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CS4955-CQ

NTSC/PAL Digital Video Encoder

Cirrus Logic 

CS4954 CS4955

The CS4954/5 is designed to function as a video

timing master or video timing slave. In both Master

and Slave Modes, all timing is sampled and assert-

ed with the rising edge of the CLK pin.

In most cases, the CS4954/5 will serve as the video

timing master. HSYNC, VSYNC, and FIELD are

configured as outputs in Master Mode. HSYNC or

FIELD can also be defined as a composite blanking

output signal in Master Mode. In Master Mode, the

timing of HSYNC, VSYNC, FIELD and Compos-

ite Blank (CB) signals is programmable. Exact hor-

izontal and vertical display timing is addressed in

the Operational Description section.

In Slave Mode, HSYNC and VSYNC are typically

configured as input pins and are used to initialize

independent vertical and horizontal timing genera-

tors upon their respective falling edges. HSYNC

and VSYNC timing must conform to the ITU-

R BT.601 specifications.

The CS4954/5 also provides a ITU R.BT656 Slave

Mode in which the video input stream contains

EAV and SAV codes. In this case, proper HSYNC

and VSYNC timing are extracted automatically

without any inputs other than the V [7:0]. ITU

R.BT656 input data is sampled with the leading

edge of CLK.

In addition, it is also possible to output HSYNC

and VSYNC signals during CCIR-656 Slave

Mode.

4.2. Video Input Formatter

The Video Input Formatter translates YCbCr input

data into YUV information, when necessary, and

splits the luma and chroma information for filter-

ing, scaling, and modulation.

4.3. Color Subcarrier Synthesizer

The subcarrier synthesizer is a digital frequency

synthesizer that produces the appropriate subcarri-

er frequency for NTSC or PAL. The CS4954/5

generates the color burst frequency based on the

CLK input (27 MHz). Color burst accuracy and

stability are limited by the accuracy of the 27 MHz

input. If the frequency varies, then the color burst

frequency will also vary accordingly.

For environments in which the CLK input varies or

jitters unacceptably, a local crystal frequency refer-

ence can be used on the XTAL_IN and

XTAL_OUT pins. In this instance, the input CLK is

continuously compared with the external crystal ref-

erence input and the internal timing of the CS4954/5

is automatically adjusted so that the color burst fre-

quency remains within tolerance.

Controls are provided for phase adjustment of the

burst to permit color adjustment and phase com-

pensation. Chroma hue control is provided by the

CS4954/5 via a 10-bit Hue Control Register

(HUE_LSB and H_MSB). Burst amplitude control

is also made available to the host via the 8-bit burst

amplitude register (SC_AMP).

4.4. Chroma Path

The Video Input Formatter delivers 4:2:2 YUV

outputs into separate chroma and luma data paths.

The chroma path will be discussed here.

The chroma output of the Video Input Formatter is

directed to a chroma low-pass 19-tap FIR filter.

The filter bandwidth is selected (or the filter can be

bypassed) via the CONTROL_1 Register. The

passband of the filter is either 650 KHz or 1.3 MHz

and the passband ripple is less than or equal to

0.05 dB. The stopband for the 1.3 MHz selection

begins at 3 MHz with an attenuation of greater than

35 dB. The stopband for the 650 KHz selection be-

gins around 1.1 MHz with an attenuation of greater

than 20 dB.

The output of the chroma low-pass filter is connect-

ed to the chroma interpolation filter in which up-

sampling from 4:2:2 to 4:4:4 is accomplished.

Following the interpolation filter, the U and V

chroma signals pass through two independent vari-

able gain amplifiers in which the chroma amplitude

DS278PP4

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