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參數(shù)資料
| 型號： | STLC7545 |
| 廠商： | 意法半導體 |
| 英文描述： | Enhanced V.34 BIS Analog Front-End(單片模擬前端) |
| 中文描述： | 國際清算銀行增強.34模擬前端（單片模擬前端） |
| 文件頁數(shù)： | 13/53頁 |
| 文件大?。?/td> | 378K |
| 代理商： | STLC7545 |
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III - FUNCTIONALDESCRIPTION
(continued)
III.3.2.2-ProgrammableDecimationFilter
(IIR2)
IIR2isaninfiniteimpulseresponsefilter.Itprovides
the low-pass filtering needed to remove the noise
remaining above half the sampling frequency
(e.g. 4800Hz) (see Figure 14). The output of the
IIR2,RxTx,will be processedbythe DSP.In ”band
split” mode (see Table 21), RxTx becomes the
inputsignal to IIR3. The RxTx will alwaysbe avail-
able on serial interface(SSIA in Figure2).
The IIR2 filter is a cascadeof seven biquads.The
filter coefficients are loaded into the associated
RAM (38 x 13).
The filter transfer function has been made pro-
grammablein orderto meet specificrequirements.
The sampling frequency is 4-times(5-times, 6-
times) the down-sampling frequency selected for
the Tx section (e.g. 9600 x 4Hz).
Tosupportecho cancellingapplicationsthe clocks
used for the A/D converter and the decimation
filtersaresynchronizedontheTxsystemclock,i.e.
on the Tx rate. It must be pointed out that using a
single clock system in A/D and D/A conversions is
importantfor reducinginduced noise.
The 12+1 bit filter coefficients are loaded into the
internalRAM2 and must be loaded from the serial
bus.All 38 coefficientshave to be loadedto imple-
ment an IIR transferfunction.
III.3.3 - Eye-diagramDisplay
Two8-bit digitalto analog convertersare provided
to monitor, on a CRT, the X and Y quadrature
signals of the eye pattern related to the demodu-
lated signal. The format of the data input is MSB
first, 8-bit two’s complement, and most significant
bytefor EYEYsampleand leastsignificantbytefor
the EYEX sample. The referencevoltage of these
two converters is the power supply voltage V
DD
.
The EYE pattern can be monitored on one or two
SynchronousSerialInterfacemode.
III.4- RECEIVERECONSTRUCTION SECTION
As theRx channel samplingis synchronizedto the
Tx system clock, it is necessaryto reconstruct the
Rx signal in order to get samplessynchronized to
the Rx symbol rate recoveredin the demodulator.
The function of the reconstruction filter (IIR3 and
FIR3) is to oversample by 128 x Fsx (160 x Fsx,
192 x Fsx) the receive signal (ResSig) comming
from the DSP after echo cancellation. The over-
sampled signal is then down-sampled at Fsr rate
to make it available to the DSP as RxSig at SSIB
or RxS1/RxS2at SSIA(seesectionIV.1andIV.2).
The down sampling process does not introduce
significant error.
The transfer function of the first section of the
reconstruction filter is programmable in the same
way as the Tx and Rx IIR filters previously de-
scribed.
III.4.1 - ProgrammableInterpolation Filter
(IIR3)
IIR3 is an infinite impulse response interpolating
filter.
The purpose of this digital filter is to interpolate
4-times(5-times,6-times)thedigitalsignalfromthe
DSP. This filter is sampled at 4-times (5-times,
6-times) the basicsampling frequency,(e.g. 9600
x 4 Hz).
The digital samples are encoded in 16-bit two’s
complementformat.
The IIR3 filter is a cascade of seven biquads. The
filter coefficients are loaded into the associated
RAM (38 x 13). Each coefficient is coded into 12
bitsand canbe doubledbyvirtueof an extrabit.All
38 coefficientshave to be loaded to implement an
IIR transferfunction.
This filter has been made programmable to offer
each user the possibility to add filtering charac-
teristics, e.g. highpass section or equalization,
matchedto a particularapplication.
For example, in a band-split MODEM application,
the first section can be a wide channel band-pass
filter (allowing the DSP to supervise boundary
audio tones) and the second section can be dedi-
cated to high band and low band splitting.
III.4.2 - FIRFilter
(FIR3)
FIR3isa finiteimpulseresponseinterpolatingfilter.
Its input sampling frequency is 4 x Fsx (5 x Fsx),
(6x Fsx) and the interpolation ratio 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
13/53
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