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MT9044

T1/E1/OC3 System Synchronizer

Mitel Networks 

MT9044

Advance Information

Input Impairment Monitor

Guard Time Circuit

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 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). The the Auto-Holdover

circuit does not use TIE correction. Consequently,

the phase delay between the input and output after

switching back to Normal Mode is preserved (is the

same as just prior to the switch to Auto-Holdover).

Automatic/Manual Control State Machine

The Automatic/Manual Control State Machine allows

the MT9044 to be controlled automatically (i.e.

LOS1, LOS2 and GTi signals) or controlled manually

(i.e. MS1, MS2, GTi and RSEL signals). With

manual control a single mode of operation (i.e.

Normal, Holdover and Freerun) is selected. Under

automatic control the state of the LOS1, LOS2 and

GTi signals determines the sequence of modes that

the MT9044 will follow.

The GTi pin is used by the Automatic/Manual Control

State Machine in the MT9044 under either Manual or

Automatic control. The logic level at the GTi pin

performs two functions, it enables and disables the

TIE Corrector Circuit (Manual and Automatic), and it

selects which mode change takes place (Automatic

only). See the Applications - Guard Time section.

For both Manual and Automatic control, when

switching from Primary Holdover to Primary Normal,

the TIE Corrector Circuit is enabled when GTi=1, and

disabled when GTi=0.

Under Automatic control and in Primary Normal

Mode, two state changes are possible (not counting

Auto-Holdover). These are state changes to Primary

Holdover or to Secondary Normal. The logic level at

the GTi pin determines which state change occurs.

When GTi=0, the state change is to Primary

Holdover. When GTi=1, the state change is to

Secondary Normal.

Master Clock

The MT9044 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 Modes of Operation

As shown in Figure 1, this state machine controls the

Reference Select MUX, the TIE Corrector Circuit, the

DPLL and the Guard Time Circuit. Control is based

on the logic levels at the control inputs LOS1, LOS2,

RSEL, MS1, MS2 and GTi of the Guard Time Circuit

(See Figure 6).

All state machine changes occur synchronously on

the rising edge of F8o. See the Controls and Modes

of Operation section for full details on Automatic

Control and Manual Control.

To

Reference

Select MUX

To TIE

Corrector

Enable

To DPLL

State

Select

RSEL

LOS1

LOS2

Automatic/Manual Control

State Machine

To and From

Guard Time

Circuit

The MT9044 can operate either in Manual or

Automatic Control. Each control method has three

possible modes of operation, Normal, Holdover and

Freerun.

As shown in Table 3, Mode/Control Select pins MS2

and MS1 select the mode and method of control.

Control RSEL

Input Reference

MANUAL

0

PRI

1

SEC

AUTO

0

State Machine Control

1

Reserved

Table 2 - Input Reference Selection

MS1 MS2

Figure 6 - Automatic/Manual Control State

Machine Block Diagram

8

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