U.S. patent number 3,710,145 [Application Number 05/111,424] was granted by the patent office on 1973-01-09 for improved switching circuitry for semiconductor diodes.
This patent grant is currently assigned to Raytheon Company. Invention is credited to Christos J. Georgopoulos, Robert T. Williamson.
United States Patent |
3,710,145 |
Williamson , et al. |
January 9, 1973 |
IMPROVED SWITCHING CIRCUITRY FOR SEMICONDUCTOR DIODES
Abstract
A driver amplifier for p-i-n diodes in the phase shifters of a
phased array antenna, such amplifier being arranged so as to
produce, in response to a command signal from a beam steering
computer, either a forward-bias or a back-bias signal for such
diodes, the particular bias signal produced by such amplifier being
delayed by substantially the same length of time after application
of a command signal.
Inventors: |
Williamson; Robert T. (Concord,
MA), Georgopoulos; Christos J. (Lowell, MA) |
Assignee: |
Raytheon Company (Lexington,
MA)
|
Family
ID: |
22338465 |
Appl.
No.: |
05/111,424 |
Filed: |
February 1, 1971 |
Current U.S.
Class: |
327/109; 333/156;
327/365; 327/403; 327/478; 327/493 |
Current CPC
Class: |
H03K
17/76 (20130101); H03K 5/14 (20130101); H03K
5/02 (20130101); H01Q 3/385 (20130101) |
Current International
Class: |
H03K
5/02 (20060101); H01Q 3/30 (20060101); H01Q
3/38 (20060101); H03K 17/51 (20060101); H03K
17/76 (20060101); H03K 5/14 (20060101); H03k
001/00 (); H03k 017/00 () |
Field of
Search: |
;307/208,246,236,256,253,260,254,262,270,317,319,241,242,259,320
;333/24.1,31R,31A ;343/854 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Miller, Jr.; Stanley D.
Claims
What is claimed is:
1. In a phased array antenna assembly for microwave energy, such
assembly incorporating a matrix of antenna elements, each one of
such elements having associated therewith a semiconductor-diode
phase shifter to change, in accordance with binary control signals,
the phase of microwave energy to and from each one of such
elements, separate circuitry for selectively forward-biasing and
back-biasing the semiconductor diodes in each semiconductor-diode
phase shifter, each such separate circuitry including:
a. first circuit means, including a first resistor, for connecting
the semiconductor diodes in an associated semiconductor-diode phase
shifter to a terminal;
b. second circuit means, including a second resistor, for
connecting a source of back-bias voltage to the terminal;
c. third circuit means, including a first transistor, for
connecting a source of forward-bias voltage to the terminal;
and
d. fourth circuit means, including a time delay circuit for
connecting a source of binary control signals to the first
transistor to switch that element from its conducting state to its
nonconducting state in accordance with the binary control signals,
the time delay of the time delay circuit also varying in accordance
with the binary control signals.
2. Circuitry as in claim 1 having, additionally:
a. a second transistor, such transistor having its collector
electrode connected through a third resistor to the source of
back-bias voltage, its base electrode connected to the terminal and
its emitter electrode connected to a junction in the first circuit
means; and
b. inductor means, disposed in the first circuit means between the
terminal and the junction and responsive to the binary control
signals, for momentarily biasing the second transistor into its
conductive state during each period of time when the first
transistor is changing from its conducting to its nonconducting
state.
3. Circuitry as in claim 2 having additionally: fifth circuit
means, including a third transistor, the emitter electrode of such
transistor being connected to the base electrode of the first
transistor, the collector electrode of such transistor being
connected to a discharging load and the base electrode of such
transistor being in circuit with the fourth circuit means and the
discharging load, the third transistor thereby being biased into
its conducting state only during each period of time when the first
transistor is changing from its conducting to its nonconducting
state.
Description
BACKGROUND OF THE INVENTION
This invention pertains generally to phased array antennas for
radar and particularly to antennas of such type suing semiconductor
diode phase shifters to collimate and direct a beam of microwave
energy.
It is known in the art that a matrix of so-called semiconductor
diode phase shifters may be used selectively to adjust the phase of
microwave energy passing to, or from, individual antenna elements
in a phased array. Such diode phase shifters are operative, in
accordance with a program determined by the parameters of the
particular array and the desired deflection angle of a beam of
microwave energy, to change the length of the electrical path of
the microwave energy between each antenna element and a source (or
detector) of such energy.
When relatively large amounts of microwave energy are to be passed
through a semiconductor diode phase shifter, it is common practice
to use so-called p-i-n diodes as the switching element in such a
phase shifter. Unfortunately, however, the characteristics of p-i-n
diodes and associated elements are such that the length of time
required to switch from a forward-bias to back-bias condition is
longer than the time required to switch in the opposite direction.
It follows therefore, in view of the fact that provision must be
made to prevent the propagation of microwave energy during the time
in which any of the p-i-n diodes is switching, that it is necessary
to inhibit generation of microwave energy for a relatively long
period of time whenever it is desired to change beam direction.
Attempts have been made to reduce the time required to operate
p-i-n diodes by using driver amplifiers with output stages having
special characteristics. That is, it is known to provide, in the
output stages of driver amplifiers for p-i-n diodes, power
transistors having low storage and fall times so that only the
delays inherent in the switching of p-i-n diodes are experienced.
It has been found, however, that the types of power transistors
required are extremely expensive and that, even with the best of
existing power transistors, marked improvement cannot be
attained.
SUMMARY OF THE INVENTION
Therefore, it is a primary object of this invention to provide
improved circuitry for operating p-i-n diodes in semiconductor
phase shifters for microwave energy.
Another object of this invention is to provide improved circuitry
as just mentioned, such circuitry being adapted to operate with
conventional, relatively inexpensive components.
These and other objects of this invention are attained generally in
a driver amplifier for p-i-n diodes by providing, in such an
amplifier, delay means operative on the control signals to a
greater degree when the p-i-n diodes are to be driven from their
back-bias to their forward-bias conditions, the amount of delay of
such control signals being substantially equal to the delay
inherent in such p-i-n diodes when being driven from their
forward-bias to their back-bias conditions.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of this invention, reference is
now made to the following description of the accompanying drawings,
in which:
FIG. 1 is a greatly simplified sketch showing the relationship of a
drive amplifier according to this invention in relation to a radar
system; and
FIGS. 2 and 3 are sketches of the waveforms appearing at the output
of driver amplifiers in response to command signals from a beam
steering computer.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1, it may be seen that the contemplated radar
system includes a controller 10, a beam steering computer 12, a
plurality of driver amplifiers 14, . . . 14n, a matrix (not
numbered) of phase shifters 18 . . . 18n, and a
transmitter/receiver 20. The just recited elements, except for the
drive amplifiers 14 . . . 14n, are conventional in construction and
operation. Thus, the controller 10 simply produces beam steering
command signals for the beam steering computer 12 and synchronizing
pulses for the transmitter/receiver 20. It is noted, however, that,
if it is desired to permit microwave energy to be propagated only
after the phase shifters 16 . . . 16n have completed any required
change in response to a change in the beam steering command signal,
the beam steering command signal line and the synchronizing signal
line should be interlocked in any convenient fashion. Such
interlocking should inhibit the transmitter/receiver 20 for a short
period of time, say 1.5 microseconds, after any change in the beam
steering command signal to permit the phase shifters 16 . . . 16n
to be forward or back-biased as required. It is also noted that,
for convenience here, each phase shifter 16 . . . 16n has been
shown as a three bit phase shifter. It is not, however, essential
to the invention that a three bit phase shifter be used.
Referring now to the exemplary driver amplifier 14, it may be seen
that each such amplifier includes a delay circuit 21, an amplifying
section 23, a pair of output power transistors 25, 27, a
discharging transistor 28 and associated elements to be described.
Suffice it to say here, however, that the various elements combine
in the steady state with a logic "one," i.e. approximately +2
volts, on the input line from the beam steering computer 12 so that
output power transistor 25 is conducting and output power
transistor 27 is cut-off. Conversely, in the steady state with a
logic "zero," i.e. approximately zero volts, on the input line from
the beam steering computer 12, both output power transistors 25, 27
are cut-off. On other words, in the first steady state, the
corresponding p-i-n diodes 29, 29a are ultimately connected, via
limiting resistors 31, 31a, cable 33, inductor 35, output power
transistor 25 and diode 37 to a forward-biasing current source,
-E.sub.f. In the second steady state, the p-i-n diodes 31, 31a are
connected, as indicated, through a resistor 39 (having a resistance
on the order of 270 kilohms), the inductor 35, cable 33 and
resistors 31, 31a to a back-bias current source, +E.sub.b.
The delay circuit 21 is made up of a resistor 43, a capacitor 45
and a transistor 47. With the arrangement shown, it is obvious
that, in the steady state, the transistor 47 is cut-off when a
logic "zero" is applied to the resistor 43 from the beam steering
computer 12. When the output signal from the latter is changed to a
logic "one," it is equally obvious that the voltage on the emitter
electrode (not numbered) of the transistor 47 rises in accordance
with the time constant of the integrating circuit (resistor 43 and
capacitor 45). It follows, therefore, that the threshold voltage
for conduction by transistor 47 is reached only after some period
of time, say 2 microseconds, has elapsed after the change of a
logic "one." When transistor 47 becomes conducting, amplifier 23
produces a positive going signal which is coupled through a diode
49 and a resistor 51 to the base electrode (not numbered) of the
output power transistor 25. It is noted that the positive going
signal out of the amplifier 23 is blocked from the base electrode
(not numbered) of a discharging transistor 28 by a diode 55. The
latter transistor is biased into its cut-off condition. The
positive going signal on the base electrode of the output power
transistor 25 is sufficient to cause the latter to conduct, thereby
producing a forward-bias signal (via inductor 35, cable 33 and
resistors 31, 31a) to the p-i-n diodes 29, 29a.
It us noted that the current path for forward-biasing the p-i-n
diodes 29, 29a initially includes a capacitor 59 (which capacitor
is charged to a voltage substantially equal to -E.sub.ff when
output power transistor 25 starts to conduct). As current is drawn
from capacitor 59, its voltage changes approaching the forward bias
voltage, -E .sub.f, to permit diode 37 to conduct. Thereafter, the
current path includes the forward bias current source, -E.sub.f.
The operation of capacitor 59, as just described, helps discharging
the cable 33 and improves rise time of the forward-bias signal at
the p-i-n diodes 29, 29a.
When the output signal from the beam steering computer 12 changes
from a logic "one" to a logic "zero," the capacitor 45 may
discharge, at least partially, through the transistor 47 because
that element is still conducting. The time constant of the
combination of the capacitor 45 and the emitter-base circuit of the
transistor 47, as long as the latter is conducting, is relatively
short as compared to the time constant of the combination of
resistor 43 and capacitor 45. Consequently, the discharge of
capacitor 45 occurs at a more rapid rate than its charge. In a
practical application, then, transistor 47 cuts off within a few
tenths of a microsecond after a logic "zero" is received from the
beam steering computer 12. When transistor 47 ceases to conduct,
amplifier 23 produces a negative going signal. Such signal is
blocked by diode 49 but is passed by diode 55 so as to appear on
the base electrode (not numbered) of discharging transistor 28. The
emitter circuit for the latter is then completed, via capacitor 59,
a diode 60 and a resistor 61 so that it conducts momentarily (until
capacitor 59 is charged). During this time, say a few tenths of a
microsecond, transistor 28 conducts, the storage charge of the
output power transistor 25 is removed, thereby causing that element
to cut-off more quickly than would be the case if discharging
transistor 28 were not in the circuit. Because the current through
the inductor 35 cannot change instantaneously, the cut-off of
output power transistor 25 causes the inductor 35 to produce, for a
short period of time, a voltage "spike" on the base electrode (not
numbered) of the output power transistor 27, which voltage spike is
sufficient to turn that transistor on. A relatively high
back-current "spike" is, consequently, passed from back-bias
source, +E.sub.b, through resistor 41, output power transistor 27,
cable 33 and resistors 31, 31a to p-i-n diodes 29, 29a. Such a
current spike is effective rapidly to deplete the storage charge of
the p-i-n diodes thereby changing them to their back-bias
condition. As noted hereinbefore, when output power transistor 27
reverts back to its cut-off condition after, say, 2 microseconds,
back-bias is maintained on the p-i-n diodes through the path from
the back-bias source, +E.sub.b, which includes resistor 39.
Having described an embodiment of a driver amplifier according to
this invention, reference is now made to FIGS. 2 and 3 of our
driver amplifier. Thus, in FIG. 2 the upper set of curves shows
that, in response to a negative-going signal, S.sub.F.sub.-B, from
a beam steering computer (such signal being a command signal to
switch p-i-n diodes in a phase shifter from a forward-bias to a
back-bias condition), some time elapses before the voltage,
V.sub.D, reaches a desired steady state back-bias level. With a
positive-going signal, S.sub.B.sub.-F, from a beam steering
computer (such signal, illustrated in the lower set of curves in
FIG. 2, being a command signal to switch p-i-n diodes in a phase
shifter from a back-bias condition to a forward-bias condition),
the requisite change in level of the voltage across the p-i-n
diodes takes place almost coincidentally with the command signal.
It is apparent, therefore, that the generation of microwave energy
in a radar system according to the prior art must be inhibited for
an interval equal to the interval between application of a command
signal and completion of the slower switching direction. Typically,
such as interval is in the order of 3 microseconds.
Referring now to FIG. 3 it may be seen that, according to our
invention, switching from a forward-bias to a back-bias condition
is accomplished in substantially the same manner (as shown in the
upper set of curves in FIG. 3) as in the prior art. Application of
a positive-going signal, S.sub.B.sub.-F, from a beam steering
computer, i.e. a command signal to switch p-i-n diodes in a phase
shifter from a back-bias to a forward-bias condition, has, however,
no immediate effect on the output signal from our driver amplifier.
After a period of time (which period is approximately the same as
the time taken to switch the p-i-n diodes from a forward to a
back-bias condition) our circuit then operates. Obviously,
therefore, the generation of microwave energy need be inhibited for
an interval, typically 1.5 microseconds, as indicated by the
vertical dashed lines.
It will be appreciated by those of skill in the art that reducing
the period of time during which generation of microwave energy is
inhibited in order to change the condition of phase shifters in a
phased array antenna is important when a large number of targets is
being tracked. It will also be appreciated that our contemplated
circuitry permits such reduction without making it necessary to use
relatively fast acting (and, therefore, expensive) semiconductor
elements. It is felt, in view of the foregoing, that this invention
should not be restricted to its disclosed embodiment, but rather
should be limited only by the spirit and scope of the appended
claims.
* * * * *