AM79C973BKC AMD (ADVANCED MICRO DEVICES), AM79C973BKC Datasheet - Page 85

• Manufacturer Part Number: AM79C973BKC
• Manufacturer: AMD (ADVANCED MICRO DEVICES)

Specifications of AM79C973BKC

• Lead Free Status / Rohs Status: Not Compliant

Serializer/Deserializer and Clock Recovery
The Physical Data Transceiver (PDX) is a CMOS all
digital core that is used in the 10/100 PHY. It employs
new circuit techniques to achieve clock and data recov-
ery.
Traditionally, Phase-Locked-Loops (PLLs) are used for
the purpose of clock recovery in data communication
areas. There are both analog and digital versions of the
PLL components such as phase detector, filter, and
charge pump. A traditional PLL always contains a volt-
age-controlled oscillator (VCO) to regenerate a clock
which is synchronized in frequency to and aligned in
phase with the received data.
The PDX employs techniques that are significantly dif-
ferent from traditional PLLs. Not only are the control
functions completely digital, the VCO function is also
replaced by a proprietary delay time ruler technique.
The result is a highly integratible core which can be
manufactured in a standard digital CMOS process.
To transmit, the PDX accepts 4B/5B encoded data
symbols from the scrambler. The 5-bit symbol is
clocked into the PDX by the rising edge of the 25-MHz
clock, serialized and converted to NRZI format. The
NRZI data is delivered to the PECL transceiver or MLT3
transceiver. The output of either of the two transceivers
goes to the TX± pair.
The PDX uses a 25-MHz clock as the frequency and
phase reference to generate the serial link data rate.
The external clock source must be continuous. All of
the internal logic of the PDX runs on an internal clock
that is derived from the external reference source. The
PDX’s clock multiplier is referenced to the rising edges
of the 25-MHz clock only.
MLT-3
1
8 ns
Figure 36. MLT-3 Waveform
0
1
0
1
0
P R E L I M I N A R Y
21510D-41
Am79C973/Am79C975
1
In order to generate the serial output wave forms con-
forming to the specifications, the external reference
clock must meet 100BASE-X frequency and stability
requirements. Under normal conditions, the frequency
of the 25-MHz clock multiplied by 5 must be within the
100BASE-X specified 100 ppm of the received data for
the PDX to operate optimally.
Note: The 100 ppm is the tolerance of the crystal-con-
trolled source.
The TX± serial output typically contains less than
0.4 ns peak-to-peak jitter at 125 Mbaud.
Receiving from the physical medium through the PMD
device, the PDX accepts encoded PECL NRZI signal
levels at the RX± inputs. The receiver circuit recovers
data from the input stream by regenerating clocking in-
formation embedded in the serial stream. The recov-
ered clock is called RSCLK (an internal signal). The
PDX then clocks the unframed symbol (5 bits) to the
descrambler interface on the falling edge of RSCLK.
The PDX receiver uses advanced circuit techniques to
extract encoded clock information from the serial input
stream and recovers the data. Its operating frequency
is established by the reference clock at 25 MHz. The
PDX is capable of recovering data correctly within
±
the frequency range defined by the 100BASE-X speci-
fication). The 100BASE-X 4B/5B encoding scheme en-
sures run-length limitation and adequate transition
density of the encoded data stream, while TP-PMD
achieves this on a statistical basis through data scram-
bling. The PDX clock recovery circuit is designed to tol-
erate a worst-case run-length of 60-bits in order to
function correctly with both fiber-optic and twisted-pair
PMDs.
The PDX receiver has input jitter tolerance characteris-
tics that meet or exceed the recommendations of Phys-
ical Layer Medium Dependent (PMD) 100BASE-X
document. Typically, at 125 Mbaud (8 ns/bit), the peak-
to-peak Duty-Cycle Distortion (DCD) tolerance is
1.4 ns, the peak-to-peak Data Dependent Jitter (DDJ)
tolerance is 2.2 ns, and the peak-to-peak Random Jit-
ter (RJ) tolerance is 2.27 ns. The total combined peak-
to-peak jitter tolerance is typically 5 ns with a bit error
rate (BER) better than 2.5 x 10
Medium Dependent Interface
The Am79C973/Am79C975 device connects directly to
low cost magnetics modules for interface to twisted pair
media (UTP and/or STP). The TX± and RX± pins pro-
vide the interface for both 10BASE-T and 100BASE-TX
allowing the use of a 1:1.41 (transmit) and 1:1 (receive)
transformer with single primary and secondary wind-
ings. No filtering is required in the magnetics module.
Refer to Figure 37 for recommended termination.
1000 ppm of the 25-MHz clock signal (which exceeds
-10
.
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