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TDA9811

Multistandard VIF-PLL with QSS-IF and AM demodulator

Philips Electronics 

Philips Semiconductors

Multistandard VIF-PLL with QSS-IF and

AM demodulator

Product specification

TDA9811

Video buffer

For an easy adaption of the sound traps an operational

amplifier with internal feedback is used in the event of B/G

and L standard. This amplifier is featured with a high

bandwidth and 7 dB gain. The input impedance is adapted

for operating in combination with ceramic sound traps. The

output stage delivers a nominal 2 V (p-p) positive video

signal. Noise clipping is provided.

SIF amplifier and AGC

The sound IF amplifier consists of two AC-coupled

differential amplifier stages. Each differential stage

comprises a controlled feedback network provided by

emitter degeneration.

The SIF AGC detector is related to the SIF input signals

(average level of AM or FM carriers) and controls the SIF

amplifier to provide a constant SIF signal to the AM

demodulator and single reference QSS mixer. The SIF

AGC reaction time is set to ‘slow’ for nominal video

conditions. But with a decreasing VIF amplitude step the

SIF AGC is set to ‘fast’ mode controlled by the VIF-AGC

detector. In FM mode this reaction time is also set to ‘fast’

controlled by the standard switch.

AM demodulator

The AM demodulator is realized by a multiplier. The

modulated SIF amplifier output signal is multiplied in

phase with the limited (AM is removed) SIF amplifier

output signal. The demodulator output signal is fed via an

integrated low-pass filter for attenuation of the carrier

harmonics to the AF amplifier.

Internal voltage stabilizer and 1⁄2VP-reference

The bandgap circuit internally generates a voltage of

approximately 1.25 V, independent of supply voltage and

temperature. A voltage regulator circuit, connected to this

voltage, produces a constant voltage of 3.6 V which is

used as an internal reference voltage.

For the audio output signal the constant reference voltage

cannot be used because large output signals are required.

Therefore this signal refers to half the supply voltage to

achieve a symmetrical headroom. For ripple and noise

attenuation the 1⁄2VP voltage has to be filtered via a

low-pass filter by using an external capacitor together with

an integrated resistor (fg = 5 Hz). For a fast setting to 1⁄2VP

an internal start-up circuit is added.

Single reference QSS mixer

The single reference QSS mixer is realized by a multiplier.

The SIF amplifier output signal is fed to the single

reference QSS mixer and converted to intercarrier

frequency by the regenerated picture carrier (VCO). The

mixer output signal is fed via a high-pass for attenuation of

the video signal components to the output pin 20. With this

system a high performance hi-fi stereo sound processing

can be achieved.

1998 Feb 09

7

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