X98021 datasheet(16/29 Pages) RENESAS

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X98021

FN8219 Rev 3.00

Page 16 of 29

March 8, 2006

image quality and requiring that the user do a manual

calibration once the monitor has warmed up.

In addition to drift, many AFEs exhibit interaction between the

offset and gain controls. When the gain is changed, the

magnitude of the offset is changed as well. This again

increases the complexity of the firmware as it tries to optimize

gain and offset settings for a given video input signal. Instead

of adjusting just the offset, then the gain, both have to be

adjusted interactively until the desired ADC output is reached.

The X98021 simplifies offset and gain adjustment and

completely eliminates offset drift using its Automatic Black

Level Compensation (ABLC™) function. ABLC™ monitors the

black level and continuously adjusts the X98021's 10 bit offset

DACs to null out the offset. Any offset, whether due to the

video source or the X98021's analog amplifiers, is eliminated

with 10 bit (1/4 of an 8 bit ADC LSB) accuracy. Any drift is

compensated for well before it can have a visible effect.

Manual offset adjustment control is still available - an 8 bit

exactly 1 ADC LSB increments. And gain is now completely

independent of offset - adjusting the gain no longer affects the

offset, so there is no longer a need to program the firmware to

cope with interactive offset and gain controls.

Finally, there should be no concerns over ABLC™ itself

introducing visible artifacts; it doesn't. ABLC™ operates at a

very low frequency, changing the offset in 1/4 LSB increments,

so it doesn't cause visible brightness fluctuations. And once

ABLC™ is locked, if the offset doesn't drift, the DACs won't

change. If desired, ABLC™ can be disabled, allowing the

firmware to work in the traditional way, with 10 bit offset DACs

under the firmware's control.

Gain and Offset Control

To simplify image optimization algorithms, the X98021 features

fully-independent gain and offset adjustment. Changing the

gain does not affect the DC offset, and the weight of an Offset

DAC LSB does not vary depending on the gain setting.

The full-scale gain is set in the three 8-bit registers (0x06-

0x08). The X98021 can accept input signals with amplitudes

ranging from 0.35VP-P to 1.4VP-P.

The offset controls shift the entire RGB input range, changing

the input image brightness. Three separate registers provide

independent control of the R, G, and B channels. Their nominal

setting is 0x80, which forces the ADC to output code 0x00 (or

0x80 for U and V channels in YUV mode) during the back

porch period when ABLC™ is enabled.

Functional Description

Inputs

The X98021 digitizes analog video inputs in both RGB and

Component (YPbPr) formats, with or without embedded sync

(SOG).

RGB Inputs

For RGB inputs, the black/blank levels are identical and equal

to 0V. The range for each color is typically 0V to 0.7V from

black to white. HSYNC and VSYNC are separate signals.

Component YUV Inputs

In addition to RGB and RGB with SOG, the X98021 has an

option that is compatible with the component YPbPr and

YCbCr video inputs typically generated by DVD players. While

the X98021 digitizes signals in these color spaces, it does not

perform color space conversion; if it digitizes an RGB signal, it

outputs digital RGB, while if it digitizes a YPbPr signal, it

outputs digital YPbPr. For simplicity’s sake we will call these

non-RGB signals YUV.

The Luminance (Y) signal is applied to the Green Channel and

is processed in a manner identical to the Green input with SOG

described previously. The color difference signals U and V are

bipolar and swing both above and below the black level. When

the YUV mode is enabled, the black level output for the color

difference channels shifts to a mid scale value of 0x80. Setting

configuration register 0x05[2] = 1 enables the YUV signal

processing mode of operation.

The X98021 can optionally decimate the incoming data to

provide a 4:2:2 output stream (configuration register 0x18[4] =

1) as shown in Table 2.

TABLE 1. YUV MAPPING (4:4:4)

INPUT

SIGNAL

X98021

INPUT

CHANNEL

X98021

OUTPUT

ASSIGNMENT

OUTPUT

SIGNAL

Green

Y0Y1Y2Y3

UBlue

Blue

U0U1U2U3

VRed

Red

V0V1V2V3

TABLE 2. YUV MAPPING (4:2:2)

INPUT

SIGNAL

X98021

INPUT

CHANNEL

X98021

OUTPUT

ASSIGNMENT

OUTPUT

SIGNAL

Green

Y0Y1Y2Y3

Blue

driven low

VRed

Red

U0V1U2V3

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