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TDA9332H/N2

I2C-bus controlled TV display processors

Philips Electronics 

Philips Semiconductors

I2C-bus controlled TV display processors

Preliminary specification

TDA933xH series

FUNCTIONAL DESCRIPTION

RGB control circuit

INPUT SIGNALS

The RGB control circuit of the TDA933xH contains three

sets of input signals:

• YUV input signals, which are supplied by the input

processor or the feature box. Bit GAI can be used to

switch the luminance input signal sensitivity between

0.45 V (p-p) and 1.0 V (b-w). The nominal input signals

for U and V are 1.33 V (p-p) and 1.05 V (p-p),

respectively. These input signals are controlled on

contrast, saturation and brightness.

• The first RGB input is intended for external signals

(SCART in 1fH and VGA in 2fH applications), which have

an amplitude of 0.7 V (p-p) typical. This input is also

controlled on contrast, saturation and brightness.

• The second RGB input is intended for OSD and teletext

signals. The required input signals have an amplitude of

0.7 V (p-p). The switching between the internal signal

and the OSD signal can be realized via a blending

function or via fast blanking. This input is only controlled

on brightness.

Switching between the various sources can be realized via

the I2C-bus and by fast insertion switches. The fast

insertion switches can be enabled via the I2C-bus.

The circuit contains switchable matrix circuits for the

colour difference signals so that the colour reproduction

can be adapted for PAL/SECAM and NTSC. For NTSC,

two different matrices can be chosen. In addition, a matrix

for high-definition ATSC signals is available.

OUTPUT AMPLIFIER

The output signal has an amplitude of approximately

2 V (b-w) at nominal input signals and nominal settings of

the controls. The required ‘white point setting’ of the

picture tube can be realized by means of three separate

gain settings for the RGB channels.

To obtain an accurate biasing of the picture tube, a CCC

circuit has been developed. This function is realized by a

2-point black level stabilization circuit.

By inserting two test levels for each gun and comparing the

resulting cathode currents with two different reference

currents, the influence of the picture tube parameters such

as the spread in cut-off voltage can be eliminated.

This 2-point stabilization is based on the principle that the

ratio between the cathode currents is coupled to the ratio

between the drive voltages according to:

II--kk---12-

=





V-V----dd---rr-11- 

γ

The feedback loop makes the ratio between cathode

currents Ik1 and Ik2 equal to the ratio between the

reference currents (which are internally fixed) by changing

the (black) level and the amplitude of the RGB output

signals via two converging loops. The system operates in

such a way that the black level of the drive signal is

controlled to the cut-off point of the gun. In this way, a very

good grey scale tracking is obtained. The accuracy of the

adjustment of the black level is only dependent on the ratio

of internal currents and these can be made very accurately

in integrated circuits. An additional advantage of the

2-point measurement is that the control system makes the

absolute value of Ik1 and Ik2 identical to the internal

reference currents. Because this adjustment is obtained

by adapting the gain of the RGB control stage, this control

stabilizes the gain of the complete channel (RGB output

stage and cathode characteristic). As a result, this 2-point

loop compensates for variations in the gain figures during

life.

An important property of the 2-point stabilization is that the

offset and the gain of the RGB path are adjusted by the

feedback loop. Hence, the maximum drive voltage for the

cathode is fixed by the relationship between the test

pulses, the reference current and the relative gain setting

of the three channels. Consequently, the drive level of the

CRT cannot be adjusted by adapting the gain of the RGB

output stage. Because different picture tubes may require

different drive levels, the typical ‘cathode drive level’

amplitude can be adjusted by means of an I2C-bus setting.

Depending on the selected cathode drive level, the typical

gain of the RGB output stages can be fixed, taking into

account the drive capability of the RGB outputs

(pins 40 to 42). More details about the design are given in

the application report (see also Chapter “Characteristics”;

note 11).

The measurement of the high and the low currents of the

2-point stabilization circuit is performed in two consecutive

fields. The leakage current is measured in each field. The

maximum allowable leakage current is 100 µA.

For extra flexibility, it also possible to switch the CCC

circuit to 1-point stabilization with the OPC bit. In this

mode, only the black level at the RGB outputs is controlled

by the loop. The cathode drive level setting has no

influence on the gain in this mode. This level should be set

to the nominal value to get the correct amplitude of the

measuring pulses.

2002 Jun 04

7

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