M65845AFP
Function Description
Microphone Amplifier
The gain (G
V
) and low cut-off frequency (fcl) of microphone amplifier are expressed as follows.
G
V
= 20log
•
R1 + 1.5 k + 334 k
R1 + 1.5 k
fcl =
1
2π
•
(R1 + 1.5 k)
•
C1
G
V
(max) = 47 dB, fcl = 50 Hz
R1 = 0
Ω,
C1 = 2.2
μF
Assuming G
V
= 37 dB, fcl = 15 Hz, for instance, the constants take the following values.
R1 = 3.3 kΩ, C1 = 2.2
μF
REF
10 kΩ (Typ)
+
MIC
1
μF
5 kΩ
2
+
–
334 kΩ
1.5 kΩ
3
R1
+
4
C1
<Attention point when M65845FP is replaced with M65845AFP>
R3 and C4 are required for the M65845FP, not for the M65845AFP. As mentioned above, the gain of microphone
amplifier can set it up with R1.
REF
10 kΩ (Typ)
+
MIC
1
μF
R2
2
+
–
3
C4
R3 and C4 are not required for
the M65845AFP.
R1 for the gain of microphone
amplifier setting in use M65845AFP.
R3
R1
C1
+
4
Recommended circuit in use M65845FP
REJ03F0170-0201 Rev.2.01 Jan 25, 2008
Page 6 of 13
RENESAS [ RENESAS TECHNOLOGY CORP ]
