AN618 Panasonic Semiconductor, AN618 Datasheet - Page 10

• Manufacturer Part Number: AN618
• Description: Recording and playing amplifier IC for answering telephones
• Manufacturer: Panasonic Semiconductor

(2) Handset(HS)Mode
2. Automatic PAD control adjustment
3. Balance network adjustment
the MIC preamplifier and the gain of the line output amplifier(21dB). How to adjust the gain/frequency characteristics of the MIC
preamplifier is described below.
AN6175K
10
2—1 Setting the Transmitter System
The balance network of the AN6175K application board is shown below. Its constants can be adjusted to application needs.
As seen from the above diagram, the gain of the transmitter system from ECM to VL in the HS mode is determined by the gain of
Automatic PAD control, or APC, is such a function as to automatically adjust transmission gain according to line current (I
The gain range of the APC of the AN6175K is 6 dB. The adjustment of the APC means setting the IL at which the APC starts
functioning. The adjustment is done by changing the R24/R25 ratio as shown in Fig.2—1.
Under the standard condition(R24=18 k , R25=12 k ), the I
as shown in Fig.2—2.
The block diagram of the transmitter system in the HS mode is shown below.
0
Smaller R24/R25 ratio
Fig.1—6 Automatic PAD Control
20
Line Current I
45
MAI
From line
R14
ECM
3
Vr
R13
L
C45
(mA)
Standard R24/R25 ratio
Fig.2—1 HS Mode Transmitter System Block Diagram
Larger R24/R25 ratio
+
–
R12
C6
120
R3
3.3k
R1
3.9k
R4
330
Fig.1—7 Balance Network
4
AN6175K
C3
0.039 F
MAO
R25
ratio as follows :
TAPC
Referring to Fig. 1—6, the APC start point depends on the R24/R25
L
18
at which the APC starts functioning(the APC start point)is 45 mA
R2
12k
APC
V
CC
R24
1
• If the ratio increases, the point becomes higher.
• If the ratio decreases, the point becomes lower.
V
To the receiver preamplifier
From the emitter of the transmission transistor
L
pin connecting to the transmission transistor
38
TRE
Q3
R34
C42
V
CC
Z
1
ICs for Telephone
L
=300
V
L
L
).