TDA9811 View Datasheet(PDF) - Philips Electronics
Part Name
Description
Manufacturer
TDA9811 Datasheet PDF : 36 Pages
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Philips Semiconductors
Multistandard VIF-PLL with QSS-IF and
AM demodulator
Product specification
TDA9811
FUNCTIONAL DESCRIPTION
The integrated circuit comprises the functional blocks as
shown in Fig.1:
• Vision IF amplifier and input switch
• 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
• Internal voltage stabilizer and 1⁄2VP-reference.
Vision IF amplifier and input switch
The vision IF amplifier consists of three AC-coupled
differential amplifier stages. Each differential stage
comprises a feedback network controlled by emitter
degeneration. The first differential stage is extended by
two pairs of emitter followers to provide two IF input
channels. The VIF input can be selected by pin 30.
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.
Video demodulator and amplifier
The video demodulator is realized by a multiplier which is
designed for low distortion and large bandwidth. The vision
IF input signal is multiplied with the ‘in phase’ signal of the
travelling wave divider output. In the demodulator stage
the video signal polarity can be switched in accordance
with the TV standard.
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 for B/G and
L standard. The standard dependent level shift in this
stage delivers the same sync level for positive and
negative modulation. The video output signal is 1 V (p-p)
for nominal vision IF modulation.
1998 Feb 09
6
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