HEWLETT-PACKARD JOURNAL TECHNICAL INFORMATION FROM THE -dp- LABORATORIE! Vol. 16, No. 4

UBLISHED BY THE HEWLETT-PACKARD COMPANY, 1501 PAGE MILL ROAD, PALO ALTO, CALIFORNIA DECEMBER, 1964

Microwave Harmonic Generation and Nanosecond Pulse Generation with the Step-Recovery

-hp-'s affiliate, hp associates, contributing to the advance of the was established four years ago to art in optoelectronics and solid-state perform research, development and devices. manufacturing in the One of hpa's developments having field. After beginning with the devel general interest to design engineers is the Step Recovery Diode. This de opment of specialized silicon, germa vice has made possible advances in nium, and gallium arsenide , fast pulse work and is unique as an hpa has gone on to achieve industry efficient generator of high-order har leadership in metal-on-semiconduc- monics. These capabilities are de tor ("hot carrier") technology and is scribed in the following article.

Fig. 1. Oscillogram showing portion of a harmonic spectrum available from a /\NY p-n junction semiconductor diode can be made to typical Step Recovery Diode. Harmon ics generated by 50 Me driving signal conduct heavily in the reverse direction for a brief time (Fig. 5) and singly detected by square- immediately following forward conduction. This mo law detector. mentarily augmented reverse conductivity results from the presence of stored minority carriers which had been injected and stored during forward conduction. In the past such reverse storage-conduction has been considered as detrimental in many applications, and so-called "fast-recovery diodes" were developed to reduce it. Recently, hp associates developed a very different class of semiconductor diodes. These were designed to enhance storage and to achieve an abrupt transition Fig. 2. Oscillogram of very fast step (300 picoseconds) formed using Step from reverse storage-conduction to cutoff. The abrupt Recovery Diode to steepen pulse-front ness of this transition is such that it can be used to as described in text. Pulse amplitude here is 4 volts. tens of volts or hundreds of milliamperes in less than a nanosecond. Such a combination of switching speed and power-handling range is not possible with any other existing device. It enables the diodes to gen erate milliwatts of power at X-band or to provide fast pulses at amplitudes of tens of volts across 50 ohms. As power generators, the diodes will generate high- order harmonics in the microwave region with greater efficiency and simplicity than is possible by any other Fig. 3. Step Recovery Diodes in glass means. In pulse work, the diodes will generate frac and ceramic packages. Ceramic pack age is designed to be especially useful tional-nanosecond pulses in which amplitude and tim u-ith coaxial structures but can also be ing can be freely controlled, as described in the latter used in other ways as in Fig. 8.

PRINTED IN USA. ©HEWLETT-PACKARD CO 1964

© Copr. 1949-1998 Hewlett-Packard Co. la,

Fig. 4. Examples of fast pulses of appreciable amplitude gen erated with Step Recovery Diodes. Pulse height is about 8 volts (2 v/cm). Sweep time is 1 nsec/cm. part of this article. Figs. 2 to 4 indi power levels approaching a milliwatt is usually found to decrease approxi cate the high multiplication factors if not higher. mately at the rate of 1/n-, where n is and fast-pulse application of the diodes. In practical work the diodes can be the harmonic number. For this reason Because their conductance during used in a single-stage multiplier to efficient harmonic generation with va reverse storage conduction follows a produce harmonics in the microwave ractors usually requires a cascade of step function, these diodes have been region with a simplicity and freedom doublers and triplers with attendant termed "Step Recovery Diodes" by hpo. from noise unmatched by other ar idlers and complications. They are also known as "snap-off" or rangements or by conventional har Variable-resistance (point-contact) "charge-storage" diodes. Their step- monic-generating diodes such as varac- diodes also suffer from poor efficiency recovery characteristic is illustrated in tors. The presently-known state of the when used for other than small multi the oscillogram of Fig. 5 which shows art in high-order multiplication with plication factors. Tube multipliers, of the diode current while the diode was the Step Recovery Diode is shown in course, are noisy and unstable among excited by a 50-megacycle sinusoid. In Table I. The variation in performance other disadvantages. the forward direction the diode con from band to band presumably results On the other hand, the Step Recov ducts in a conventional way. As the from various degrees of design effort. ery Diode has a reverse-bias capaci excitation becomes negative, however, Even the performance shown in tance that varies only slightly with the diode current also reverses until Table I is expected soon to become bias voltage. The contribution of this the supply of stored minority carriers obsolete as a result of work in progress mechanism to harmonic generation is becomes exhausted. At this point ces at hp associates and elsewhere. Step thus negligible, and the step-recovery sation of reverse current occurs very Recovery Diodes should soon become mechanism is the important one. Fur- rapidly — in less than a nanosecond — available which will be capable of ap resulting in a fast current step that is proaching 1 watt in the 1 to 2 Gc range rich in harmonics. In fact, harmonics and 50 to 100 milliwatts in the 8 to to above the 100th can be obtained at 12 Gc range. "" ' Self Bias Voltage In harmonic-generating work the high efficiency of the Step Recovery Diode compared to conventional di odes occurs because of the basically-dif ^ ferent generating mechanism involved in the two cases. Conventional diodes, such as varactors, are operated within their reverse saturation region so as to avoid both forward conduction and -i(eb-o) avalanche breakdown. Under these conditions the diode acts as a voltage- variable having some dissi Fig. 5. Oscillogram of current through a pation. The resulting capacitance-volt Step Recovery Diode when driven by a sine wave (50 Me). Abrupt transition on age characteristic is smooth and thus negative half-cycle occurs when stored does not generate appreciable high- Fig. 6. Drawing showing how level of bias charge becomes depleted and is an effi order harmonic power. For such diodes affects the amplitude of the diode current cient mechanism for generating discontinuity and thus the efficiency of harmonics (Fig. 1). the conversion efficiency in this mode harmonic generation.

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© Copr. 1949-1998 Hewlett-Packard Co. TABLE I. PRESENT STATE OF THE ART IN HIGH ORDER MULTIPLICATION WITH STEP RECOVERY DIODES

Fig. 7. Functional block diagram of harmonic multiplier.

ther, the output power of the Step Re 5. Provide high Q energy storage at onant at the output frequency, a con covery Diode can be shown by Fourier the output frequency. dition normally difficult to calculate analysis to decrease only as 1 /n when n 6. Provide appropriate bias for the since it depends upon geometric de is larger than 5. As a result, the Step diode, as described above. tails of diode mounting, the diode Recovery Diode is the most practical These criteria are met by either of parameters, the output circuit and the means available for generating moder the two designs shown in Figs. 9 and driving reactance. The diode should ate-power harmonics and is probably 10. In Fig. 9, a broadband input cir not be resonant at other harmonic fre the only practical means for generat cuit is utilized to permit making quencies. In practice one usually pro ing high-order harmonics. changes in frequency without retuning vides some reactive tuning device at the input. Fig. 10 shows a resonant the diode to adjust for best operation. DIODE BIAS input circuit which is simpler for fixed One such device is shown in Fig. 1 1 . Bias is required for these diodes frequency applications and still de Energy storage at the output fre in harmonic generators because they couples harmonics efficiently from the quency is needed to develop voltage on would otherwise conduct during the source. In either circuit self-bias of the the diode for maximum efficiency and entire drive-frequency cycle and no diode is satisfactory, but in some ap to eliminate undesired adjacent har electrical discontinuity would be pro plications it may be desirable to use monics. In the examples of Figs. 9 and duced. Under bias, however, and with fixed bias, and to control the bias 10, a double-tuned, quarter- wave-stub, lifetime much longer than the excita resistance. iris-coupled cavity is indicated. Any of tion period, the time integral of for The diode in its associated package many other configurations of wave ward current will be slightly larger and the output circuit should be res guide coaxial cavity could be used. than that of the reverse current. A large discontinuity may then be produced when conduction ceases, as shown in Fig. 6. In a circuit that is optimized hpa for efficient harmonic generation, the STEP RECOVERY DIODES current waveform may not be as sim HARMONIC GENERATION APPLICATIONS ple as is indicated in this figure since TYPICAL PERFORMANCE strong oscillatory components will be supported, and the conduction angle hpa Diode Upper Output will be strongly influenced by the Numbers Freq. Power Configuration reactance elements that are present. 0112,0113,0114 3Gc Milliwatts Glass HARMONIC MULTIPLIER 0151,0152,0153,0154 10 Gc Milliwatts Glass DESIGN 0251,0252,0253,0254 10 Gc Milliwatts Ceramic The functional block diagram of a single-stage multiplier is shown in Fig. 7. PULSE-SHAPING APPLICATIONS The design of the Step Recovery Di TYPICAL PERFORMANCE ode harmonic generator circuit should: hpa 1. Resonate the diode at the output Diode frequency. Numbers 2. Provide a broadband reactive ter 0151, 0152, 0153, 0154 mination for unwanted harmonics. 0251, 0252, 0253, 0254 .1. Match input power down to the diode impedance (1-1 On). 0102, 0103 4. Tune out the circuit susceptance 0112, 0113 at the input frequency.

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© Copr. 1949-1998 Hewlett-Packard Co. I

Fig. Step Broadband stripline circuit used in bench work with Step Recovery Diode. Either glass or ceramic style diodes can be accommodated as shown.

The cavities should have high Q to then adjusted for maximum power insertion loss. The estimated total cir reduce insertion loss at the desired out output and efficiency. cuit losses of the circuit described are put frequency while simultaneously Additional application information approximately 2.5 to 3 db. eliminating adjacent harmonics. An is given in the hpa Application Note The operation of the circuit is sim alternative description of the require "Harmonic Generation with Step Re ple and replacing a diode requires a ment is to say that enough energy covery Diodes!' minimum of retuning time to achieve should be stored so that it is not de A TYPICAL SINGLE-STAGE a stable maximum output power. The pleted appreciably by the load in the X20 MULTIPLIER tuning requires only that the variable interval between impulses from the A single-stage X20 Step Recovery and capacitor be adjusted lor drive frequency. This means suppress Diode multiplier was designed using best input match and the sliding short ing tiie AM modulation of the output the principles previously cited. An ef be positioned for maximum output at the drive frequency. The degree of ficiency in excess of 10%, or 2/n where power. suppression desired will depend upon n is the harmonic number, was Various hpo Step Recovery Diodes the application and will determine the achieved by this technique using vari were substituted in this X20 multi amount of output filtering required. ous bpcr Step Recovery Diodes. The plier and Table II shows a summary To i educe neighboring sidebands in a circuit of the multiplier and associated of the average experimental results X20 multiplier by 20 db, for example, filter are shown schematically in Fig. obtained with the different types of a loaded Q of about 300 is needed. 12. diodes. In addition, single-stage Xlf> Adjustment of multipliers using the The Step Recovery Diode is placed multipliers have been built which Step Recovery Diode is a simple pro in series with the input resonator have conversion efficiencies greater cedure. The output resonator should which is of the shorted type. The only than 20% and outputs greater than be pre-aligned to resonate at the adjustment of the diode reactance and 100 mw at 1.5 Gc. At 10 Gc output proper frequency, and the input fre microwave circuit impedance required levels in excess of 20 mw have been quency and power level set. The diode is by use of the sliding short shown in obtained when driven by 1.25 Gc. self-bias resistance, the output circuit the figure. The 2000 Me output filter DIODE SELECTION resonance with the packaged diode, is a six-resonator interdigital structure With respect to Step Recovery Diode and the input matching circuit are with a bandwidth of 20 Me and a 2 db requirements for efficient harmonic

Fig. 9. Basic circuit of a broadband type harmonic generator.

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© Copr. 1949-1998 Hewlett-Packard Co. Fig. 10. Basic circuit of a single-frequency harmonic generator. generation, it is usually desirable that the minority carrier lifetime T be at TABLE. II. AVERAGE OPERATING RESULTS least three times the period of the ex X20 MULTIPLIER citation frequency, and that the transi tion time t, be shorter than i/2 the period of the output frequency. A long value of Tallows for a large amount of stored charge for conversion to har monic power. It also simplifies estab lishing appropriate bias conditions lor the diode. The conversion efficiency depends on the speed and amplitude of the tions are lacking, diode efficiencies up The efficiency at the diode is plotted transition time tt. Step Recovery Di to 30% have been achieved experi against transition time tt which is odes with transition times less than mentally in the previously cited X20 measured in units of the period T of one-half of the period of the desired multiplier. the output frequency. The region tt/T output frequency achieve efficiencies The probable practical limit of ef <0.2 is extrapolated. Approximately in excess of 1/n. The efficiency in ficiency for high-order multiplication •10 different diodes were used to obtain creases as the transition time becomes obtained by extrapolating data to the the data for this graph. Data on many short compared to the period of the limit of zero transition time is approx more diodes in C-band multipliers output frequency until it is one-tenth imately 40%. confirm the general relation shown or less. Although theoretical predic Fig. 1 3 shows the efficiency obtained here. tions other than the 100% efficiency using the hpa X20 multiplier from For a given output frequency, it is permitted by the Manley-Rowe rela- a 100 Me input to a 2000 Me output. also desirable to select a diode with the

Coaxial Cavity

Tuning Step Recovery Screw Diode

Fig. 11. Drawing showing use of tuning Fig. 12. Basic circuit of a X20 harmonic multiplier using a Step screw to resonate Step Recovery Diode at Recovery Diode providing a 2000-Mc output at the efficiencies desired output frequency. shown in Table II.

© Copr. 1949-1998 Hewlett-Packard Co. and the large voltage which they can 50 100 switch— more than 10 volts at 50 ohms. No other device presently offers this to- speed, amplitude variation, and con JO- venience. PULSE-FRONT SQUARING 20 Fig. 17 shows several basic circuits using the Step Recovery Diode for - 10- pulse-front squaring, for generating fixed delays, and for trailing-edge O 0.5 1.0 0 50 100 squaring. Fig. 17 (a) shows a basic cir cuit for pulse-front squaring in which li BREAKDOWN VOLTAGE the diode is placed in shunt with the I (VOLTS) load. It can be seen from this circuit Fig. 13. Efficiency of multiplier in Fig. 12 Fig. 14. Power output of multiplier in that, following the application of the as a function of diode transition time. Fig. 12 as a function of diode breakdown driving pulse which acts as a reversing voltage. current, the diode will reverse-conduct for a period of time. It then abruptly lowest values of diode series resistance acteristics make the Step Recovery Di exhausts its stored minority carriers so Ra and junction capacitance Cj to ode a very important device. It can be that the abrupt transition to cutoff oc achieve good circuit efficiency. used to square the rise and fall of fast curs, thereby generating a step in cur The effect on power output of diode pulses or to produce short, fixed de rent and voltage. This step can now be breakdown voltage and of input drive lays. Impulses, in turn, can be gen used as the sharpened front of the out level in a particular harmonic multi erated from the fast pulses. put pulse. Very fast output pulse rise plier are shown in Figs. 14 and 15. The value of the diodes in fast pulse times of a fraction of a nanosecond PULSE SHAPING work arises from a combination of can be generated by this means in one AND GENERATION their fast transition times, which are or more stages, depending upon the In fast pulse work its unique char- presently less than 100 picoseconds, speed of the driving pulse. Sufficient

DESIGN LEADERS

Robert D. Hall Stewart M. Krakauer

Bob Hall joined hpa in 1963 to work on an Stew Krakauer joined the — hp— Oscilloscope advanced program concerned with integrated Division in 1958 where he participated in the microwave semiconductor components. While development of the -hp— Model 185A/187A at hpa, he has applied network synthesis tech Sampling Oscilloscope. He subsequently be niques to obtain improved performance from came head of applications engineering in the diode , frequency multipliers, mixers — hp— Semiconductor Laboratories and con and other components and has developed tributed to the development of other fast- novel methods for constructing the necessary switching and high-frequency circuits that use circuits. A member of the American Physical semiconductor devices. He transferred to Society, Bob obtained a BA degree in Physics -hp- associates in 1962 where he now heads at Reed College and an MS degree in Mathe the applications group. Stew earned a BSEE matics at Stanford. Prior to joining hpa, he degree at Cooper Union and an MEE from spent five years as a research engineer con Polytechnic Institute of Brooklyn. Prior to join cerned with solid-state microwave components ing -hp-, he worked on electronic instrumen during which time he made important contri tation as applied to inertial navigation and to butions to the theory of oscilla physiological and radiological research. tors and . He holds several patents.

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© Copr. 1949-1998 Hewlett-Packard Co. bias current will generally be required to delay the transition until the ap r 20 plied pulse comes to a steady-state value. Figs. 17 (b) and (c) show the use of fast-recovery diodes to avoid small pedestal voltages and dc offsets. In these circuits the fast-recovery diode 100 200 300 400 500 600 700 isolates the load from the Step Recov P,n ery Diode until the voltage across the Fig. 15. Typical power output at 6000 Me as a function of input power for a diode with 28-uolt Step Recovery Diode has begun its breakdown voltage. Multiplication of input fre transition. Fig. 17 (c) also shows the quency is from 10 to 20 times. use of two stages to increase the speed of pulse-front squaring. Since the pulse In addition to pulse-front squaring, ing the bias current suitably tempera rise time that is applied to the second the circuits can be used to generate ture-dependent. stage is faster than the excitation impulses by differentiating the output pulse-front. TRAI LING-EDGE SQUARING pulse, less storage is required in the To square the trailing edge of pulses, second-stage diode. Hence, its transi PULSE DELAY the Step Recovery Diode can be placed tion speed can be faster. The actual In Fig. 17 (a) it can be seen that the in series with the load, as shown in rise times will depend upon the im time interval between the application Fig. 17 (d). Very fast trailing edges are pedance of the associated circuitry. of the drive pulse and the occurrence thus possible. Combinations of lead However, tens of volts or hundreds of of the sharpened pulse-front will de ing- and trailing-edge squaring can be milliamperes can be switched by this pend on the stored charge and hence used to obtain square, fast pulses, as arrangement with fractional nanosec on the forward bias current. Accord shown in Fig. 4. ond risetimes. ingly, this time interval can be varied The voltage and current levels are from about 1 to 1,000 nanoseconds by GENERAL established by the external circuit and varying the bias current. Thus, a con The Step Recovery Diode is unique are limited only by the reverse break venient method is available for gen in its efficient conversion of power up down voltage of the diode and diode erating delay. The method is simple to high harmonic order in a single dissipation. Thus, the diode can switch and has a sharply-defined end point. stage. It exceeds the performance of many watts without exceeding its The effect of temperature changes on the conventional varactor diode be rated dissipation. the delay can be compensated by mak cause its functional non-linearity is

SPECIFICATIONS TYPICAL hpa STEP RECOVERY DIODES

hpa 0103 hpa 0106 hpa 0112 hpa 0151 hpa 0253 Sym. Characteristic Min. Typ. Max. Min. Typ. Max. Min. Typ. Max. Min. Typ. Max. Min. Typ. Max. Units Test Conditions

Lifetime : Transition Time 200 300 100 150 100 150 Capacitance 20.0 : • VR = O V, f = 1 me B, Breakdown Voltage Leakage Current ,^ -10 V, TA = Forward Current Vc= 1.0 V Inductance Package Std. Glass Ceramic Std. Glass Small Glass Ceramic Unit price $18.75; $14.00 $75.00; $50.00 $18.75; $14.00 $25.00; $16.70 $125.00; $85.00 (1 and 100 lots)

Specifications on other hpa diodes available on request. Data subject to change without notice. Prices f.o.b. factory. hp associates 620 Page Mill Road Palo Alto, California 94304 (415) 321-8510

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© Copr. 1949-1998 Hewlett-Packard Co. Step Recovery Diode

(SHUNT-SINGLE STAGE) (A) PULSE- FRONT SQUARING

/-Fast Recovery Diode

i-VW-KHt Vf* -o

Õi(TjjI U-^_ Step Recovery Diode (SHUNT- WITH CLIPPING) (B) PULSE-FRONT SQUARING

Recovery Diodes

Fig. 16. (a). Very fast step (200 picosec onds) obtained with Step Recovery Diode; Step Recovery Diodes (b) driving step. Sweep time 2 nsec/cm. (SHUNT -2 STAGE WITH CLIPPING) (0 PULSE-FRONT SQUARING greater. It also has the distinct advan ti tage over all other multiplying tech |j> /Step Recovery Diode niques that it is attractively simple. It can accomplish in a single stage what 'Hl·lVt o requires a series of stages of other mul e tipliers and does so without the com < plexity anil complication of idlers and with very little parametric up-conver- (SERIES) sion of noise. (D) TRAILING-EDGE SQUARING In pulse applications the diode can be used to achieve pulses with a com Fig. 17. Circuit arrangements using Step Recovery Diodes to sharpen leading and trailing edges of pulses and to obtain pulse bination of speed and amplitude not delay. obtainable with other devices. ACKNOWLEDGMENT Several people have contributed to the design of the hpa Step Recovery hpa "Hot Carrier Diodes" Diodes, but the undersigned wish to "The PIN Diode" DIODE "The Hot Carrier Microwave Mixer cite particularly the contributions of Diode" M. M. Atalla and Mason A. Clark. APPLICATION NOTES -Robert D. Hall and hp associates, -hp-'s affiliate which Any of these are available on request. Stewart AI. Krakauer designs and produces the Step Recovery Address all requests as well as any and Diodes discussed in this issue, has pre all questions concerning hpa devices pared several application notes giving directly to: REFERENCES further information on these and other hp associates S. Krakauer, "Harmonic Generation, Rectifica diodes. Titles are: tion, and Lifetime Evaluation with the Step Re 620 Page Mill Road covery Diode," Proc. IRE, Vol. 50, July, 1962. "Harmonic Generation with Step Palo Alto, California 94304 2 R. Hall, "Harmonic Generation with Step Recov Recovery Diodes" (415) 321-8510 ery Diodes," hpa Application Note No. 2. ' Moll, Krakauer, and Shen, "P-N Junction Charge Storage Diodes," Proc. IRE, Vol. 50, pp 4353; January, 1962.

© Copr. 1949-1998 Hewlett-Packard Co.