ASAHI KASEI

[AK4358]

MS0203-E-01

2006/02

- 33 -

4. External Analog Filter

It is recommended by SACD format book (Scarlet Book) that the filter response at SACD playback is an analog low pass

filter with a cut-off frequency of maximum 50kHz and a slop of minimum 30dB/Oct. The AK4358 can achieve this filter

response by combination of the internal filter (Table 18) and an external filter (Figure 27).

Frequency

Gain

20kHz

-0.4dB

50kHz

-2.8dB

100kHz

-15.5dB

Table 18. Internal Filter Response at DSD mode

1.8k

4.3k

1.0k

1.8k

1.0k

4.3k

270p

+Vop

270p

-Vop

AOUT-

AOUT+

3300p

Analog

Out

2.0k

2.0k

2200p

-

+

2.5Vpp

5.65Vpp

2.5Vpp

Figure 27. External 3rd order LPF Circuit Example

Frequency

Gain

20kHz

-0.05dB

50kHz

-0.51dB

100kHz

-16.8dB

DC gain = 1.07dB

Table 19. 3rd order LPF (Figure 27) Response

3.9k

4.7k

R1

3.9k

R1

4.7k

470p

+Vop

470p

-Vop

AOUT-

AOUT+

3900p

When R1=180Ω

When R1=150Ω

fc=90.1kHz, Q=0.735, g=-0.04dB at 40kHz

fc=99.0kHz, Q=0.680, g=-0.23dB at 40kHz

Analog

Out

2.5Vpp

2.5Vpp

6.05Vpp

Figure 28. External 2