ZHCS927G May 2012 – January 2018 CDCM6208
PRODUCTION DATA.
As shown in Figure 50, the bandwidth of TX and RX is the frequency range in which clock jitter adds without any attenuation to the jitter budget of the link. Outside of these frequencies, the SERDES link will attenuate clock jitter with a 20 dB/dec or even steeper roll-off.
Example: SERDES link with KeyStone™ I DSP
The SERDES TX PLL of the TI KeyStone™ I DSP family (see Hardware Design Guide for KeyStone Devices (SPRABI2)) for the SRIO interface has a 13-MHz PLL bandwidth (Low Pass Characteristic, see Figure 50). The CDCM6208V2, pin-mode 27, was characterized in this example over Process, Voltage and Temperature (PVT) with a low-pass filter of 13 MHz to simulate the TX PLL. The attenuation is higher or equal to 20 dB/dec; therefore, the characterization used 20 dB/dec as worst case.
Table 41 shows the maximum total jitter over PVT with and without a low-pass filter.
OUTPUT | FREQUENCY
[MHz] |
MAX TJ [ps]
DSP SPEC |
MAX TJ [ps]
WITHOUT LOW-PASS FILTER |
MAX TJ [ps]
WITH 13-MHZ LOW-PASS FILTER |
---|---|---|---|---|
Y0 | 122.88 | 56 | 9.43 | 8.19 |
Y2 | 30.72 | 56 | 9.60 | 7.36 |
Y3 | 30.72 | 56 | 9.47 | 7.42 |
Y4 | 156.25
(6 bit fraction) |
56 | 57.66 | 17.48 |
Y5 | 156.25
(20 bit fraction) |
56 | 76.87 | 32.32 |
Y6 | 100.00 | 56 | 86.30 | 33.86 |
Y7 | 66.667 | 300 | 81.71 | 35.77 |
Figure 51 shows the maximum Total Jitter with and without low-pass filter characteristic and the maximum TI KeyStone™ I specification.
NOTE
Due to the damping characteristic of the DSP SERDES PLLs, the actual TJ data can be worse.