sx8725 Semtech Corporation, sx8725 Datasheet - Page 38

• Manufacturer Part Number: sx8725
• Description: Sx8725 Zoomingadc? For Pressure And Temperature Sensing
• Manufacturer: Semtech Corporation

ADVANCED COMMUNICATIONS & SENSING
Frequency Response
The incremental ADC is an over-sampled converter with two main blocks: an analog modulator and a low-pass
digital filter. The main function of the digital filter is to remove the quantization noise introduced by the
modulator. This filter determines the frequency response of the transfer function between the output of the ADC
and the analog input V
OSR / f
conversions N
and are repeated every f
Information on the location of these notches is particularly useful when specific frequencies must be filtered out
by the acquisition system. This chip has no dedicated 50/60 Hz rejection filtering but some rejection can be
achieved by using Equation 24 and setting the appropriate values of OSR, f
Examples:
V1.5 © 2007 Semtech Corp.
Rejection [Hz]
Figure 21 - Frequency Response: Normalized Magnitude vs. Frequency for Different N
s
. The plots of Figure 21 also show that the frequency response changes with the number of elementary
60
50
1.2
0.8
0.6
0.4
0.2
1.2
0.8
0.6
0.4
0.2
1
0
1
0
ELCONV
0
0
performed. In particular, notches appear for N
Normalized Frequency - f *(OSR/f
Normalized Frequency - f *(OSR/f
IN
f
s
1
1
. Notice that the frequency axes are normalized to one elementary conversion period
NOTCH
/ OSR.
f
NOTCH
) (
i
61
61
61
53
46
46
Table 32 - 60/50 Hz Line Rejection Examples
[Hz]
2
2
OSR
ZoomingADC™ for Pressure and Temperature Sensing
i
N
N
N
ELCONV
ELCONV
f
3
S
3
S
ELCONV
) [-]
s
) [-]
= 1
Equation 24
= 4
f
s
38
62.5
62.5
4
[kHz]
125
250
500
125
4
(Hz) for
1.2
0.8
0.6
0.4
0.2
1.2
0.8
0.6
0.4
0.2
1
0
1
0
0
0
i
ELCONV
1
2 ,
Normalized Frequency - f *(OSR/f
,...,
Normalized Frequency - f *(OSR/f
1
1
(
2. These notches occur at:
s
OSR [-]
N
and
1024
1024
1024
1024
1024
1024
ELCONV
NELCONV
2
2
) 1
.
N
N
ELCONV
3
ELCONV
3
www.semtech.com
S
S
) [-]
) [-]
N
= 2
= 8
ELCONV
ELCONV
SX8725
2
4
8
8
4
8
4
4
[-]