saa7392 NXP Semiconductors, saa7392 Datasheet - Page 20

• Manufacturer Part Number: saa7392
• Description: Channel Encoder/decoder Cdr60
• Manufacturer: NXP Semiconductors

Philips Semiconductors
7.5.1
The digital PLL will recover the channel bit clock. As the
capture range of the PLL itself is limited, lock detectors and
2 capture aids are present. In total three different PLL
operation modes exist: In-lock, Inner-lock aid and
Outer-lock aid.
The PLL behaviour during in-lock (the normal on-track
situation) can be best explained in the frequency domain.
The PLL operation is completely linear during in-lock
situations. The open-loop response of the PLL is given in
Fig.7. The three frequencies, f
frequency), f
bandwidth) are programmable via register PLLSet.
To extend the PLL capture range two lock aids are used:
Two outer lock aids can be used:
Programmability/observability is built into the PLL. Its
operation can be influenced in two ways:
The operation of the bit detector can be monitored by the
microprocessor and via the MEAS1 pin. Four signals are
available for measurement:
2000 Mar 21
Inner lock aid: has a capture range of 10% and will
bring the PLL frequency to the lock point
Outer lock range: has no limitation on capture range,
and will bring the PLL within the range of the inner lock
range.
Run length 3 deviation detector: this circuit is known to
be sensitive to systematic over/under equalization; this
over/under equalization can be counter-acted by writing
a non-zero phase offset value to register PLLLock.
Frequency measurement detector: this circuit regulates
the PLL frequency so that the average number of EFM
transitions is a fixed fraction of the PLL bit clock; the
transition frequency is settable via register PLLFMeas.
It is possible to select the state the PLL is in (in-lock,
near-lock, outer-lock) via register PLLLock
It is possible to preset the PLL frequency to a certain
value via registers PLLEqu and PLLFreq.
Channel encoder/decoder CDR60
D
IGITAL
1
(PLL bandwidth) and f
PLL
0
(integrator cross-over
2
(low-pass
20
handbook, halfpage
PLL frequency signal: the most significant 8 bits are
available via register PLLLock
Asymmetry signal: the 8-bit signal in 2’s complement
form is available via register PLLSet
Jitter signal: the most significant 8 bits are available via
register PLLFreq. This gives an impression of the
detection jitter after all processing is done.
jitter<9:0> = average ((jitter individual
transition)
To obtain the jitter in the bit clocks the jitter<9:0> value
must be divided by 8192 and square routed. Note that
the jitter<9:0> overestimates the jitter (by approximately
rms jitter increase of 0.03 bit clock), because the
quantization of the zero transitions is in 4 intervals.
Note the jitter is measured before the bit detection and
contains contributions due to various imperfections in
the complete signal path; i.e. disc, preamplifier, ADC,
limited bitwidths, PLL performance, internal filter noise,
asymmetry compensation, equalizer.
Internal lock flags: The internally generated inner-lock
signal (f_lock_in), lock signal (lock_in) and flag that
indicates when a run length 14 is detected
(long_symbol) are available via register PLLEqu.
amplitude
(dB)
2
8192)
Fig.7 PLL bode diagram.
f 0
f 1
Preliminary specification
f 2
frequency (Hz)
SAA7392
MGR797