FS401LF datasheet(78/104 Pages) ETC2

78 / 104 page

FS401, FS403

PRODUCT SPECIFICATION

REV. NO. 1.7

JANUARY 24, 2007

5.1.6 Digital RGB Multiplexer

The EXADSEL pin in conjunction with BIPGEN in the CRE register controls a triple 24-bit multiplexer that

selects the source of RGB data to be supplied to the digital gain block. 24-bit RGB data can be accepted

from:

•

TTL compatible RGB input port

•

A/D converter outputs

•

BiPGen, the internal test pattern generator

5.1.7 RGB Gain

Following each A/D converter is a digital gain stage that allows the A/D converter to accommodate either

700 mV or 1000 mV RGB input video signals. Gain is set by the RGBGAIN bit of the Command Register.

When using RGBGAIN, VADCREF should be set to 1000 mV.

5.1.8 RGB/YUV Matrix

Pixels are converted from the 24-bit RGB format to the 24-bit YUV format by an RGB/YUV matrix. UV

data is filtered and decimated prior to realignment with Y data forming a 16-bit YUV422 data stream.

5.1.9 Vertical Scaler

16-bit YUV422 data from the Transcoder is passed to the Vertical Scaler that operates on columns of

pixels. Programming the VSC registers sets vertical scale factor. VSC is the Vertical Scale Coefficient, n

which determines the vertical scaling factor:

Vertical Scaling = (1 – VSC/256)

n is the reduction (caused by the scaling filter), modulo 256, in the number incoming vertical lines. With a

range: 0

≤ n ≤ 192; 1 ≤ VSC ≤ 1/4.

5.1.10 Flicker Filter

The FS400 flicker filter includes a variable vertical filter response in addition to a sharpness function.

The vertical averaging part of the filter is decomposed into an impulse function (no filtering) and a vertical

flicker function. Adjusting the FLK Coefficient modifies the vertical filter from no filtering (FLK = 0) to a

Three Line Average (FLK = 21), giving the user a wide choice in filtering options. A value of 16 provides

the normal 3 line flicker filter response of ¼, ½, and ¼.

In addition to the variable vertical settings, the FS400 flicker filter has a sharpness function. This function

is a two dimensional peaking function with accentuates the joint high vertical - high horizontal spatial

frequencies.

The three line variable two dimensional flicker filter is formed by summing the unit impulse function with a

vertical flicker function scaled by FLK (Flicker Coefficient) and the peaking function which is scaled by

SHP (Sharpness Coefficient). The FLK and SHP variables have 5 bits of resolutions, with a usable a

range from 0 to 21/32 for FLK, and 0 to 31/32 for SHP.

The perception of flicker varies with the angle of the flicker source to the horizontal. Experimentally it was

determined that the perceived flicker threshold was between 20 and 35 degrees. Above 35 degrees few

viewers can notice a line flicker and below 20 degrees most viewers can.

The vertical response of the flicker filter varies with the angle from horizontal and only modifies parts of

the video input that contain flicker. The plot of the filter response is shown below at 0, 14, 27, and 45

degrees from horizontal.

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