Functional Description 10 May 24, 2006
IDT82V3011 T1/E1/OC3 WAN PLL WITH SINGLE REFERENCE INPUT
The mode changes between Normal (S1) and Auto-Holdover (S2)
are triggered by the Invalid Input Reference Detection Circuit and are
irrelative to the logic levels on the MODE_sel0 and MODE_sel1 pins. At
the stage of S1, if the input reference is invalid (out of the capture
range), the operating mode will be changed to Auto-Holdover (S2)
automatically. When the input reference becomes valid, the operating
mode will be changed back to Normal (S1) automatically. Refer to “2.4
Invalid Input Signal Detection” for more information.
When the operating mode is changed from one to another, the TIE
control block is automatically disabled as shown in Figure - 3, except the
changes from Holdover (S3) or Auto-Holdover (S2) to Normal (S1). In
the case of changing from S3 or S2 to S1, the TIE control block is
enabled or disabled by the TIE_en pin.
2.1.1 NORMAL MODE
The Normal mode is typically used when a slave clock source
synchronized to the network is required.
In this mode, the IDT82V3011 provides timing (C1.5o, C3o, C2o,
C4o, C8o, C16o, C19o, C32o) and synchronization (F0o, F8o, F16o,
F19o, F32o, TSP, RSP) signals. All these signals are synchronous to the
input reference. The nominal frequency of the input reference can be 8
kHz, 1.544 MHz, 2.048 MHz or 19.44 MHz.
After reset, the IDT82V3011 will take 30 seconds at most to make the
output signals synchronous (phase locked) to the input reference.
Whenever the IDT82V3011 works in the Normal mode, the NORMAL
pin will be set to logic high.
2.1.2 FAST LOCK MODE
The Fast Lock mode is a submode of the Normal mode. It allows the
DPLL to lock to a reference more quickly than the Normal mode allows.
Typically, the locking time in the Fast Lock mode is less than 500 ms.
When the FLOCK pin is set to high, the Fast Lock mode will be
enabled.
2.1.3 HOLDOVER MODE
The Holdover mode is typically used for short duration (e.g., 2
seconds) while network synchronization is temporarily disrupted.
In the Holdover mode, the IDT82V3011 provides timing and
synchronization signals that are not locked to an external reference
signal, but are based on storage techniques. In the Normal mode, when
the output frequency is locked to the input reference signal, a numerical
value corresponding to the output frequency is stored alternately in two
memory locations every 30 ms. When the device is changed to the
Holdover mode, the stored value from between 30 ms and 60 ms is used
to set the output frequency of the device.
The frequency accuracy in the Holdover mode is ±0.025 ppm, which
corresponds to a worst case of 18 frame (125 µs per frame) slips in 24
hours. This meets the AT&T TR62411 requirement of ±0.37 ppm (255
frame slips per 24 hours).
Whenever the IDT82V3011 works in the Holdover mode, the
HOLDOVER pin will be set to logic high.
2.1.4 FREERUN MODE
The Freerun mode is typically used when a master clock source is
required, or used when a system is just powered up and the network
synchronization has not been achieved.
In this mode, the IDT82V3011 provides timing and synchronization
signals which are based on the master clock frequency (OSCi) only, and
are not synchronized to the input reference signal.
The accuracy of the output clock is equal to the accuracy of the
master clock (OSCi). So if a ±32 ppm output clock is required, the
master clock must also be ±32 ppm. Refer to “2.7 OSC” for more
information.
Whenever the IDT82V3011 works in the Freerun mode, the
FREERUN pin will be set to logic high.
2.2 FREQUENCY SELECT CIRCUIT
The input reference can be 8 kHz, 1.544 MHz, 2.048 MHz or 19.44
MHz, as determined by the F_sel1 and F_sel0 pins. See Table - 2 for
details.
Every time the frequency is changed, the device must be reset to
make the change effective.
2.3 REFERENCE INPUT MONITOR
The Telcordia GR-1244-CORE standard recommends that the DPLL
should be able to reject the references that are off the nominal frequency
by more than ±12 ppm. The IDT82V3011 monitors the frequency of the
input reference and outputs a signal at MON_out pin to indicate the
monitoring result. Whenever the reference frequency is off the nominal
frequency by more than ±12 ppm, the MON_out pin will go high. The
signal at MON_out pin is updated every 2 seconds.
2.4 INVALID INPUT SIGNAL DETECTION
This circuit is used to detect if the input reference is out of the
capture range. Refer to “3.6 Capture Range” for details. This includes a
complete loss of the input reference and a large frequency shift in the
input reference.
If the input reference is invalid (out of the capture range), the
IDT82V3011 will be automatically changed to the Holdover mode (Auto-
Holdover). When the input reference becomes valid, the device will be
changed back to the Normal mode and the output signals will be locked
to the input reference.
In the Holdover mode, the output signals are based on the output
reference signal 30 ms to 60 ms prior to entering the Holdover mode.
The amount of phase drift while in holdover can be negligible because
the Holdover mode is very accurate (e.g., 0.025 ppm). Consequently,
the phase delay between the input and output after switching back to the
Normal mode is preserved.
Table - 2 Input Frequency Selection
Frequency Selection Pins
Input Frequency
F_sel1 F_sel0
0 0 19.44 MHz
01 8 kHz
1 0 1.544 MHz
1 1 2.048 MHz
