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Teilenummer | SAN2202b |
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Beschreibung | SINGLE CHIP SPEAKERPHONE WITH 8 - OHM LOUDSPEAKER AMPLIFIER | |
Hersteller | Sames | |
Logo | ||
Gesamt 9 Seiten sames
SAN2202
APPLICATION NOTE
SINGLE CHIP “SPEAKERPHONE” WITH
8 - OHM LOUDSPEAKER AMPLIFIER
1 Scope
This application note describes a low-cost add-on circuit for driving an 8Ω-Loudspeaker to get a simple loudhearing
(“Speakerphone”) Telephone.
To possible ways of supplying the amplifier are shown:
SAN2202a:
SAN2202b:
Amplifier supply in shunt transistor path
Amplifier supply by power extraction circuit (SAN3020)
It can be added to any SA253x application without interfering with PTT-relevant 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
8 Measurement results & curves
8.1 Frequency response
Fig. 2 shows the frequency
response curve of the loudspeaker
amplifier. The curve shows the
output level on an 8Ω resistor
(solid line) and an 8Ω loudspeaker
(dotted line; PHILIPS AD3371
series 80mm∅ 8Ω speaker)
measured with maximum volume
and
-10dBm Rx level on line. The peak
at 200Hz is a resonant frequency
of the specific loudspeaker type.
Gain of the amplifier is set by the
resistors R6 and the attenuation of
VR1. The bandwidth is adjusted by
CC4.
-12
-13
-14
-15
-16
-17
-18
100
Frequency responseof LS-Amplifier
8 OhmResistor
8 OhmLoudspeaker
1000
f [Hz]
10000
8.2 maximum sending level
Fig.3 shows the maximum
Transmit sending level, measured
at LI vs. line current, assuming a
total harmonic distortion (THD) of
less than 1%.
AN2201a (dotted line): At line
currents >40mA, VPP will rise up to
2.5V (@ 90mA) and sending level
will be slightly distorted before it
reaches the soft clip level (± 2Vpeak
).
AN2202b (solid line):There is no
influence in maximum sending
level, the transmit signal can be up
to the soft clip level at line currents
of >12mA.
Fig. 2:Frequency response of loudspeaker amplifier (PLine=-10dBm)
max. sending level @ THD <1%
4,4
4,2
4
3,8
3,6
3,4
3,2
3 SAN2202a
2,8 SAN2202b
2,6
15 20 25 30 35 40 45 50 55 60
Line current [mA]
Fig. 3: maximum sending level vs. line current (@ THD <1%)
8.3 maximum output power
Fig.4 and Fig.5 show the maximum output power on an 8Ω loudspeaker at f=1kHz: the curves indicate the
maximum output power with <2% and <3% total harmonic distortion.
SAN2202a: The lower output drive capability at higher line currents results from nonlinearities at higher collector
currents and mismatch in the complementary transistor types.
SAN2202b: Maximum output power is not decreased with higher line currents.
6/9 sames
6 Page | ||
Seiten | Gesamt 9 Seiten | |
PDF Download | [ SAN2202b Schematic.PDF ] |
Teilenummer | Beschreibung | Hersteller |
SAN2202 | SINGLE CHIP SPEAKERPHONE WITH 8 - OHM LOUDSPEAKER AMPLIFIER | Sames |
SAN2202a | SINGLE CHIP SPEAKERPHONE WITH 8 - OHM LOUDSPEAKER AMPLIFIER | Sames |
SAN2202b | SINGLE CHIP SPEAKERPHONE WITH 8 - OHM LOUDSPEAKER AMPLIFIER | Sames |
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