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MT9041

Multiple Output Trunk PLL

Mitel Networks 

Advance Information

MT9041

Freerun Accuracy

Jitter Transfer Function

The Freerun accuracy of the PLL is a measure of

how accurately the PLL can reproduce the desired

output frequency. The freerun accuracy is a function

of master clock frequency which must be 20 MHz

±32 ppm in order to meet AT & T TR62411 and ETSI

specifications.

Jitter Performance

The output jitter of a digital trunk PLL is composed of

intrinsic jitter, measured using a jitter free reference

clock, and frequency dependent jitter, measured by

applying known levels of jitter on the references

clock. The jitter spectrum indicates the frequency

content of the output jitter.

Intrinsic Jitter

Intrinsic jitter is the jitter added to an output signal by

the processing device, in this case the enhanced

PLL. Tables 3 and 4 show the average measured

intrinsic jitter of the T1 and E1 outputs. Each

measurement is an average based upon a ±100 ppm

deviation (in steps of 20 ppm) on the input reference

clock. Jitter on the master clock will increase intrinsic

jitter of the device, hence attention to minimization of

master clock jitter is required.

The jitter transfer function is a measure of the

transfer characteristics of the PLL to frequency

specific jitter on the referenced input of the PLL. It is

directly linked to the loop bandwidth and the

magnitude of the phase error suppression

characteristics of the PLL. It is measured by applying

jitter of specific magnitude and frequencies to the

input of the PLL, then measuring the magnitude of

the output jitter (both filtered and unfiltered) on the

T1 or E1 output.

Care must be taken when measuring the transfer

characteristics to ensure that critical jitter alias

frequencies are included in the measurement (i.e.,

for digital phase locked loops using an 8 kHz input).

Tables 5 and 6 provide measured results for the jitter

transfer characteristics of the PLL for both a 1.544

MHz and 2.048 MHz reference input clock. The

transfer characteristics for an 8 kHz reference input

will be the same.

Figures 4 and 5 show the jitter attenuation

performance of the T1 and E1 outputs plotted

against AT & T TR62411 and ETSI requirements,

respectively.

Output Jitter in UIp-p

Reference Input

FLT0 Unfiltered

FLT1

10Hz - 8kHz

FLT2

10Hz - 40kHz

FLT3

8kHz - 40kHz

8 kHz

.011

.004

.006

.002

1.544 MHz

.011

.001

.002

.001

2.048 MHz

.011

.001

.002

.001

Table 3 -Typical Intrinsic Jitter for the T1 Output

Typical figures are at 25°C and are for design aid only: not guaranteed and not subject to production testing.

Output Jitter in UIp-p

Reference Input

FLT0 Unfiltered

FLT1

20Hz - 100kHz

FLT2

700Hz - 100kHz

8 kHz

.011

.002

.002

1.544 MHz

.011

.002

.002

2.048 MHz

.011

.002

.002

Table 4 - Typical Intrinsic Jitter for the E1 Output

Typical figures are at 25°C and are for design aid only: not guaranteed and not subject to production testing.

3-87

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