TDA9819 데이터 시트보기 (PDF) - Philips Electronics
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TDA9819 Datasheet PDF : 40 Pages
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Philips Semiconductors
Multistandard vision and sound-IF PLL with
DVB-IF processing
Product specification
TDA9819
FUNCTIONAL DESCRIPTION
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 to control the IF gain. 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 SWIF 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 converted
into a current which represents the AFC output signal.
The VCO centre frequency can be decreased by activating
an additional internal capacitor. With a variable resistor at
VCOADJ (pin 11) the frequency for the M, B/G and L mode
can be tuned to the picture carrier frequency. 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 M, 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.
Video buffer
For an easy adaption of the sound traps an operational
amplifier with internal feedback is used in the event of M,
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.
1998 Jul 14
6
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