT-
5208M circuit interface, there are
a few fundamental guidelines to
follow. For example, in the
Recommended Circuit Schematic,
Figure 4, the differential data
lines should be treated as 50 ohm
Microstrip or stripline
transmission lines. This will help
to minimize the parasitic
inductance and capacitance
effects. Proper termination of the
differential data signal will
-10
than the required BER = 1 x 10
of the 622 MBd ATM Forum
622.08 Mb/s Physical Layer
Standard and the ANSI T1.646a.
The typical trade-off of BER
versus Relative Input Optical
Power is shown in Figure 1. The
Relative Input Optical Power in
dB is referenced to the Input
Optical Power parameter value in
the Receiver Optical
Characteristics table. The 0 ns
sampling time position for this
Characteristics table. For better
BER condition than 1 x 10
more input signal is needed (+dB).
For example, to operate the
prevent reflections and ringing
-10
,
Figure 2 refers to the center of the which would compromise the
Baud interval for the particular signal fidelity and generate
signaling rate. The Baud interval is unwanted electrical noise. Locate
the reciprocal of the signaling rate termination at the received signal
in MBd. For example, at 622 MBd
the Baud interval is 1.61 ns, at
155 MBd the Baud interval is
6.45 ns. Test conditions for this
tub diagram are listed in Figure 2.
10-2
10-3
LINEAR EXTRAPOLATION OF
end of the transmission line. The
length of these lines should be
kept short and of equal length to
prevent pulse-width distortion
from occurring. For the high-speed
signal lines, differential signals
should be used, not single-ended
signals. These differential signals
need to be loaded symmetrically
to prevent unbalanced currents
from flowing which will cause
distortion in the signal.
10-4 THROUGH 10-7 DATA
10-4
ACTUAL DATA
10-5
10-6
10-7
10-8
10-9
The HFBR/HFCT-5208M receiver
input optical power requirements
vary slightly over the signaling
rate range of 20 MBd to 700 MBd
for a constant bit-error-ratio
10-10
10-11
10-12
10-13
10-14
10-15
-5
-1
1
2
-4 -3 -2
0
3
-10
(BER) of 10 condition. Figure 3
Figure 1. Relative Input Optical Power -
dBm Average.
illustrates the typical receiver
2
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