Note: Descriptions are shown in the official language in which they were submitted.
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1 The present invention relates especially to
the transistorization of a channel switch for use in
a telephone exchange. r
Most of the attempts which have hitherto
been made to transistorize the channel switch used
in a telephone exchange9 resort to the use of PNPN
switches (referred to as thyristors or SCR). A PNPN
switch has a comparatively small impedance in its
conducting state and a high insulating resistance in
the cut-off state5 and moreover, once it is turned on
even with a small gate signal~ it remains conductive
until the load or main current is interrupted~ that is~
the swi~ch has a self-holding action. Hence~ such a
PNPN swltch is very use~ul 1~ it is used as an elect-
ronic device in the electronic speech path of atelephone exchange. With a telephone exchange, however,
since the ringing (bell signal) is in the form of a
high a.c. voltage, the speech path must permit current
to flow in either9 positive or negative, direction,
and moreover since the current is interrupted usually
by dialing and hooking operationsg th~ channel switch
must be closed even during the operations. Accordingly,
the self-holding action of the PNPN switch cannot be
fully utilized in this sort of applications and in the
past~ dialing and ringing signals has been separately
treated while only a speech signal (small sLgnal) super-
posed upon a d-c- signal has been processed by the PNPN
switch.
It is thPrefore one object of the present
invention to provide a semiconductor channel switch
t
~3~
which can directly treat the speech signal~ dialing
and hooking signals~ and a ringing signal together.
In accordance with the foregoing objects, there
is provided a semiconductor channel switch for connecting two
points between which a communication path is to be established
comprising;
gate control type PNPN switch means comprising a
pair of PNPN switches each having a gate terminal and a self-
holding action and connected in anti-paraliel configuration,
gate current circuit means for operatively providing
a constant current to the gate terminals o~ said pair switches
during its ON state and means for preventing reverse current
flow in tne circuit of said gate term:inals, said gate current
circuit means haviny high impedance and controlled to the ON
or OFF state;
memory circuit means connected to said gate current
circuit means and controlled to a set or reset state for main-
taining said gate current circuit means in the ON or OFF state
in accordance with its set or reset state, respectively; and
selecti~g circuit means for setting and resetting
said memory circuit.
Other objects, features and advantages of
the present invention will be apparent when one reads
the following description of the preferred embodiments
in conjunction with the accompanying drawings~ in which:
Fig. 1 shows the structure of a basic unit
of a first embodiment Or the present invention;
Fig. 2 shows t~e structure of a basic unit
Or a second embodiment o~ the present invention; and
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Fig. 3 shows a structure of a 2 x 2 balanced
type switch fabricated according to the present inven-
- tion.
In Fig. 1 showing a basic structure Or a
semiconductor channel switch as one embodiment of the
present invention, a gate control type bidirectional
PNPN switch 1 has its main terminals Tl and T2 connected
respectively with speech paths Xi and Yj and is disposed
at a cross point of a row and a column of a channel
matrix as well as each of the other PNPN switches (not
shown) is disposed at each cross point thereo~. The
gate terminal G o~ the switch 1 is connected through
a diode 2 for preventi~g reverse current ~'low with a
gate current clrcuit 3 having a high impedance with
¦ respect to alternating current. The diode 2 may be
omitted if the gate current circuit itself 3 is pro~ided
with a means to block the reverse current. The gate
current circuit 3 is controlled by a memory ~, which
is set and reset by a cross-point selecting circuit 5.
In the embodiment shown in Fig. 1~ the memory 4 is
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l a flip-flop and the cross-point seIecting circuit 5
is a circuit which can set or reset the memory 4 in
accordance with the logical product of the signals on
select channels xi and y; or xi and yj~ When pulse
signals appear simulta~eously on the select channels
Xi and yj~ the memory 4 is set so that the gate current
circuit 3 starts continuously delivering a gating current
to turn on the switch l. If the memory ~ is reset
according to the logical product of the signals on
; lO the select channels xi and y;~ the gate current circuit
3 stops supplying the gating currentO Howe~er~ the
I switch l must be opened by another artl~ice ~ince it
ha~ a self-holding action as descrlbed above. In most
practical cases~ the speech current is interrupted by
the hook switch of a telephone unit upon completion
of conversation, and no special control is needed.
The unit structures as described above, one of which
is shown in Fig. l, are combined in the form of an
m ~ n matrix with each pa1r of incoming and outgoing
speech paths wired in the form of a balanced circuit.
The respective elements of the structure
shown in Flg. 1 will now be described in further detail.
m e gate controlled type bidirectional PNPN
¦ switch refers to one which has a control gate terminal
¦ 25 and permits the bidirectional flows of current and a
switch called "triac" is a typical example thereof.
The same function can also be obtained by a pair of
ordinary PNPN switches connected in antiparallel
configuration. The exclusive use of the PNPN switch
is due to the fact that it has an advantage of low
~38()6~3
1 conduction impedance and high insulating resistance
as mentioned above 9 that it has a much better charac-
teristic superior to a transistor or other elements
since it has a high breakdown voltage against current
1 5 in either direction when it is used in the circuit of
f the present invention in which alternating current as
well-as direct current is treated~ and that its self- ;
holding action can be utilized~ as described later~
for a certain distribution of potentials on the speech
10 channels.
, ,' The reason why a memory means such as memory
1 4 is provided while the switch is provided wikh a self~
, hoIding action~ i9 that the gate current circult 3
, is to be aIways at operation so as to immediately
, 15 supply current for speech paths without receiving pulses
again from the select channel when the speech paths
, are restored even in case where the switch 1 is turned
off since the channel,current temporarily becomes zero
¦ due to hooking or dlaling or due to the instantaneous
~' 20 disappearance of current as in an alternating current.
The purpose of the.gate current circuit 3
~ having a high impedance is to prevent the speech signal
3 from leaking out through the gate G or into another
t circuit during conversation for which the circuit 3
l 25 is at a operation and the amplitude or variation of
-,l the value of the gating current causes no problem if
it is large enough to actuate the switch. In general~
~, a simply designed constant-current circuit will suffice
for the purpose.
The cross-point selectlng circuit 5 may be
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1 so designed as to be set and reset by another selecting
. circuit9 as in the embodiment shown in Fig. 1, or as
to be automatically reset when any other cross-point
is selected, depending upon the purposes of channel ~ r
switchesO The gate current circuit 3 and the memory
.4 are provided for each cross-point while a part of
the cross point selecting circuit 5 may be commonly
used for a matrix of the speech pathsO
In a circuit using the commercial a.c. supply~
1 10 a pulsating gating current in synchronism with the
I alternating current may be usually suppl~ed for the
A~ ~
bidirectional PNPN switch. Howe~er~ since the bell
signal or the dialing and hooking signals are usually
asynchronous with the alternating current or take place
. 15 unexpectedly~ the control circuit which performs the
pulse control by continuously supervising these signals
must be necessarily provided in a complicated circuit
configuration and therefore not effective.
When the memory 4 is set and the PNPN switch
1 becomes conductive, the potentials at the channels
Xi and Yj sometimes exceed the upper limit voltage
obtainable by the gate current circuit 3. This condi
tion will occur if the terminals Xi and Yj are connected
respectively with a high positive voltage source and.
a load resistance. In this case, the conduction between
.I the terminals Xi and Yj is maintained onl~ through the
self-holding action of the switch 1 and the gating current
is substantially zero although the gate current circuit
3 is at operation and in a limiting case the reverse
current would flow without the diode 2. However, it is
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~03130~B
1 possible for the gate current to flow i~ediately if
the PNPN switch 1 is turned off for some cause or other.
Therefore~ in this specification, the meaning of "to
cause the gating current to flow continuously" involves
the state where the circuit 3 is operating ko supply
the gating current though the gating current cannot
flow actually.
. Fig. 2 shows the structure of a basic unit
o~ a semiconductor channel switch as a second embodi-
o ment of the present invention~ the basic unlt beingassociated ~ith a cross-point of the channel swltch,
1 as described with F~g. 1. In Fig. 2~ ordlnary PNPN
: switches 11 and 12, each ha~ing a gate control terminal~
are connected in antiparallel configuration w th each
: 15 other to form a bidirectional PNPN switch. Diodes 21
and 22 are connected with the respective gate terminals
of the PNPN switches 11 and 12 to pre~ent the reverse
currentO A gate current circuit 3 shown here is the
same as that shown in Fig~ 1 but the memory 4 and the
cross point selecting circuit 5 are replaced by a
set-preference flip-flop 6. With this structure, when
pulse signals appear simultaneously on the select channels
Xi and yj~ the set-preference flip-flop 6 is set so
. that the gate current circuit 3 starts delivering
continuous gating current to turn on the switches 11
and 12. When a pulse signal again appears on the
select channel y~ for the selection of another cross-
point, the set-preference flip-flop 6 is reset. This
circuit configuration shown in Fig. 2 needs no select
channel for reset tcorresponding to the channel xi in
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1 Figo 1) and therefore has an advantage that the number
of the select channels is comparatively small for its
capacity9 so that the structure is very useful for use
in a semiconductor channel switch of an electronic. '
telephone exchange. These unit structures, one of
which is shown in Fig. 2~ are combined in the form of
an m x n matrix with each pair of an incoming and
an outgoing speech paths in the form of a balanced
circuit~ ~
~` 10 Fig. 3 shows a case where the unit s-tructures
, according to the present invention are wired in the
I form o~ a balanced t~pe 2 x 2 matrix. In Fig. 3~ the
cross-point selecting circuit etc. are omitted for the
simplicity of the figureO As shown in Fig. 3~ the
channel switch is usually constructed in the form of
:
an m x n matrix ~ith each pair of an incoming and an
outgoing paths (line A and line B) wired in a balanced
circuitO In this case9 a memory M has to be provided
~or each cross-point but since the potentials at the
lines A and B are different from each other, two separate
gate current circuits must be provided respectively
for the line~ A and B.
As described above9 the semiconductor channel
switch according to the present invention can treat~
in the same manner as the conventional mechanical
channel switch does~ the ringing~ dialing and hooking
signals together with the speech signal.
Moreover, in the above embodiments, it ls
assumed that the PNPN switch is turned on by feeding
current into the gate, but if it is desired to turn on
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1 the switch by drawing current from the gate, it is
only necessary to invert the senses of the gate current
circuit and the associated diodes. Further, each of
such elements need not be in the form of an integraliy
rabricated part but has only to be composed of dis
crete parts connected with one another by wires.
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