參數(shù)資料
型號(hào)： STLC7545
廠商： 意法半導(dǎo)體
英文描述： Enhanced V.34 BIS Analog Front-End(單片模擬前端)
中文描述： 國(guó)際清算銀行增強(qiáng).34模擬前端（單片模擬前端）
文件頁(yè)數(shù)： 12/53頁(yè)
文件大?。?/td> 378K
代理商： STLC7545
III - FUNCTIONALDESCRIPTION
(continued)
III.2- TRANSMIT D/A SECTION
The functions included in the Tx D/A section are
detailedhereafter.
III.2.1 - InterpolationFilters
The oversampling is performed by two cascaded
digitalinterpolatingfilters: IIR1andFIR1.The IIR1
and FIR1 filters are sampled at 4 x Fsx and 128 x
Fsx(5x Fsxand 160 x Fsx)(6 Fsxand 192x Fsx),
respectively.
III.2.1.1-ProgrammableInterpolationFilter(IIR1)
IIR1 is an infinite impulse response interpolating
filter.
The purpose of this digital filter is to interpolate
4-times (5 times, 6 times)the digital signalcoming
from the DSP. This filter is sampled at the basic
samplingfrequency,(e.g. 9600 x 4 Hz), and must
exhibit,as a minimum, a low-passsectionwhichis
mandatoryto removereplicas abovehalf thesam-
pling frequency (e.g. 4800Hz) (see Figure 13).
The digital samples are encoded in 16-bit two’s
complement format.
The IIR1 filter is a cascade of seven biquads (see
Figure A1). The filter coefficients are loaded into
the associated RAM (38 x 13). Each coefficient is
coded into 12bits and can be doubledby virtue of
an extra bit. All 38 coefficients have to be loaded
to implement an IIR transfer function (see An-
nexe A).
This filter has been made programmable to offer
each user the possibility to add filtering charac-
teristics, e.g. high-pass section or equalization,
matchedto a particularapplication.
III.2.1.2- FIR Filter
(FIR1)
FIR1isafiniteimpulseresponseinterpolatingfilter.
Itsinput samplingfrequency is 4 x Fsx(or 5 x Fsx)
(or 6 x Fsx) and its interpolationratio is 32. The Z
transferfunctionof thisFIR is :
H
(
z
) =
1
z
32
32
(
1
z
1
)
3
withZ = exp (j2
π
F/Txoclk)
and Txoclk = 128 (160, 192) x Fsx
III.2.2 - D/AConverter
The128-times(160times,192times)oversampled
D/Aconverterincludesasecondorderdigitalnoise
shaper, a one bit D/A converter and a single pole
analog low-pass filter. The gain of the last output
stage can be programmed to 0dB,-6dB or infinite
attenuation.Thecut-offfrequencyofthesinglepole
switch-capacitorlow-passfilter is :
fc-3dB=Txoclk/(2 x
π
x 10)
where Txoclk = 128 (160, 192) x Fsx
Continuous-time filtering of the analog differential
output is necessaryusing an off-chip amplifierand
a few external passive components (see Fig-
ure 16).
At least 86dB signal to noise plus distortion ratio
can be obtained in the frequency band 300-
3400Hz,with a -6dBr output signal.
III.3 - RECEIVE A/D SECTION
The different functions included in the Rx A/D
section are detailed hereafter. The format used at
the digital interfaces of the Rx channel is two’s
complementencoded 16-bit.
III.3.1 - A/DConverter
The 128 (160, 192) oversampledA/D converteris
based on a second order sigma-delta modulator.
Thesignalto noiseplusdistortionratioobtainedfor
a signal spectrum limited to the 300-3400Hztele-
phone band, is typically 86dB with a -6dBr input
signal.
III.3.2 - DecimationFilters
The128 (160,192)decimationis performedby two
interpolatingdigitalfilters: FIR2andIIR2,whichare
sampled at 128 x Fsx and 4 x Fsx (160 x Fsx and
5 x Fsx) (192 x Fsx and 6 x Fsx), respectively.
III.3.2.1- FIR Filter
(FIR2)
FIR2 is a finite impulse response decimatingfilter.
Its sampling frequencyis 128 x Fsx (or 160 x Fsx
or 192 x Fsx)and its decimationratio is 32. The Z
transferfunction of thisFIR is :
H
(
z
) =
1
z
32
32
(
1
z
1
)
3
with Z = exp (j2
π
F/Txoclk)
and Txoclk= 128 (160, 192) x Fsx
STLC7545
12/53
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