TVP70025IPZP datasheet(13/55 Pages) TI

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Programmable Gain Control

Programmable Offset Control

TVP70025I

www.ti.com ...................................................................................................................................................................................................... SLES232 – JUNE 2008

The selection between bottom- and mid-level clamping is performed by I2C subaddress 10h (see Section

Sync-On-Green Threshold). The fine clamps also must be enabled via I2C register 2Ah for proper operation. The

internal clamping time can be adjusted using the I2C clamp start and width registers at subaddress 05h and 06h,

respectively (see Clamp Start and Clamp Width).

Table 1. Recommended Clamp Setting by Video Mode

SOG INPUT

GREEN ADC CHANNEL

RED ADC CHANNEL

BLUE ADC CHANNEL

VIDEO MODE

(Y/G)

(Pr/R)

(Pb/B)

YPbPr Component

Coarse

Fine Bottom Level

Fine Mid Level

PC Graphics

Coarse

Fine Bottom Level

SCART-RGB

Coarse

Fine Bottom Level

A single-pole low-pass filter with three selectable cutoff frequencies (0.5, 1.7, and 4.8 MHz) is implemented in the

feedback loop of the sync-tip clamp circuit.

The TVP70025I provides a 4-bit coarse analog gain control (before A/D conversion) and an 8-bit fine digital gain

control (after A/D conversion). The coarse analog gain and the fine digital gain are both independently

programmable for each ADC channel.

Coarse Gain Control

The 4-bit coarse analog gain control has a 4:1 linear gain control range defined by the following equation.

Coarse Gain = 0.5 + NCG/10, where 0 ≤ NCG ≤ 15

0.5

≤ Coarse Gain ≤ 2.0

Default: NCG = 7 (Coarse Gain = 1.2)

The 4-bit coarse gain control can scale a signal with a voltage-input compliance of 0.5 VPP to 2 VPP to a full-scale

10-bit A/D output code range. The minimum gain corresponds to a code 0h (2-VPP full-scale input, –6-dB gain)

while the maximum gain corresponds to code Fh (0.5-VPP full scale, +6-dB gain). The 4-bit coarse gain control is

independently controllable for each ADC channel (Red Coarse Gain, Green Coarse Gain, and Blue Coarse

Gain).

Fine Gain Control

The 8-bit fine digital gain control has a 2:1 linear gain control range defined by the following equation.

Fine Gain = 1.0 + NFG/256 where 0 ≤ NFG ≤ 255

1.0

≤ Fine Gain < 2.0

Default: NFG = 0 (Fine Gain = 1.0)

The 8-bit fine gain control is independently controllable for each ADC channel (Red Fine Gain, Green Fine Gain,

and Blue Fine Gain). For a normal PC graphics input, the fine gain is used mostly.

The TVP70025I provides a 6-bit coarse analog offset control (before A/D conversion) and a 10-bit fine digital

offset control (after A/D conversion). The coarse analog offset and the fine digital offset are both independently

programmable for each ADC channel.

Coarse Offset Control

A 6-bit code sets the coarse offset (Red Coarse Offset, Green Coarse Offset, Blue Coarse Offset) with individual

adjustment per channel. The coarse offset ranges from –32 counts to +31 counts. The coarse offset registers

apply before the ADC.

Fine Offset Control

A 10-bit fine offset registers (Red Fine Offset, Green Fine Offset, Blue Fine Offset) apply after the ADC. The fine

offset ranges from –512 counts to +511 counts.

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