Hammershaimb, E.

Jeppesen, Palle

Jeppsson, B

Jondrup, P

Kallback, B

Schjær-Jacobsen, Hans

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On the Design of Transferred Electron Oscillators and Amplifiers

Online Research Database In Technology

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Downloaded from orbit.dtu.dk on: Dec 17, 2017On the Design of Transferred Electron Oscillators and AmplifiersHammershaimb, E.; Jeppesen, Palle; Jeppsson, B; Jondrup, P; Kallback, B; Schjær-Jacobsen, HansPublished in:3rd European Microwave ConferenceLink to article, DOI:10.1109/EUMA.1973.331623Publication date:1973Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Hammershaimb, E., Jeppesen, P., Jeppsson, B., Jondrup, P., Kallback, B., & Schjær-Jacobsen, H. (1973). Onthe Design of Transferred Electron Oscillators and Amplifiers. In 3rd European Microwave Conference (Vol.Volume 1, pp. 1-5). IEEE. DOI: 10.1109/EUMA.1973.331623A.1.3.ON THE DESIGN OF TRANSFERRED ELECTRON OSCILLATORS ANDAMPLIFIERSE. Hammershaimb, P. Jeppesen, B. Jeppsson, P. J$ndrup, B. Kallback"H. Schjaer-JacobsenLaboratory of Electromagnetic Theory 'Microwave Institute FoundationTechnical University of Denmark StockholmLyngby SwedenDenmark1. IntroductionGaAs transferred electron devices can be operated both as oscillators andstable, reflection-type, amplifiers. A most important feature of the supercriti-cally doped stable device is the very large gain-bandwidth product potentiallyavailable. Therefore section 2 of this paper presents a computer aided optimi-zation procedure for the design of amplifiers in order to fully utilize the wide-band properties of the device. It is of importance also for the construction ofoscillators, both single frequency and tunable, to be able to establish simple de-sign criterions. In section 3 it is shown that there exists a gradual transitionfrom the small signal properties of the stable device to the large signal behav-iour of the oscillator and that therefore it is a fruitful approach to treat Xt CWtransferred electron oscillator from the amplifier point of view rather than asthe conventional travelling high-field domain device. Thus useful oscillator de-sign criterions can be derived from the easily evaluated properties of the stabledevice.2. Amplifier designIn this section a computer aided design of a multiple slug coaxial trans-ferred electron amplifier is presented. The strength of the method stems fromthe fact that it is based directly on the measured small signal impedance of thepackaged device and on an accurate model of the microwave circuit. Thus thedesign does not involve any assumptions of the device impedance. Instead themeasured small signal impedance is used directly in a nonlinear optimizationprocedure, in which the calculated minrimum gain in the prescribed frequencyrange is maximized while the resulting ripple is kept under control.A multiple slug 50 2 coaxial circuit is used serving the double purpose ofproviding both reactive response shaping and real impedance transformation be-tween the load and the diode. Loss in the coaxial transmission line as well asstep susceptances are included in the computer model of the circuit.The stable GaAs device is mounted at the end of a 50 Q coaxial line and cha-racterized by the measured small signal device impedance, Zd. Fig. 1 showsa typical example of the frequency dependent Zd = Rd + jXd measured on a Hew-lett Packard automatic network analyzer. Fig. I also shows the correspondingchip impedance, Z c' for the unpackaged device.Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on June 30,2010 at 11:45:26 UTC from IEEE Xplore.  Restrictions apply. A Nyquist stability analysis shows that the unpackaged device is both opencircuit stable (OCS) and short circuit stable (SCS). For a driving source impe-dance, R, it will thus remain stable for any Rg. The packaged device howeveris OGS bd't SCU and therefore it will remain statle for Rg>xRd ('K) but becomeunstable for Rg <-Rd (fQ. This is the reason why the packaged device is stablein a 50Qmatched transmission line When the packaged device is tuned by a cir-cuit impedance, ZL = Rb + jXL, stability can be ensured by keeping RL >--Rd, mi irrespective of XL.For the sake of brevity the theoretical optimization and the correspondingexperimental verification is restricted to an illustrative example based on thepackaged device impedance Zd in Fig. 1. The theoretical and experimentalgain-frequency response for this example is shown in Fig. 2. A coaxial circuitwith three slugs was used here giving a voltage gain- 3 db bandwidth product of6. 5 GHz.3. Oscillator designIt has been found that GaAs devices normally used in CW oscillators alsoeasily can be stabilized and used as amplifiers. It is suggested here that CWtransferred electron oscillators often operate in a mode that can be characte-rized from an amplifier point of view rather than from the conventional ap-proach assuming travelling high-field domains. For these cases, that of courseexclude highly non-sinusoidal voltage excitations, useful design criterions foroscillator construction can be established fronm the easily obtained propertiesof the stable devices. Thus also bias voltage and temperature effects can be in-cluded. Evidence for the gradual transition from the small signal properties ofthe stable device to the large signal behaviour of the oscillating device is givenbelow.Typical measuredsmall-signal admittances for stable GaAs n+nn+-devicgsare shown in Figs. 3 and 4. The diodes are doped to approximately 1. 2 101cm- shave low-field resistances around 10 ohms and thermal resistances a-round 1 00°C/W The admittances given in these figures are chip admittances.The microwave package has been modelled by an optimization and modellingprocedure described at this conference (1)Figs. 3 and 4 show that for increasing bias voltage and temperature the ne-gative conduictance curve moves towards lower frequencies. For this type ofdevice very wide-band amplifier or oscillator operation can therefore be ac-complished over a broad temperature range by means of voltage compensation.Diodes of the type above have been operated as o3cillators in a coaxial slugcircuit. For a fixed circuit Fig. 5 shows the operating frequency and outputpower as a function of bias voltage The diode oscillates at 11. 327 GHz with anoutput power of 9.0 mW for a bias voltage of 7. 5 volts and at 11. 200 GHz with20 mW at 9 volts. The impedance ZL (f) of the circuit, measured after remov-ing the diode, is plotted from 11. 0 to 11. 4 GHz in the Smith chart in Fig. 5.The stable device impedance, Zd (I1) as a function of RF-drive was then mea-sured in a 50 Q circuit at 11 200 GHz for a bias of 9 volts and at 11. 327 for7. 5 volts. The resulting curves for -Zd (I ) are also shown in the Smith chart.As expected the crossover point between ZL(f) and -Zd(I1) occurs for a higherRF-drive level for the highest power operation at 11. 200 GHz. For this fre-quency and the bias voltage of 9 volts the device impedance is shown in moreAuthorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on June 30,2010 at 11:45:26 UTC from IEEE Xplore.  Restrictions apply. detail in Fig. 6 along with the added power, both as a function of RF-drive. Thecircuit impedance ZL = RL + jXL =(3. 5 + j5. 8) Q and the oscillator output powerof 20 mW have been indicated. Excellent agreement is obtained and the smalldifference in measured oscillator power and added power is probably caused bylosses in the oscillator circuit.The experiment presented above demonstrates that accurate and detaileddesign criterions for CW transferred electron oscillators can be derived froman analysis of the stable device impedance and its dependence on RF-drive,bias voltage and temperature. For a great number of applications however onlya measurement of the small signal properties provides the necessary informa-tion for the oscillator design.Reference(1) Altmae, M. "Interactive microwave circuit design program package forminicomputers", Proc. 1973 European Microwave Conf. This issue,Brussels Sept. 4-7, 1973.iz4I-rhFREQUENCY (GHz)101GAINI X BW a 6.5 GHzEXPERIMENTAL5; XATHEORETICALSWaB 3.67 GHz0 a6 i_6 7 8 9 10 11 12FREQUENCY (GHz)Typical measured imped-O.54wz4I~-U4chiance for packaged(zd =Rd + jxd) andpackaged (Zc = RB +TED. Device data:1.5 X 10X cm-3Un-jX)jxcn =0L = 12pm, Ro = 5.6Q,VO = 7.8V. Package data:L = 0.325 nH, L2 = 0.300nH and C = 0.385 pF.Fig. 2Experimental and theoret-ical gain-frequency re-sponse of a three-slugamplifier for packageddevice impedance Zd ofFig. 1.a~01o0zAuthorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on June 30,2010 at 11:45:26 UTC from IEEE Xplore.  Restrictions apply. 12 14FREQUENCY IGHz)EEwL)zA111U)w0E-Fig. 3Typical measured frequency and biasdependence for small-signal chip ad-mittance for stable GaAs n nn+- de-vice. Device data: n = 1.2 x 10150cm 3, L = lOpm, R = lOQ, thermalresistance 1000 C/W.Fig. 4Typical measured frequency and tem-perature dependence for small-signalchip admittance for device in Fig. 3..FREQUENCY 1GHz)E 10Ew056-152-105-0Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on June 30,2010 at 11:45:26 UTC from IEEE Xplore.  Restrictions apply. Fig. 5 Oscillator output power and frequency versus bias voltage for devicein Fig. 3 mounted in fixed coaxial circuit. Also shown are corres-ponding coaxial circuit impedance ZL from 11.0 to 11.4 GHz andnegative device impedance-ZD vs. increasing drive level for twosets of bias voltage and frequency.a)w111c)w0-aCr20 50 100INCIDENT POWER (mW)Fig. 6 (a) Negative resistance and reactance vs. incident power for oneof the device impedances in Fig. 5. (b) Corresponding added power.'iu5 _ _ f /REACTANCE 1l _ _ _ m_ _ _I RESISTANCEO0I I1 25 10 20 50 1 100 200 500 1000IAuthorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on June 30,2010 at 11:45:26 UTC from IEEE Xplore.  Restrictions apply. 

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On the Design of Transferred Electron Oscillators and Amplifiers

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