DS125DF410_13 Datasheet, PDF (9/44 Pages) Texas Instruments – DS125DF410 Low Power Multi-Rate Quad Channel Retimer

DS125DF410
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FUNCTIONAL DESCRIPTION
SNLS398E – JANUARY 2012 – REVISED MAY 2013
The DS125DF410 is a low-power, multi-rate, 4-channel retimer. Each of the four channels operates
independently. Each channel includes a Continuous-Time Linear Equalizer (CTLE) which compensates for the
presence of a dispersive transmission channel between the source and the DS125DF410's input.
The DS125DF410 also includes a Decision-Feedback Equalizer (DFE) in each of the four channels. This
operates on the signal at the output of the CTLE. The DFE can improve the Bit Error Rate (BER) of the CDR
circuitry by reducing the effects of noise and crosstalk in the transmission channel at the input to the
DS125DF410.
Each channel includes an independent Voltage-Controlled Oscillator (VCO) and Phase-Locked Loop (PLL) which
produce a clean clock. The clean clock produced by the VCO and the PLL is phase-locked to the incoming data
clock and the high-frequency jitter on the incoming data is attenuated by the PLL, producing a clean clock with
substantially reduced jitter. This clean clock is used to retime the incoming data, removing high-frequency jitter
from the data stream and producing a data output signal with reduced jitter.
Each channel of the DS125DF410 features an output driver with programable differential output voltage and
output de-emphasis control. The output de-emphasis compensates for dispersion in the transmission channel at
the output of the DS125DF410.
These three functions together make up the data path for the DS125DF410.
RXPn
RXNn
EQ
100
SMBus
Signal
Detect
RETIMER
DRIVER
CDR
SMBus
100
SMBus
TXPn
TXNn
SDC
SDA
Figure 1. DS125DF410 Data Path Block Diagram — One of Four Channels
Device Data Path Operation
The data path operation of the DS125DF410 comprises three functional sections as shown in the data path block
diagram of Figure 1. The three functional sections are as follows.
• Channel Equalization
• Clock and Data Recovery
• Output Driver
Channel Equalization
Physical transmission media such as traces on printed circuit boards (PCBs) or copper cables exhibit a low-pass
frequency response characteristic. The magnitude of the high-frequency loss varies with the length of the
transmission media and with the loss of the materials which comprise it. This differential high-frequency loss and
the frequency-dependent group delay of the transmission media introduce inter-symbol interference in the high-
speed broadband signals propagating through the transmission media.
The DS125DF410 applies a frequency-response equalization function to the incoming data stream. The
equalization function reduces the effect of the frequency-dependent loss in the transmission media between the
transmitter output and the input of the DS125DF410. The DS125DF410 includes a Continuous Time Linear
Equalizer or CTLE which applies the frequency-response equalization. The CTLE is designed to provide a
controlled-amount of high-frequency boost to the signal in the frequency domain to compensate for the
frequency-dependent loss in the transmission media.
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