Stratum III Timing Module : VCT1000B

Application: Dual Input Timing Module

Page 1 of 8

Rev. “5” 1/20/04

1.0

DESCRIPTION AND APPLICATION

The VCT1000B is a hitless-switching dual-input stratum 3 low jitter timing module with status

outputs and alarms. Dual 8 kHz references are independently selected to lock a digital phase

lock loop resulting in excellent long and short-term stability. Two control inputs are used to

steer the state machine decisions for the operation of the module. The state machine will enter

and maintain the operation in the free run, holdover, or locked condition. The state machine

operates under the requirements of section 3.4 of the Telcordia GR-1244-CORE. Four status

pins indicate the condition, which the unit is operating, and two alarm outputs indicate the loss of

lock and holdover or free run operation. The signal outputs are the low jitter oscillator output

and the divided 8kHz output. Input phase rearrangement allows the output to remain hitless upon

the switching of the references, regardless of input phase. Dimensions are 2” x 2” x 0.55”. A

state machine is used to assure that switching to a bad reference is not allowed, and that both

references are qualified.

Figure 1 VCT1000B Block Diagram

System

Control and

State Machine

Main Status Alarm

Ref 1

Ref 2

Free Run

Holdover

Input Buffer

Phase

Alignment

Reference

Qualification

Input Buffer

Phase

Alignment

Reference

Qualification

Hitless

Switching

MUX

Phase

Detector

Holdover

History and

Digital

Filtering

DAC

Divider

Stratum

III OCXO

Buffer

Buffer

Divider

System control lines to all blocks

CNTL A

CNTL B

REF 1

8 kHz

REF 2

8 kHz

Alarm

Out

Loss of

Lock

Alarm

8 kHz

Output

19.440

MHz

Output