TDA9880 datasheet(8/40 Pages) PHILIPS

8 / 40 page

1999 Jul 21

Philips Semiconductors

Product speciﬁcation

Alignment-free multistandard vision and

FM sound IF-PLL demodulator

TDA9880

The demodulator output signal is fed via an integrated

low-pass filter for attenuation of the carrier harmonics to

the video amplifier. The video amplifier is realized by an

operational amplifier with internal feedback and high

bandwidth. A low-pass filter is integrated to achieve an

attenuation of the carrier harmonics. The video signal of

1.1 V (p-p) for nominal vision IF modulation is fed

internally to the integrated sound carrier trap as well as to

the VIF-AGC detector. The second stage of the video

amplifier converts and amplifies the differential output

signal from the sound carrier trap to the single-ended

CVBS output signal at pin 13 with a 2 V (p-p) amplitude.

Noise clipping is provided. Furthermore the trap can be

bypassed by the implemented input switch of the second

amplifier stage, forced by connecting pin 12 to ground.

Sound carrier trap

The sound carrier trap consists of a reference filter, a

phase detector and the sound trap itself.

A sound carrier reference signal is fed into the reference

low-pass filter and is shifted by a nominal 90 degrees.

The phase detector compares the original reference signal

with the signal shifted by the reference filter and produces,

at the external capacitor CTR, a DC voltage by charging or

discharging the capacitor with a current proportional to the

phase difference between both signals, respectively to the

frequency error of the integrated filters. The DC voltage is

converted to currents which control the frequency position

of the reference filter and the sound trap.

The sound trap itself is constructed of three separate traps

to realize sufficient suppression of the first and second

sound carrier. The right frequency position of the different

standards is set by the sound carrier reference signal.

Intercarrier mixer

The intercarrier mixer is realized by a multiplier, operating

in quadrature mode for suppression of low frequency video

signals. The VIF amplifier output signal is fed to the

intercarrier mixer and converted to an intercarrier

frequency by the regenerated 90 degree picture carrier

from the VCO. The mixer output signal is fed via a

band-pass filter and amplifier for attenuation of the high

frequency video signal components and carrier harmonics

to the output pin 11. The intercarrier signal is fed also to

the integrated FM demodulator.

FM demodulator and acquisition help

The FM demodulator is realized as a narrow-band PLL

with external loop filter, which provides the necessary

selectivity. To achieve good selectivity, a linear phase

detector and constant input level are required.

The intercarrier signal from the intercarrier mixer is fed via

a gain controlled amplifier to the phase detector and it’s

output signal controls (via the loop filter) the integrated

relaxation oscillator. The possible frequency range is from

4 to 7 MHz. As a result of locking the oscillator frequency

tracks with the FM modulation of the input signal;

therefore, the oscillator control voltage is superimposed by

the AF voltage. In this way the FM-PLL operates as an

FM demodulator. The AF voltage is present at the loop

filter and is fed via a buffer with 0 dB gain to the audio

amplifier.

The digital acquisition help operates in the same way as

described in Section “Digital acquisition help and AFC”.

Audio ampliﬁer

The audio amplifier consists of two parts:

1. The AF preamplifier is an operational amplifier with

internal feedback, high gain and high common mode

rejection. The AF voltage from the PLL demodulator,

by principle a small output signal, is amplified by

30 dB. A DC operating point control circuit (pin 6)

decouples the AF amplifier from the DC voltage of the

PLL. The low-pass characteristic of the amplifier

reduces the harmonics of the intercarrier signal at the

sound output terminal. If required, a de-emphasis

network can be realized by the amplifier output

resistance and an external capacitor.

2. The AF output amplifier (10 dB) provides the required

output level by a rail-to-rail output stage. This amplifier

makes use of an input selector for switching to mute

state, automatically controlled by the mute switching

voltage from the digital acquisition help in order to

avoid lock-in noise. During normal operation the

automatic audio mute function is not active.

Application of a 2.2 k

Ω resistor between the

intercarrier output (pin 11) and ground will activate the

automatic audio mute function.

Internal voltage stabilizer

The band gap circuit internally generates a voltage of

approximately 2.4 V, independent of the supply voltage

and the temperature. A voltage regulator circuit, controlled

by this voltage, produces a constant voltage of 3.55 V

which is used as an internal reference voltage.

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