MT8941 Mitel Networks Corporation, MT8941 Datasheet - Page 7

• Manufacturer Part Number: MT8941
• Description: CMOS ST-BUS FAMILY Advanced T1/CEPT Digital Trunk PLL
• Manufacturer: Mitel Networks Corporation

When MS3 is HIGH, DPLL #2 operates in any of the
major modes selected by MS0 and MS1. When MS3
is LOW, it overrides the major mode selected and
DPLL#2 accepts an external clock of 4.096 MHz on
C4b (pin 13) to provide the 2.048 MHz clocks (C2o
and C2o) and the 8 kHz frame pulse (F0b)
compatible with the ST-BUS format. The mode select
bit MS2 controls the direction of the signal on F0b
(pin 6).
When MS2 is LOW, the F0b pin is an 8 kHz frame
pulse input. This input is effective only when MS3 is
also LOW and pin C4b is fed by a 4.096 MHz clock,
which has a proper phase relationship with the
signal on F0b (refer Figure 18). Otherwise, the input
on pin F0b will have no bearing on the operation of
DPLL #2, unless it is in FREE-RUN mode as
selected by MS0 and MS1. In FREE-RUN mode,
the input on F0b is treated the same way as the
C8Kb input is in NORMAL mode. The frequency of
the signal on F0b should be 16 kHz for DPLL #2 to
lock and generate the ST-BUS compatible clocks at
4.096 MHz and 2.048 MHz.
When MS2 is HIGH, the F0b pin provides the frame
pulse output compatible with the ST-BUS format and
locked to the internal or external input signal as
determined by the other mode select pins.
Table 4 summarizes the modes of the two DPLL. It
should be noted that each of the major modes
selected for DPLL #2 can have any of the minor
modes, although some of the combinations are
Notes:
Table 5. Functions of the Bidirectional Signals
Mode
10
11
12
13
14
15
#
0
1
2
3
4
5
6
7
8
9
o
X
i
(kHz)
: Input
: Output
: “don’t care” input. Connect to V
F0b
i:16
o:8
o:8
o:8
o:8
o:8
o:8
o:8
o:8
i:8
i:X
i:8
i:X
i:8
i:8
i:X
in Each Mode
o:4.096
o:4.096
o:4.096
o:4.096
o:4.096
o:4.096
o:4.096
o:4.096
i:4.096
i:4.096
i:4.096
i:4.096
i:4.096
i:4.096
i:4.096
i:4.096
(MHz)
C4b
C8Kb
(kHz)
o:8
o:8
o:8
o:8
i:X
i:8
i:X
i:8
i:X
i:X
i:X
i:X
i:X
i:X
i:X
i:X
DD
or V
o:1.544
o:1.544
o:1.544
o:1.544
o:1.544
o:1.544
o:1.544
o:1.544
i:1.544
i:1.544
i:1.544
i:1.544
i:2.408
i:2.408
i:2.408
i:2.408
(MHz)
CVb
SS.
functionally similar. The required operation of both
DPLL #1 and DPLL #2 must be considered when
determining MS0-MS3.
The direction and frequency of each of the
bidirectional signals are listed in Table 5 for each of
the given modes in Table 4.
Jitter Performance and Lock-in Range
The output jitter of a DPLL is composed of the
intrinsic jitter, measured when no jitter is present at
the input, and the output jitter resulting from jitter on
the input signal. The spectrum of the intrinsic jitter
for both DPLLs of the MT8941 is shown in Figure 5.
The typical peak-to-peak value for this jitter is
0.07UI. The transfer function, which is the ratio of
the output jitter to the input jitter (both measured at a
particular frequency), is shown in Figure 6 for DPLL
#1 and Figure 7 for DPLL #2. The transfer function
is measured when the peak-to-peak amplitude of the
sinusoidal input jitter conforms to the following:
The ability of a DPLL to phase-lock the input signal
to the reference signal and to remain locked
depends upon its lock-in range. The lock-in range of
the DPLL is specified in terms of the maximum
frequency variation in the 8 kHz reference signal. It
is also directly affected by the oscillator frequency
tolerance. Table 6 lists different values for the lock-in
range and the corresponding oscillator frequency
tolerance for DPLL #1 and DPLL #2. The smaller
the tolerance value, the larger the lock-in range.
The T1 and CEPT standards specify that, for free
running equipment, the output clock tolerance must
be less than or equal to ±32ppm and ±50ppm
respectively. This requirement restricts the
Table 6. Lock-in Range vs. Oscillator Frequency
* Please refer to the section on “Jitter Performance and Lock-in
Range” for recommended oscillator tolerances for DPLL #1 & #2.
Tolerance (±ppm)
Oscillator Clock*
10 Hz - 100 Hz
100 Hz - 10 kHz
> 10 kHz
100
150
175
10
20
32
50
5
Tolerance
DPLL #1
CMOS
: 13.6 µs
: 20 dB / decade roll-off
: 97.2 ns
2.55
2.51
2.43
2.33
2.19
1.79
1.39
1.19
Lock-in Range (±Hz)
MT8941
DPLL #2
1.91
1.87
1.79
1.69
1.55
1.15
.75
.55
3-49