PCM1715U

6

®

0

–100

–120

–140

–160

0

5

10

15

20

Frequency (kHz)

0

–100

–120

–140

–160

0

5

10

15

20

Frequency (kHz)

THEORY OF

DELTA-SIGMA OPERATION

The delta-sigma section of the PCM1715 is based on a 5-

level amplitude quantizer and a 4th-order filter. This con-

verts the oversampled 16-bit input data to 5-level delta-

sigma form. A block diagram of the 5-level modulator is

shown in Figure 1.

FIGURE 3. Quantization Noise Spectrum (256fs).

FIGURE 4. Quantization Noise Spectrum (384fs).

FIGURE 2. Block Diagram of the Hf(z).

A block diagram of the 4th-order filter section Hf(z) in the

delta-sigma modulator is shown in Figure 2.

In general, high order 1-bit delta-sigma modulators have

disadvantages due to loop instability. The 5 level delta-

sigma modulator of the PCM1715 uses phase compensation

techniques to obtain stable operation. In Figure 2, the coef-

ficients, b1 to b4, give the basic form of the filter and –a1

and –a2 are used for phase compensation of the feedback

loop.

The theoretical quantization noise performance of the 5-

level delta-sigma modulator is shown in Figures 3 and 4. In

the audio band, the quantization noise floor level of the

PCM1715 is less than –130dB (384fs).

MODE OF OPERATION

Serial inputs to MD, MC, and ML (Pins 26, 27 and 28)

control the following functions:

(1) Digital Attenuator [AL0 ~ AL7, AR0 ~ AR7]

Attenuation data is constructed by 8-bit/Lch, 8-bit/Rch

(total 16-bit), can be controlled as 255 step attenuation

by individual channel. AL0 and AR0 are LSB, and AL7

and AR7 are MSB. Attenuation Level ATT is given by:

FIGURE 1. Block Diagram of 5-Level Delta-Sigma Quan-

tizer.

This 5-level delta-sigma modulator has the advantage of

stability of delta-sigma loop and jitter sensitivity over the

typical 1-bit (2-level) delta-sigma modulator.

The combined oversampling rate of the delta-sigma modu-

lator and the internal 8x oversampling digital filter is 48fs at

a system clock speed of 384fs, 32fs at a system clock speed

of 256fs.

In

Out

+

+

–

+

4

3

2

1

0

Hf(Z)

5-level Quantizer

32fs/48fs

5-level

8fs/

16 bits

Out

In

–a1

b4

b3

b2

b1

–a2

++

++

+

++

+