he construction of a high‐voltage (up to 1000 V) bipolar metal‐oxide‐semiconductor field‐effect transistor square‐wave generator is described. This generator is capable of producing both positive and negative going square waves with variable amplitude, repetition rate, and width. The circuit was designed for ferroelectrics research, however other applications are possible. The rise time of the prototype was 200 ns which was quite satisfactory for the present ferroelectric research project however the rise time can be decreased to 50 ns if necessary. The reader with a modest knowledge of electronics should be able to construct the circuit. Possible pitfalls and critical points are discussed

McAuley, Grant A.

Usher, T. D.

English

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California State University, San Bernardino CSUSB ScholarWorks Physics Faculty Publications Physics 7-1993 High-voltage MOSFET bipolar square-wave generator T. D. Usher California State University - San Bernardino, tusher@csusb.edu Grant A. McAuley Follow this and additional works at: https://scholarworks.lib.csusb.edu/physics-publications  Part of the Physics Commons Recommended Citation Usher, T. D. and McAuley, Grant A., "High-voltage MOSFET bipolar square-wave generator" (1993). Physics Faculty Publications. 3. https://scholarworks.lib.csusb.edu/physics-publications/3 This Article is brought to you for free and open access by the Physics at CSUSB ScholarWorks. It has been accepted for inclusion in Physics Faculty Publications by an authorized administrator of CSUSB ScholarWorks. For more information, please contact scholarworks@csusb.edu. High-voltage MOSFET bipolar square-wave generator T. D. Usher and Grant A. McAuley@ Department of Physics, California State University San Bernardino, San Bernardino, California 92407-2397 (Received 25 January 1993; accepted for publication 25 February 1993) The construction of a high-voltage (up to 1000 V) bipolar metal-oxide-semiconductor field-effect transistor square-wave generator is described. This generator is capable of producing both positive and negative going square waves with variable amplitude, repetition rate, and width. The circuit was designed for ferroelectrics research, however other applications are possible. The rise time of the prototype was 200 ns which was quite satisfactory for the present ferroelectric research project however the rise time can be decreased to 50 ns if necessary. The reader with a modest knowledge of electronics should be able to construct the circuit. Possible pitfalls and critical points are discussed. 1. INTRODUCTION A high-voltage (up to 1000 V) bipolar solid-state square-wave generator will be described. Aside from the simple solid-state design the most unique feature of this generator is its ability to produce both positive and nega- tive polarities. The rise time of the prototype circuit was 200 11s. If necessary, the rise time could approach 50 ns. The period of the bipolar pulse pair is variable as is the time between positive and negative pulses. The amplitude is also variable. The generator was designed for ferroelec- tries research, however other applications are possible. If bipolar pulses are not required simpler designs are avail- able. A monopolar solid-state circuit is described by Bernius and Chutjian.“2 Commercial manufacturers in- clude Cobe? (a tube design), and Directed Energy (solid- state design).4 In some cases it may be possible to build a bipolar generator using two monopolar generators. The circuit is described from the standpoint of an ex- perimental physicist, not from the standpoint of an electri- cal engineer. The reader, with a modest knowledge of elec- tronics at the level of Horowitz and Hil1,5 should be able to construct the circuit. Possible pitfalls and critical points are discussed. II. BACKGROUND Typically ferroelectrics are studied by applying a series of square waves to a ferroelectric capacitor and monitoring the current as a function of time in a series resistor. This current is known as the switching current and was first reported by Mertz.6 The square-wave generator used in such studies should have the following characteristics: (i) high voltage: This depends on the coercive field of the ferroelectric and the thickness of the sample. (ii) low output impedance: a high output impedance will contribute to the “width” of the RC peak ‘)Prescnt address: Department of Physics, University of California Riverside, Riverside, CA 9252 1. which should be kept to a minimum so as not to mask the switching current. (iii) fast rise time: obviously we desire a pulse which reaches its full value well before the switching current peak. Another important characteristic is flexibility, that is, the ability to choose, repetition rate, amplitude, and time be- tween polarities. Three circuit designs which could accomplish the aforementioned objectives immediately present themselves: high-voltage tubes, mercury-wetted relays, and high- voltage metal-oxide semiconductor field-effect transistors ( MOSFETs). High-voltage tubes are becoming less com- monplace for a number of reasons including high power consumption, relatively high cost, and reliability. Mercury- wetted relays have been employed by some investigators.“’ These relays were typically driven at line voltage frequen- cies, 50 or 60 Hz. In cases where switching at these fre- quencies can damage the crystal, a logic circuit could be used to drive the relays.‘*” These relays offer the advantage of extremely fast rise times, on the order of a nanosecond, depending on the attention to construction. l1 Their disad- vantages include a finite lifetime and limited voltage, on the order of 100 V. While in typical application these disad- vantages can be overcome with arc suppression circuitry, such circuitry is not appropriate for ferroelectric applica- tions, one problem being an increase in the rise time of the applied pulse. High-voltage MOSFETs are relatively new compared to the other two alternatives. At the present 1000-V MOSFETs are the highest available ratings. They offer the simplicity in design and reliability typical of solid- state circuitry. The rise time is approximately 50 ns, de- pending on factors which will be discussed later. III. CIRCUIT DESIGN The circuit will be described beginning at the output and working backwards. Figures 1 and 2 represent a com- plete circuit except for the high-voltage power supply. It should be pointed out that neither the plus or minus of the 2027 Rev. Sci. Instrum. 64 (7), July 1993 0034-6748/93/64(7)/2027/4/$6.00 @  1993 American institute of Physics 2027 ext. FIG. 1. The logic circuit for producing pulses A and 3 delayed with respect to each other by an amount i3. The circuit can be triggered externally, by single-shot push-button, or by an internal repetitive trigger. high-voltage power supply should be referenced to ground in order to avoid electrical shorts, as revealed by careful examination of Fig. 3. The heart of the generator is made up of the four high- voltage MOSFETs Ql, Q2, Q3, and Q4 shown in Fig. 4. The configuration is somewhat similar to a flying capacitor invertor circuit. This arrangement takes advantage of the diode properties of a MOSFET in the off state. Even if the plus and minus outputs of the high-voltage power supply are isolated from ground, as mentioned above, care must be taken to avoid another short circuit situation resulting from (Ql and Q3) or (Q2 and Q4) being on at the same time. This condition can occur in the case of improper timing, however, it can also occur due to overlap of the finite rise and fall times of the MOSFETs. The short delay (a few hundred nanosecorids) depicted as d in Fig. 5 rem- edies this problem by producing the intermediate state shown in Fig. 3. This problem is discussed in Bernius and Chutjian’s second paper.2 The different possibilities are represented in Fig. 3 and described by Table I. The remainder of the circuit is simply the low-voltage drive circuit for turning the MOSFETs on and off in the correct sequence. A timing schematic is given in Fig. 5. r5Y *,p L-i MM- FIG. 2. The complete circuit excluding logic circuit depicted in Fig, 1. The four branches are almost identical. Two branches are inverted with respect to the other two. The commons after the optical isolators are referenced to different points. A brief delay d is provided by the RC combination preceding the third input into the 7411, Out: EARTH GND t2: out: mmrAl-E t,: Out: INTERMEDIATE Out: INTERMEDIATE FIG. 3. The time-sequenced states c )f the four MOSFETs with corre- Out:+V sponding outputs. The intermediate state is brief, allowing enough time to prevent a particular MOSFET rise time from overlapping with another MOSFET fall time, therefore shorting out the power supply during this overlap. 2028 Rev. Sci. Instrum., Vol. 64, No. 7, July 1993 Square-wave g;enerator 2028 FIG. 4. A schematic showing the four high-voltage MOSFETs which form the heart of the circuit. The rt through ts designations are correlated with the dif- ferent configurationals shown in Fig. 3. The monostable and astable vibrator circuit shown in Fig. 1 produces a pair of pulses, A and B, which are delayed with respect to one another. This long delay D should not be confused with the short delay d. This tim ing could be accomplished by any number of suitable circuits. The circuit also provides for three methods of triggering the circuit; (a) single-shot push-button, (b) external source, (c) internal repetitive triggering. Any number of references” can aid in the se- lection of proper resistor and capacitor combinations to produce the desired tim ing. Pulses A and B are further divided to produce a total of four pulses Al, A2, B3, and B4; see Fig. 5. Pulses Al and A2 are inverted with respect to each other, as are B3 and B4. Moreover Al and A2 are slightly delayed d with re- spect to each other, likewise for B. The numbers 1, 2, 3, and 4 correspond to the MOSFETs which are being driven by each pulse. The short delay d is accomplished by the 820-pF capacitor and the l&K! variable resistor on each of the four branches. As mentioned before, the purpose of this slight delay is to prevent the shorting of the power supply due to the rise time of one MOSFET overlapping with the fall time of the other. Figure 6 shows a representative rise time. The rise of the circuit is purposely over damped to avoid overshoot. t-D---l -d d d. d j j ’ I B4 I; II .i ; I I I I I I II i’ I I I I I I I I I I I t, t? 5 t t5 t6 5 b FIG. 5. A timing diagram showing MOSFET drive pulses and the high- voltage output. The various times I, through rs correspond to the various amiigurations in Fig. 3 and Table I. The long delay D between Al and B3 determina the time the output is at ground. The short delay d is greatly exaggerated and prevents overlapping rise times and fall t imes in the MOSFETs. 2029 Rev. Sci. Instrum., Vol. 64, No. 7, July 1993 Square-wave generator TABLE I. Time sequence of MOSFET states, corresponding to Fig. 3. Tie Ql ez 6 tz 13 4 t5 t6 t1 ts on Off Off Off Off Off on on on on on Off Off Off Off Off Off Off Off Off on Off on Off on on Off on Off on Off Off output ground intermediate neg. high voltage intermediate ground intermediate pos. high voltage intermediate Rise times of approximately 200 ns were quite acceptable in this particular ferroelectric application, while overshoot was not desirable. IV. KEY POINTS Note that the sources of all but one of the MOSFETS are not connected to ground. Therefore, the gate drivers are not connected to ground, consequently the optoisola- tons are used to communicate the drive signal from the low-voltage logic circuit (which is referenced to ground) to the gate divers. Switching these voltages at these speeds can produce radio frequency noise. In fact, it may be advisable to phys- ically separate the multivibrator circuit from the other cir- cuitry. This also facilitates alternative tim ing drives such as from a computer, since the four wires carrying the logic level signals can be easily disconnected or reconnected. Good grounds and shielding are also needed. The speed of the circuit is primarily determined by the rate at which the gate capacitances are charged. Conse- quentially, the selection of a high current gate driver is important. The TSC-429 by Teledyne Semiconductor was selected because of its high-speed (30 ns) and high-current output ( 1.5 A). The TCS-4426 is a tougher design and pin ‘. I” ‘/a..-/‘.,- .‘~‘l....,....,L...,.‘., li m . Qi’d v .f. :iddti; : . : + I! j ,:,, ,; : : ., ,,// / II FIG. 6. An oscilloscope trace depicting a typical rise time of the square wave. The leading edge of the 211-V square wave has a rise time of 245.2 ns. The lack of overshoot or ringing is due to intentional overdamping. If ringing or overshoot can be tolerated the rise time could be improved. 2029 compatible with the TSC-429. The driver should be as University of South Carolina is recognized, Abdallah Tab- close, physically, to the MOSFET as possible. In the future bara and Ming Vang, students at California State Univer- some manufactures may incorporate gate drives into MOS- sity San Bernardino, participated in the construction of the FET designs. A fast optoisolator was also selected. circuit. Depending on the nature of the high-voltage power supply it may be advisable to use a capacitor bank close to the MOSFETs to ease peak demands on the power supply as well as reduce ringing in the output. Note that ‘only one of the MOSFETs has its source connected to ground; in fact, the source of one MOSFET is tied to the output. This makes it necessary for the power supplies for the associated gate drivers and optical isolators to be referenced to output, positive high voltage, negative high voltage, and ground, respectively. Because of this, careful attention has to be paid to insulation characteristics of these power supplies which is not normally the case. ‘PA. Bern&s and A. Chutjian, Rev. Sci. Instrum. 60, 779 (1989). 2M. Bernius and A. Chutjian, Rev. Sci. Instrum. 61, 927 ( 1990). 3Cober Electronics. Inc. 102 Hamilton Ave., Stamford, CT 06902. ‘Directed Energy, Inc. 2301 Research Blvd., Ste. 101, Fort Collins, CO 80526. It should be possible to increase the voltage capabilities of the circuit by adding an additional MOSFET in series to each of the four original MOSFETs. This modification was not necessary for the present application. An article by Miro Glogolja and John Kerr should aid in this.13 ‘P. Horowitz and W. Hill, 7% Art of EZectmzics, 2nd ed. (Cambridge University Press, New York, 1989). 6W. Merz, Phys. Rev. 95, 690 (1954). ‘P. Guyon and J. Lajzerowicz, Phys. Status Solidi 16, 525 ( 1966), *Z. Surowiak and J. Dee, Rev. Sci. Instrum. 49, 1719 (1978). 9T. D. Usher, C. P. Poole, and I-I. A. Farach, Ferroelectrics 110, 67 (1990). loI’. D. Usher, C. P. Poole, and H. A. Farach, Ferroelectrics 120, 201 f 1991). “I A D. Lewis and F. Ii. Wells, MilIimicrosecond Pulse Techniques . (Pergamon, London, 1954). ‘*D. Lancaster, 77X Cookbook (Howard W. Sams & Co., Indianapolis, ACKNOWLEDGMENTS The creative input of Professor Roger A. Dougal of the Electrical and Computer Engineering Department at The 1979). “M. Glogolja and John Kerr, IEEE Publication on EIectro/llS, The Application of High-Power MOS-Gated Structures, Professional Pro- gram Session Record 21. 2030 Rev. Sci. Instrum., Vol. 64, No. 7, July 1663 Square-wave generator 2030 

High-voltage MOSFET bipolar square-wave generator

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High-voltage MOSFET bipolar square-wave generator

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