1998 Jun 23

8

Philips Semiconductors

Product specification

negative video modulation and FM sound

TDA8722

The bits T0 to T2 are available for test purposes and the possibilities are shown in Table 5.

Table 5

Test modes

Notes

1. In ‘TPSG on’ mode the video carrier is modulated by the test signal consisting of a synchronization pulse and two

vertical white bars on a black screen. This mode should be selected to adjust the TV set receiving the modulated

signal to the right frequency.

2. In ‘RF oscillator off’ mode, the RF oscillator and the RF mixer are switched-off and there is no RF carrier coming out

of the device. This mode can be selected to avoid RF radiation to other parts when the modulator output is not used.

3. In ‘balance test’, the video carrier is over modulated. This simplifies residual carrier measurements.

5. The ‘high-impedance test’ mode may be used to inject an external tuning voltage to the RF tank circuit, to test the

oscillator. In this mode, the phase detector is disabled and the external transistor of the tuning amplifier is

switched-off. The AMP output (pin 7) is LOW (<200 mV).

6. In the ‘phase detector disabled’ mode, it is possible to measure the leakage current at the input of the tuning amplifier,

on the CP pin. In this mode the RF oscillator is off, and the baseband TV channel signal is present on the RF outputs

for testing the audio and video parts.

T0

T1

T2

OPERATIONAL MODE

0

0

0

normal operation

0

0

1

Test Pattern Signal Generator (TPSG) on; note 1

0

1

0

RF oscillator off; note 2

0

1

1

balance test; note 3

100

1

0

1

high-impedance test; note 5

110

1

1

1

phase detector disabled; baseband signals on RF outputs; note 6

The possibilities of bit P0, which controls the output Port

(pin 14) are given in Table 6.

The Port is an NPN open-collector type. For monitoring the

logic 0 to let the output Port free.

Table 6

Output Port programming

P0

OUTPUT PORT STATE

0

off; high impedance

1

on; sinking current