SM5865AM

NIPPON PRECISION CIRCUITS—9

FUNCTIONAL DESCRIPTION

Quantization Noise Reduction

The SM5865AM employs a 3rd-order 23-level quantizer noise shaper to effectively reduce quantization noise

in the audio band. The quantization noise component at 16fs to 96fs operation is shown in figure 1.

Internal Oversampling Operation

The SM5865AM accepts data output from an 8-times or 4-times oversampling digital filter, and oversampled

internally again up to the noise shaper operating rate. The internal oversampling factor is determined automati-

cally from the system clock input frequency and the input sampling frequency. This internal oversampling fac-

tor (n) must be an integer satisfying the conditions shown in table 1.

Figure 1. Quantization noise level

Table 1. Operating conditions

Parameter

CKDVN = HIGH

CKDVN = LOW

1

where n = 1, 2, 3, ...

where n = 1, 2, 3, ...

Noise shaper operating frequency

0.5

1

1.5

2

2.5

3

3.5

4

180

170

160

150

140

130

120

110

100

90

80

70

60

50

40

30

20

10

0

0

Frequency (fs)

Quantization noise

(dB)

16fs

24fs

32fs

48fs

64fs

96fs

0 dB sine wave equivalent white noise level

16-bit, fs quantization noise level

20-bit, fs quantization noise level

24-bit, fs quantization noise level

f

CKI

f

WCKI

8

×

n

×

=

f

CKI

f

WCKI

16

×

n

×

=

f

ns

f

WCKI

n

f

CKI

8

-----------

=

×

=

f

ns

f

WCKI

n

f

CKI

16

-----------

=

×

=