®

15

PCM1721

FIGURE 15. 5-Level

∆Σ Modulator Block Diagram.

Out

48f

64f

In

8f

S

18-Bit

+

+

+

4

3

2

1

0

5-level Quantizer

+

–

+

+

–

+

+

+

THEORY OF OPERATION

The delta-sigma section of PCM1721 is based on a 5-level

amplitude quantizer and a 3rd-order noise shaper. This

section converts the oversampled input data to 5-level delta-

sigma format.

A block diagram of the 5-level delta-sigma modulator is

shown in Figure 15. This 5-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 modu-

theoretical quantization noise performance of the 5-level

delta-sigma modulator is shown in Figure 16.

FIGURE 16. Quantization Noise Spectrum.

3rd ORDER

∆Σ MODULATOR

Frequency (kHz)

20

0

–20

–40

–60

–80

–100

–120

–140

–160

0

5

10

15

20

25