AN618 Panasonic Semiconductor, AN618 Datasheet - Page 13

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

(3) Hands-Free (HF) Mode
2. Receiver Amplifier Gain Adjustment
Use R26, R27, and C21 to adjust the receiver amplifier gain as shown in Fig.2–7.
ICs for Telephone
3–1 Setting the Transmitter System
of the MIC preamplifier, transmitter attenuator(T ATT), and line output amplifier. The gain of the T ATT is 0 dB, and the gain of
the line output amplifier is 21 dB(see 1-2, Setting the AC Characteristics). How to adjust the gain of the MIC preamplifier is the
same as that in the HS mode. The gain, G(HSMIC), is calculated as follows :
In the standard condition, R9=26 k , R10=10 k , C5=102 pF, and C44=0.1 F.
As seen from the above diagram, the gain of the transmitter system from ECM to VL in the HF mode is determined by the gains
G
(HSMIC)
The block diagram of the transmitter system in the HF mode is shown below.
V
C22
Fig.2–7 Receiver Amplifier
CC
1
= 20log
R11
22
MAI
Receiver amplifier
DO
AN6175K
ECM
R27
Vr
2
R10
{1/(2 f C44)} + R10
{1/(2 f C5)}// R9
C44
+
–
Handset receiver
21
R9
C5
R26
DI
Fig.3–1 HF Mode Transmitter System Block Diagram
MAO
C21
1
TATT
AN6175K
(dB)
TAO
Referring to Fig.2–7, the receiver amplifier gain, G
follows :
G
In the standard condition, R26=1 k , R27=100 k , and C21=10 F.
18
(REC)
C37
= 20log
36
HFI
C22
TAPC
R26 + {1/(2 f C21)}
20
R27
V
R24
R25
38
CC
TRB
1
Q3
R34=27
C42
(dB)
V
CC
Z
(REC)
1
L
=300
V
L
, is calculated as
AN6175K
13