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| 型号： | TA2069AF |
| 元件分类： | 音频控制 |
| 英文描述： | 2 CHANNEL(S), TONE CONTROL CIRCUIT, PDSO24 |
| 封装： | 0.300 INCH, 1 MM PITCH, PLASTIC, SSOP-24 |
| 文件页数： | 3/14页 |
| 文件大小： | 298K |
| 代理商： | TA2069AF |
TDA9885_TDA9886_3
NXP B.V. 2008. All rights reserved.
Product data sheet
Rev. 03 — 16 December 2008
11 of 56
NXP Semiconductors
TDA9885; TDA9886
I2C-bus controlled multistandard alignment-free IF-PLL demodulators
8.8 Sound carrier trap
The sound trap is constructed of three separate traps to realize sufcient suppression of
the rst and second sound carriers.
For frequency control of the sound trap additionally a reference low-pass lter and a
phase detector are built in.
A sound carrier reference signal is fed into the reference low-pass lter and is shifted by
nominal 90 degrees. The phase detector compares the original reference signal with the
signal shifted by the reference lter and produces a DC voltage by charging or discharging
an integrated capacitor with a current proportional to the phase difference between both
signals, respectively to the frequency error of the integrated lters. The DC voltage
controls the frequency position of the reference lter and the sound trap. So the accurate
frequency position for the different standards is set by the sound carrier reference signal.
8.9 SIF amplier
The SIF amplier consists of three AC-coupled differential stages. Gain control is
performed by emitter degeneration and collector resistor variation. The total gain control
range is typically 66 dB. The differential input impedance is typically 2 k
in parallel with
3pF.
8.10 SIF-AGC detector
SIF gain control is performed by detection and controlling to a reference value 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 amplier 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 amplier of the SIF-AGC detector via the I2C-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.
Via a comparator, the integrated AGC capacitor is charged or discharged for providing the
required SIF gain. Due to AM sound, the AGC reaction time is slow (fc < 20 Hz for the
closed AGC loop). For reducing this AM sound time constant in the event of a decreasing
IF amplitude step, the charge/discharge 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 simplied application without a SIF SAW lter, the single reference QSS
mixer can be switched to the intercarrier mode via the I2C-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 amplier 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.
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