m65845afp Renesas Electronics Corporation., m65845afp Datasheet - Page 10

• Manufacturer Part Number: m65845afp
• Description: Digital Echo With Microphone Mixing Circuit
• Manufacturer: Renesas Electronics Corporation.

M65845AFP
2. Auto mute function
3. Input and output LPF
REJ03F0170-0201 Rev.2.01 Jan 25, 2008
Page 10 of 13
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.
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 =
2
At power up
At switching on MIC SW
R8 R9 C13 C14
1
MIC SW OFF
Reset Time
R7
24 k
REF
LPF1
12
Switching on MIC SW
R8
24 k
C13
C14
+
–
R9
24 k
13
Mute time
Mute time
(400 ms)
(400 ms)
R7
24 k
REF
LPF2
23
R8
24 k
C13
C14
+
–
R9
24 k
24