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參數(shù)資料
| 型號： | TDA4691T |
| 廠商： | NXP SEMICONDUCTORS |
| 元件分類： | 信號分離 |
| 英文描述： | Sync Processor with Clock SPC |
| 中文描述： | SYNC SEPARATOR IC, PDSO20 |
| 封裝： | PLASTIC, SOT-163-1, SO-20 |
| 文件頁數(shù)： | 5/26頁 |
| 文件大小： | 206K |
| 代理商： | TDA4691T |
September 1993
5
Philips Semiconductors
Preliminary specification
Sync Processor with Clock (SPC)
TDA4691
FUNCTIONAL DESCRIPTION
(See block diagram Fig.1 and timing
Figs 12 to 16)
Sync separator
Top-sync and blacklevel are stored
and H and V sync pulses are sliced in
the middle of both levels (50%).
Sync-output buffer
This circuit turns the current pulse
from the sync separator into a TTL
signal.
Sync processing
This circuit assures that phase
comparison can operate correctly
during V-pulses. Phase jumps
initiated by alternating headpulses of
VCR recorders are quickly recovered.
The sync processing contains the
functions H/2 suppression, sync
extension and sync interruption.
These three functions are only active
if successive pulses have a minimum
distance of 1.6
μ
s.
The H/2 suppression operates with a
gate
15
μ
s up to
+
14
μ
s around the
PHI1-reference and is necessary for
suppression of the equalizing pulses.
For sync interruption this gate is
closed earlier if the detected sync is
longer than 4.8
μ
s.
Only during V-pulses will the duration
of the applied pulses be tested. If they
are longer than 1.6
μ
s they will be
recognized as sync pulses and
enlarged up to 4.6
μ
s.
Phase detector (PHI1)
The phase detector has separate
filters for the fast time constant T
1
(pin
17) and normal time constant T
2
(pins
17 and 16). The slow time constant T
3
uses the normal time constant T
2
with
reduced control current. For reduction
of H-pulse modulation the filter at pin
16 is switched off during sync time if
normal time constant T
2
is on. Thus
no frequency shifting of the oscillator
is possible during sync.
Time-constant switching
This block contains a switch and an
impedance converter (buffer). The
switch connects the filters at pin 16
and 17 in parallel (normal time
constant T
2
or slow time constant T
3
).
The buffer transfers the control
voltage at pin 17 to pin 16 (fast time
constant T
1
). Which of the 2 functions
is active is determined by the blocks
noise detector, V-logic or signal
identification.
VCO 13.5 MHz
The adjustment of the nominal
frequency (13.5 MHz) is achieved at
pin 15. The VCO control voltage is
applied (from the phase detector) at
pin 16.
The control range can be adjusted by
the current at pin 18.
Pin 15 can be used to feed in an
external frequency. Under these
circumstances the internal VCO is
switched off by application.
The control voltage at pin 16 can be
used to control the external VCO.
VCO-buffer
The VCO-buffer delivers a TTL
compatible signal of 13.5 MHz to pin
13.
ECL-prescaler
This block consists of a :16
asynchronous prescaler.
H-divider
This is a divider by 54. It is split into a
prescaler :2 and a divider by 27. Out
of this block several signals are taken
for generation of H-frequently pulses
in the H-logic block. These signals
must have good timing. This is
achieved by special synchronization.
H-logic
This block creates all pulses
necessary for the SSC generator, the
signal identification, the phase
detector, the sync preparation and the
V-divider.
V-divider
The V-divider consists of an
asynchronous 10-bit divider and a
decoder logic. The divider is clocked
with twice the line frequency. The
decoder circuit delivers the pulses
necessary for the V-logic.
V-logic
In the V-logic the V-syncs from the
sync separator are evaluated and
noise reduced. Also certain operation
states are switched ON and OFF.
Additionally the reset pulse for the
V-divider and the 50/60 Hz
information is generated.
H-pulse former
The H-pulse starting point can be
shifted in this stage, also the gate
pulse of
～
2.4
μ
s is generated for use
in the digital noise identification block.
H-pulse buffer
In this circuit the line signal will be
pre-synchronized by output signal of
the :16 divider and synchronized by
the 13.5 MHz clock. The buffer
delivers TTL output signals.
V-pulse buffer
The signal out of the V-divider is
synchronized with 13.5 MHz clock
and converted to a TTL output level.
Gap reference
This circuit operates with the
gap-principle and is stable with regard
to temperature and supply voltage
changes.
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