CIC7
Order = 7th
Decimation = 10
CIC1
Order = 1st
Decimation = 2, 4, 8, 16
Truncate
14
Truncate
14
.DALGN .OBR
Formatter
.SHIFT
16
SDHSCTL1.OSR
14
.DFMSEL
SDHSCTL0.
-240
-220
-200
-180
-160
-140
-120
-100
-80
-60
-40
-20
0
0
0.25
0.5
0.75
1
Gain (dB)
F/Fs
-260
SDHS Functional Operation
573
SLAU367P – October 2012 – Revised April 2020
Copyright © 2012–2020, Texas Instruments Incorporated
Sigma-Delta High Speed (SDHS)
Figure 22-6. SDHS Filter Frequency Response Within f
s
, SDHSCTL1.OSR = 10
22.2.3.2 CIC
1
Filter
The second-stage filter is a 1
st
-order CIC filter, 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. By cascading the CIC
7
and CIC
1
filters, the OSR ratio can be 10, 20, 40, 80, or 160.
22.2.3.3 Digital Filter Output
shows the block diagram of the SDHS digital filter. The CIC
7
is a 7th-order CIC filter with
decimation of 10. The CIC
1
is a 1
st
-order CIC filter with programmable decimation of 2, 4, 8, or 16. By
cascading the two filters, OSR of 10, 20, 40, 80, or 160 is offered. The OSR ratio is configured by the
SDHSCTL1.OSR bits. Each output of the CIC
7
and CIC
1
is truncated to 14 bits. The final output data is
16 bit, but the effective number of bits and data format are programmable through the
SDHSCTL0.DALGN, SDHSCTL0.OBR, SDHSCTL0.SHIFT, and SDHSCTL0.DFMSEL bits.
Figure 22-7. Digital Filter Block Diagram
The final frequency response of the SDHS digital filter is determined by SDHSCTL1.OSR bit.
shows the frequency response of cascading CIC
7
and CIC
1
beyond f
s
(normalized) when SDHSCTL1.OSR
= 20.