CN8330 Datasheet, PDF (99/101 Pages) Conexant Systems, Inc – DS3/E3 Framer with 52 Mbps HDLC Controller

C
Appendix C
100441E
Here's what we've recommended as a starting point for those customers who need
a jitter attenuation PLL for TBR24 compliance in E3 mode.
An external jitter attenuation PLL can be implemented for CN8330 with one
VCXO and a passive LPF (low pass filter). The VCO output from CN8330 is
passed through the LPF to create a control voltage input to the VCXO. The
VCXO output then connects to RXCKI (and optionally to TXCKI) input of
CN8330.
VCXO Specifications:
T3
E3 Units
Center Frequency:
44.736 34.368 MHz
Frequency Accuracy:
+/- 20 +/- 20 ppm
Frequency Pullability:
+/- 200 +/- 200 ppm
Note: +/- 100 ppm frequency pullability may be adequate.
The LPF circuit is shown below with the RC time constants used to establish
the filter's cutoff frequencies as follows:
T1 = R1 x C2
T2 = R2 x C2
T3 = R2 x C1
R1
From VCO
Output
1M
C1
10 nF
R2
1M
C2
100 nF
To VCXO
Control
Input
GND
(Analog)
R and C values shown above are calculated for typical applications.
8330_001
Conexant
C-1