SPT2110 Просмотр технического описания (PDF) - Signal Processing Technologies

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SPT2110

NTSC/PAL VIDEO DECODER

Signal Processing Technologies 

COLOR BAND PASS FILTER

Color band-pass filters ensure that only the chrominance

signal frequencies are passed on to the demodulators.

AUTOMATIC COLOR CONTROL

Automatic color control (ACC, or AGC of the chrominance

signals) is enabled by register AH. The process is used to

monitor the amplitude of the burst signal level. The amplitude

of the color burst is expected to be of a specific amplitude.

When this amplitude is not of the correct level, an adjustment

of the color amplitude is made. This, in turn, corrects the

amplitude of the entire color level pre-demodulated color

signal.

COLOR BURST DETECTION & PHASE

Monitoring of the color burst is a continuous process. The

burst is evaluated for amplitude to ensure that color informa-

tion is being processed. See the Color Kill section. The burst

signal is phase-locked to the local DTO. Without a color burst

synchronized local oscillator, the demodulation of the chroma

signal will not be correct.

COLOR KILL

The color information is controlled by register BH. It may be

killed (turned-off) by setting a bit in the register or allowed to

automatically be shutdown if the burst level is not the proper

amplitude.

COLOR DEMODULATION

Chrominance demodulation is performed by a quadrature

amplitude demodulator. The demodulation is performed by a

multiplication of the incoming signal with the value of the local

Discrete-Time Oscillator (DTO). This local oscillator is multi-

plied with the 9-bit chrominance data to provide quadrature

demodulation. This multiplication produces a chrominance

signal that has a data bit width of the sum of the two

multiplying terms. This resultant value is rounded and low-

pass filtered. The low pass filter produces the color difference

signals (I and Q, for NTSC and U and V for PAL). To

demodulate the two difference color signals, there is a

separate demodulator for each path. Each has a local oscil-

lator signal that is 90 degrees out of phase with the other and

synchronous with the burst signal.

DISCRETE TIME OSCILLATOR

An on-board Discrete-Time Oscillator (DTO) provides two

color subcarrier local oscillators phase shifted 90°. The DTO

is synchronized with the color burst (color reference) signal

with a digital phase-locked loop.

COLOR SATURATION

Color saturation (amplitude) is controlled by register 9H. The

value of the register is a multiplicative of the color difference

signals produced from the demodulators.

COLOR HUE

Color hue (angle of the color position) is performed post

demodulation with a vector multiplication process. This ensures

accurate hue control for the NTSC and PAL system format.

CHROMINANCE SAMPLE ALIGNMENT

Sample alignment circuitry ensures the same number of

chroma pixels per line and lines/field. Counting registers,

based on the mode of operation, determine the number of

pixels per line and the number of lines per field.

CHROMINANCE COLOR SPACE CONVERSION

The color space conversion block uses the chrominance

difference signal values to transform from the NTSC or PAL

system format that was originally digitized to either RGB or

YCrCb. This process requires the values of both luminance

and color difference signals to be synchronized in time to

make this conversion correctly. The transformation to RGB or

YCrCb is performed using the I and Q (for NTSC) or U and V

(for PAL) color difference signals.

SYNCHRONIZATION AND FIELD DETECTION

Both incoming horizontal and vertical synchronization sig-

nals are detected to create the timing for the decoder. The

timing is necessary to produce the correct number of pixels

per line and the correct number of lines per field/frame and to

determine which field (odd or even) is being output. This

maps the image into the final digital storage format.

Timebase generation is digitally controlled using a fixed clock

data sampling scheme with digital phase-locked loop to

control the internal digital shifting of the sampled data. The

data from the luminance and chrominance signals are pro-

cessed by the sample alignment circuit to ensure the same

number of pixels per line and lines/field. The robust timebase

generation circuitry can operate over a wide range of video

source quality levels. This may include VCR fast-forward and

pause modes.

SPT

7

SPT2110

3/27/98

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