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Патент USA US3068335

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Dec. 11, 1962
Filed June 10, 1957
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@iiit?ti grates Fatent flice
Rudolf Streit, Solothurn, Switzerland, assignor to Auto
phon Aktiengeseilschaft, Soiothurn, Switzerland
Filed Jane 10, 1957, Ser. No. 664,813
Claims priority, application Switzerland June 19, 1956
7 Claims. ((31. 179-81)
Patented ‘Dec. 11, 1962
customary carbon microphone, the station includes a
magnetic microphone and a transistor ampli?er corre
lated therewith.
Referring now to the drawing, the resistances are de
5 noted with R, the condensers with C and the transistors
with T. The station is connected with the exchange by
the line L, the exchange placing a direct voltage on the
line in a manner well known in the art. In view of the
of the transistors, the polarity must correspond This invention relates to telephony, and more particu 10 presence
to that shown in the drawing. In the state of rest of the
larly to telephone sub-stations including transistors.
station when, as shown in the drawing, the cradle switches
The use of transistors has rendered it possible to pro
GK are open, only the bell G1, which may be supple
vide telephone sub-stations including one or several built
mented if desired by a second hell (not shown in the
in ampli?ers which are supplied with direct current via
drawing) connected to the terminals WK, and a con
the subscriber’s line. These ampli?ers, preferably, serve 15 denser C1 are connected with the line. If the station is
for microphone amplifying purposes and permit the use
to be called, the exchange passes alternating current on
of microphones, the performance of which is superior to
the line in a well known manner so as to actuate the
that of carbon microphones, but which are at the same
hell or bells. When thereupon the receiver is removed
time materially less sensitive. In audio frequency se
and consequently, the cradle switches GK are closed, a
lector systems, the ampli?ers may be used to generate 20
direct current passes from the plus-pole through the re
sistance R9 and windings W2 and W1 of the differential
problems by one and the same expedient.
transformer U to the minus-pole of the line. The mode
A telephone sub-station incorporating a system of this
of function of the differential transformer is su?’iciently
kind is distinguished by the characteristic that the same
well known that it requires no detailed description. Inso
audio frequencies, thus permitting solutions of several
line which serves as a current supply for the ampli?ers, 25
far as the balancing network, consisting of the elements
R? and C6 which are connected in parallel to one an
serves also for delivering the ampli?ed signal. If the
supplies of the voltage dividers generating ?xed bias
voltages, and of the transistors-except those the output
signal of which is passed on the line-were branched di
rectly 01f the line, such powerful positive or negative
feedback would result that the system would be inopera
tive. The supplies referred to, therefore, must be ef
fected through a ?lter section formed by at least one
resistance or an inductance coil and a condenser. If,
for this purpose, a resistance is selected which because
of the voltage drop caused thereby, must not- exceed a
certain size, a comparatively large condenser is required,
which is undesirable on the basis of space and cost con
other, with due consideration of the turn’s ratio of
windings W1 and W2, corresponds to the impedance of
the line, the winding W3 of the differential transformer
and consequently the receiver H remain, with respect to
voltages which are applied between the tap of the trans
former and the plus-pole of the line, without current.
The dial or number plate comprises the well known
impulse contact 1' and the short-circuit contacts k. When
the dial is wound up, at ?rst a k-contact short-circuits
the receiver in order to avoid clicking noises. There
after, the second k-contact bridges in a well known man
ner, the entire circuit of the station, in order to prevent
siderations. When an inductance coil is used especially
the bell from ringing during the dialing procedure, and
for this purpose, the condenser required may be smaller 40 to lower the resistance of the station to a minimum.
but the inductance coil itself gives rise to additional cost
The i-contact opens the line impulsively.
and space requirements so the same reasons which mili
The microphone ampli?er comprises a preliminary
tate against the use of a resistance, apply also in the
containing the transistor T1, and a terminal stage
case of the inductance coil.
containing the transistor T2. Apart from the supply of
It is an object of the present invention to avoid these
the collector of the transistor T2, all supplies for the
drawbacks, and to provide a telephone sub-station with
ampli?er are taken off between the bell G1 and the bell
transistors distinguished by a simpli?ed design and a re
duced cost.
Other objects, and the manner in which the same are
attained, will become apparent as this speci?cation
The invention contemplates the use, for the ?ltering
condenser C1 connected in series therewith. If a second
bell is connected to the terminals WK, it is short-circuited
by the cradle switch so the resistance conditions are not
in?uenced by such an additional bell. For this supply,
the bell, together with the condenser C1, constitutes a
low-path ?lter which ?lters the voice current from the
purposes referred to above, of the bell and the correlated
supply of the ampli?er. The resistance R1 forms, to
condenser which anyhow form part of the telephone sub~
with the bell, a voltage divider which reduces the
station. The telephone sub-station includes transistors 55 gether
voltage passed to the ampli?er to a suitable value.
supplied via the subscriber’s line, and includes further an
The operation of the ampli?er is as follows: the micro
alternating current bell connected in series with a con
phone M passes the voice voltage via the condenser ‘C2
denser. The control electrodes of the transistors are
to the base of the transistor T1. This base receives from
biased by means of voltage dividers. The station is dis
resistances R2 and R3 connected as voltage dividers,
tinguished in that the supply for these voltage dividers 60 a negative
bias relative to the plus-pole of the subscriber’s
and those of the transistors, the output signal of which
line and consequently the emitter. Owing to the ampli~
does not pass on the line, is fed from a point located
fying action of the transistor, a current ampli?ed relative
between the bell and the condenser connected in series
to the microphone current passes through the emitter
In the drawing attached to this speci?cation and form 65 and collector. The resistance R5 which is uncoupled for
alternating current by the condenser C4 and which is
ing part thereof, one embodiment of the invention is
in series with the emitter, exerts, by inverse.
illustrated diagrammatically by way of example.
feedback, a stabilizing effect in that the current passing
‘In the drawing, the sole FIGURE is a wiring diagram
through it reduces the voltage between the emitter and
of a telephone sub-station according to the invention.
base, which in turn effects a reduction of the releas
The telephone sub-station illustrated in the drawing 70 ing current.
On the resistance R4, an ampli?ed voltage
includes a bridge circuit containing a diiferential trans
is generated which is passed through the condenser C3
former, a dial and cradle switches. In the place of the
to the terminal stage. This terminal stage which contains
the transistor T2, is similarly‘ constructed as the prelim
inary stage in that the voltage divider consisting of R6
and R7 generates the bias for the base, and the resistance
R8, bridged by the condenser C5, stabilizes the current.
The output of the ampli?er is formed by the emitter and
ter elements for supplying direct current potential from
the lines to said supply circuit.
2. The combination according to claim 1 wherein said
supply circuit includes a collector electrode connected to
the junction of said inductive bell and said ?lter capaci
tor and further includes an emitter connected to one of
collector of the transistor T2 of the terminal stage. This
said lines.
ampli?er output is connected between the tap of the dif
3. A combination according to claim l wherein is
ferential‘ transformer U and the plus-pole of the line and
a resistive voltage divider connected’ in shunt to
thus, takes the place of the carbon microphone in con
said capacitor, said transistor ampli?er including a tran
ventional circuits. The supply of the collector of the
sistor having an emitter, a base and a collector, means
terminal stage‘ is effected through the winding W1 of the
connecting said collector to one side of said capacitor,
differential transformer. Inasmuch as the alternating
means connecting said base to an intermediate voltage
voltage‘ generated at the output of the terminal stage
point of said voltage divider, means connecting said emit
must be passed on the line‘ and therefore, anyhow cor
the other side of said capacitor.
responds to this" voltage, in this case a ?ltering is unneces 15 The
combination accordingto claim 3 wherein is
sary, whereas for the reasons explained above, the supply
further provided a microphone coupled between said
voltage for the remaining elements must not contain the
base and‘ said emitter.
alternating voltage of the line.
5. The combination accordingv to claim 11 wherein is
The invention is' not limited3 to subscr'ibe'rsf sub-sta
a two stage cascaded transistor ampli?er, a
tions equipped with microphone‘ ampli?ers. The inven
?rst stage: of said ampli?er including a’ ?rst transistor
tion is: also susceptible of use in‘ stations wherein the
having a‘- ?rst emitter, base and collector, a second stage
ampli?er incorporated therein, is’v usedE as an audio fre
of said ampli?er’ having a second emitter, base and col‘
quency‘ generator, for‘ audio frequency selection, or al
lector, means connecting said ?rst and second emitters
ternatingl'y' as' a microphone ampli?er and an‘ audio fre
to‘ one terminal‘ of said capacitor, a1 ?rst resistive voltage
quency‘ generator. The invention is also applicable to
divider connected‘ across said capacitor, a second‘ resistive
stations‘ including‘ two‘ ampli?ers-1 where the supply of all
circuit: elements the output signal of which is not passed
voltage divider connected across said1 capacitor, means
connecting the‘ collector of the ?rst stage transistor to
on the line, takes place from a‘ point located’ between
the‘s'econd terminal of- said capacitor, means connecting
the bell' and the" correlated‘ hell‘ condenser. Stations in‘
said ?rst base to' an intermediate point of said ?rst volt'-'
cluding“ t'wo- ampli?ers lend'themselves' for use in‘ select‘ 30 age divider,‘ means connecting said second‘ base to' an in‘
ing systems involvingthe simultaneous emission of two
termediate point of said voltage‘ divider, a‘ capacitive
audio'freque'nc'ies, as well5 asfor use in telephone systems
coupling network coupling said ?rst collector‘ to said
wherein speech‘ in- the two directions‘ is transmitted on
second‘base, an output load‘ for said second collector con‘
different? frequency bands through the subscriber’s line,
nected‘ between‘ said second collector and one of said
where ampli?ers must be resorted to for speech in both
directions. on the‘ other hand, the invention is also
6. The combination according to claim! 5- wherein is
applicable to’ subscribers" stations which contain but a
provided’ a- balanced transformer having a'?rst and asse
single transistor wherein, possibly, only the voltage‘ di
ond primary winding connected’ in series across‘said line,
vider' for‘gencrating' the‘ bias for thc‘base' is supplied via
and a direct connection from said second collector to the
junction’ of said ?rst and second primary windings.
I~ wish. it to be understood that I do not intend to be
7. in a-telephone substation, a pair‘ of incoming sig
limited to the details’ of construction, design and opera
nal lines having a predetermined‘ direct‘ voltage‘ dif
tion shown and: described as numerous modi?cations
ference therebetween, a ringing. circuit connected across
within the scope of the following claims and involving
said pair of lines, said‘ ringing circuit including an in
no departure from the spirit’ of the invention nor any
ductive bell and a ?lter capacitor in series, a transistor
sacri?ce of the advantages thereof, are likely to occur to
having electrodes, and means connecting said electrodes
workers in this ?eld.
to said lines only across said capacitor, whereby said
inductive bell and said ?lter capacitor also serve as a
1. In a telephone substation, a ?rst line, a secondline, 50 voltage supply ?lter for supplying the direct voltagefrom
a ringer circuitlconnectedbetween said ?rst line and said
the lines to‘ said electrodes.
second line, said ringer circuit including an inductive
References Cited inthe ?l'e of this patent
bell and a?lter capacitor. in series, a transistor ampli?er
including‘ atleast one transistor, said transistor ampli?er
includingan output circuit connected between, said lines, 55 2,277,623
Allen __~_____~_______ __ Mar. 24; 1942
said transistor- ampli?er including a direct current power
Patry et ah ____ __-____'__ Mar. '28, 1950
supply circuit, andmeansfor connecting the power sup
Jones ____________ ______ Oct. 28, 1958
ply' circuit of said' transistor ampli?er to said ?rst and
Cerofolini _______ __-___.__ May 5, 1959
second: lines only'by connections in shunt with said ca
pacitor; the inductance of said-inductive‘ bell and capaci
Great Britain ______ __,_____ I an. 4, 195-6
tance of: said capacitor also providing direct current ?l
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