CN8330 Datasheet, PDF (100/101 Pages) Conexant Systems, Inc – DS3/E3 Framer with 52 Mbps HDLC Controller

Appendix C
CN8330
DS3/E3 Framer with 52 Mbps HDLC Controller
The overall jitter transfer function also depends on the VCXO control
voltage/frequency conversion ratio (Ko) parameter measured in radians per
second per volt. In our PLL loop filter calculations, Ko equals approximately
400 for a VCXO with +/- 200 ppm pullability. Given Ko, a 10Hz break frequency
is calculated for R1=R2=500K. With a 10Hz break, attenuation at 100Hz is
around -12dB, barely sufficient to meet 0.4UI output jitter required with 1.5UI
input and 0.08UI intrinsic jitter.
For added margin, R1=R2=1M puts the break frequency at 7Hz.
Several CN8330 customers have tested the jitter attenuation PLL with
successfull results using R1=R2=1M. While this LPF should work for both T3
and E3 applications, we have not tested the PLL to comply with any regulatory or
interface requirements. LPF cutoff frequencies might have to be scaled to match
desired loop timing characteristics or to have the desired cutoff frequency. We
recommend all customers conduct performance evaluation and characterization
testing of the PLL before sending equipment for certification.
C-2
Conexant
100441E