
XRT79L71
PRELIMINARY
335
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
3.
If the Jitter Attenuator block has been configured to operate in the "Receive Direction", then the "In_CLK" signal
(as depicted in
Figure 154, above) will be a buffered version of the "Recovered" clock signal (from the "Receive
DS3/E3 LIU Block).
Now that we have briefly described how the Jitter Attenuator block functions, we can now go into more details
on how the individual functional blocks (within the Jitter Attenuator block) function.
5.2.5.2.1.1
The Jitter Attenuator PLL
The purpose of the Jitter Attenuator PLL block is to (1) receive and lock onto an input "jittery" clock signal, and
(2) to regenerate a clock signal, of the exact same frequency, but with considerably less jitter. In performing
this task, the Jitter Attenuator PLL block is said to be "attenuating jitter". A very simplistic illustration of what
the Jitter Attenuator PLL has been designed to accomplish is presented below in Figure 155.
The Jitter Attenuator PLL receives the input "jittery" clock signal via the "In_CLK" input pin. It outputs the
"smoothed" (e.g., clock signal with reduced jitter) clock signal via the "Out_CLK" output pin.
The Jitter Attenuator PLL accomplishes this "Jitter Attenuation" task because it is a "very narrow-band" PLL.
The corner (e.g., -3dB) frequency of the Loop-Filter (within the Jitter Attenuator PLL) is about 23Hz. A simple
illustration of the "Jitter Gain (or Attenuation) Transfer Characteristics of the Jitter Attenuator PLL (within the
FIGURE 155. A SIMPLISTIC ILLUSTRATION OF THE ROLE/FUNCTION OF THE JITTER ATTENUATOR PLL BLOCK
WITHIN THE
XRT79L71.
Jitter
Attenuator
PLL
Jitter
Attenuator
PLL
Input “Jittery”
Clock Signal
Output “Smoothed”
Clock Signal