TDA9105 ST Microelectronics, TDA9105 Datasheet - Page 16

• Manufacturer Part Number: TDA9105
• Description: DEFLECTION PROCESSOR FOR MULTISYNC MONITORS
• Manufacturer: ST Microelectronics

TDA9105
OPERATING DESCRIPTION (continued)
The PLL1 ensures the coincidence between the
leading edge of the synchro signal and a phase
reference obtained by comparison between the
sawtooth of the VCO and an internal DC voltage
adjustable between 2.4V and 4V (by Pin 15). So a
Figure 11 : PLL1 Timing Diagram
The two VCO threshold can be filtered by connect-
ing capacitor on Pins 8-9.
The TDA9103 also includes a LOCK/UNLOCK
identification block which senses in real-time
Figure 12 : LOCK/UNLOCK Block Diagram
16/32
Phase REF1 is obtained by comparison between the sawtooth and
a DC voltage adjustable between 2.4V and 4V. The PLL1 ensures
the exact
HSYNS . A
From
Phase
Comparator
45 phase adjustment is possible (see Figure 11).
H Osc
Sawtooth
Phase REF1
H Synchro
coincidence between the signals phase REF and
T/8 phase adjustment is possible.
0.75T
NOR1
0.25T
A
2.4V<Vb<4V
6.4V
Vb
1.6V
20k
220nF
H-Lock CAP
13
6.5V
whether the PLL is locked on the incoming horizon-
tal sync signal or not. The resulting information is
available on HLOCKOUT output (Pin 2). The block
diagram of the LOCK/UNLOCK function is de-
scribed in Figure 12.
The NOR1 gate is receiving the phase comparator
output pulses (which also drive the charge pump).
When the PLL is locked, on point A there is a very
small negative pulse (100ns) at each horizontal
cycle, so after R-C filter, there is a high level on
Pin 13 which force HLOCKOUT to high level (pro-
vided that HLOCKOUT is pulled up to V
When the PLL is unlocked, the 100ns negative
pulse on A becomes much larger and consequently
the average level on Pin 13 will decrease. When it
reaches 6.5V, point B goes to low level forcing
HLOCKOUT output to ”0”.
The status of Pin 13 is approximately the following :
- Near 0V when there is no H-SYNC,
- Between 0 and 4V with H-SYNC frequency differ-
- Between 4 and 8V when H-SYNC frequency
- Near to 8V when PLL is locked.
It is important to notice that Pin 13 is not an output
pin and must only be used for filtering purpose (see
Figure 12).
ent from VCO,
= VCO frequency but not in phase,
B
2
HLOCKOUT
CC
).