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TDA9816M

Multistandard multimedia IF-PLL and FM radio demodulator

Philips Electronics 

Philips Semiconductors

Multistandard multimedia IF-PLL and FM

radio demodulator

Preliminary specification

TDA9816M

FUNCTIONAL DESCRIPTION

The TDA9816M is comprised of the functional blocks

shown in Fig.1:

• Vision IF amplifier and AGC detector

• Tuner (TV/radio) and VIF AGC

• Frequency Phase Locked Loop (FPLL) detector

• VCO, Travelling Wave Divider (TWD) and TV AFC

• Video demodulator and amplifier

• SIF amplifier and AGC detector

• Single reference QSS mixer

• AM demodulator

• RIF amplifier and AGC detector

• FM-PLL demodulator, level detector and radio AFC

• AF (Audio Frequency) signal processing

• Internal voltage stabilizer

• Logic.

Vision IF amplifier and AGC detector

The vision IF amplifier contains three AC-coupled

differential amplifier stages. Each differential stage

includes a feedback network controlled by emitter

degeneration.

The AGC detector generates the required VIF gain control

voltage for constant video output by charging/discharging

the AGC capacitor. The sync level of the video signal is

therefore detected for negative video modulation, while the

peak white level is detected for positive video modulation.

In order to reduce the reaction time for positive modulation,

where a very large time constant is needed, an additional

level detector is used to increase the discharge 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.

Tuner (TV/radio) and VIF AGC

For TV operation, the AGC capacitor voltage is converted

to an internal IF control signal and then fed to the tuner

AGC to generate the tuner AGC output current at

pin TAGC (open-collector output). The tuner AGC

takeover point can be adjusted at pin TADJ. This allows

the tuner to be matched to the SAW filter in order to

achieve the optimum IF input level.

For FM radio operation, an AGC detector is provided to

obtain some adjacent channel protection.

Frequency Phase-Locked Loop detector (FPLL)

The VIF amplifier output signal is fed, via a limiting

amplifier, to a frequency and phase detector. During

acquisition, the frequency detector generates a DC current

proportional to the difference in frequency between the

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

the phase detector generates a DC current proportional to

the phase difference between the input signal and the

VCO signal. The DC current generated by the frequency or

phase detector is converted to a DC voltage via the loop

filter, which controls the VCO frequency. For positively

modulated signals, the phase detector is gated by

composite sync in order to avoid signal distortion with

overmodulated VIF signals.

VCO, TWD and TV AFC

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

in parallel), at double the Picture Carrier (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 double the PC frequency

is generated by the FPLL and fed via the loop filter to the

first variable capacitor. This control voltage is amplified

and 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 using logic ports LP0 and LP1. A variable

resistor connected to LADJ can be used in conjunction

with the second variable capacitor to set the VCO centre

frequency to the required L accent value. At the centre

frequency, the AFC output current is zero.

The TWD divides the oscillator signal by 2 and generates

two differential output signals with a 90° phase difference

independent of frequency.

Video demodulator and amplifier

Video demodulation is realized by a multiplier designed for

low distortion and wide bandwidth. The vision IF input

signal and the ‘in-phase’ signal of the travelling wave

divider output are multiplied together. The video signal

polarity can be switched in the demodulator stage in

accordance with the relevant TV standard.

The demodulated output signal is fed to the video amplifier

via an integrated low-pass filter used to attenuate the

carrier harmonics. This is an operational amplifier with

internal feedback and wide bandwidth. A low-pass filter is

integrated to attenuate the carrier harmonics for B/G and

L standard.

1997 Nov 19

6

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