X-BAND MMIC AMPLIFIER WITH ANON-CHIP TEMPERATURE COMPENSATION CIRCUIT

Kazuhisa Yamauchi, Yoshitada Iyama, Mamiko Yamaguchi, Yukio Ikeda, Tadashi Takagi and Yutaka Kazekami

MITSUBISHI ELECTRIC CORPORATION5-1-1 Ofuna, Kamakura, Kanagawa, 247, Japan

ABSTRACTAn X-band MMIC amplifier with an on-chip

temperature compensation circuit has been presented.The temperature compensation circuit is composed of adiode and a resistor. The compensation circuit isapplied to a 4 stage X-band MMIC amplifier. The gainvariation is improved from 5.5dB to 1.3dB in thetemperature range between -10deg and +80deg.

I. INTRODUCTIONIn recent years, there have been increasing demands

for amplifiers with small variation of gain and outputpower with temperature. However, it is known thatGaAs FET amplifiers are seriously affected bytemperature variation resulting in gain spread ofseveral dB for amplifiers. Therefore it is necessary toimprove temperature characteristics of the amplifier.

In order to compensate gain variation withtemperature, drain current and input power of theamplifiers are controlled by off-chip regulators withtemperature sensors in transmitter modules. As a result,the modules become larger. To realize the smallmodules, the preferable design solution is theamplifiers with an on-chip temperature compensationcircuit [1,2].

In this paper, we present an X-band MMICamplifier with an on-chip temperature compensationcircuit. The compensation circuit is composed of adiode and a resistor. The presented compensate circuitutilizes the temperature characteristics of the diode,that is, the decreasing threshold voltage of the diodewith the increase of temperature. The gain variation iscompensated by controlling gate voltage of theamplifier. It has be noted that the presented circuit isthe one of the most miniature temperaturecompensation circuits. Such a circuit can be easilyintegrated into a single GaAs MMIC chip. Thecompensation circuit is applied to a 4 stage X-bandMMIC amplifier with a small gain of 32dB at 25deg at

center frequency. With the presented circuit, the gainvariation is improved from 5.5dB to 1.3dB in thetemperature range between -10deg and +80deg.

II. GAIN OF AMPLIFIER WITH TEMPERATUREThe gain of a GaAs FET amplifier decreases with

the increase of temperature, while the gain of the FETamplifier whose drain current is at class AB increaseswith the increase of the gate voltage. To compensategain variation of an amplifier with temperature,controlling gate voltage of FET with temperature canbe used. Fig.1 shows the measured small signal gain ofthe amplifier at the three temperature points, -20deg,+25deg and +70deg, as a function of gate voltage. Thesingle stage amplifier employs a MESFET with gatewidth of 900um. Fig.1 shows that the gain can be keptconstant in the temperature range between -20deg and+70deg by adjusting gate voltage of the amplifier whenthe gain of the amplifier is less than 7dB. The gain isexpected to be as high as possible. The gate voltage isnecessary to be varied from -3.4V to -3V to achieveconstant gain of 7dB in the temperature range between-20deg and 70deg as shown in Fig.1. Therefore thecompensation circuit is demanded that the gate voltageof the amplifier is varied from -3.4V to -3V in thetemperature range between -20deg and +70deg.

III. TEMPERATURE COMPENSATION CIRCUITThe gain variation of the amplifier can be

compensated by increasing the gate voltage with theincrease of temperature as mentioned in previoussection. Therefore, the circuit providing the increase ofgate voltage with temperature is required tocompensate gain variation. In this chapter thetemperature compensation circuit which is composedof a diode and a resistor is presented, and the operationprinciple of the compensation circuit is explained.Fig.2 shows the schematic diagram of the temperaturecompensation circuit. The compensation circuit

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realizes an on-chip circuit configuration. It has to benoted that the presented circuit is the one of the mostminiature temperature compensation circuits. Value ofgate voltage Vg is determined by reference voltage Vrand gate control voltage Vgc as shown in Fig.2.

The compensation circuit shown in Fig.2 utilizesthe temperature characteristics of the diode, that is, thedecreasing threshold voltage of the diode with theincrease of temperature. To verify the increase of gatevoltage under the varying temperature, the gate voltagewith temperature has been measured in a widetemperature range as shown in Fig.3. The MESFETconnected drain with source is employed instead of thediode. The gate voltage becomes larger with theincrease of temperature and the rate of increasing gatevoltage is 1mV/deg as shown in Fig.3. To achieve thevariable range of 0.4V presented in Fig.1, the 4 diodesshould be connected in series.

IV. APPLICATION TO AN X-BAND AMPLIFIERThe presented temperature compensation circuit is

applied to an X-band amplifier. Fig.4 shows theschematic diagram of the 4 stage MMIC amplifier withthe temperature compensation circuit. It is required forthe MMIC amplifier to simultaneously achieve bothlow power consumption and high gain. 4 stage MMICconfiguration is used to provide high gain. To achievelow power consumption, the drain circuit is operated atclass AB. Further, more it is required for the MMICamplifier to achieve good gain flatness in broadfrequency band. Every inter-stage of the MMICamplifier is matched to achieve a good gain flatness inbroad frequency band. To miniaturize the chip size,matching circuit with short stubs are employed at eachstage. The short stubs can be useful as both matchingcircuits and dc feed lines. Gate width of each FET ischosen to achieve low power consumptionsimultaneously. The X-band MMIC amplifier with thecompensation circuit has been developed. Fig.5 showsthe photograph of the MMIC amplifier. Thecompensation circuit is integrated with the X-bandMMIC aplifier on a sigle GaAs chip.

To demonstrate the capability of the temperaturecompensation circuit, temperature characteristics of theMMIC amplifier is measured. The measured small

signal gain of the MMIC amplifier with and withouttemperature compensation circuit at -10deg, 25deg and80deg are shown in Fig.6. The bias of the MMICamplifier is fixed at 25deg. It is clearly shown in Fig.6that the designed circuit compensates the gain variationwith temperature. The amplifier achieves the smallsignal gain of 32dB at 25deg at the center frequency.The measured gain variation with temperature at centerfrequency is shown in Fig.7. It demonstrated in Fig.6and Fig.7 that the gain variation of the MMIC amplifieris improved from 5.5dB to 1.3dB in the temperaturerange between -10deg and +80deg by using thecompensation circuit. Therefore, the compensationcircuit is suitable to compensate gain variation of amicrowave amplifier within wide temperature range.

V. CONCLUSIONSAn X-band MMIC amplifier with an on-chip

temperature compensation circuit has been presented.The temperature compensation circuit is composed of adiode and a resistor. The compensation circuit utilizesthe temperature characteristics of the diode. Thevariation of the amplifier is compensated withtemperature by increasing the gate voltage with theincrease of temperature.

The compensation circuit is applied to a 4 stage X-band MMIC amplifier with a small gain of 32dB at25deg at center frequency. The gain variation isimproved from 5.5dB to 1.3dB in the temperaturerange between -10deg and +80deg with the circuitpresented. The compensation circuit is suitable tocompensate gain variation of a microwave amplifierwithin wide temperature range.

References[1] Kevin W. Kobayashi, Keven MacGowan, Richard

Kono,and Ling-Shine Jane Lee, "A Monolithic DCTemperature Compensation Bias Scheme forMultistage HEMT Integrated Circuits", IEEETrans., Microwave Theory Tech., Vol.44,No.2,February 1996

[2]V.Alleva and F. Di Paolo, "TemperatureCompensation Circuit for Linear MicrowaveAmplifier", IEEE MGWL, Vol.6, No.6, June 1996

-3.5 -3 -2.50

2

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10

Vg[V]

Gai

n[dB

]

-20deg +25deg +70deg

∆Vg=0.4V

Figure 1 Measured small signal gain of the amplifierwith temperature

Vr

Vg

Vgc R

RF IN RF OUT

temperature compensation circuit

Figure 2 Schematic diagram of the temperaturecompensation circuit

-20 0 20 40 60 80-0.8

-0.7

-0.6

-0.5

Temperature [deg]

Vg[

V]

Vr=-1V Vr=-3V Vr=-5V

Vgc=0VR=1kΩ

Figure 3 Measured gate voltage of the temperature compensation circuit

RF IN

RF OUT

Figure 4 Schematic diagram of the 4 stage MMIC amplifier with the temperature compensation circuit

3.7mm

3.4m

m temperaturecompensation circuit

Figure 5 Photograph of the X-band MMIC amplifier with the temperature compensation circuit

without compensation circuit05

10152025303540

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Gai

n[dB

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80deg25deg-10deg

05

10152025303540

6 7 8 9 10 11f [GHz]

Gai

n[dB

]

with compensation circuit

80deg25deg-10deg

Figure 6 Measured small signal gain of the MMIC amplifier

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-10 0 10 20 30 40 50 60 70 80

Temperature [deg]

Gai

n[dB

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without compensation circuitwith compensation circuit

Figure 7 Measured gain variation of the MMIC amplifier with temperature