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参数资料
| 型号： | PBL38813 |
| 厂商： | ERICSSON |
| 英文描述： | Voice-switched Speakerphone Circuit with built in loudspeaker amplifier |
| 中文描述： | 语音交换与内置免提扬声器放大器电路 |
| 文件页数： | 14/16页 |
| 文件大小： | 299K |
| 代理商： | PBL38813 |
14
PBL 388 13
To design the speech control function,
seven different signal paths have to be
considered and understood. See fig. 28.
The signal paths:
G1
is the acoustic signal into the
microphone, further transformed to an
electrical signal in an amplifier which gain
can be controlled 12,5 dB up or down from
an idle point, further to a point where it is
rectified to a negative signal and compared
with its counterpart from the receiver
channel.
G2
is the corresponding signal to G1
on the receiver side. The signal from the
line that goes via the sidetone balancing
network and an amplifier which gain can be
controlled 12,5 dB up or down from an idle
point, further to a point where its rectified to
a positive signal and compared with its
counterpart from the transmitter channel.
G3
starts the same as G1 but does not
go to the rectifier, instead passes through
further an amplifier which gain can be
controlled 12,5 dB up or down from an idle
point, further to the transmitter of the speech
circuit and out on the telephone line.
G4
is the corresponding signal to G3
on the receiver side. Starts the same as G2
but does not go to the rectifier, instead
passes through further an amplifier which
gain can be controlled 12,5 dB up or down
from an idle point, via loudspeaker volume
control, loudspeaker amplifier and out as
an acoustic signal of the loudspeaker.
G5
starts the same way as G4 ends.
From the receiver rectifier through
loudspeaker amplifier, loudspeaker,
acoustic signal path (loudspeaker -
microphone) and is terminated, like G1, at
transmitter rectifier.
G6
is the corresponding signal to G5
but goes through the sidetone network.
Starts the same way as G3 ends. From the
transmitter rectifier, amplifier via speech
circuit transmitter, sidetone balancing
network and the line, to be terminated at
receiver rectifier like G2.
G7
is the closed loop signal that can
be considered to start or end at any point in
the loop. The summ of G5 and G6.
Hints how to design a handsfree telephone with PBL 388 13.
Figure 28. Schematic
diagram of the various
signal paths that affect on
the design of a handsfree
telephone.
General:
The first thing that comes into ones
mind when looking at a ”handsfree”
telephone solution like the one with PBL
388 13 is, that it must be able to prevent
oscillation in the closed loop G7. The circuit
does this by having 50 dB less gain in the
opposite direction against the open channel
this being either the receiving or transmit-
ting direction. Nor does it oscillate when
having proper gain values, sidetone
balance, loudspeaker volume and small
acoustic coupling between the loudspeaker
and microphone. Actually, one needs a lot
of margin against oscillation so that no
positive feedback is created in the loop G7.
This would destroy the frequency
characteristic through the increasing gain
at the "would oscillate frequency" in case
of somewhat higher gain in the loop. The
speech would sound harsh. This is normally
not the most difficult requirement on the
gain in the G7 loop. The most difficult
requirement is set by the telephone set
impedance towards the line. The signal
originates from the line, rounds the loop G7
and enters the line again. This way the
impedance of the telephone set towards
the line is influenced by the gain in the loop
G7. The impedance of the telephone
towards the line has to measured in the
”handsfree” mode under correct acoustic
circumstances and at maximum
loudspeaker volume.
A major problem in many cases is
the acoustical coupling between
loudspeaker and microphone.The
telephone designer gets often an order to fit
a ”handsfree” telephone system into a fully
unsuitable ready made casing. The design
of a ”hansfree” telephone with a speech
control starts with the acoustical design of
the casing. PBL 388 13 makes a good
acoustical design to sound as close a perfect
”handsfree” telephone as it is possible.
This means that there are no audible
swiching noises and speech is conveyed in
one direction at the time. In opposite case
having a bad acoustic design with a large
coupling between the loudspeaker and the
microphone, no electronics in the world,
using the speech switching principle, can
make it to sound good. Why, will be studied
later.
Acoustic design:
Any amount of time can be spent on
the acoustic design. It depends largely if
the task is to make a "just working
COMPARATOR
SPEECH
CIRCUIT
VOLUME
SIDETONE
BALANCE
Line
acoustical
coupling
G
1
G
6
G
7
G
2
G
3
G
4
G
5
Receiver channel
Transmitter channel
相关PDF资料 |
PDF描述 |
|---|---|
| PBL388131N | Voice-switched Speakerphone Circuit with built in loudspeaker amplifier |
| PBL388131SO | Voice-switched Speakerphone Circuit with built in loudspeaker amplifier |
| PBL38814 | Voice - switched 2-channel Circuit with loudspeaker amplifier |
| PBL388141N | Voice - switched 2-channel Circuit with loudspeaker amplifier |
| PBL388141SO | Voice - switched 2-channel Circuit with loudspeaker amplifier |
相关代理商/技术参数 |
参数描述 |
|---|---|
| PBL388131N | 制造商:ERICSSON 制造商全称:Ericsson 功能描述:Voice-switched Speakerphone Circuit with built in loudspeaker amplifier |
| PBL388131SO | 制造商:ERICSSON 制造商全称:Ericsson 功能描述:Voice-switched Speakerphone Circuit with built in loudspeaker amplifier |
| PBL388131SOT | 制造商:ERICSSON 制造商全称:Ericsson 功能描述:Voice-switched Speakerphone Circuit with built in loudspeaker amplifier |
| PBL38814 | 制造商:ERICSSON 制造商全称:Ericsson 功能描述:Voice - switched 2-channel Circuit with loudspeaker amplifier |
| PBL388141N | 制造商:ERICSSON 制造商全称:Ericsson 功能描述:Voice - switched 2-channel Circuit with loudspeaker amplifier |
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