AN618 Panasonic Semiconductor, AN618 Datasheet - Page 9

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

2. Setting the degree of shifting of the I
affects the AC characteristics of the line interface.
1—2 Setting the AC Characteristics
1. Line output gain adjustment
ICs for Telephone
As shown in Fig.1—3, the resistance of R33 determines the degree of vertical shifting of the I
Referring to Figs.1—1 and 1—3, the resistance of R33 is now set to 820 (standard).
AN6175K
AN6175K
• If R33's resistance is decreased, the curve shifts downward.
• If R33's resistance is increased, the curve shifts upward.
MIC amp.
MIC amp.
Fig.1—5 Line Output Block Diagram
37
38
39
Fig.1—4 Line Output
37
38
39
V
TRB
TRE
CC
V
TRB
TRE
2
CC
R33
2
R33
Q3
Q3
12
C38
R34
0
C38
R34
0
L
—V
Z
L
=300
20
L
characteristics
V
V
V
Fig.1—3 I
CC
L
CC
V
V
V
1
1
CC
L
CC
1
1
I
L
L
(mA)
—V
L
Referring to Fig.1—4, the AC impedance(ZAC)of the line inter-
face is calculated as follows :
If the impedance of transistor Q3 is 2 k (ZQ3=2 k), and the
resistance of R33 is 820 , then ZAC is determined as follows :
Use R34 to adjust the line output gain as shown in Fig.1—1.
calculated as follows :
G
If R34 is 27 , G
Characteristics
(38)
ZAC= 820//2k
The line output amplifier gain, G
= 20 log (Z
ZAC= R33/ZQ3
= 600
L
(38)
120
/R34)
is 21dB.
R33=1.3k
R33=820 (
R33=330
L
standard)
—V
(38)
L
characteristics. R33 also
, as seen from Pin38, is
AN6175K
9