N.L. Wang

Ultrahigh power efficiency operation of common-emitter and common-base HBT's at 10 GHz

The DC and RF characteristics of microwave power HBTs are described. Ultrahigh power-added efficiency is reported for AlGaAs-GaAs HBTs operating at 10 GHz in common-emitter (CE) and common-base (CB) modes. A record high 67.8% power-added efficiency with 11.6 dB associated gain was achieved with a CE HBT at a CW output power of 0.226 W, corresponding to a power density of 5.6 W/mm. With a CB HBT, 62.3% power-added efficiency with 11.85 dB gain and 0.385 W total CW power was demonstrated. Power saturation characteristics of CE and CB HBTs are compared. The importance of bias schemes is discussed. High-efficiency operation in near class B mode is described and compared with FET operation. An advantage of HBT over FET is the low leakage current during the off half cycle in class B operation. Stability conditions for CE and CB HBTs are discussed. >

High-performance MOCVD-grown AlGaAs/GaAs heterojunction bipolar transistors with carbon-doped base

Excellent microwave performance is demonstrated by metalorganic chemical vapor deposition (MOCVD) grown AlGaAs/GaAs heterojunction bipolar transistors (HBTs) with carbon-doped base. These devices achieve a current-gain cutoff frequency of 76 GHz and a maximum frequency of oscillation of 102 GHz. Varying the device structures allows the current gain to reach over 300 in structures with a base doping of 2*10/sup 19 /cm/sup -3/. A static divide-by-four divider implemented with C-doped base HBTs has been operated up to a frequency of 20.4 GHz. These results indicate the suitability of carbon doping for high-performance HBTs.<<ETX>>

A 30 GHz bandwidth AlGaAs-GaAs HBT direct-coupled feedback amplifier

A DC to 30 GHz broadband amplifier based on the Darlington connected transistors with series and shunt resistive feedback was implemented with self-aligned AlGaAs-GaAs heterojunction bipolar transistor (HBT) technology. The measured performance shows 7.8 dB of gain with -3-dB roll-off bandwidth of 30 GHz. Measured at 1 GHz, the noise figure was 5.7 dB, 1-dB compression power was 11 dBm, and the third-order intermodulation product intercept point (IP3) was 23.9 dBm.<<ETX>>

18 GHz high gain, high efficiency power operation of AlGaAs/GaAs HBT

Outstanding power performance has been achieved from an AlGaAs/GaAs heterostructure bipolar transistor (HBT) at 18 GHz. A common emitter HBT has achieved 48.5% added efficiency, 6.2-dB associated gain, and 0.17-W output power. Common base operation of the HBT exhibits higher gain at 18 GHz: 0.358 W (3.58 W/mm) was achieved with 11.4-dB gain and 43% added efficiency; at a reduced power level of 0.174 W (1.74 W/mm), 15.3-dB associated power gain was achieved with 40% efficiency. This performance compares favorably with the results reported for MESFETs, HEMTs (high-electron-mobility transistors), and PBTs (permeable-base transistors).<<ETX>>

4 W, 7-12 GHz, compact CB HBT MMIC power amplifier

Extremely compact, broadband, heterojunction bipolar transistor (HBT) power amplifiers (PAs) were demonstrated with excellent performance. Common base (CB) HBTs were used in three single-stage broadband power amplifier designs, 1 W, 2 W, and 4 W, covering 7 to 11 GHz. In addition, a 1-W common emitter (CE) HBT linear amplifier was studied for its intermodulation property for communication application. The CB HBT PAs show good scaling relation in output power level. The peak power added efficiency is 40% for both the 1-W and 2-W versions, and 34% for the 4-W version. The chip size is only 2.15 mm by 2.9 mm for the 4-W CB HBT power amplifier. The CE HBT PA provides 1-W saturated output power in class B operation. In class A linear operation, 0.4-W output power was achieved. A two-tone test showed that IM/sub 3/ is better than -20 dBc at 1-dB compression point.<<ETX>>

A high-efficiency HBT MMIC power amplifier

An AlGaAs/GaAs heterojunction bipolar transistor monolithic microwave IC (HBT MMIC) power amplifier is developed that demonstrates very high power-added efficiency, high gain, and broad bandwidth. It uses a cascode structure with four 200- mu m common-emitter HBT cells driving four common-base cells of the same size. This amplifier achieves over 14-dB gain from 6 to 10 GHz, with a peak power-added efficiency (PAE) of 47% at 7.5 GHz at an output power level of 31 dBm. This corresponds to a power density of over 3 W per millimeter of emitter length. Input and output matching networks, as well as biasing networks, are all contained within the chip, which measures 80*80 mils (2*2 mm).<<ETX>>

0.7 W X-Ku-band high-gain, high-efficiency common base power HBT

Small sized AlGaAs-GaAs HBTs (heterojunction bipolar transistors) have achieved excellent power performance throughout the microwave frequency band. With the implementation of the multi-via-hole design, the HBT performance (gain and efficiency) is maintained as the size increases. A 0.7 W common-base (CB) power HBT with performance around 10 dB gain and 50% PAE well into the Ku band is reported. The performance is comparable to the pseudomorphic HEMT in this frequency range. The yield and uniformity are excellent. The high bias voltage (9.3 V V/sub ce/) is also desirable from a system viewpoint. >

AlGaAs/GaAs P-n-p HBTs with high maximum frequency of oscillation

An investigation of P-n-p HBTs (heterojunction bipolar transistors) with an f/sub max/ of 39 GHz and an f/sub t/ of 19 GHz is presented. Power-added efficiency of 31% was obtained in an amplifier at 10 GHz. The design of the high-speed AlGaAs/GaAs P-n-p HBTs takes account of the large degeneracy in the heavily n-type GaAs base. This doping-dependent degeneracy can induce gradients in the valence-band edge to improve the base transit time. High injection efficiency can be maintained in spite of the large degeneracy by increasing the aluminum content of the emitter. HBTs with emitter aluminum contents of 40% and 75% are described.<<ETX>>

A multifunctional HBT technology

A self-aligned AlGaAs/GaAs HBT technology has been developed for the fabrication of both high-performance microwave circuits and high-performance digital circuits. The technology provides transistors with high f/sub max/ (up to 218 GHz), high f/sub t/ (up to 98 GHz), and high efficiency (power added efficiency higher than 67.8% at 10 GHz) microwave amplification to at least 20 GHz. A MMIC amplifier has demonstrated 7-dB gain between 14 and 24 GHz. Excellent performance of high-speed digital circuits, such as ring oscillators, frequency dividers, MUXs, DEMUXs, and phase detectors has also been achieved on the same wafer. A multifunction chip covering the entire microwave band is feasible. The technology requirements and self-aligned AlGaAs/GaAs HBT process for multifunction chip application are described. The performances of HBTs, MMIC, and high-speed digital circuits fabricated on the same wafer are reported.<<ETX>>

High power efficiency X-band GaAlAs/GaAs HBT

Excellent power performance from a common-emitter GaAlAs/GaAs HBT (heterojunction bipolar transistor) at 10 GHz is reported. Record high added efficiency of 67.8% and 11.6-dB associated gain were obtained, with 0.226-W output power. HBTs of various sizes were tested, and 55% added efficiency and 10-dB associated gain were obtained regularly. From the largest available device 0.63 W with 8-dB gain was obtained. The base current crowding effect does not appear in the HBTs tested. The operation of the HBT is analyzed and shown to be close to that of the class-B amplifier. The collector-current behavior with respect to the power level is explained. Harmonic content is found to be very low. Compared with other solid-state power devices at 10 GHz the HBT demonstrates the highest added efficiency and associated gain at high-output-power condition. In addition, the low HBT input Q factor eases broadband matching, making it the best candidate for microwave power application.<<ETX>>