TDA837X datasheet(13/72 Pages) PHILIPS

13 / 72 page

1997 Jul 01

Philips Semiconductors

Preliminary speciﬁcation

I2C-bus controlled economy PAL/NTSC

and NTSC TV-processors

TDA837x family

FUNCTIONAL DESCRIPTION

Vision IF ampliﬁer

The IF 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

using a frequency divider circuit.

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 by a factor of 3. The setting is realized with

the AFW bit.

Depending on the device type the AGC detector operates

on top-sync level (single standard versions) or on top-sync

and top-white level (multistandard versions).

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 frame 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 method of operation the circuit will

only switch to black level AGC in the internal mode.

The circuits contain a second fast video identification

circuit which is independent of the synchronization

identification circuit. Consequently, search tuning is also

possible when the display section of the receiver is used

as a monitor. However, this identification circuit cannot be

made as sensitive as the slower sync identification circuit

(SL) and it is recommended to use both identification

outputs to obtain a reliable search system.

The identification output is applied to the tuning system via

the I2C-bus.

The input of the identification circuit is connected to pin 13,

the internal CVBS input (see Fig.1). This has the

advantage that the identification circuit can also be made

operative when a scrambled signal is received

[descrambler connected between the IF video output

(pin 6) and pin 13]. A second advantage is that the

identification circuit can be used when the IF amplifier is

not used (e.g. with built-in satellite tuners).

The video identification circuit can also be used to identify

the selected CBVS or Y/C signal. The switching between

the two modes can be realized with bit VIM.

Video switches

The circuit has two CVBS inputs (CVBSint and CVBSext)

and a Y/C input. When the Y/C input is not required pin 11

can be used as the third CVBS input. The switch

configuration is illustrated in Fig.7. The selection of the

various sources is made via the I2C-bus.

The output signal of the CVBS switch is externally

available and can be used to drive the teletext decoder, the

SECAM add-on decoder and a comb filter.

In applications with comb filters a Y/C input is only possible

when additional switches are added. In applications

without comb filters the Y/C input signal can be switched

to the CVBS output.

TDA837X Datasheet(PDF) 13 Page - NXP Semiconductors

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