tda9808t NXP Semiconductors, tda9808t Datasheet - Page 6

• Manufacturer Part Number: tda9808t
• Description: Single Standard Vif-pll With Qss-if And Fm-pll Demodulator
• Manufacturer: NXP Semiconductors

Philips Semiconductors
FUNCTIONAL DESCRIPTION
The integrated circuit comprises the functional blocks as
shown in Fig.1:
1. Vision IF amplifier and VIF AGC detector
2. Tuner AGC
3. Frequency Phase Locked Loop (FPLL) detector
4. Voltage Controlled Oscillator (VCO), Travelling Wave
5. Video demodulator and amplifier
6. SIF amplifier and SIF AGC
7. Single reference QSS mixer
8. FM-PLL demodulator
9. Audio Frequency (AF) signal processing
10. Internal voltage stabilizer.
Vision IF amplifier and VIF AGC detector
The vision IF amplifier consists of three AC-coupled
differential amplifier stages. Each differential stage
comprises 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. Therefore, for negative video
modulation the synchronisation level of the video signal is
detected.
Tuner AGC
The AGC capacitor voltage is converted to an internal IF
control signal, and is 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 to match the tuner to the SAW filter
in order to achieve the optimum IF input level.
Frequency Phase Locked Loop (FPLL) detector
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 the frequency detector or the
phase detector is converted to a DC voltage via the loop
filter, which controls the VCO frequency.
1999 Jun 04
Single standard VIF-PLL with QSS-IF and
FM-PLL demodulator
Divider (TWD) and AFC
6
VCO, Travelling Wave Divider (TWD) and 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 frequency-phase detector of the 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. At the
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.
The demodulator output signal is fed to the video amplifier
via an integrated low-pass filter for attenuation of the
carrier harmonics. 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 at pin V
modulation. Noise clipping is provided.
SIF amplifier and SIF AGC
The sound IF amplifier consists of two AC-coupled
differential amplifier stages. Each differential stage
comprises a controlled feedback network provided by
emitter degeneration.
The SIF AGC detector is related to the SIF input signal
(average level of FM carrier) and controls the SIF amplifier
to provide a constant SIF signal to the single reference
QSS mixer.
o(vid)
is 1.35 V (p-p) for nominal vision IF
Product specification
TDA9808