WM8756

Advance Information

AI Rev 1.3 October 2001

36

SUGGESTED ANALOGUE LOW PASS POST DAC FILTERS

For PCM operation, the low out of band noise from the WM8756 means that a low order post DAC filter can be used such

as 2

External 2nd OrderLPF

x2 for Stereo Operation

680pF

-

+

7.5k

Ω

1000pF

1.8k

Ω

Filtered

Analogue

Output

OUTnR

OUTnL

10k

Ω

10k

Ω

Figure 31 Second order active RC low pass filter

For SACD operation a 3

minimum 30dB attenuation at 100kHz) when combined with the filter response of the internal FIR filter. Such a filter may be

built using a single opamp in similar fashion to the second order filter above, so costing little extra to implement. The same

filter may also be used very satisfactorily for PCM operation.

External 3rd OrderLPF

x2 for Stereo Operation

100pF

-

+

10k

Ω

1500pF

10k

Ω

680pF

10k

Ω

Filtered

Analogue

Output

OUTnR

OUTnL

10k

Ω

10k

Ω

Figure 32 Third order active RC low pass filter

RECOMMENDED APPLICATIONS

Audio data carrier

DSD decoder

PCM Decoder

e.g. AC-3, DTS

WM8756

6-channel

DAC

Front left

Surround left

LFE

Centre

Surround right

Front right

Figure 33 Combined PCM and DSD Circuit Configuration