PCA8514T PHILIPS [NXP Semiconductors], PCA8514T Datasheet - Page 46

• Manufacturer Part Number: PCA8514T
• Description: Stand-alone OSD
• Manufacturer: PHILIPS [NXP Semiconductors]

Philips Semiconductors
11 OSD CLOCK
The on-chip clock generator comprises Phase-Locked
Loop circuitry and is shown in Fig.39. The frequency of the
OSD clock is programmable and is determined by the
contents of the 6-bit counter, which is loaded using
Command 6. The OSD clock frequency is calculated as
shown below; frequencies within the range 4 to 14 MHz
can be selected.
Where: 16 < (PLLCN) < 40; (PLLCN) is the decimal value
held in the 6-bit counter.
The Voltage Controlled Oscillator (VCO) is synchronized
to the HIGH-to-LOW edge of f
always on the trailing edge of f
active level detector will pass the HSYNC signal if it is
programmed as active HIGH or invert the HSYNC signal if
it is programmed as active LOW. The 4-bit prescaler
increments or decrements the output of the VCO in steps
of (16
1995 Nov 27
f
handbook, full pagewidth
OSD
Stand-alone OSD
=
HSYNC
f
f
HSYNC
HSYNC
).
16
DETECTOR
ACTIVE
LEVEL
PLLCN
1
HSYNC
(see Fig.39) which is
f 1
. The programmable
Fig.39 Block diagram of OSD oscillator.
PROGRAMMABLE
FREQUENCY
6-BIT COUNTER
DETECTOR
PHASE/
divided by N
46
The OSD clock is enabled/disabled using Command 7;
see Section 9.8. When the OSD clock is disabled, the
oscillator remains active, therefore the transient time from
the OSD clock start-up to locking into the external H
signal is reduced. As the on-chip oscillator is always active
after power-on, when the OSD clock is enabled no large
currents flow (as for RC or LC oscillators); therefore
radiated noise is dramatically reduced.
Character width is a function of the OSD clock frequency;
decreasing f
Therefore, for optimum character display quality the
choice of the OSD clock frequency is important; this is
explained in Chapter 12.
PRESCALER
CHARGE PUMP
LOOP FILTER
4-BIT
AND
OSD
OSD disable
increases the width of the characters.
f PLL
CONTROLLED
OSCILLATOR
VOLTAGE
Product specification
PCA8514
C
MLC349
f OSD
R 1
C 1
SYNC