Datasheet
SAMPLING MODE
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
PCM1789
SBAS451A – OCTOBER 2008 – REVISED JANUARY 2009 ..............................................................................................................................................
www.ti.com
The PCM1789 supports three sampling modes (single rate, dual rate, and quad rate) in DAC operation. In single
rate mode, the DAC operates at an oversampling frequency of x128 (except when SCKI = 128 f
S
and 192 f
S
);
this mode is supported for sampling frequencies less than 50 kHz. In dual rate mode, the DAC operates at an
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 (that is, single rate for 512 f
S
,
768 f
S
, and 1152 f
S
; dual rate for 256 f
S
and 384 f
S
; and quad rate for 128 f
S
and 192 f
S
), but manual selection is
also possible for specified combinations through the serial mode control register.
Table 3 and Figure 19 show the relationship among the oversampling rate (OSR) of the digital filter and Δ Σ
modulator, the noise-free shaped bandwidth, and each sampling mode setting.
Table 3. Digital Filter OSR, Modulator OSR, and Noise-Free Shaped Bandwidth for Each Sampling Mode
SAMPLING NOISE-FREE SHAPED BANDWIDTH
(1)
MODE SYSTEM CLOCK (kHz)
REGISTER FREQUENCY DIGITAL FILTER MODULATOR
SETTING (xf
S
) f
S
= 48 kHz f
S
= 96 kHz f
S
= 192 kHz OSR OSR
512, 768, 1152 40 N/A N/A × 8 x128
Auto 256, 384 20 40 N/A x8 x64
128, 192
(2)
10 20 40 x4 x32
512, 768, 1152 40 N/A N/A x8 x128
Single 256, 384 40 N/A N/A x8 x128
128, 192
(2)
20 N/A N/A x4 x64
256, 384 20 40 N/A x8 x64
Dual
128, 192
(2)
20 40 N/A x4 x64
Quad 128, 192
(2)
10 20 40 x4 x32
(1) Bandwidth in which noise is shaped out.
(2) Quad mode filter characteristic is applied.
Figure 19. Δ Σ Modulator and Digital Filter Characteristic
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