TDA9554PS datasheet(63/125 Pages) PHILIPS

63 / 125 page

2000 Jun 22

Philips Semiconductors

Tentative Device Speciﬁcation

TV signal processor-Teletext decoder with

embedded

µ-Controller

TDA955X/6X/8X PS/N1 series

FUNCTIONAL DESCRIPTION OF VIDEO PROCESSOR

Vision IF ampliﬁer

The vision IF amplifier can demodulate signals with

positive and negative modulation. The PLL demodulator is

completely alignment-free.

The VCO of the PLL circuit is internal and the frequency is

fixed to the required value by using the clock frequency of

the

µ-Controller/Teletext decoder as a reference. The

setting of the various frequencies (38, 38.9, 45.75 and

58.75 MHz) can be made via the control bits IFA-IFC in

subaddress 27H. Because of the internal VCO the IF

circuit has a high immunity to EMC interferences.

QSS Sound circuit

The sound IF amplifier is similar to the vision IF amplifier

and has an external AGC decoupling capacitor.

The single reference QSS mixer is realised 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 realised by a multiplier. The

modulated sound IF 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. The AM signal is supplied to the

output (AUDOUT/AMOUT) via the volume control.

Switching between the QSS output and AM output is made

by means of the AM bit in subaddress 29H (see also

Table 1).

FM demodulator

The FM demodulator is realised as narrow-band PLL with

external loop filter, which provides the necessary

selectivity without using an external band-pass filter. To

obtain a good selectivity a linear phase detector and a

constant input signal amplitude are required. For this

reason the intercarrier signal is internally supplied to the

demodulator via a gain controlled amplifier and AGC

circuit. To improve the selectivity an internal bandpass

filter is connected in front of the PLL circuit. This bandpass

filter can be switched off by means of the BPB bit in

subaddress 2CH.

The nominal frequency of the demodulator is tuned to the

required frequency (4.5/5.5/6.0/6.5 MHz) by means of a

calibration circuit which uses the clock frequency of the

µ-Controller/Teletext decoder as a reference. It is also

possible to frequencies of 4.74 and 5.74 MHz so that a

second sound channel can be demodulated. In the latter

application an external bandpass filter has to be applied to

obtain sufficient selectivity (the sound input can be

activated by the SIF bit in subaddress 28H). The setting to

the wanted frequency is realised by means of the control

bits FMA, FMB and FMC in the control bit 29H.

From the output status bytes it can be read whether the

PLL frequency is inside or outside the window and whether

the PLL is in lock or not. With this information it is possible

to make an automatic search system for the incoming

sound frequency. This can be realised by means of a

software loop which switches the demodulator to the

various frequencies and then select the frequency on

which a lock condition has been found.

The deemphasis output signal amplitude is independent of

the TV standard and has the same value for a frequency

deviation of

±25 kHz at the 4.5 MHz standard and for a

deviation of

±50 Khz for the other standards.

In versions with QSS amplifier and mono intercarrier

sound circuit the FM radio mode is available. This mode is

activated by means of the FMR-bit (subaddress 2CH). The

selectivity must be made by means of a SAW filter at the

sound input with a centre frequency of 33.4 MHz for

Europe and 41.25 MHz for the USA. For this application

the IF demodulator must be set to a fixed frequency (42

MHz for Europe and 48 MHz for the USA). The resulting

input frequency for the FM demodulator is then 8.6 MHz for

Europe and 6.75 MHz for the USA. This frequency must be

selected by means of the bits FMA, FMB and FMC (see

table 108).

Audio circuit and input signal selection

The audio control circuit contains an audio switch with 1

external input and a volume control circuit. The selection

of the various inputs is made by means of the ADX bit. In

various versions the Automatic Volume Levelling (AVL)

function can be activated. The pin to which the external

capacitor has to be connected depends on the IC version.

For the 90

° types the capacitor is connected to the EW

output pin. For the 110

° types a choice must be made

between the AVL function and a sub-carrier output for

comb filter applications. This choice is made via the

CBM0/1 bits (in subaddress 22H). When the AVL is active

it automatically stabilises the audio output signal to a

certain level.

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