SD16_A Operation
28-8
SD16_A
28.2.7 Digital Filter
The digital filter processes the 1-bit data stream from the modulator using a
SINC
3
comb filter. The transfer function is described in the z-Domain by:
H
(
z
)
+
ǒ
1
OSR
1
*
z
*
OSR
1
*
z
*
1
Ǔ
3
and in the frequency domain by:
H
ǒ
f
Ǔ +
ȧ
ȱ
Ȳ
sinc
ǒ
OSR
p
f
fM
Ǔ
sinc
ǒ
p
f
fM
Ǔ ȧ
ȳ
ȴ
3
+
ȧ
ȡ
Ȣ
1
OSR
sin
ǒ
OSR
p
f
fM
Ǔ
sin
ǒ
p
f
fM
Ǔ ȧ
ȣ
Ȥ
3
where the oversampling rate, OSR, is the ratio of the modulator frequency f
M
to the sample frequency f
S
. Figure 28−4 shows the filter’s frequency response
for an OSR of 32. The first filter notch is at f
S
= f
M
/OSR. The notch’s frequency
can be adjusted by changing the modulator’s frequency, f
M
, using
SD16SSELx and SD16DIVx and the oversampling rate using the SD16OSRx
and SD16XOSR bits.
The digital filter for each enabled ADC channel completes the decimation of
the digital bit-stream and outputs new conversion results to the corresponding
SD16MEMx register at the sample frequency f
S
.
Figure 28−4. Comb Filter’s Frequency Response with OSR = 32
−140
−120
−100
−80
−60
−40
−20
0
Frequency
GAIN [dB]
f
S
f
M
Содержание MSP430x4xx Family
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Страница 348: ...8 8 16 Bit Hardware Multiplier ...
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Страница 400: ...10 28 DMA Controller ...
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Страница 466: ...15 24 Timer_A ...
Страница 522: ...17 30 USART Peripheral Interface UART Mode ...
Страница 544: ...18 22 USART Peripheral Interface SPI Mode ...
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Страница 692: ...24 20 LCD Controller ...
Страница 746: ...26 28 ADC12 ...