PCM1789 datasheet(14/39 Pages) TI

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SAMPLING MODE

100

120

140

160

180

200

2.0

NormalizedFrequency(f )

0.5

1.0

1.5

DSM_Dual

DSM_Single

DSM_Quad

DF_Dual

DF_Single

DF_Quad

PCM1789

SBAS451 – OCTOBER 2008.............................................................................................................................................................................................. 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 fS and 192 fS);

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 fS,

768 fS, and 1152 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 register.

Table 3 and Figure 19 show the relationship among the oversampling rate (OSR) of the digital filter and

ΔΣ

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)

FREQUENCY

DIGITAL FILTER

MODULATOR

SETTING

(xfS)

fS = 48 kHz

fS = 96 kHz

fS = 192 kHz

OSR

512, 768, 1152

N/A

×8

x128

Auto

256, 384

N/A

x64

128, 192(2)

x32

512, 768, 1152

N/A

x128

Single

256, 384

N/A

x128

128, 192(2)

N/A

x64

256, 384

N/A

x64

Dual

128, 192(2)

N/A

x64

Quad

128, 192(2)

x32

(1)

Bandwidth in which noise is shaped out.

(2)

Quad mode filter characteristic is applied.

Figure 19.

ΔΣ Modulator and Digital Filter Characteristic

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