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TDA9321

I2C-bus controlled TV input processor

Philips Electronics 

Philips Semiconductors

I2C-bus controlled TV input processor

Preliminary specification

TDA9321H

Video switches

The circuit has 3 CVBS inputs (1 internal and 2 externals)

and 2 Y/C inputs. The Y/C inputs can also be used as

additional CVBS inputs. The switch configuration is given

in Fig.3. The various sources can be selected via the

I2C-bus.

The circuit can be set in a mode in which it automatically

detects whether a CVBS or a Y/C signal is supplied to the

Y/C inputs. In this mode the TV-standard identification first

takes place on the added Y/CVBS and the C input signal.

Then both chrominance input signal amplitudes are

checked once and the input signal with the highest burst

signal amplitude is selected. The result of the detection

can be read via the I2C-bus.

The IC has 2 inputs (AV1 and AV2) which can be used to

read the status levels of pin 8 of the SCART plug.

The information is available in the output status byte 02 in

bits D0 to D3.

The 3 outputs of the video switches (CVBSCF, CVBSTXT

and CVBSPIP) can be independently switched to the

various input signals. The names are just arbitrary and it is,

for instance, possible to use the CVBSCF signal to drive

the comb filter and the teletext decoder in parallel and to

supply the CVBSTXT signal to the SCART plug (via an

emitter follower).

For comb filter interfacing the circuit has the CVBSCF

output, a 3rd Y/C input, a reference signal output REFO

and 2 control pins (SYS1 and SYS2) which switch the

comb filter to the standard of the incoming signal (as

detected by the ident circuit of the colour decoder). When

a signal is recognized which can be combed and the comb

filter is enabled by bit ECMB the Y/C signals coming from

the comb filter are automatically selected. This is indicated

via bit CMB in output status byte 02 (D5). For signals

which cannot be combed (such as SECAM or

black-to-white signals) the Y/C signals coming from the

comb filter are not selected.

Chrominance and luminance processing

The circuits contain a chrominance band-pass, a SECAM

cloche filter and a chrominance trap circuit. The filters are

realized by means of gyrator circuits and they are

automatically calibrated by comparing the tuning

frequency with the crystal frequency of the decoder.

The luminance delay line is also realized by means of

gyrator circuits. The centre frequency of the chrominance

band-pass filter is switchable via the I2C-bus so that the

performance can be optimized for ‘front-end’ signals and

external CVBS signals.

The luminance output signal which is derived from the

incoming CVBS or Y/C signal can be varied in amplitude

by means of a separate gain setting control via the I2C-bus

control bits GAI1 and GAI0. The gain variation which can

be realized with these bits is −1 to +2 dB.

Colour decoder

The colour decoder can decode PAL, NTSC and SECAM

signals. The PAL/NTSC decoder contains an

alignment-free crystal oscillator with 4 separate pins for

crystal connection, a killer circuit and two colour difference

demodulators. The 90° phase shift for the reference signal

is produced internally.

Because it is possible to connect 4 different crystals to the

colour decoder, all colour standards can be decoded

without external switching circuits. Which crystals are

connected to the decoder must be indicated via the

I2C-bus. The crystal connection pins which are not used

must be left open-circuit.

The horizontal oscillator is calibrated by means of the

crystal frequency of the colour PLL. For a reliable

calibration it is very important that the crystal indication

bits XA to XD are not corrupted. For this reason

bits XA to XD can be read in the output bytes so that the

software can check the I2C-bus transmission.

The IC contains an Automatic Colour Limiting (ACL) circuit

which is switchable via the I2C-bus and prevents

oversaturation occuring when signals with a high

chrominance-to-burst ratio are received. The ACL circuit is

designed such that it only reduces the chrominance signal

and not the burst signal. This has the advantage that the

colour sensitivity is not affected by this function. The ACL

function is mainly intended for NTSC signals but it can also

be used for PAL signals. For SECAM signals the ACL

function should be switched off.

The SECAM decoder contains an auto-calibrating PLL

demodulator which has two references: the 4.43 MHz

subcarrier frequency which is obtained from the crystal

oscillator which is used to tune the PLL to the desired

free-running frequency and the band gap reference to

obtain the correct absolute value of the output signal.

The VCO of the PLL is calibrated during each vertical

blanking period, when the IC is in search or SECAM mode.

The circuit can also decode the PALplus helper signal and

can insert the various reference signals: set-ups and

timing signals which are required for the PALplus decoder

ICs.

The baseband delay line (TDA4665 function) is integrated.

1998 Dec 16

8

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