MT9044AP datasheet(13/30 Pages) MITEL

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Advance Information

MT9044

MT9044 Measures of Performance

The following are some synchronizer performance

indicators and their corresponding deﬁnitions.

Intrinsic Jitter

Intrinsic

jitter

the

jitter

produced

the

synchronizing circuit and is measured at its output.

It is measured by applying a reference signal with no

jitter to the input of the device, and measuring its

output jitter.

Intrinsic jitter may also be measured

when the device is in a non-synchronizing mode,

such as free running or holdover, by measuring the

output jitter of the device.

Intrinsic jitter is usually

measured with various bandlimiting ﬁlters depending

on the applicable standards.

Jitter Tolerance

Jitter tolerance is a measure of the ability of a PLL to

operate properly (i.e., remain in lock and or regain

lock in the presence of large jitter magnitudes at

various jitter frequencies) when jitter is applied to its

reference.

The applied jitter magnitude and jitter

frequency depends on the applicable standards.

Jitter Transfer

Jitter transfer or jitter attenuation refers to the

magnitude of jitter at the output of a device for a

given amount of jitter at the input of the device. Input

jitter

applied

various

amplitudes

and

frequencies, and output jitter is measured with

various

ﬁlters

depending

the

applicable

standards.

For the MT9044, two internal elements determine

the jitter attenuation.

This includes the internal

1.9Hz low pass loop ﬁlter and the phase slope

limiter.

The phase slope limiter limits the output

phase slope to 5ns/125us.

Therefore, if the input

signal exceeds this rate, such as for very large

amplitude low frequency input jitter, the maximum

output phase slope will be limited (i.e. attenuated) to

5ns/125us.

The MT9044 has thirteen outputs with three possible

input frequencies for a total of 39 possible jitter

transfer functions. However, the data sheet section

on AC Electrical Characteristics - Jitter Transfer

speciﬁes transfer values for only three cases, 8kHz

to 8kHz, 1.544MHz to 1.544MHz and 2.048MHz to

2.048MHz.

Since all outputs are derived from the

same signal, these transfer values apply to all

outputs.

It should be noted that 1UI at 1.544MHz is 644ns,

which is not equal to 1UI at 2.048MHz, which is

488ns.

Consequently,

transfer

value

using

different input and output frequencies must be

calculated in common units (e.g. seconds) as shown

in the following example.

What is the T1 and E1 output jitter when the T1 input

jitter is 20UI (T1 UI Units) and the T1 to T1 jitter

attenuation is 18dB?

Using the above method, the jitter attenuation can be

calculated for all combinations of inputs and outputs

based on the three jitter transfer functions provided.

Note that the resulting jitter transfer functions for all

combinations of inputs (8kHz, 1.544MHz, 2.048MHz)

and

outputs

(8kHz,

1.544MHz,

2.048MHz,

4.096MHz, 8.192MHz, 16.384MHz) for a given input

signal (jitter frequency and jitter amplitude) are the

same.

Since

intrinsic

jitter

always

present,

jitter

attenuation will appear to be lower for small input

jitter signals than for large ones.

Consequently,

accurate jitter transfer function measurements are

usually made with large input jitter signals (e.g. 75%

of the speciﬁed maximum jitter tolerance).

Frequency Accuracy

Frequency accuracy is deﬁned as the absolute

tolerance of an output clock signal when it is not

locked to an external reference, but is operating in a

free running mode.

For the MT9044, the Freerun

accuracy is equal to the Master Clock (OSCi)

accuracy.

Holdover Accuracy

Holdover accuracy is deﬁned as the absolute

tolerance of an output clock signal, when it is not

OutputT 1

InputT 1

–

-------





×10

OutputT 120

–

---------





×10

2.5UI T 1

()

OutputE1

OutputT 1

644ns

()

488ns

()

-------------------

3.3UI T 1

()

OutputE1

OutputT 1

1UIT 1

()

1UIE1

()

----------------------

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