TC90A53N/F
2001-02-08 7/17
DESCRIPTION OF FUNCTIONS
(1) CLAMP (Input clamp)
Circuit used to Sync tip clamp composite signal.
Apply feedback clamp so that at Y / C separation, the minimum data value after A / D conversion is the
internally-fixed level.
(2) ADC (A / D converter)
High-speed series-parallel 8-bit A / D converter (Dynamic Range: 2.0V).
Input composite video signal with amplitude of 1.5 V
p-p
(sync to white 100%).
(3) 1 H memory
Line memory consisting of DRAM for 1 H delay. Two line memories configure a 3-line comb filter.
Because the system clock is 4 f
sc
(14.3 MHz), 910 clocks / 1 H is set.
(4) VENH (Vertical enhancer circuit)
After coring (2LSB) the non-correlation component among the three lines of the luminance signal, this
block enhances the vertical outline. The enhance amount can be selected from three settings : large
( 1.25), medium ( 0.75), and small ( 0.25).
The vertical enhance amount is added to the luminous signal obtained by subtracting the color signal
from the composite signal, then the luminous signal is output via the D / A converter. Note that if the
luminous signal is lower than the pedestal level (internally-fixed value), the vertical enhance amount is
not added to.
(5) BPF (Horizontal bandpass filter)
Uses f
sc
as the center frequency. Filters the composite signal delayed by 0 H, 1 H, or 2 H and extracts the
color signal.
The bandpass filter for outputting the color signal at a later stage can be switched on or off to select
output of a narrow- or wide-band color signal.
(6) DCF (Vertical dynamic comb filter)
Vertical bandpass filter which extracts the color signal by detecting vertical non-correlation. Using
Toshiba logic, determines the correlation among three lines. If no correlation, determines as the luminous
signal and suppresses output of the color signal.
(7) 1-line color dot interference reducer circuit
Improves color dot interference on a screen where only 1 line has color so that the C signal is processed as
the Y signal.
Extracts 1-line color dot component and the result is added to the output from the dynamic comb filter.
(8) RTIM (Clock / memory timing generator)
This block supplies × 4 f
sc
(14.3 MHz) obtained using the VCO via a buffer to the blocks and generates
the timing signal necessary for memory.
(9) PLL (× 4 clock generator)
Multiplies f
sc
(3.58 MHz) by 4 and generates system clock 4 f
sc
(14.3 MHz).
(10) DAC (D / A converter)
High-speed 8-bit D / A converter. The output amplitudes are : Y output of 1.5 V
p-p
(typ.) and C output at
burst level of 572 mV
p-p
(typ.).
(11) Color killer circuit
When the input video signal is a monochrome image, this circuit enables effective use of the luminance
signal information regardless of whether there is a burst signal. It does this by preventing the chroma
signal output from the comb filter from being subtracted from the luminance signal.
While the VBI signal is active it is better not to use the comb function. Setting the KILLER pin to High
at this time enables the use of character multiplex and other signals from the Y output unchanged.
But since Vertical edge enhancement does not become OFF, be careful when using with Vertical edge
enhancement.