MT9040
Data Sheet
Phase Detector
- the Phase Detector compares the reference signal with the feedback signal from the Frequency
Select MUX circuit, and provides an error signal corresponding to the phase difference between the two. This error
signal is passed to the Loop Filter. The Frequency Select MUX allows the proper feedback signal to be externally
selected (e.g., 8 kHz, 1.544 MHz, 2.048 MHz or 19.44 MHz).
Reference
Phase
Detector
Loop Filter
Digitally
Controlled
Oscillator
DPLL Reference
to
Output Interface Circuit
Feedback Signal
from
Frequency Select MUX
State Select
from
Input Impairment Monitor
Control
Circuit
State Select
from
State Machine
Figure 3 - DPLL Block Diagram
Loop Filter
- the Loop Filter is similar to a first order low pass filter with a 1.9 Hz cutoff frequency for all four
reference frequency selections (8 kHz, 1.544 MHz, 2.048 MHz or 19.44 MHz). This filter ensures that the network
jitter transfer requirements are met.
Control Circuit
- the Control Circuit uses status and control information from the State Machine and the Input
Impairment Circuit to set the mode of the DPLL. The two possible modes are Normal and Freerun.
Digitally Controlled Oscillator (DCO)
- the DCO receives the filtered signal from the Loop Filter, and based on its
value, generates a corresponding digital output signal. The synchronization method of the DCO is dependent on
the state of the MT9040.
In Normal Mode, the DCO provides an output signal which is frequency and phase locked to the input reference
signal.
In Freerun Mode, the DCO is free running with an accuracy equal to the accuracy of the OSCi 20 MHz source.
Lock Indicator - If the PLL is in frequency lock (frequency lock means the center frequency of the PLL is identical to
the line frequency), and the input phase offset is small, then the lock signal will be set high. For specific Lock
Indicator design recommendations, see the Applications - Lock Indicator section.
Output Interface Circuit
The output of the DCO (DPLL) is used by the Output Interface Circuit to provide the output signals shown in Figure
4. The Output Interface Circuit uses four Tapped Delay Lines followed by a T1 Divider Circuit, an E1 Divider Circuit,
and a DS2 Divider Circuit to generate the required output signals.
Four tapped delay lines are used to generate 16.384 MHz, 12.352 MHz, 12.624 MHz and 19.44 MHz signals.
The E1 Divider Circuit uses the 16.38 4MHz signal to generate four clock outputs and five frame pulse outputs. The
C8o, C4o and C2o clocks are generated by simply dividing the C16o clock by two, four and eight respectively.
These outputs have a nominal 50% duty cycle.
The T1 Divider Circuit uses the 12.384 MHz signal to generate the C1.5o clock by dividing the internal C12 clock
by eight. This output has a nominal 50% duty cycle.
The DS2 Divider Circuit uses the 12.624 MHz signal to generate the clock output C6o. This output has a nominal
50% duty cycle.
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Zarlink Semiconductor Inc.
XILINX [ XILINX, INC ]
