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HMP8112A

NTSC/PAL Video Decoder

Harris Semiconductor 

HMP8112A

Hue or Tint Adjust

The Hue adjustment is applied to the U and the V color dif-

ference signal. The Hue adjusts the phase of the given UV

data. The Hue can be adjusted by ±30 degrees in 1/4 degree

increments. This is achieved by changing the Burst Phase

Locked reference point. Figure 11 shows the block diagram

for the color adjustment section. This default value for this

register is 0.

VIDEO

DATA

DEMODULATED

COLOR

UV DATA

DECODER

CHROMA

AGC AND

USER

SETTINGS

HUE OFFSET

UV DATA

+

HUE

ADJUST

The Color Killer

(AGC Hysteresis and Loop Limits)

The color killer will disable the color difference path and set

the U and V components to zero. The automatic color killer

circuitry uses the AGC threshold to determine the maximum

and minimum gain factor limits. The loop filter determines

how much the AGC gain factor can be changed within one

line. The maximum gain factor (Max = 8) and the minimum

gain factor (Min = 0.5) will limit the range of the AGC. When

the gain factor exceeds the maximum gain factor of 8, the

gain factor is limited to 8. Once the signal has an amplitude

of 1/16th, the nominal video the color killer is enabled and

the chroma phase locked loop holds it’s last phase refer-

ence. While the color killer is enabled, the U and V compo-

nents are forced to zero. Once the input video signal reaches

1/7th the optimum amplitude the color killer is disabled and

the color is returned.

TO INPUT SAMPLE

RATE

CONVERTER

CHROMA

PHASE LOCKED

LOOP

FIGURE 11. HUE ADJUST BLOCK DIAGRAM

Horizontal/Vertical Sharpness

The frequency characteristics of the video waveform can be

altered to enhance the sharpness of the picture. The Hori-

zontal Sharpness register acts as a 4 band equalizer where

the amplitude of specific frequency ranges can be

enhanced or diminished. The Sharpness Control Register

allows the Low (LF), Mid (MF) and High Frequency (HF)

bands of the luminance signal to be enhanced. Vertical

Sharpness can be adjusted to 1 or a factor of 0. The

RESET default is a factor of 1.0

The 2-bit values allow 4 choices of scaling factors. The

sharpness control helps to compensate for losses in the

scaling interpolators that can reduce the amplitude of high

frequency components.

TABLE 2. SHARPNESS GAIN FACTOR SELECTS

XF1

XF0

GAIN FACTOR

0

0

Scaled By 1.0

UV

DATA

÷4096

I2C

LINE

COUNT

MAX

GAIN

FACTOR

MIN

GAIN

FACTOR

AGC

ENABLE

COLOR

KILLER

AGC

GAIN

FACTOR

FIGURE 12. LOOP FILTER BLOCK DIAGRAM (HYSTERESIS)

The dynamic range of the AGC allows it to compensate for

video that is 1/8 to 2 times the specified nominal of 1VP-P.

Saturation

The color saturation component is controlled via the Color

Saturation Registers. The color saturation is applied to the

UV components after the AGC function. The saturation value

is multiplied by the UV data to increase the color intensity.

This is an 8-bit number (as shown below) that ranges from 0

to 1.992.

X.XXXXXXX

The default register value of 1.2266 (0x9D) is calculated as

follows:

Register = Factor * 128 = 1.2266 * 128 = 157 = 0x9D

0

1

Scaled By 2.0

1

0

Scaled By 4.0

1

1

Scaled By 0

4-10

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