0
20
40
60
80
100
120
140
160
180
200
-
2.0
Amplitude(dB)
NormalizedFrequency(f )
S
0
0.5
1.0
1.5
DSM_Dual
DSM_Single
DF_Single
DF_Dual
0
20
40
60
80
100
120
140
160
180
200
-
2.0
Amplitude(dB)
NormalizedFrequency(f )
S
0
0.5
1.0
1.5
DSM_Dual
DSM_Single
DSM_Quad
DF_Dual
DF_Single
DF_Quad
www.ti.com ......................................................................................................................................................................................... SBAS452 – SEPTEMBER 2008
oversampling frequency of x64; this mode is supported for sampling frequencies less than 100 kHz. In quad rate
mode, the DAC operates at an oversampling frequency of x32. The sampling mode is automatically selected
according to the ratio of system clock frequency and sampling frequency by default (for example, single rate for
512 fS and 768 fS, dual rate for 256 fS and 384 fS, and quad rate for 128 fS and 192 fS), but manual selection is
also possible for specified combinations through the serial mode control resistor.
Table 5 and
Figure 31 show the relation between the oversampling rate (OSR) of the
ΔΣ modulator, noise-free
shaped bandwidth, and each sampling mode setting for ADC operation.
Table 6 and
Figure 32 describe the
relation between the oversampling rate of the digital filter and
ΔΣ modulator, noise-free shaped bandwidth, and
each sampling mode setting for DAC operation.
Table 5. ADC Modulator OSR and Noise-Free Shaped Bandwidthfor Each Sampling Mode
NOISE-FREE SHAPED BANDWIDTH (kHz)
SAMPLING MODE
SYSTEM CLOCK RATE
REGISTER SETTING
(fS)
fS = 48 kHz
fS = 96 kHz
MODULATOR OSR
512, 768
40
N/A
x128
Auto
256, 384
20
40
x64
512, 768
40
N/A
x128
Single
256, 384
40
N/A
x128
Dual
256, 384
20
40
x64
Table 6. DAC Digital Filter OSR, Modulator OSR, and Noise-Free Shaped Bandwidth
for Each Sampling Mode
NOISE-FREE SHAPED
BANDWIDTH
SAMPLING MODE
SYSTEM CLOCK
fS = 48
fS = 96
fS = 192
REGISTER SETTING
RATE (fS)
kHz
DIGITAL FILTER OSR
MODULATOR OSR
512, 768
40
N/A
x8
x128
Auto
256, 384
20
40
N/A
x8
x64
128, 192(1)(2)
10
20
40
x4
x32
512, 768
40
N/A
x8
x128
Single
256, 384
40
N/A
x8
x128
128, 192(1)(2)
20
N/A
x4
x64
256, 384
20
40
N/A
x8
x64
Dual
128, 192(1)(2)
20
40
N/A
x4
x64
Quad
128, 192(1)(2)
10
20
40
x4
x32
(1)
Supported only by DAC operation.
(2)
Quad mode filter characteristic is applied.
Figure 31. ADC
ΔΣ Modulator and Digital Filter
Figure 32. DAC
ΔΣ Modulator and Digital Filter
Characteristic
Copyright 2008, Texas Instruments Incorporated
21