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參數(shù)資料
| 型號： | TDA7338 |
| 廠商： | 意法半導(dǎo)體 |
| 元件分類： | 通用總線功能 |
| 英文描述： | STEREO DECODER |
| 中文描述： | 立體聲解碼器 |
| 文件頁數(shù)： | 6/11頁 |
| 文件大?。?/td> | 103K |
| 代理商： | TDA7338 |
frequency is reduced down to 1kHz to improve
the signal to noise ratio. Furthermore the condi-
tions of the stereo separation (see fig.2) can be
controlled through the signal applied to Pin 16
(VSB). Both signal levels (VSB and VHCC) are
referred to Pin 17 (VR), with the characteristic
that the control range is 11% of V
R
.
By modifying the feedback resistor value of the
output stages (Pin 9 - 10, Pin 11 - 12) the total
gain of the stereodecodercan be modified.
Pin 7 and Pin 8 have an additional function. By
pulling them to ground the VCO-OFF (Pin 7) and
the MUTE (Pin 8) function are activated. The
MUTE signal disconnects the MPX-signal from
the circuit, while in combination with VCO-OFF
also the output buffers are disconnected from the
circuit. In this mode the output buffers can be
used for AM-stereo, cassette play back and other
purposes.
AM MonoMode
By selecting VCO-OFF (Pin 7 to GND) the VCO
is switched off and the SB and HCC are disabled.
The deemphasis time constant is changed to
40
μ
s (f
c
= 4KHz).
DESCRIPTION OFTHE NOISE BLANKER
In the normal automotive environment the MPX
signal is disturbed by ignition spikes, motors and
high frequencyswitches etc.
The aim of the noise blanker part is to cancel the
influence of the spikes producedby these compo-
nents. Therefore the output of the stereodecoder
is switched off for a time of 40
μ
s (average spike
duration).
In a first stage the spikes must be detectedbut to
avoid a wrong triggering on high frequency noise
a complextrigger control is implemented.
Behind the triggerstage a pulseformer generates
the 40
μ
s ”blanking”pulse.
This duration of 40
μ
s can be varied by changing
the capacitorat pin 7.
1.1 TriggerPath
The incoming MPX signal is highpass-filtered,
amplified and rectified(block RECT-PEAK).
The second order highpass-filterhas a corner-fre-
quency of 140KHz.
The rectifier signal, RECT, is used to generate by
peak-rectification a signal called PEAK, which is
available at the PEAK pin 8.
Also noise with a frequency >100KHz increases
the PEAK voltage. The value of the PEAKvoltage
influences the trigger threshold voltage Vth (block
ATC). The higher the noise level the higher the
threshold.
Both signals, RECT and PEAK+Vth are fed to a
comparator (block PEAK-COMP) which outputs a
sawtooth-shapedwaveform at the TBLANK pin 7.
A second comparator (block BLANK-COMP)
forms the internal blankingdurationof 40
μ
s.
The noise blanker is supplied by his own biasing
circuit (block BIAS-MONO) to avoid any crosstalk
to the signal path (blockBIAS-MONO).
1.2 Noise Controlled Threshold Adjustment
(ATC)
The behaviour of the noise controlled threshold
adjustmentis shown in fig. 4. It can be influenced
slightly by adding a resistor in parallel to the
PEAK capacitor at Pin 8 either to GND or V
DD
. A
resistor to GND will decrease the threshold
whereas a resistor to V
DD
will increase it. But it is
recommended to choose one of the internal
thresholdsby use of the PROG pin (see table1)
1.3 AutomaticThreshold Control by the
Stereoblendvoltage (ATC-SB)
Besides the noise controlled thresholdadjustment
there is an additionalpossibility for influencingthe
trigger. It is controlled by the difference between
Vsb and Vr, similar to the Stereoblend. The rea-
son for implementing such a second control will
be explainedin the following:
The point where the MPX signal starts to become
noisy is fixed by the RF part. Therefore also the
starting point of the normal noise controlled trig-
ger adjustment is fixed (fig.5). But in some cases
the behaviour of the noiseblanker can be im-
proved by increasing the threshold even in a re-
gion of higher fieldstrength, for the MPX signal
often shows distortion in this range, which leads
to an undesired triggering.
Because of the overlap of this range and the
range of the stereo/mono transition it can be con-
trolled by Vsb and Vr. This threshold increase is
programmable(seefig.5).
1.4 BlendMode
Another possibility to avoid a disturbing triggering
on modulation is to use the spikes on the field-
strength signal (LEVEL pin). But in the range of
higher fieldstrength the signal saturates and no
more spike detection is possible. For this reason
the TDA7338 offers the ”BLEND MODE”. When
”BLEND MODE” is activated a smooth transition
between the LEVEL- and the MPX-signal is used
to detectthe spikeseither on LEVEL or on MPX.
In the lower fieldstrength range mainly the
LEVEL-signal is used whereas in the higher
range mainly the MPX is used. This switching is
controlled also by the normal Stereoblend signal
to avoid additionalpins.
”BLEND MODE OFF” is activated by connecting
the LEVEL pin to GND (LEVEL must be also con-
nectedto GND if notused).
TDA7338
6/11
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| TDA7338D | STEREO DECODER |
| TDA7339 | 3 BAND DIGITAL CONTROLLED AUDIO PROCESSOR |
| TDA7340G | AUDIO SIGNAL PROCESSOR |
| TDA7340 | AUDIO SIGNAL PROCESSOR |
| TDA7340P | AUDIO SIGNAL PROCESSOR |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| TDA7338_05 | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:STEREO DECODER |
| TDA7338D | 功能描述:接口—CODEC Stereo Decoder RoHS:否 制造商:Texas Instruments 類型: 分辨率: 轉(zhuǎn)換速率:48 kSPs 接口類型:I2C ADC 數(shù)量:2 DAC 數(shù)量:4 工作電源電壓:1.8 V, 2.1 V, 2.3 V to 5.5 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:DSBGA-81 封裝:Reel |
| TDA7338D013TR | 功能描述:接口—CODEC Stereo Decoder RoHS:否 制造商:Texas Instruments 類型: 分辨率: 轉(zhuǎn)換速率:48 kSPs 接口類型:I2C ADC 數(shù)量:2 DAC 數(shù)量:4 工作電源電壓:1.8 V, 2.1 V, 2.3 V to 5.5 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:DSBGA-81 封裝:Reel |
| TDA7339 | 功能描述:音頻 DSP Digital Audio Proc RoHS:否 制造商:Texas Instruments 工作電源電壓: 電源電流: 工作溫度范圍: 安裝風(fēng)格: 封裝 / 箱體: 封裝:Tube |
| TDA7340 | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:AUDIO SIGNAL PROCESSOR |
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