SAMES SAN2202 Datasheet
SAN2202
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APPLICATION NOTE
SINGLE CHIP “SPEAKERPHONE” WITH
8 - OHM LOUDSPEAKER AMPLIFIER
1 Scope
This application note describes a low-cost add-on cir c uit f or dr iving an 8Ω-Loudspeaker to get a sim ple loudhearing
(“Speakerphone”) Telephone.
To possible ways of supplying the amplifier are shown:
SAN2202a: Amplifier supply in shunt transistor path
SAN2202b: Amplifier supply by power extraction circuit (SAN3020)
It can be added to any SA253x application without interfering with PTT-r elevant parameters, like AC-impedance,
Sidetone cancellation or DC-mask.
2 Key Features
•
Low cost additional circuit enables use of loudhearing function
•
Full duplex “handsfree” operation via handset microphone and loudspeaker (at distances <2m between
telephone and user)
•
Can be added to any SA253x- application
•
Enables use of low cost 8Ω - Loudspeaker
•
High output power with low distortion
•
Entirely powered from the telephone line
•
No influence of loudspeaker amplifier in AC-impedance, sidetone cancellation or DC-mask
•
Loudspeaker volume adjustable by potentiometer
•
Excellent sidetone cancellation of SAS253x circuits enables high loudspeaker volume without howling between
handset microphone and loudspeaker
SAN2202 PDS038-SA2531/2-001 Rev. B 21-03-00
SAN2202
TABLE OF CONTENTS
1 SCOPE.............................................................................................................................................................................................................1
2 KEY FEATURES..............................................................................................................................................................................................1
3 OTHER APPLICABLE DOCUMENTS AND PAPERS......................................................................................................................................3
4 REVISION STATUS .........................................................................................................................................................................................3
5 GENERAL DESCRIPTION...............................................................................................................................................................................3
MPLIFIER SUPPLY
5.1 A
6 BLOCK DIAGRAM...........................................................................................................................................................................................4
HOW TO AVOID HOWLING
6.1
7 CIRCUIT DESCRIPTION..................................................................................................................................................................................5
LOUDSPEAKER AMPLIFIER
7.1 8Ω
MPLIFIER SUPPLY IN SHUNT TRANSISTOR PATH
7.2 A
MPLIFIER SUPPLY BY POWER EXTRACTION CIRCUIT
7.3 A
8 MEASUREMENT RESULTS & CURVES.........................................................................................................................................................6
REQUENCY RESPONSE
8.1 F
MAXIMUM SENDING LEVEL
8.2
MAXIMUM OUTPUT POWER
8.3
N-RESISTANCE IN PULSE DIALING
8.4 O
9 APPLICATION SCHEMATIC ............................................................................................................................................................................8
10 LIABILITY AND COPYRIGHT STATEMENT ..................................................................................................................................................9
OMPARISON OF
: C
SAN2202
A AND
SAN2202B:..............................................................................................................3
.............................................................................................................................................................................4
.......................................................................................................................................................................5
............................................................................................................................................5
SAN3020 ......................................................................................................................5
..............................................................................................................................................................................6
............................................................................................................................................................................6
...........................................................................................................................................................................6
...............................................................................................................................................................7
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SAN2202
3 Other applicable documents and papers
1. Data Sheet SA2531/2 Single Chip Telephone
2. Application Note SAN3020: Power extraction for external loads
4 Revision status
SAN2202 Application Note (this document)
5 General description
The amplifier is a simple, low cost add-on circuit to the SA253x s ingle chip telephone family. It is supplied by the
line current and amplifies the receive signal, taken from either RO1 or RO2 (Receive outputs), see Fig.1.
Compared to more complex “real” handsfree circuits there is no channel switching or anti-larsen circuit
implemented, therefore the receive and transmit gains must be lower to avoid howling.
However, at short distances between user and telephone (<2m , which is adequate for nor mal of fice work ) there is
even full duplex “handsfree” operation possible, when the handset is placed next to the telephone with the
microphone facing to the user.
Due to the excellent sidetone cancellation of the SA253x circuits, howling between handset microphone and
loudspeaker will only occur, when both are put very close to each other. In norm al operation, no howling will oc cur,
even with maximum loudspeaker volume.
Due to the unique structure of the SA253x family’s line adaption, adding the amplifier has no influence on the
important PTT related parameters, like AC-impedance, DC-mask, etc. (see Pt. 5.1 below).
Note: all subsequent component numbering refers to the schemat i c, shown in Pt. 9
5.1 Amplifier supply: Comparison of SAN2202a and SAN2202b:
The following table describes the difference between the two types of amplifier supply: while the simple SAN2202a
supply shows slight influence in maximum sending level and “Make”-resistance in pulse dialing , the SAN2202b (3
extra components) s upply has no influence in these parameters and has a m ore stable maximum output driving
capability at high line currents (see Fig.4 & 5).
Parameter SAN2202a (Shunt path supply) SAN2202b (Power extraction)
AC impedance no influence no influence
off -hook DC mask no influence no influence
Tx-/Rx-gains no influence no influence
“Make”-resistance in pul se dialing
max. sending level
(soft clip level = 4Vpp)
<4Vpp for I
max. 8Ω output power; THD <2%
max. 8Ω output power; THD <3%
number of extra components none 3parts:
<230Ω @ 20mA <160Ω @20mA
no influence for I
>40mA (see.Fig.3)
Line
≈
26mW
≈
32mW
<40mA
Line
no influence ; soft clip level
1 transistor,1diode,1resistor
≈
27mW
≈
34mW
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