f
Signal
f /2
s
f
s
Quantization Noise
a)
f
Signal
f /2
s
Quantization Noise
“Shaped” Quantization Noise
Signal
b)
Signal
OSR × f
s
f
Signal
f /2
s
Noise filtered out by digital filter
Signal
c)
OSR × f
s
2
OSR × f
s
OSR × f
s
2
Noise filtered out by digital filter
Digital Filter
Digital Filter
SDHS Functional Operation
571
SLAU367P – October 2012 – Revised April 2020
Copyright © 2012–2020, Texas Instruments Incorporated
Sigma-Delta High Speed (SDHS)
Figure 22-3. Sigma-Delta Principle
22.2.3 Digital Output
The SDHS digital filter processes the data stream from the modulator. The filter consists of two stages.
The first stage is a 7
th
-order CIC filter (CIC
7
), which is always enabled and its decimation ratio is 10. The
second-stage filter is a 1
st
-order CIC filter (CIC
1
) which is automatically enabled when the OSR ratio is
greater than 10. The second-stage filter can have decimation ratio of 2, 4, 8, or 16. With an OSR ratio
greater than 10, both of the CIC filters are enabled and cascaded. See
for details.
22.2.3.1 CIC
7
Filter
shows the structure of a CIC
7
filter, which is selected when SDHSCTL1.OSR = 10.