Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1~L54:~L()3
1.
Technical Field
This invention relates to control circuitry for
use with gated diode switches.
sackground Art
Gated diode switches (GDSs) have an ON
(conducting) state and an OFF (blocklng) state. These
switches are capable of blocking relatively large
potential differences in the OFF state. The OFF state
occurs when the potential of the gate is held more
positive than that of both the anode and the cathode.
The magnitude of the needed potential of the gate relative
to the anode and cathode to turn oef a GDS is a function
of the geometry and doping levels of the semiconductor
regions of the GDS. Conduction between anode and cathode
is cut off (interrupted) because carriers from the cathode
are diverted out of the gate and carriers from the anode
are repelled before they can reach the cathode. The
control circuitry used to apply a blocking voltage to the
gate must be able to sustain a more positive voltage than
is at the anode and cathode and must be able to supply
current which is at least of the same magnitude as flows
through the switch itself.
GDSs of the type referred to above are relatively
new in the art and, accordingly, there is little published
information describing the control circuitry utilized
therewith.
It is desirable to have solid-state control
circuitry for use with GDSs which can be fabricated on the
same substrate as the switches which are to be controlled.
Summar~_of the Invention
In accordance with an aspect of the invention
there is provided circuitry for use with a first gated
diode switch of the type comprising a semiconductor body a
bulk portion of which is of a relatively high resistivity,
a first region of a first conductivity type and of a
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relatively low resistivity, a second region of a second
conductivity type opposite that of the first cond~ctivity
type, the first and second regions being connected to
output terminals of the switching device, a gate region of
the second conductivity type, the first, second and gate
regions being mutually separated by portions of the
semiconductor body bulk portion, the parameters of the
device being such that, with a first voltage applied to
the gate region, a depletion region is formed in the semi-
conductor body which substantially prevents current flowbetween the first and second regions, and that, with a
second voltage applied to the gate region and with
appropriate voltages applied to the first and second
regions, a relatively low resistance current path is
15 established between the first and second regions by dual
carrier injection characterized by a second gated diode
switch of the same type as said first gated diode switch,
an output terminal of the second gated diode switch being
coupled to the gate of the first gated diode switch; and a
20 voltage control branch circuit coupled to the second gated
diode switch for controlling conduction between the first
and second regions thereof.
A solution to the proble~ of controlling the
state of a first gated diode switch (GDSl) in accordance
25 with the present invention is circuitry characterized in
that it comprises a second gated diode switch (GDS2)
coupled by the cathode thereof to the gate of GDSl and a
voltage control branch circuit coupled to GDS2 for
controlling conduction between the anode and cathode
30 thereof.
The state of GDS2 is controlled essentially by
the voltage control branch circuit which selectively
adjusts the gate-anode voltage. A relatively low voltage
pulse triggers the voltage control circuit. The voltage
35 control circuit has high voltage capability but only
modest current supply capability. Thus, any steady-state
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current flowing through GDS2 must be of only a modest
value for the voltage control circuit to be capable of
switching GDS2 ~rom the ON to the OFF state.
With GDS2 in the OFF state the potential of the
gate of GDSl is at a level that is no more positive than
that of the anode and cathode thereof and, accordingly,
GDSl is in the ON state and conduction between the anode
and cathode thereof can
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occur. To switch GDSl to the OFF state requires that
` the potential of the gate thereof be increased to a
'~ value more positive than that of the anode and cathode
i.~ and that electrons, at least of the order of magni-
~s 5 tude as flows between ca~hode and anode thereof, be
collected at the ga~e and then pulled out of the
~' gate. Considered from a circuit design view, the
pulling out of electrons from the gate of GDSl is
the equivalent of the driving ~sourcing) of positiye
charge ~current) into the gate of GDSl. The anode
;~ of GDS2 is coupled to a potential sowrce which is
selected to be more positive than the potential at
' the anode of GDSl. ~hen GDS2 is in the ON state
the potential at the gate of GDSl ~also the cathode
of GDS2) is more positive than that at the anode
' of GDSl, and GDS2 is capable of supplying sufficient
' positive current such'that GDSl is switched to or
maintained in an OFF state.
These and other features of the invention
are better understood from a consideration of the
- following detailed description taken in conjunction
with the accompan~ing drawings.
~Brie Description of the Dr'aw'i'ngs
FIG. 1 illustrates a switch with an
' 25 embodiment of control circuitry in accordance with
the invention;
FIG. 2 illustrates a bidirectional switch
which also can be controlled by the control circuit
of FIG. l; and
~' 30 FIG. 3 illustrates a switch with another
~` embodiment o control circuitry in accordance with
~' the present invention.
Detailed Description
. Referring now to the FIG. 1, there is
~ 35 illustrated control circuitry 10 ~illustrated within
:' the larg0r dashed line rectangle) which is coupled
to a gated diode switch GDSl having anode, rathode,
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and gate terminals.
. Control circuitry 10 comprises a gated
diode switch GDS2 having anode, cathode, and
gate terminals, first and second current limiters
5 CLl and CL2, an n-p-n transistor Ql, p-n diodes
Dl, D2, and D3, resistors Rl, R2, and R3, and
capacitor Cl. Ql may be denoted as a switching
- device. The base may be denoted as a control
terminal and the collector and emittter which may
be denoted as first and second output terminals.
The anodes of Dl and D3 and a first terminal of CLl
-~ are all coupled to a terminal 12. The collector of
~ Ql is coupled to the cathode of D3 and to a
: terminal 11. The cathode o~ Dl is coupled to the gate
: 15 of GDS2 and to a terminal 20. The base of Ql is
coupled to an input terminal 16 through diode D2.
The emitter of Ql is coupled to one terminal of Rl
and to a terminal 17. A second terminal o Rl is
coupled to a terminal 18 and to power supply VSS.
A second terminal of CLl is coupled`to power supply
~Vl and to a terminal 14. CL2 is coupled by a first
terminal to the cathode of GDS2~ the gate of GDSl,
and to a terminal 22. CL2 is coupled by a second
terminal to power supply -V3 and to a terminal 28.
A third current limiter CL3 is coupled by a first
,~ terminal thereof to terminal 20 and by a second
terminal thereof to a power supply -V4 and to a
terminal 26. CL3 and -V4 are both optional. -V4
.;} can be the same as VSS or -V3 in potential.
The anode of GDS2 is coupled to one terminal
of R3 and to a terminal 21. A second terminal of R3
is coupled to a first termi.nal of R2 and to a terminal
23 and to a first terminal of Cl. A second terminal
of R2 is coupled to power supply ~V2 and to a
terminal 24. A second terminal of Cl is coupled to
terminal 18. ~Vl is selected to be more positive in
potential than ~V2.
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The combination of Dl, D2, D3, Ql, CLl, Rl,
and CL3 Cillustrated within dashed line rectangle A)
serves as a voltage control branch circuit and is
adapted to set the potential of the terminal 20 Cthe
gate terminal of GDS2) so as to control the state of
GDS2. Cl and R3 are optional. Without Cl and R3,
terminals 21 and 23 would be directly connected together.
Cl serves as a limited source of charge which is used
to aid in the switching of GDSl to the OPF state.
` 10 ~ithout Cl it is necessary to have greater steady-state
current flow through GDS2 when it is in the ON state
~i in order to inswre that there is sufficlent available
current that can be supplied to the gate of GDSl to
turn GDSl off.
. 15 The basic operation is as follows: Assuming
the anode and cathode terminals of GDSl are coupled to
+220 volts and -220 -,rolts, respectively, conduction
can occur between the anode and cathode thereo~ if the
gate Cterminal 22~ is less positive than +220 volts.
Conduction is cut off Cinterrupted~ by increasing the
potential of the gate Cterminal 22~ above +220 volts
and by providing a source of positive current which
10ws into the gate Cterminal 22) of GDSl. With ~Vl =
+280 volts, VSS = ~ero volts, ~V2 = ~250 volts, -V3 =
. 25 -250 volts, -V4 - -250 volts and current limiters CLl,
CL2, and CL3 limiting current therethrough to 50, 5,
and 5 microamperes, respectively, circuitry lO is
' capable of providing the needed potentials at terminal
22 and the source of current into term,inal 22 necessary
30 to control the state of GDSl.
Assuming first that it is desired to allow
;~3 conduction through GDSl, an input signal having a
?." potential level between O and 0.4 volts ls applied to
;, terminal 1,~,. This biases Ql off and allows terminal 12
35 to assume a potential of approximately +Vl ~approxi-
' mately +280 volts). Without CL3 present, Dl conducts
`,~ in the forward direction until terminal 20 reaches within
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several tenths of a volt of thc potential of terminal
12 and then ceases to conduct. With CL3 present there
is a flow of current fro~ ~Vl through CLl, Dl, CL3
and into -V4. CLl and CL3 are selected such that the
5 voltage appearing at terminal 20, with Ql biased off,
is at a level which is significantly more positive
than that of ~V2. Por thls case, terminal 20 likewise
assumes a potential of close to ~280 volts. This
;~ condition biases GDS2 to the OFF state and thus isolates
terminal 22 from potential ~V2. Terminal 22 there-
fore follows the negative potential -V3 ~-250 volts~
S until the gate-to-anode junction of GDSl becomes forward-
~, biased. Terminal 22 no~ remains at a potential close
;i to but not greater than the po~ential of the anode of
, 15 GDSl. Accordingly, GDSl is biased to the ON state and
~, conduction occurs between the anode and cathode thereof.
', The current flowing ro~ the anode to gate of GDSl is
limited by CL2 to an insignificant fraction o the
anode-to-cathode current through GDSl.
~ 20 If GDS2 had been in the ON state prior to the
.~$ application o the 0-0.4 volt input level to terminal
S~'! . 16, then positive current flows from ~Vl, through Dl,
and into the gate of GDS2. CLl is selected to allow
,~ a greater current flow therethrough than through CL2
~, 25 to insure that sufficient positive current is available
. to flow into the gate of GDS2 so as to cut off conduction
~i between the anode and cathode thereof. Only a relatively
~ modest amount o positive current must flow into the
,~' gate of GDS2 to cut off conduction therethrough since
the conduction through GDS2 is only 5 microamperes. It
is thus not necessary to use a high current device to
` provide the needed current sourcing unction necessary
to cause GDS2 to assume the OPF state.
` The potential of terminal 16 is raised to a
' 35 level of 2-5 volts to cause GDSl to switch to the OFF
!,'' (blocking) state. This input voltage level biases Ql
ON and allows Ql to operate in saturation. The potential
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o terminal 12 is pulled down to approximately ~1.6 volts
~assuming an input ~oltage at terminal 16 o 2 volts, a
VCF.~SAT) o~ 0.3 volts for Ql and a voltage drop across
D3 of 0.7 yolts). The potential of terminal 12 at this
time is a function of the input voltage level, the
VC~CSAT) of Ql and the forward voltage drop across D3.
~ithout CL3 present, terminal 20 is pulled to a value
close to that of ~V2 or to a more negative potential
because of leakage through Dl. The potential of terminal
2Q cannot drop below one diode voltage drop below the
potential of the anode of GDS2 because a junction diode
comprising the anode and gate of GDS2 beco~es ~orward-
biased and pulls up the pokential of terminal 2U. ~ith
i CL3 present, terminal 20 is rapidly and actively held
at a value close to one diode drop below the potential
of the anode of GDS2. In either case, this suitches
GDS2 to the ON state.~ This causes the potential of
;, terminal 22 to be at ~V2 minus the voltage drop across
R3 and R2 and minus the orward voltage drop across the
anode-cathode of GDS2. The voltage drops across R2, R3,
and GDS2 are selected such that the potential o$
terminal 22 is more positive than ~hat o the anode o$
GDSl by a suf~icient amount to switch GDSl to the OFF
(blocking) state. In addition, there is a sufficient -
positive current flow inko the gate of GDSl to switch
it to the OFF state. Once GDSl is switched of the
; current 10w into the gate thereof ceases. The geometry
and impurity concentrations of GDSl determine exactly
how much more o a positive potential must exist at
the gate relati~e to the anode and cathode to turn
-~l GDSl of$.
-; Minority carriers emitted at the cathode o
GDSl and collected by the gate constitute the equivalent
of positive current flow ro~ ~V2 through R2, R3,
~`~ 35 GDS2, and into the gate of GDSl. This current 10w can
}i be substantial and as a result it is necessary to have
~`'! a high voltage and current device such as GDS2 to
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switch GDSl to the OFF state. The high cost of a high
~; voltage and high current transistor limits its appli-
cation in this control circuit.
R2 and R3 limit current flow from +V2 ~hrough
~`~ 5 GDS2, and into the gate of GDSl. In addition, R3
limits current flow from Cl. This helps insure
against the burn out of GDSl and/or GDS2. In many
telephone switching applications GDSl operates with
only 48 volts ~etween anode and cathode when in the
~ 10 OFF state; however, it is possible that + 220 volts
;~- exist at the anode and/or cathode due to ringing,
~- testing, coin telephone controlling, and induced
60 Hz voltages and, accordingly, control circuit 10
is designed to block these high voltages.
When Ql operates in saturation the base-
collector junction thereof is potentially forward-
biased. D3 serves to help insure against a flow of
~ current from input terminal 16, through the collector-
- base junction of Ql and then through Dl.
The circuit of FIG. 1, excluding CL3, R2, R3,
and Cl, has been fabricated on a single integrated ~-
circuit chip.
~ The fabricated control circuit allowed the blockin~
; of 500 volts across the anode and cathode of GDSl ands 25 cut off (interrupted) 100 miliamperes of current flow
therethrough. ~he values of Rl and R3 are 1000 and
; 30ao ohms, respectively, without Cl and R2 being used
and with R3 coupled directly to +V2. Cl and R2, when
used, reduce the time needed to switch GDSl from the
!' 30 ON to the OFF state. One preferred value of Cl is
;~ 0.1 ~F with Rl = 1000 ohms, R2 = 2x105 ohms, and
1 R = 3000 ohms.
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~ Refexring now to FIG. 2, there is illustrated a
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bidirectional switch which comprises gated diode
switches GDS3 and GDS4, with the anode of GDS3 coupled
to the cathode of GDS4, the cathode of GDS3 coupled
to the anode of GDS4, and the gates of both being
coupled together. The gates of GDS3 and GDS4 can
be coupled to terminal 22 of the control circuit 10 of
; FIG. 1 instead of GDSl being coupled thereto. The state
of GDS3 and of GDS4 can thus be controlled in
essentially the same manner as is described for the aontrol
, 10 of GDSl.
.
Referring now to FIG. 3, there is illustrated
control circuitry 100 which is coupled to a gated
~` diode switch GDS10 having anode, cathode, and gate
terminals. Control circuit 100 is similar to control
~ 15 circuit 10 of FIG. 1, except that diodes Dl and D3
; are eliminated and a current mirror circuit con-
`~ figuration comprising p-n~p transistors Q2 and Q3 is
used. Q2 and Q3 are switching devices in which the
bases may be denoted as control terminals and the
collectors and emitters may be denoted as first and
second output terminals, respectively. Components
~ and terminals of FIG. 3 which are similar to those of
,~ FIG. 1 have the same reference denotation with an
additional "0" at the end. -
The emitters of Q2 and Q3 are coupled together
to terminal 140 and to power supply +V10. The bases
of Q2 and Q3 are coupled together to the collector of
Q2 and to a first terminal of CL10 and to a terminal
30. The collector of Q3 is coupled to the gate of
GDS20, a first terminal of CL30, and to a circuit
terminal 200. Essentially all other components and
interconnections are similar to those of the circuitry
- of EIG. 1.
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The combination of D20~ Q10, R10, Q27 Q37
CL10, and CL30 'illustrated within dashed line
-` ` rectangle B) is denoted as a voltage control branch
circuit and is adapted to set the potential o
terminal 200 so as to control the state of GDS20.
~ With an appropriate high level voltage
i; Ctypically +2 to 5 volts~ applied to terminal 160,
~ Q10 is biased on and conduction from power supply
`?," ~V10 through Q2, CL10, Q10, R10, and into po~er
~`~ 10 supply VSS0 occurs. Q2 and Q3 are essentially
-` identical transistors. It is well known that this
configuration of Q2 and Q3 results in essentially the
same current flow through Q2 as flows through Q3. With
-` Q10 biased on~ the potential o$ terminal 200 is at the
;~ 15 potential o$ ~V10 minus the VCE of Q3. With a low ``"
~`~ level input signal ~0-0.4 volts) applied to ter~inal
1607 Q10 is biased off and there is no conduction
through Q10 and Q2. Thus there is no conduction through
'`~ Q3. Terminal 20Q is thus pulled towards the potential
of approximately -V40 until the anode-gate junction of
GDS20 is for~ard-biased and causes terminal 200 to
. assu~e a potential level near but somewhat less positive
than that of ~V20.
~V10 is selected to be more positive than
, 25 ~V20 and the potential of -V~0 is selected to be more
negative than ~V20. The operation of GDS20 to control
the state of GDS10 is essentially the same as has ~een
described for the operation of GDS2 of FIG. 1. The use
- of the same potentials for the power supplies of FIG. 3
as the corresponding power supplies of FIG. 1 results in
~ a circuit which facilitates the control of the state of
GDS10 with ~220-volts at the anode and/or cathode. The
varying of the potential of terminal 200 causes GDS20 to
, operate in a similar mode as corresponding GDS2 o~
FIG. 1. Thus the state of GDSlQ is controlled in the
same manner as the state of corresponding GDSl of FIG. 17
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- but with an opposite polarity input signal.
The complementary transistors Q10 and Q2 or
Q3 can be fabricated on the same integrated circuit
chip as GDS20 with both formed using dielectric
isolated structures.
;~ The embodiments described herein are intended
to be illustrative of the general principles of the
~ present invention. Various modifications are possible
`~ consistent with the spirit of the invention. For
example, various other control circuits can be substituted
for those illustrated coupled to the gates of GDS2
and GDS20 of FIGS. 1 and 3, respectively, in order to
provide the voltage levels and current drive (sourcing)
capability needed to control the state thereof. Still
further, the n-p-n transistors can be replaced by
p-n p transistors provided the polarities o~ the power
supplies are appropriately modified as is well known
in the art. Still further Rl and R10 can be pinch -~
resistors. StiIl further the emitters of Ql, and Q10
can be coupled directly to VSS and VSS0, respectively.
. In this case, current limiting means, typically a
resistor, would then be inserted in series with the
- respective input terminals, 16 and 160.
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