Advance Information
MT9074
dB
-0.5
0
-20 dB/decade
19.5
10
40
400
10K
Frequency (Hz)
Figure 11- TR 62411 Jitter Attenuation Curve
Phase Lock Loop (PLL)
Mode Name
BS/LS
S/FR
Note
System Bus
Synchronous
1
1
PLL locked to C4b.
The MT9074 contains a PLL, which can be locked to
either an input 4.096 Mhz clock or the extracted line
clock.The PLL will attenuate jitter from less than
2.5 Hz and roll-off at a rate of 20 dB/decade. Its
intrinsic jitter is less than 0.02 UI. The PLL will meet
the jitter transfer characteristics as specified by ATT
Line Synchronous
Free-Run
0
x
1
0
PLL locked to E1.5o.
PLL free - running.
Table 5 - Selection of clock jitter attenuation
modes using the M/S and MS/FR pins
document
TR
62411
and
the
relevant
recommendations as shown in Figure 11.
the internal PLL before being used to synchronize
the transmitted data. The clock extracted (with no
jitter attenuation performed) from the receive data
can be monitored on pin E1.5o.
Clock Jitter Attenuation Modes
MT9074 has three basic jitter attenuation modes of
operation, selected by the BS/LS and S/FR control
pins. Referring to the mode names given in Table 5
the basic operation of the jitter attenuation modes
are:
In Line Synchronous mode, the clock extracted from
the receive data is dejittered using the internal PLL
and then output on pin C4b. Pin E1.5o provides the
extracted receive clock before it has been dejittered.
The transmit data is synchronous to the clean
receive clock.
•
•
•
System Bus Synchronous Mode.
Line Synchronous Mode.
Free-run mode.
In Free-Run mode the transmit data is synchronized
to the internally generated clock. The internal clock
is output on pin C4b. The clock signal extracted from
the receive data is not dejittered and is output
directly on E1.5o.
In System Bus Synchronous mode pins C4b and F0b
are always configured as inputs, while in the Line
Synchronous and Free-Run modes C4b and F0b are
configured as outputs.
Depending on the mode selection above, the PLL
can either attenuate transmit clock jitter or the
receive clock jitter. Table 5 shows the appropriate
configuration of each control pin to achieve the
In System Bus Synchronous mode an external clock
is applied to C4b. The applied clock is dejittered by
13
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