參數(shù)資料
型號(hào)： TDA9885
廠商： NXP Semiconductors N.V.
英文描述： I2C-bus controlled single and multistandard alignment-free IF-PLL demodulators
中文描述： 的I2C控制的單一和多路巴士免費(fèi)中頻鎖相環(huán)解調(diào)器
文件頁數(shù)： 12/56頁
文件大小： 248K
代理商： TDA9885
2003 Oct 02
12
Philips Semiconductors
Product specification
I
2
C-bus controlled single and multistandard
alignment-free IF-PLL demodulators
TDA9885; TDA9886
8.10
SIF-AGC detector
SIF gain control is performed by the detection of the
DC component of the AM demodulator output signal. This
DC signal corresponds directly to the SIF voltage at the
output of the SIF amplifier so that a constant SIF signal is
supplied to the AM demodulator and to the single
reference QSS mixer.
By switching the gain of the input amplifier of the SIF-AGC
detector via the I
2
C-bus, the internal SIF level for
FM sound is 5.5 dB lower than for AM sound. This is to
adapt the SIF-AGC characteristic to the VIF-AGC
characteristic. The adaption is ideal for a picture-to-sound
FM carrier ratio of 13 dB.
Viaacomparator,theintegratedAGCcapacitorischarged
or discharged for the generation of the required SIF gain.
Due to AM sound, the AGC reaction time is slow
(f
c
< 20 Hz for the closed AGC loop). For reducing this
AM sound time constant in the event of a decreasing
IF amplitude step, the load current of the AGC capacitor is
increased (fast mode) when the VIF-AGC detector (at
positive modulation mode) operates in the fast mode too.
An additional circuit (threshold approximately 7 dB)
ensures a very fast gain reduction for a large increasing
IF amplitude step.
8.11
Single reference QSS mixer
With the present system a high performance Hi-Fi stereo
sound processing can be achieved. For a simplified
application without a SIF SAW filter, the single reference
QSSmixercanbeswitchedtotheintercarriermodeviathe
I
2
C-bus.
The single reference QSS mixer generates the 2nd FM
TV sound intercarrier signal. It is realized by a linear
multiplier which multiplies the SIF amplifier output signal
and the VIF-PLL VCO signal (90 degrees output) which is
locked to the picture carrier. In this way the QSS mixer
operates as a quadrature mixer in the intercarrier mode
and provides suppression of the low frequency video
signals.
The QSS mixer output signal is fed internally via a
high-pass and low-pass combination to the
FM demodulator as well as via an operational amplifier to
the intercarrier output pin SIOMAD.
8.12
AM demodulator
The amplitude modulated SIF amplifier output signal is fed
both to a two-stage limiting amplifier that removes the AM
and to a linear multiplier. The result of the multiplication of
the SIF signal with the limiter output signal is
AM demodulation (passive synchronous demodulator).
The demodulator output signal is fed via a low-pass filter
that attenuates the carrier harmonics and via the input
amplifier of the SIF-AGC detector to the audio amplifier.
8.13
FM demodulator and acquisition help
The narrow-band FM-PLL detector consists of:
Gain controlled FM amplifier and AGC detector
Narrow-band PLL.
The intercarrier signal from the intercarrier mixer is fed to
the input of an AC-coupled gain controlled amplifier with
two stages. The gain controlled output signal is fed to the
phase detector of the narrow-band FM-PLL
(FM demodulator). For good selectivity and robustness
against disturbance caused by the video signal, a high
linearity of the gain controlled FM amplifier and of the
phase detector as well as a constant signal level are
required. The gain control is done by means of an ‘in
phase’ demodulator for the FM carrier (from the output of
the FM amplifier). The demodulation output is fed into a
comparator for charging or discharging the integrated
AGC capacitor. This leads to a mean value AGC loop to
control the gain of the FM amplifier.
The FM demodulator is realized as a narrow-band PLL
with an external loop filter, which provides the necessary
selectivity(bandwidthapproximately100 kHz).Toachieve
good selectivity, a linear phase detector and a constant
input level are required. The gain controlled intercarrier
signal from the FM amplifier is fed to the phase detector.
The phase detector controls via the loop filter the
integratedlowradiationrelaxationoscillator.Thedesigned
frequency range is from 4 to 7 MHz.
The VCO within the FM-PLL is phase-locked to the
incoming 2nd SIF signal, which is frequency modulated.
As well as this, the VCO control voltage is superimposed
by the AF voltage. Therefore, the VCO tracks with the FM
of the 2nd SIF signal. So, the AF voltage is present at the
loop filter and is typically 5 mV (RMS) for 27 kHz
FM deviation. This AF signal is fed via a buffer to the audio
amplifier.
The correct locking of the PLL is supported by the digital
acquisition help circuit (see Section 8.6).
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
TDA9885HN/V3 制造商:PHILIPS 制造商全稱:NXP Semiconductors 功能描述:I2C-bus controlled single and multistandard alignment-free IF-PLL demodulators
TDA9885HN/V3,118 功能描述:調(diào)節(jié)器/解調(diào)器 TDA9885HN/HVQFN32/REEL13//V3 RoHS:否 制造商:Texas Instruments 封裝 / 箱體:PVQFN-N24 封裝:Reel
TDA9885HN/V3,518 功能描述:調(diào)節(jié)器/解調(diào)器 DEMODUL NEG MODULTN RoHS:否 制造商:Texas Instruments 封裝 / 箱體:PVQFN-N24 封裝:Reel
TDA9885HN/V3/S1,11 功能描述:調(diào)節(jié)器/解調(diào)器 DEMODUL NEG MODULTN RoHS:否 制造商:Texas Instruments 封裝 / 箱體:PVQFN-N24 封裝:Reel
TDA9885HN/V3/S1-T 功能描述:調(diào)節(jié)器/解調(diào)器 DEMODUL NEG MODULTN VIF AND SIF RoHS:否 制造商:Texas Instruments 封裝 / 箱體:PVQFN-N24 封裝:Reel
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