MT9046(2003) Ver la hoja de datos (PDF) - Zarlink Semiconductor Inc

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Fabricante

MT9046
(Rev.:2003)

T1/E1 System Synchronizer with Holdover

Zarlink Semiconductor Inc 

Data Sheet

MT9046

MT9046 Measures of Performance

The following are some synchronizer performance indicators and their corresponding definitions.

Intrinsic Jitter

Intrinsic jitter is the jitter produced by 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. In the MT9046, the intrinsic Jitter is limited to less than 0.02UI on the

2.048 MHz and 1.544 MHz clocks.

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 is applied at various amplitudes and frequencies, and output jitter is

measured with various filters depending on the applicable standards.

For the MT9046, 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 MT9046 has twelve outputs with three possible input frequencies (except for 19.44MHz, which is internally

divided to 8KHz) for a total of 36 possible jitter transfer functions. Since all outputs are derived from the same

signal, the jitter transfer values for the four cases, 8kHz to 8kHz, 1.544MHz to 1.544MHz and 2.048MHz to

2.048MHz can be applied 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, a 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?

OutputT1

=

InputT





1×10

–-2---A0--





–--2--1-0--8-

OutputT1 = 20×10

= 2.5UI(T1)

OutputE1 = OutputT1 × ((---11---UU-----II--TE----11----))

OutputE1 = OutputT1 × ((---64---48---48---nn----ss---))= 3.3UI(T1)

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.

Zarlink Semiconductor Inc.

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