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MT9045

T1/E1/OC3 System Synchronizer

Zarlink Semiconductor Inc 

MT9045

Data Sheet

Input Impairment Monitor

This circuit monitors the input signal to the DPLL and automatically enables the Holdover Mode (Auto-Holdover)

when the frequency of the incoming signal is outside the Auto-Holdover capture range. (See AC Electrical

Characteristics - Performance). This includes a complete loss of incoming signal, or a large frequency shift in the

incoming signal. When the incoming signal returns to normal, the DPLL is returned to Normal Mode with the output

signal locked to the input signal. The holdover output signal in the MT9045 is based on the incoming signal 30ms

minimum to 60ms prior to entering the Holdover Mode. The amount of phase drift while in holdover is negligible

because the Holdover Mode is very accurate (e.g., ±0.05ppm). Consequently, the phase delay between the input

and output after switching back to Normal Mode is preserved.

State Machine Control

As shown in Figure 1, this state machine controls the Reference Select MUX, the TIE Corrector Circuit and the

DPLL. Control is based on the logic levels at the control inputs RSEL, MS1, MS2 and PCCi (See Figure 6). When

switching from Primary Holdover to Primary Normal, the TIE Corrector Circuit is enabled when PCCi = 1, and

disabled when PCCi = 0.

All state machine changes occur synchronously on the rising edge of F8o. See the Control and Mode of Operation

section for full details.

To

Reference

Select MUX

To TIE

Corrector

Enable

To DPLL

State

Select

RSEL

Control

State Machine

PCCi

MS1

MS2

Figure 6 - Control State Machine Block Diagram

Master Clock

The MT9045 can use either a clock or crystal as the master timing source. For recommended master timing

circuits, see the Applications - Master Clock section.

Control and Mode of Operation

The active reference input (PRI or SEC) is selected by the RSEL pin as shown in Table 2.

RSEL

Input Reference

0

PRI

1

SEC

Table 2 - Input Reference Selection

9

Zarlink Semiconductor Inc.

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