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參數(shù)資料
| 型號： | TDA4472-MSD |
| 英文描述： | Video-IF and Quasi Parallel Sound Processing |
| 中文描述： | 視頻- IF和準并行聲音處理 |
| 文件頁數(shù)： | 3/14頁 |
| 文件大小： | 170K |
| 代理商： | TDA4472-MSD |
TDA4472-M
Preliminary Information
TELEFUNKEN Semiconductors
Rev. A2, 15-Oct-96
3 (14)
Circuit Description
Vision IF Amplifier
The video IF signal (VIF) is fed through a SAW filter to
the differential input (Pin 6-7) of the VIF amplifier. This
amplifier consists of three AC-coupled amplifier stages.
Each differential amplifier is gain controlled by the auto-
matic gain control (VIF-AGC). The output signal of the
VIF amplifier is applied to the FPLL carrier generation
and the video demodulator.
Tuner-and VIF-AGC
At Pin 8, the VIF-AGC charges/discharges the AGC
capacitor to generate a control voltage for setting the gain
of the VIF amplifier and tuner in order to keep the video
output signal at a constant level. Therefore, in the case of
all negative modulated signals (e.g., B/G standard) the
sync. level of the demodulated video signal is the
criterion for a fast charge/discharge of the AGC capacitor.
The control voltage (AGC voltage at Pin 8) is transferred
to an internal control signal, and is fed to the tuner AGC
to generate the tuner AGC current at Pin 11 (open
collector output). The take over point of the tuner AGC
can be adjusted at Pin 10 by a potentiometer or an external
dc voltage (from interface circuit or microprocessor).
FPLL, VCO and AFC
The FPLL circuit (frequency phase locked loop) consists
of a frequency and phase detector to generate the control
voltage for the VCO tuning. In the locked mode, the VCO
is controlled by the phase detector and in unlocked mode,
the frequency detector is superimposed. The VCO
operates with an external resonance circuit (L and C par-
allel) and is controlled by internal varicaps. The VCO
control voltage is also converted to a current and repre-
sents the AFC output signal at Pin 22.
A practicable VCO alignment of the external coil is the
adjustment to zero AFC output current at Pin 22. At center
frequency the AFC output current is equal to zero.
The optional potentiometer at Pin 26 allows an offset
compensation of the VCO phase for improved sound
quality (fine adjustment). Without a potentiometer (open
circuit at Pin 26), this offset compensation is not active.
The oscillator signal passes a phase shifter and supplies
the in-phase signal (0
°
) and the quadrature signal (90
°
)of
the generated picture carrier.
Video Demodulation and Amplifier
The video IF signal, which is applied from the gain
controlled IF amplifier, is multiplied with the inphase
component of the VCO signal. The video demodulator is
designed for low distortion and large bandwidth. The
demodulator output signal passes an integrated low pass
filter for attenuation of the residual vision carrier and is
fed to the video amplifier. The video amplifier is realized
by an operational amplifier with internal feedback and
8 MHz bandwidth (–3 dB). An additional noise clipping
is provided. The video signal is fed to VIF-AGC and to the
video output buffer. This amplifier with a 6 dB gain offers
easy adaption of the sound trap. For nominal video IF
modulation the video output signal at Pin 12 is 2 V
pp.
Sound IF Amplifier and SIF-AGC
The SIF amplifier is nearly identical with the 3-stage VIF
amplifier. Only the first amplifier stage exists twice and
is switchable by a control voltage at Pin 3. Therefore with
a minimal external expense it is possible to switch
between two different SAW filters. Both SIF inputs
features excellent cross-talk attenuation and an input
impedance which is independent from the switching
condition.
The SIF-AGC is related to the average level of FM-carrier
and controls the SIF amplifier to provide a constant SIF
signal to the QPS mixer.
Quasi-Parallel-Sound (QPS) Mixer
The QPS mixer is realized by a multiplier. The SIF signal
(FM or NICAM carrier) is converted to the intercarrier
frequency by the regenerated picture carrier (quadrature
signal) which is provided from the VCO. The intercarrier
signal is fed via an output amplifier to Pin 24.
AFC Switch
The AFC output signal at Pin 22 can be controlled by a
switching voltage at Pin 19. It is possible to switch off the
AFC.
VCR Mode
For the VCR mode in a TV set (external video source
selected), it is recommendable to switch off the IF circuit.
With an external switching voltage at Pin 6 or 7, the IF
amplifiers are switched off and all signal output levels at
Pins 12 and 24 are according to the internal dc voltage.
Internal Voltage Stabilizer
The internal bandgap reference ensures constant perfor-
mance independent of supply voltage and temperature.
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