M65845AFP

REJ03F0170-0201 Rev.2.01 Jan 25, 2008

Page 10 of 13

2. Auto mute function

The IC carries out auto mute function at the time of powering up and switching on MIC SW in order to suppress

shock noise that the digital delay may produce.

Reset Time

Mute time

(400 ms)

• At power up

Switching on MIC SW

MIC SW OFF

Mute time

(400 ms)

• At switching on MIC SW

3. Input and output LPF

Signal through frequency fsig is also determined by LPF of digital echo cut off frequency.

2 degree LPF of digital echo is formed by external resistance and capacitor. (refer to next figure)

So, cut off frequency is determined by next formula.

fsig =

1

2

π R8 • R9 • C13 • C14

LPF1

+

–

12

R7

24 k

Ω

REF

R8

24 k

Ω

C13

C14

R9

24 k

Ω

13

LPF2

+

–

23

R7

24 k

Ω

REF

R8

24 k

Ω

C13

C14

R9

24 k

Ω

24