PCM1741ESLASH2K datasheet(18/24 Pages) TI2

18 / 24 page

PCM1741

SBAS175

FIGURE 14. 8-Level Delta-Sigma Modulator.

Z–1

8-Level Quantizer

Z–1

–

Z–1

64f

PCM1741

DGND

Output

Circuits

RF Choke or Ferrite Bead

Common

Ground

AGND

DIGITAL SECTION

ANALOG SECTION

Power Supplies

+3.3V

AGND

REG

–V

FIGURE 13. Single-Supply PCB Layout.

Separate power supplies are recommended for the digital

and analog sections of the board. This prevents the switching

noise present on the digital supply from contaminating the

analog power supply and degrading the dynamic perfor-

mance of the PCM1741. In cases where a common +3.3V

supply must be used for the analog and digital sections, an

inductance (RF choke, ferrite bead) should be placed be-

tween the analog and digital +3.3V supply connections to

avoid coupling of the digital switching noise into the analog

circuitry. Figure 13 shows the recommended approach for

single-supply applications.

THEORY OF OPERATION

The delta-sigma section of the PCM1741 is based on an

8-level amplitude quantizer and a fourth-order noise shaper. This

section converts the oversampled input data to 8-level delta-sigma

format. A block diagram of the 8-level delta-sigma modulator is

shown in Figure 14. This 8-level delta-sigma modulator has the

advantage of stability and clock jitter sensitivity over the typical

one-bit (2-level) delta-sigma modulator. The combined

oversampling rate of the delta-sigma modulator and the interpo-

lation filter is 64fS.

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