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TDA9814

Multistandard VIF-PLL with QSS-IF and dual FM-PLL/AM demodulator

Philips Electronics 

Philips Semiconductors

Multistandard VIF-PLL with QSS-IF

and dual FM-PLL/AM demodulator

Product specification

TDA9814T

FUNCTIONAL DESCRIPTION

The integrated circuit comprises the functional blocks as

shown in Fig.1:

• Vision IF amplifier

• Tuner and VIF-AGC

• Frequency Phase Locked Loop detector (FPLL)

• VCO, Travelling Wave Divider (TWD) and AFC

• Video demodulator and amplifier

• Video buffer

• SIF amplifier and AGC

• Single reference QSS mixer

• AM demodulator

• FM-PLL demodulator

• Internal voltage stabilizer and 1⁄2VP-reference.

Vision IF amplifier

The vision IF amplifier consists of three AC-coupled

differential amplifier stages. Each differential stage

comprises a feedback network controlled by emitter

degeneration.

Tuner and VIF-AGC

The AGC capacitor voltage is transferred to an internal IF

control signal, and is fed to the tuner AGC to generate the

tuner AGC output current (open-collector output). The

tuner AGC takeover point can be adjusted. This allows the

tuner and the SAW filter to be matched to achieve the

optimum IF input level.

The AGC detector charges/discharges the AGC capacitor

to the required voltage for setting of VIF and tuner gain in

order to keep the video signal at a constant level.

Therefore for negative video modulation the sync level and

for positive video modulation the peak white level of the

video signal is detected. In order to reduce the reaction

time for positive modulation, where a very large time

constant is needed, an additional level detector increases

the discharging current of the AGC capacitor (fast mode)

in the event of a decreasing VIF amplitude step. The

additional level information is given by the black level

detector voltage.

Frequency Phase Locked Loop detector (FPLL)

The VIF-amplifier output signal is fed into a frequency

detector and into a phase detector via a limiting amplifier.

During acquisition the frequency detector produces a DC

current proportional to the frequency difference between

the input and the VCO signal. After frequency lock-in the

phase detector produces a DC current proportional to the

phase difference between the VCO and the input signal.

The DC current of either frequency detector or phase

detector is converted into a DC voltage via the loop filter,

which controls the VCO frequency. In the event of positive

modulated signals the phase detector is gated by

composite sync in order to avoid signal distortion for

overmodulated VIF signals.

VCO, Travelling Wave Divider (TWD) and AFC

The VCO operates with a resonance circuit (with L and C

in parallel) at double the PC frequency. The VCO is

controlled by two integrated variable capacitors. The

control voltage required to tune the VCO from its

free-running frequency to actually double the PC

frequency is generated by the frequency-phase detector

(FPLL) and fed via the loop filter to the first variable

capacitor. This control voltage is amplified and additionally

converted into a current which represents the AFC output

signal. The VCO centre frequency can be decreased

(required for L accent standard) by activating an additional

internal capacitor. This is achieved by using the L accent

switch. In this event the second variable capacitor can be

controlled by a variable resistor at the L accent switch for

setting the VCO centre frequency to the required L accent

value. At centre frequency the AFC output current is equal

to zero.

The oscillator signal is divided-by-two with a TWD which

generates two differential output signals with a 90 degree

phase difference independent of the frequency.

1998 Feb 09

6

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