TDA9321 datasheet(7/44 Pages) PHILIPS

7 / 44 page

1998 Dec 16

Philips Semiconductors

Preliminary speciﬁcation

I2C-bus controlled TV input processor

TDA9321H

FUNCTIONAL DESCRIPTION

Vision IF ampliﬁer

The VIF amplifier contains 3 AC-coupled control stages

with a total gain control range which is higher than 66 dB.

The sensitivity of the circuit is comparable with that of

modern IF-ICs.

The video signal is demodulated by a PLL carrier

regenerator. This circuit contains a frequency detector and

a phase detector. During acquisition the frequency

detector will tune the VCO to the correct frequency.

The initial adjustment of the oscillator is realized via the

I2C-bus. The switching between SECAM L and L’ can also

be realized via the I2C-bus. After lock-in the phase

detector controls the VCO so that a stable phase

relationship between the VCO and the input signal is

achieved. The VCO operates at twice the IF frequency.

The reference signal for the demodulator is obtained by

means of a frequency divider circuit. To get a good

performance for phase modulated carrier signals the

control speed of the PLL can be increased by bit FFI.

The AFC output is obtained by using the VCO control

voltage of the PLL and can be read via the I2C-bus.

For fast search tuning systems the window of the AFC can

be increased with a factor 3. The setting is realized with

bit AFW.

The AGC detector operates on top-sync and

top-white-level. The demodulation polarity is switched via

the I2C-bus. The AGC detector time constant capacitor is

connected externally; this is mainly because of the

flexibility of the application. The time constant of the AGC

system during positive modulation is rather long, this is to

avoid visible variations of the signal amplitude. To improve

the speed of the AGC system a circuit has been included

which detects whether the AGC detector is activated every

frame period. When, during 3 field periods, no action is

detected the speed of the system is increased. For signals

without peak white information the system switches

automatically to a gated black level AGC. Because a black

level clamp pulse is required for this mode of operation the

circuit will only switch to black level AGC in the internal

mode.

The circuits contain a video identification (ident) circuit

which is independent of the synchronization circuit.

Therefore search tuning is possible when the display

section of the receiver is used as a monitor. However, this

ident circuit cannot be made as sensitive as the slower

sync ident circuit (bit SL). It is recommended to use both

ident outputs to obtain a reliable search system. The ident

output is supplied to the tuning system via the I2C-bus.

The input of the ident circuit is connected to pin 14

(see Fig.3). This has the advantage that the ident circuit

can also be made operative when a scrambled signal is

received (descrambler connected between pins 10

and 14). A second advantage is that the ident circuit can

be used when the VIF amplifier is not used (e.g. with

built-in satellite tuners). The video ident circuit can also be

used to identify the selected CBVS or Y/C signal.

The switching between the 2 modes can be realized with

bit VIM.

The TDA9321H contains a group delay correction circuit

which can be switched between the BG and a flat group

delay response characteristic. This has the advantage that

in multistandard receivers no compromise has to be made

for the choice of the SAW filter. Both the input and output

of the group delay correction circuit are externally

available so that the sound trap can be connected

between the VIF output and the group delay correction

input. The output signal of the correction circuit can be

supplied to the internal video processing circuit and to the

external SCART plug.

The IC has several (I2C-bus controlled) output ports which

can be used to switch sound traps or other external

components.

When the VIF amplifier is not used the complete VIF

amplifier can be switched off with bit IFO.

Sound circuit

The SIF amplifier is similar to the VIF amplifier and has a

gain control range of approximately 66 dB. The AGC

circuit is related to the SIF carrier levels (average level of

AM or FM carriers) and ensures a constant signal

amplitude to the AM demodulator and the QSS mixer.

The single reference QSS mixer is realized by a multiplier.

In this multiplier the SIF signal is converted to the

intercarrier frequency by mixing it with the regenerated

picture carrier from the VCO. The mixer output signal is

supplied to the output via a high-pass filter for attenuation

of the residual video signals. With this system a high

performance hi-fi stereo sound processing can be

achieved.

The AM sound demodulator is realized by a multiplier.

The modulated SIF signal is multiplied in phase with the

limited SIF signal. The demodulator output signal is

supplied to the output via a low-pass filter for attenuation

of the carrier harmonics.

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