XE8000EV101 Semtech, XE8000EV101 Datasheet - Page 115

• Manufacturer Part Number: XE8000EV101
• Description: EVAL BOARD FOR XE8801AMI027LF
• Manufacturer: Semtech
• Type: MCUr

Specifications of XE8000EV101

• Contents: Fully Assembled Evaluation Board
• For Use With/related Products: XE88LC01AMI027
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

16.9.4
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. As
shown in Figure 16-26, this filter determines the frequency response of the transfer function between the output of
the ADC and the analog input V
period OSR/f
elementary 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. For example, consider a 5Hz-bandwidth, 16-bit sensing system where 50Hz line rejection is
needed. Using the above equation and the plots below, we set the 4th notch for N
= 50Hz. The sampling frequency is then calculated as f
also good attenuation of 50Hz harmonics.
© Semtech 2005
4)
5)
6)
f
For highest linearity and lowest noise performance, bypass all PGAs and use the ADC alone (applications
where no "zooming" is needed); i.e. set ENABLE[3:0] = '0001'.
For low-noise applications where power consumption is not a primary concern, maintain the largest bias
currents in the PGAs and in the ADC; i.e. set IB_AMP_PGA[1:0] = IB_AMP_ADC[1:0] = '11'.
For lowest output offset error at the output of the ADC, bypass PGA2 and PGA3. Indeed, PGA2 and PGA3
typically introduce an offset of about 5 to 10 LSB (16 bit) at their output. Note, however, that the ADC
output offset is easily calibrated out by software.
NOTCH
Frequency Response
S
. The plots of Figure 16-26 also show that the frequency response changes with the number of
) (
i
=
OSR
i
⋅
S
⋅
N
/OSR.
ELCONV
f
ELCONV
S
performed. In particular, notches appear for N
IN
. Notice that the frequency axes are normalized to one elementary conversion
(Hz)
for
i
=
1
2 ,
16-30
S
,...,
= 20.48kHz for OSR = 512. Notice that this choice yields
(
N
ELCONV
−
) 1
ELCONV
(Eq. 23)
ELCONV
XE8801A – SX8801R
≥ 2. These notches occur at:
= 4 to 50Hz, i.e. 1.25⋅f
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S
/OSR