TDA9806/V1 Просмотр технического описания (PDF) - Philips Electronics
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TDA9806/V1 Datasheet PDF : 24 Pages
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Philips Semiconductors
Multistandard VIF-PLL and
FM-PLL demodulator
Preliminary specification
TDA9806
FUNCTIONAL DESCRIPTION
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 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 of
the video signal is detected.
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.
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.
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. 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. 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.
Intercarrier mixer
The intercarrier mixer is realized by a multiplier. The VIF
amplifier output signal is fed to the intercarrier mixer and
converted to intercarrier frequency by the regenerated
picture carrier (VCO). The mixer output signal is fed via a
high-pass for attenuation of the video signal components.
VCO, travelling wave divider 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
and fed via the loop filter to the first variable capacitor
(FPLL). This control voltage is amplified and additionally
converted into a current which represents the AFC output
signal. At centre frequency the AFC output current is equal
to zero.
The oscillator signal is divided-by-two with a Travelling
Wave Divider (TWD) which generates two differential
output signals with a 90 degree phase difference
independent of the frequency.
1995 Sep 05
6
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