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1997 Nov 17
10
Philips Semiconductors
Preliminary specification
ISO/MPEG Audio Source Decoder
SAA2502
7.2.3.1
XOR mode
PHDIF is the XOR function of SIG and REF. The frequency
is twice the frequency of SIG and REF. The PHDIF output
carries a signal, switching between GND and V
DD
, with an
average value V
avg
which is a function of the phase
difference between SIG and REF (see left part of Fig.6).
The locking range in this mode of operation is maximum
for even values of N
3
(180 degrees phase difference) but
less for odd values of N
3
. It is minimum for N
3
= 3
(120 degrees phase difference).
7.2.3.2
Edge triggered mode
PHDIF is only influenced by the rising edges of SIG and
REF. Consequently its frequency is equal to the SIG and
REF frequency.
The electrical behaviour of the PHDIF output pin in this
mode is special:
PHDIF is HIGH from the rising edge of REF to the rising
edge of SIG and 3-stated elsewhere if REF is leading and
PHDIF is low from rising edge of SIG to rising edge of REF
and 3-stated elsewhere if REF is trailing. Therefore PHDIF
is NOT 3-stated during a portion t
up
of each cycle when it
acts as a pull-up device or during a portion t
down
of each
cycle when it acts as a pull-down device (see right part of
Fig.6).
As a result the locking range is always 360 degrees phase
difference. The output behaviour as function of phase
difference is non-symmetrical with reference to the vertical
axis, but a reversed mode is also available (by setting the
control flag PHSRVS).
Fig.6 PHDIF output behaviour.
handbook, full pagewidth
MGE473
REF to SIG phase difference
REF to SIG phase difference
max
min
0
o
180
o
360
o
180
o
0
o
+
180
o
0
1
5/6
1/6
Vavg
VDD
100%
100%
0%
tup
tdown
T
t1
t2
T
t
PHDIF
3-stated
XOR mode
edge triggered mode