tda9885ts NXP Semiconductors, tda9885ts Datasheet - Page 10

• Manufacturer Part Number: tda9885ts
• Description: I2c-bus Controlled Single And Multistandard Alignment-free If-pll Demodulators
• Manufacturer: NXP Semiconductors

Philips Semiconductors
8
Figure 1 shows the simplified block diagram of the device
which comprises the following functional blocks:
8.1
The VIF amplifier consists of three AC-coupled differential
stages. Gain control is performed by emitter degeneration.
The total gain control range is typically 66 dB. The
differential input impedance is typically 2 k in parallel with
3 pF.
8.2
This block adapts the voltages, generated at the VIF-AGC
and SIF-AGC detectors, to the internal signal processing
at the VIF and SIF amplifiers and performs the tuner AGC
control current generation. The onset of the tuner AGC
control current generation can be set either via the I
(see Table 13) or optionally by a potentiometer at pin TOP
(in case that the I
related to the device). The presence of a potentiometer is
automatically detected and the I
Furthermore, derived from the AGC detector voltage, a
comparator is used to test if the corresponding VIF input
voltage is higher than 200 V. This information can be
read out via the I
2003 Oct 02
VIF amplifier
Tuner AGC and VIF-AGC
VIF-AGC detector
Frequency Phase-Locked Loop (FPLL) detector
VCO and divider
AFC and digital acquisition help
Video demodulator and amplifier
Sound carrier trap
SIF amplifier
SIF-AGC detector
Single reference QSS mixer
AM demodulator
FM demodulator and acquisition help
Audio amplifier and mute time constant
Internal voltage stabilizer
I
I
alignment-free IF-PLL demodulators
2
2
C-bus transceiver and MAD (module address).
FUNCTIONAL DESCRIPTION
C-bus controlled single and multistandard
VIF amplifier
Tuner AGC and VIF-AGC
2
2
C-bus (bit VIFLEV = 1).
C-bus information cannot be stored,
2
C-bus setting is disabled.
2
C-bus
10
8.3
Gain control is performed by sync level detection (negative
modulation) or peak white detection (positive modulation).
For negative modulation, the sync level voltage is stored at
an integrated capacitor by means of a fast peak detector.
This voltage is compared with a reference voltage
(nominal sync level) by a comparator which charges or
discharges the integrated AGC capacitor for the
generation of the required VIF gain. The time constants for
decreasing or increasing the gain are nearly equal and the
total AGC reaction time is fast to cope with ‘aeroplane
fluttering’.
For positive modulation, the white peak level voltage is
compared with a reference voltage (nominal white level)
by a comparator which charges (fast) or discharges (slow)
the external AGC capacitor directly for the generation of
the required VIF gain. The need of a very long time
constant for VIF gain increase is because the peak white
level may appear only once in a field. In order to reduce
this time constant, an additional level detector increases
the discharging current of the AGC capacitor (fast mode)
in the event of a decreasing VIF amplitude step controlled
by the detected actual black level voltage. The threshold
level for fast mode AGC is typically 6 dB video amplitude.
The fast mode state is also transferred to the SIF-AGC
detector for speed-up. In case of missing peak white
pulses, the VIF gain increase is limited to typically +3 dB
by comparing the detected actual black level voltage with
a corresponding reference voltage.
8.4
The VIF amplifier output signal is fed into a frequency
detector and into a phase detector via a limiting amplifier
for removing the video AM.
During acquisition the frequency detector produces a
current proportional to the frequency difference between
the VIF and the VCO signals. After frequency lock-in the
phase detector produces a current proportional to the
phase difference between the VIF and the VCO signals.
The currents from the frequency and phase detectors are
charged into the loop filter which controls the VIF VCO and
locks it to the frequency and phase of the VIF carrier.
For a positive modulated VIF signal, the charging currents
are gated by the composite sync in order to avoid signal
distortion in case of overmodulation. The gating depth is
switchable via the I
VIF-AGC detector
FPLL detector
2
C-bus.
TDA9885; TDA9886
Product specification