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Pulse generation and processing with GaAs bistable switches
Solid-Slate
Electronics, 1976, Vol. 19, pp. 129-132.
Pefgamon Press. Printed in Great Britain
PULSE GENERATION AND PROCESSING WITH GaAs BISTABLE SWITCHES S. H. Electrical and Electronics
IZADPANAH
Engineering Department, School of Engineering. Pahlavi University, Shiraz. Iran (Received 17Aprif 1975; in revisedform 26June 1975)
Abstract-Successful operation of high current drop “b&able switching” from X-band supercritical transferred electron devices is reported. Also the potential use of this type of switches in applications such as pulse generation, amplification, and processing is demonstrated. This class of switches with high switching speed offers exciting prospects in the field of fast pulse processing and logic circuits.
1. INTRODUCTION
The switching potential of supercritical Transferred Electron Devices (TED) have already been established[l-61. The early use of switching characteristics of TED’s for pulse, logic and functional circuit applications employed long oscillating devices[1-4]. It is comprised of a two or multi-terminal device operating into resistive load and generally with a bias level below the oscillation threshold field. When a short triggering pulse of sufficient amplitude is applied, the device field will momentarily be raised above the threshold field, causing the formation of a trauelling high field domain. During formation of the domain and its growth, the device current switches to lower values accordingly. For devices of high n . 1 product, the domain saturates in a relatively short time and consequently the current becomes constant and remains low during domain transit. When the domain reaches the positive contact and discharges through, the current rises to corresponding initial high value. The amplitude of the domain current pulse can easily reach 50% of the maximum threshold current offering an inherently high regenerative pulse gain[4]. These attractive features together with fast rise time of pulse train make them highly suitable for applications in high-amperage digital communication systems and computer circuits [3,4]. In order for the domain regenerated pulse to be nearly square and high quality, the domain transit-time should be, by a reasonable factor, longer than the domain growth and discharging times. Typical growth time is a fraction of nanosecond setting a value of, say, one nanosecond for transit-time, i.e. L = 100 pm. Therefore high required operating voltage (>30 V) and current leads to inconvenient power dissipation and heat removal. However, devices constructed by planar techniques can stand CW operation but having lower switching speed. Such restrictions for the above switching devices in the so called “Monostable” mode of operation make them less attractive than the other class of TED switches discussed below. The second type of switches employs supercritically doped TEDS. In these devices the switching function is performed by the formation of a stationary diffusion stabilized high field domain at the anode. After formation of the first domain, the device current switches to a lower
value and stays low as long as the applied device voltage remains above the threshold voltage. Aspects on the stability of and the current drop associated with the stable state of these switches has been discussed by several authors [6-lo]. Experimental verification of bistable switching of high current drop has been presented recently[ll-131. This class of switches with two stable states and higher switching speeds offers more exciting prospects in the field of fast pulse and logical circuits than the first type of switches. In this paper, we present some experiments on ON-OFF operation and pulse formation using bistable switches. Also, results on multi-stage operation of bistable switches will be presented. In measurements to be discussed in the following, TEDS were operated pulsed with low duty cycles. The packaged devices were mounted in the center conductor of a 7 mm short coxial air line and operated into a resistive load. The frequency response of the mount and the surrounding microwave circuit was satisfactory up to 18 GHz, and a 28Ps sampling oscilloscope was used to display the voltage and/or current waveforms. 2. TRIGGERED
MODE
OF OPERATION
It is well known that high field domain in GaAs devices once formed can be sustained even if the applied voltage is decreased below the threshold field [3,4]. This also is true for bistable switches with the static high field distribution. Hence, a GaAs bistable device could be triggered to switch from one stable state to another stable state in the same manner of monostable mode. When the applied bias exceeds the threshold voltage, the device current switches from higher value to lower value. The low current state is maintained when the triggering pulse on the background bias disappears. However, a minimum value of bias voltage V,,,, is required to sustain the high field domain[l], and the bias voltage in the triggered mode should be chosen somewhat higher than this sustaining voltage[4]. Figure 1 shows waveforms obtained in triggered mode of operation. A small short triggering spike is superposed on a device bias and when the spike and bias voltage becomes sufficient and cross the threshold voltage the device is switched into the ON state. Traces (V) and (I) respectively 129
s. H.
130
“,I?--+
0
IV)
I
1ov
;:-*q
’
I200
mA
Fig. I. Experimental recorded voltage and current waveforms obtained from triggered mode of operation of a b&able switch.
voltage and current in the ON state. It is seen that the current stays low even when the triggering spike disappears and the bias voltage VH is lower than the the threshold voltage V,,,. show the device
3.
ON-OFF OPERATION
With reference to the triggered mode described in the previous section, a device operating in the ON state can be switched into the OFF state if the total applied bias (the composite of a bias plus applied trigger voltage) is taken below the minimum sustaining voltage V,,,, Consider a prethreshold case for a device which is biased with a voltage V, < V, “,,“, and a superposed triggering spike: Now. if the amplitude of triggering pulse is made large enough, it causes the device to be switched into the ON state. The ON state voltage and current waveforms are shown by traces VI and I, with the ON switching instant at time t, in Fig. 2. However. since VH < V, ,,,,“. the ON state
vth-
1I
100mA
-
2ns
Fig. 2. Recorded waveforms from ON-OFF operation (V, and I,). single pulse generated using the ON-OFF mechanism (I, and I,), and train of pulses generated by successive ON-OFF operation (14)of adistable switch.
IZADPAhAH
of the switch cannot be maintained as the triggering spike disappears. Instead, the device current switches back into the OFF state at the instant when the total triggering and bias voltage value drop below V,.,,,, Waveforms V, and I, of Fig. 2 clearly demonstrate the OFF switching at time t:. 4. PULSE
GENERATION 4ND AMPLIFIC.4TION
The possibility of ON-OFF operation described in the previous section implies that for V,,, -- V,, > V, ,,1,,,a trigger spike of sufficient amplitude with polarity opposite to the device bias can be applied to switch a device from the ON state back into the OFF state. In this case. the current in the low state switches to a relatively higher value determined by the background bias Vi+Therefore, one has an ON-OFF operation performed with two opposite polarity triggering spikes and hence an output pulse. Recorded waveforms of the triggered ON-OFF operation is also shown in Fig. 2 by traces IZ and I,. The two positive and negative triggering spikes superposed on the background bias are seen on trace 1:. Trace I7 shows the device current switched from the prethreshold case into the ON state at time t, by the positive spike and is switched back into the OFF state at time tz by the negative spike. In this way one has a square pulse (here with negative polarity) of duration t,, = rz ~ t, and controlled by the separation of triggering spikes. However, for a sharp square output pulse, the time interval t,>must be larger than 2t, where t, is the device switching time[l]. For typical value of measured switching times t, = 1OOps. nearly square pulses can be obtained at frequencies well into the microwave region of spectrum. The results discussed in this section suggest that one could construct a “square” pulse generator using GaAs bistable switch. The pulses are generated when alternative positive-negative triggering spikes switch the device into the ON and the OFF states. Trace IJ shown in Fig. 2 demonstrates experimental square current pulses generated by device No. D 15. No attempt has been made to optimize the duration and the amplitude of the triggering spike for more perfect output “square” pulse. It is very important to note that the duration and repetition rate of generated pulses are almost independent of device length, i.e. wide band operation. This flexibility is highly desirable in circuit design in many application\. Amplification of current pulses is possible with bistable GaAs high current drop switches as well as in the monostable mode. The pulse to be amplified is differentiated to produce the two opposite triggering spikes required for ON-OFF switching, and a typical current gain of IOdB from high current drop switches is feasible[l4]. This feature makes GaAs pulse amplifiers highly suitable to be employed in PCM repeater stations where the incoming data pulses, of any frequency. can be regenerated with a constant high inherent gain. 5. MULTISTAGE
OPERATION OF TRANSFERRED ELECTRON BISTABLE SWITCHES
In this section we will describe the successful operation of multistage bistable switches. The possibility of switching one device with the current or voltage of another device gives evidence of their potential in performing complex electronic functions.
GaAs bistable switches 5.1. Parallel operation of two switches The circuit arrangement inserted in Fig. 3 employs two b&table switches in parallel, operating into a common load of 50 ohm. The switches are selected from devices made from the same wafer with almost equal threshold voltage. In order to demonstrate the function of the two parallel switches operating simultaneously, let us first employ a variable attenuator A in front of Dz to separate the switching events of individual diods, and latter remove the attenuator. Now assume that, for a given minimum applied voltage to the points BC, the device Dl is switched into the ON state at time t, and the device Dz is kept in the OFF state. In this case the current I, obtained across the 50 R load is shown by trace (1) in Fig. 3. The down-step in current after time tl is the current drop due to device D, only. However, the up-step in current I, at time tZis due to the increase of device voltage caused by reflection. Now, if the value of attenuator A is sufficiently lowered, the applied voltage across D2 at time tz becomes sufficient to switch this device into the ON state. Consequently there will be an additional current drop after tz in the current Iz shown by trace (2) in Fig. 3. However, if the attenuator A is removed from the circuit, i.e. same voltage across D, and DZ,the switching instant of device Dz can be shifted to the switching instant of DI at time t, and the whole operation resembles a single bistable switch. This is shown by the recorded current waveform I, in Fig. 3. The parallel operation makes it possible for obtaining high currents in application of the switch such as the drive source of a semiconductor laser. It should be pointed out that the achievement of a “clean” parallel operation is only possible with stable devices. That is, if any oscillation is produced by device D,, it will cause a jitter in the switching instance for device DI. Hence, as the recorded trace is composed of several randomly collected samples, the sharp and coherent current drop I,, in Fig. 3 is an indication of stable operation. 5.2. Series operation In series configuration, the operating state of one device is determined by the current state of another device. Consider the two stage circuit inserted in Fig. 4. In this Figure the current waveforms obtained across RL, at the
131
I
0
20
40
60
11 1
80
Fig. 4. Circuit arrangement and the waveforms series operation of two switches.
nS
obtained from
output stage is shown under the following conditions: (i) The magnitude of applied voltage to each device is less than the corresponding threshold voltage. Therefore both devices are at high current of the OFF states. The current obtained for this case is shown by trace (i). As it is seen from this trace, in order to have a reference for the switching instant of device Dz, a small triggering spike is superposed on the applied voltage. (ii) If the value of the interstage attenuator is sufficiently decreased and the applied voltage Vo, is made larger such that Vo,> Vlh2. device D2 can be switched into the ON state and a current step will appear at the output. The current waveform recorded in this case is shown by trace (ii) in Fig. 4. Here, the device DI remains at pre-threshold and that the trigger pulse is below Vthl. (iii) For a smaller value of interstage attenuator, i.e. higher applied voltage to device DZ,it can be switched into the ON state at an earlier time fI (Note the form of bias with positive slope). In this case, a corresponding decrease in its currents is resulted. It would seem that at time t,, device D1 is still operating at a pre-threshold voltage and that its threshold is exceeded at f2. At this time, the voltage across RL, decreases due to D, turning on, and falls below V,,, 2 turning device D2 off as it is seen from trace (iii) in Fig. 4. This is the operation of a bistable Flip-Flop in that when D, is in the OFF state, its high current produces enough voltage for DZ to be in the ON state. However, if an input pulse is applied to D, and is switched into the ON state, it causes D1 to switch into the OFF state. Such device has many applications in logic circuits. The reliable of series connected switches also verifies the devices’ stability. 6. CONCLUSION
__,I
1
[RL
O/P
Fig. 3. Circuit arrangement and the waveforms obtained from paralleloperation of two switches.
Experimental results obtained from GaAs bistable switches indicate their potential use in the field of pulse formation, amplification, and some complex electronic functions. It has been pointed out that the width and repetation frequency for regeneration of pulses are almost independent of device length. These new high current drops and the short switching times should contribute to the usefulness of the bistable switch in the field of high speed pulse applications such as optical PCM systems. Acknowledgements-l
am greatly
indebted
to Lit. Techn. P.
132
S.
H. IZADPANAH
Jeppesen. and Mr. P. Jrrndrup of the Electromagnetic Institute. Technical University of Denmark for manv helpful discussions and suggestion. Also. I wish to express my sincere’thanks to Tech. Dr. B. Jeppsson of Microwave Institute (Stockholm) for providing manv excellent high aualitv devices. REFEREWES
I. 2. 3 4.
J. A. Copeland, IEEE Sprclntrn 4. 71-82 (19671. M. Shoji. IEEE Trans. Elrctron Dwices ED-14 535-47( 1967). R. S. Engelbrecht. Bell Lab. Recwrtl. pp, 192-300 (19671. S. H. Izadpanah and H. L. Hartnagel. Thr Rudio and Elec~tronit Engirleur 39. 329 (19701. 5. H. W. Thim and S. Knight. Appl. Phps. Left. II. 85 (lYh71. 6. H. W. Thim. Electron. Left. 7. 246 (1971). 7. J. Magarshack and A. Mircea. Proc,. I,lt. Couj on MOGA (Amsterdam. The Netherlands, Sept. lY70). pp. 16.9-16.23.
8. H. W. Thim. Proc,. IEEE (Letters). 59. 1285 (1971). 9. P. Jeppesen and B. Jeppsson. Proc,. IEEE (Letters) 60. 452 (1972). IO. P. Jeppessen and B. Jeppsson. KEE Trans. Electron Deri(,e.s. ED-20, 371 (1973). I I. S. H. Izadpanah, B. Jeppsson. P. Jeppesen and I’. Jondrup. Presented at 5th Colloauium on Microwave Communication. Budapest 24-30 June (iY74l. 12. S. H. Izadpanah. B. Jeppsson. P. Jcppesen and P. Jmtdrup. Presented at 4th European Microwave Conference. Montreux (IO-13 Sept. 1974). 13. S. H. Izadpanah. B. Jeppsson. P. Jeppeaen and P. Jnndrup. Proc. IEEE 62. 1166 (19741. 14. S. H. Izadpanah. Report No. Rl23. Electromagnetic Institute. The Technical University of Denmark (1974).
Electronics, 1976, Vol. 19, pp. 129-132.
Pefgamon Press. Printed in Great Britain
PULSE GENERATION AND PROCESSING WITH GaAs BISTABLE SWITCHES S. H. Electrical and Electronics
IZADPANAH
Engineering Department, School of Engineering. Pahlavi University, Shiraz. Iran (Received 17Aprif 1975; in revisedform 26June 1975)
Abstract-Successful operation of high current drop “b&able switching” from X-band supercritical transferred electron devices is reported. Also the potential use of this type of switches in applications such as pulse generation, amplification, and processing is demonstrated. This class of switches with high switching speed offers exciting prospects in the field of fast pulse processing and logic circuits.
1. INTRODUCTION
The switching potential of supercritical Transferred Electron Devices (TED) have already been established[l-61. The early use of switching characteristics of TED’s for pulse, logic and functional circuit applications employed long oscillating devices[1-4]. It is comprised of a two or multi-terminal device operating into resistive load and generally with a bias level below the oscillation threshold field. When a short triggering pulse of sufficient amplitude is applied, the device field will momentarily be raised above the threshold field, causing the formation of a trauelling high field domain. During formation of the domain and its growth, the device current switches to lower values accordingly. For devices of high n . 1 product, the domain saturates in a relatively short time and consequently the current becomes constant and remains low during domain transit. When the domain reaches the positive contact and discharges through, the current rises to corresponding initial high value. The amplitude of the domain current pulse can easily reach 50% of the maximum threshold current offering an inherently high regenerative pulse gain[4]. These attractive features together with fast rise time of pulse train make them highly suitable for applications in high-amperage digital communication systems and computer circuits [3,4]. In order for the domain regenerated pulse to be nearly square and high quality, the domain transit-time should be, by a reasonable factor, longer than the domain growth and discharging times. Typical growth time is a fraction of nanosecond setting a value of, say, one nanosecond for transit-time, i.e. L = 100 pm. Therefore high required operating voltage (>30 V) and current leads to inconvenient power dissipation and heat removal. However, devices constructed by planar techniques can stand CW operation but having lower switching speed. Such restrictions for the above switching devices in the so called “Monostable” mode of operation make them less attractive than the other class of TED switches discussed below. The second type of switches employs supercritically doped TEDS. In these devices the switching function is performed by the formation of a stationary diffusion stabilized high field domain at the anode. After formation of the first domain, the device current switches to a lower
value and stays low as long as the applied device voltage remains above the threshold voltage. Aspects on the stability of and the current drop associated with the stable state of these switches has been discussed by several authors [6-lo]. Experimental verification of bistable switching of high current drop has been presented recently[ll-131. This class of switches with two stable states and higher switching speeds offers more exciting prospects in the field of fast pulse and logical circuits than the first type of switches. In this paper, we present some experiments on ON-OFF operation and pulse formation using bistable switches. Also, results on multi-stage operation of bistable switches will be presented. In measurements to be discussed in the following, TEDS were operated pulsed with low duty cycles. The packaged devices were mounted in the center conductor of a 7 mm short coxial air line and operated into a resistive load. The frequency response of the mount and the surrounding microwave circuit was satisfactory up to 18 GHz, and a 28Ps sampling oscilloscope was used to display the voltage and/or current waveforms. 2. TRIGGERED
MODE
OF OPERATION
It is well known that high field domain in GaAs devices once formed can be sustained even if the applied voltage is decreased below the threshold field [3,4]. This also is true for bistable switches with the static high field distribution. Hence, a GaAs bistable device could be triggered to switch from one stable state to another stable state in the same manner of monostable mode. When the applied bias exceeds the threshold voltage, the device current switches from higher value to lower value. The low current state is maintained when the triggering pulse on the background bias disappears. However, a minimum value of bias voltage V,,,, is required to sustain the high field domain[l], and the bias voltage in the triggered mode should be chosen somewhat higher than this sustaining voltage[4]. Figure 1 shows waveforms obtained in triggered mode of operation. A small short triggering spike is superposed on a device bias and when the spike and bias voltage becomes sufficient and cross the threshold voltage the device is switched into the ON state. Traces (V) and (I) respectively 129
s. H.
130
“,I?--+
0
IV)
I
1ov
;:-*q
’
I200
mA
Fig. I. Experimental recorded voltage and current waveforms obtained from triggered mode of operation of a b&able switch.
voltage and current in the ON state. It is seen that the current stays low even when the triggering spike disappears and the bias voltage VH is lower than the the threshold voltage V,,,. show the device
3.
ON-OFF OPERATION
With reference to the triggered mode described in the previous section, a device operating in the ON state can be switched into the OFF state if the total applied bias (the composite of a bias plus applied trigger voltage) is taken below the minimum sustaining voltage V,,,, Consider a prethreshold case for a device which is biased with a voltage V, < V, “,,“, and a superposed triggering spike: Now. if the amplitude of triggering pulse is made large enough, it causes the device to be switched into the ON state. The ON state voltage and current waveforms are shown by traces VI and I, with the ON switching instant at time t, in Fig. 2. However. since VH < V, ,,,,“. the ON state
vth-
1I
100mA
-
2ns
Fig. 2. Recorded waveforms from ON-OFF operation (V, and I,). single pulse generated using the ON-OFF mechanism (I, and I,), and train of pulses generated by successive ON-OFF operation (14)of adistable switch.
IZADPAhAH
of the switch cannot be maintained as the triggering spike disappears. Instead, the device current switches back into the OFF state at the instant when the total triggering and bias voltage value drop below V,.,,,, Waveforms V, and I, of Fig. 2 clearly demonstrate the OFF switching at time t:. 4. PULSE
GENERATION 4ND AMPLIFIC.4TION
The possibility of ON-OFF operation described in the previous section implies that for V,,, -- V,, > V, ,,1,,,a trigger spike of sufficient amplitude with polarity opposite to the device bias can be applied to switch a device from the ON state back into the OFF state. In this case. the current in the low state switches to a relatively higher value determined by the background bias Vi+Therefore, one has an ON-OFF operation performed with two opposite polarity triggering spikes and hence an output pulse. Recorded waveforms of the triggered ON-OFF operation is also shown in Fig. 2 by traces IZ and I,. The two positive and negative triggering spikes superposed on the background bias are seen on trace 1:. Trace I7 shows the device current switched from the prethreshold case into the ON state at time t, by the positive spike and is switched back into the OFF state at time tz by the negative spike. In this way one has a square pulse (here with negative polarity) of duration t,, = rz ~ t, and controlled by the separation of triggering spikes. However, for a sharp square output pulse, the time interval t,>must be larger than 2t, where t, is the device switching time[l]. For typical value of measured switching times t, = 1OOps. nearly square pulses can be obtained at frequencies well into the microwave region of spectrum. The results discussed in this section suggest that one could construct a “square” pulse generator using GaAs bistable switch. The pulses are generated when alternative positive-negative triggering spikes switch the device into the ON and the OFF states. Trace IJ shown in Fig. 2 demonstrates experimental square current pulses generated by device No. D 15. No attempt has been made to optimize the duration and the amplitude of the triggering spike for more perfect output “square” pulse. It is very important to note that the duration and repetition rate of generated pulses are almost independent of device length, i.e. wide band operation. This flexibility is highly desirable in circuit design in many application\. Amplification of current pulses is possible with bistable GaAs high current drop switches as well as in the monostable mode. The pulse to be amplified is differentiated to produce the two opposite triggering spikes required for ON-OFF switching, and a typical current gain of IOdB from high current drop switches is feasible[l4]. This feature makes GaAs pulse amplifiers highly suitable to be employed in PCM repeater stations where the incoming data pulses, of any frequency. can be regenerated with a constant high inherent gain. 5. MULTISTAGE
OPERATION OF TRANSFERRED ELECTRON BISTABLE SWITCHES
In this section we will describe the successful operation of multistage bistable switches. The possibility of switching one device with the current or voltage of another device gives evidence of their potential in performing complex electronic functions.
GaAs bistable switches 5.1. Parallel operation of two switches The circuit arrangement inserted in Fig. 3 employs two b&table switches in parallel, operating into a common load of 50 ohm. The switches are selected from devices made from the same wafer with almost equal threshold voltage. In order to demonstrate the function of the two parallel switches operating simultaneously, let us first employ a variable attenuator A in front of Dz to separate the switching events of individual diods, and latter remove the attenuator. Now assume that, for a given minimum applied voltage to the points BC, the device Dl is switched into the ON state at time t, and the device Dz is kept in the OFF state. In this case the current I, obtained across the 50 R load is shown by trace (1) in Fig. 3. The down-step in current after time tl is the current drop due to device D, only. However, the up-step in current I, at time tZis due to the increase of device voltage caused by reflection. Now, if the value of attenuator A is sufficiently lowered, the applied voltage across D2 at time tz becomes sufficient to switch this device into the ON state. Consequently there will be an additional current drop after tz in the current Iz shown by trace (2) in Fig. 3. However, if the attenuator A is removed from the circuit, i.e. same voltage across D, and DZ,the switching instant of device Dz can be shifted to the switching instant of DI at time t, and the whole operation resembles a single bistable switch. This is shown by the recorded current waveform I, in Fig. 3. The parallel operation makes it possible for obtaining high currents in application of the switch such as the drive source of a semiconductor laser. It should be pointed out that the achievement of a “clean” parallel operation is only possible with stable devices. That is, if any oscillation is produced by device D,, it will cause a jitter in the switching instance for device DI. Hence, as the recorded trace is composed of several randomly collected samples, the sharp and coherent current drop I,, in Fig. 3 is an indication of stable operation. 5.2. Series operation In series configuration, the operating state of one device is determined by the current state of another device. Consider the two stage circuit inserted in Fig. 4. In this Figure the current waveforms obtained across RL, at the
131
I
0
20
40
60
11 1
80
Fig. 4. Circuit arrangement and the waveforms series operation of two switches.
nS
obtained from
output stage is shown under the following conditions: (i) The magnitude of applied voltage to each device is less than the corresponding threshold voltage. Therefore both devices are at high current of the OFF states. The current obtained for this case is shown by trace (i). As it is seen from this trace, in order to have a reference for the switching instant of device Dz, a small triggering spike is superposed on the applied voltage. (ii) If the value of the interstage attenuator is sufficiently decreased and the applied voltage Vo, is made larger such that Vo,> Vlh2. device D2 can be switched into the ON state and a current step will appear at the output. The current waveform recorded in this case is shown by trace (ii) in Fig. 4. Here, the device DI remains at pre-threshold and that the trigger pulse is below Vthl. (iii) For a smaller value of interstage attenuator, i.e. higher applied voltage to device DZ,it can be switched into the ON state at an earlier time fI (Note the form of bias with positive slope). In this case, a corresponding decrease in its currents is resulted. It would seem that at time t,, device D1 is still operating at a pre-threshold voltage and that its threshold is exceeded at f2. At this time, the voltage across RL, decreases due to D, turning on, and falls below V,,, 2 turning device D2 off as it is seen from trace (iii) in Fig. 4. This is the operation of a bistable Flip-Flop in that when D, is in the OFF state, its high current produces enough voltage for DZ to be in the ON state. However, if an input pulse is applied to D, and is switched into the ON state, it causes D1 to switch into the OFF state. Such device has many applications in logic circuits. The reliable of series connected switches also verifies the devices’ stability. 6. CONCLUSION
__,I
1
[RL
O/P
Fig. 3. Circuit arrangement and the waveforms obtained from paralleloperation of two switches.
Experimental results obtained from GaAs bistable switches indicate their potential use in the field of pulse formation, amplification, and some complex electronic functions. It has been pointed out that the width and repetation frequency for regeneration of pulses are almost independent of device length. These new high current drops and the short switching times should contribute to the usefulness of the bistable switch in the field of high speed pulse applications such as optical PCM systems. Acknowledgements-l
am greatly
indebted
to Lit. Techn. P.
132
S.
H. IZADPANAH
Jeppesen. and Mr. P. Jrrndrup of the Electromagnetic Institute. Technical University of Denmark for manv helpful discussions and suggestion. Also. I wish to express my sincere’thanks to Tech. Dr. B. Jeppsson of Microwave Institute (Stockholm) for providing manv excellent high aualitv devices. REFEREWES
I. 2. 3 4.
J. A. Copeland, IEEE Sprclntrn 4. 71-82 (19671. M. Shoji. IEEE Trans. Elrctron Dwices ED-14 535-47( 1967). R. S. Engelbrecht. Bell Lab. Recwrtl. pp, 192-300 (19671. S. H. Izadpanah and H. L. Hartnagel. Thr Rudio and Elec~tronit Engirleur 39. 329 (19701. 5. H. W. Thim and S. Knight. Appl. Phps. Left. II. 85 (lYh71. 6. H. W. Thim. Electron. Left. 7. 246 (1971). 7. J. Magarshack and A. Mircea. Proc,. I,lt. Couj on MOGA (Amsterdam. The Netherlands, Sept. lY70). pp. 16.9-16.23.
8. H. W. Thim. Proc,. IEEE (Letters). 59. 1285 (1971). 9. P. Jeppesen and B. Jeppsson. Proc,. IEEE (Letters) 60. 452 (1972). IO. P. Jeppessen and B. Jeppsson. KEE Trans. Electron Deri(,e.s. ED-20, 371 (1973). I I. S. H. Izadpanah, B. Jeppsson. P. Jeppesen and I’. Jondrup. Presented at 5th Colloauium on Microwave Communication. Budapest 24-30 June (iY74l. 12. S. H. Izadpanah. B. Jeppsson. P. Jcppesen and P. Jmtdrup. Presented at 4th European Microwave Conference. Montreux (IO-13 Sept. 1974). 13. S. H. Izadpanah. B. Jeppsson. P. Jeppeaen and P. Jnndrup. Proc. IEEE 62. 1166 (19741. 14. S. H. Izadpanah. Report No. Rl23. Electromagnetic Institute. The Technical University of Denmark (1974).