WM8768

Production Data

w

PD Rev 4.1 March 2005

36

SUGGESTED ANALOGUE LOW PASS POST DAC FILTERS

It is recommended that a lowpass filter be applied to the output from each DAC channel for Hi Fi

applications. Typically a second order filter is suitable and provides sufficient attenuation of high

frequency components (the unique low order, high bit count multi-bit sigma delta DAC structure used

in WM8768 produces much less high frequency output noise than normal sigma delta DACs. This

filter is typically also used to provide the 2x gain needed to provide the standard 2Vrms output level

from most consumer equipment. Figure 32 shows a suitable post DAC filter circuit, with 2x gain.

Alternative inverting filter architectures might also be used with as good results.

7.5k

Ω

Ω

Ω

Ω

1.8k

Ω

Ω

Ω

Ω

10uF

1.0nF

47k

Ω

Ω

Ω

Ω

4.7k

Ω

Ω

Ω

Ω

680pF

4.7k

Ω

Ω

Ω

Ω

51

OP_FIL

VOUT1L

OP_FIL

VOUT1R

OP_FIL

VOUT2R

OP_FIL

VOUT2L

OP_FIL

VOUT3L

OP_FIL

VOUT3R

OP_FIL

VOUT4L

OP_FIL

VOUT4R

Figure 32 Recommended Post DAC Filter Circuit