S.L.G. Chu

A highly linear MESFET

A highly linear GaAs MESFET has been developed. This device incorporates a spike profile in its active channel and was designed specifically for linearity. A third-order intercept (IP3) and a 1 dB compression power of 43 dBm and 19 dBm, respectively, have been measured on a 400 mu m device at 10 GHz. The difference between these two numbers, 24 dB, is the largest yet reported for a MESFET. This device also dissipates only 400 mW of DC power yielding a linearity figure-of-merit (IP3/P/sub DC/) of 50.<<ETX>>

A novel 4-18 GHz monolithic matrix distributed amplifier

The authors describe the design, fabrication, and performance of a 4-18 GHz matrix distributed amplifier which incorporates a novel biasing scheme enabling the amplifier to run at higher voltages while drawing only half of the current of conventional multistage amplifiers having comparable gain levels. A voltage divider is used at the input of the FET pair to derive the gate bias, ensuring that both FETs are biased at the same point. This scheme enables the stages to be connected in cascade at RF frequencies and in cascode for DC biasing, thus conserving current. The amplifier shows >13 dB gain across the frequency band using a chip area of only 1.9 mm*2.1 mm.<<ETX>>The authors describe the design, fabrication, and performance of a 4-18-GHz matrix distributed amplifier. This amplifier incorporates a novel biasing scheme which enables the stages to be connected in cascade at RF frequencies and in cascode for DC biasing, thus conserving current. A gain of 14 dB+or-1.5 dB has been measured over the 4-18-GHz frequency band in a chip area of only 1.9 mm*2.1 mm.<<ETX>>

High linearity monolithic broadband pseudomorphic spike-doped MESFET amplifiers

A highly linear pseudomorphic spike-doped MESFET has been developed. This highly linear MESFET has been demonstrated at 10 GHz. Based on this device, two types of monolithic broadband amplifiers were designed and fabricated. Both the device and circuits achieved state-of-the-art linearity results while maintaining a low DC power consumption.<<ETX>>

A single chip 2.20 GHz T/R module

A single chip 2-20-GHz transmit/receive (T/R) module has been demonstrated. This MMIC (monolithic microwave integrated circuit) included a four-stage power amplifier chain, a four-stage low-noise amplifier chain, and two T/R switches. A selective ion implantation process was used. One implant profile was optimized for low-noise operation, and a second was optimized for power performance. All circuits were designed to be relatively insensitive to process variations to ensure adequate yield, despite the complexity of the chip. Distributed amplifiers were used throughout, and the T/R switches used a standard series-shunt FET configuration. All circuits were miniaturized to keep the total chip size small. The entire T/R is only 0.143 in*0.193 in (3.6 mm*4.9 mm).<<ETX>>

Modeling intermodulation distortion in GaAs MESFETs using pulsed I-V characteristics

A technique has been developed for modeling intermodulation distortion of GaAs MESFETs using pulsed I-V drain characteristics. The technique involves measuring the drain I-V characteristic using short drain and gate pulses from a DC operating point. This pulsed I-V characteristic is used to model the nonlinearity of the drain current source. In addition, S-parameters measured about the DC bias point are used to model the gate capacitance nonlinearity. These nonlinearities are combined into a single model, and the harmonic balance method is used to simulate intermodulation performance. This technique has been used to simulate the third-order intermodulation distortion of a spike-doped MESFET and to investigate sensitivities of source and load impedance and device nonlinearities on intermodulation performance.<<ETX>>

A 7.4 to 8.4 GHz high efficiency PHEMT three-stage power amplifier

This paper describes the design, fabrication, and performance of a 7.4 GHz to 8.4 GHz 3-stage PHEMT power amplifies. To the best of our knowledge, this amplifier has achieved the highest efficiency, power, and gain ever for a three-stage power amplifier at X-band. At a drain voltage of 6 volts, measured power added efficiency was between 50% to 60% with a CW power output of 35 dBm and an associated gain of 24 dB. The amplifier was stable over all measured biases and all drive levels.

A novel broadband bidirectional matrix amplifier

The design, fabrication, and performance of a 6-18 GHz, 2*5 bidirectional matrix distributed amplifier is described. This amplifier, having two bidirectional distributed amplifier chains stacked together, shares the same gain elements in both the transmit and receive directions. The amplifier has shown >10 dB gain with better than +or-0.5 dB of gain tracking and +or-5.0 degrees of phase tracking between the transmit and receive directions over the 7-17 GHz frequency band. In addition, the biasing scheme of this amplifier enables the stages to be connected in cascade at RF frequencies and in cascode for DC biasing, thus conserving current.<<ETX>>

A comparison of GaAs transistors as passive mode mixers

A number of GaAs transistors were evaluated as passive mode mixers with a 10 GHz RF and 2 GHz IF. Both single-tone and two-tone performance were measured for an ion implanted MESFET, spike-doped PsMESFET, a power PsHEMT and a npn power HBT. All were shown to have a substantially lower distortion than a comparable diode mixer. One transistor, the spike-doped PsMESFET, has a relative third order intercept point 20 dB higher than that of a diode mixer.<<ETX>>

A high linearity, high efficiency pseudomorphic HEMT

The authors report the third-order intermodulation distortion and phase deviation of 1.2-mm periphery double pulsed doped pseudomorphic high-electron-mobility transistors (HEMTs) at high levels of power and efficiency. A device tuned for single-tone power-added efficiency (PAE) of 59% with 0.87-W output power and 10.4 associated gain at 10 GHz could provide two-tone PAE of 50% with -19 dBc IM3/C and 0.30 W/tone. Single-tone phase deviation never exceeded 18 degrees from small signal with a phase deviation slope less than 3 degrees /dB. These measurements compare favorably to those of reported GaAs-based devices with comparable output power. A dry etched double recess structure was incorporated in the device for obtaining high reverse breakdown voltage and therefore high efficiency.<<ETX>>

A millimeter-wave monolithic matrix distributed amplifier

A millimeter-wave monolithic two-stage matrix distributed amplifier with greater than 11-dB gain from 16 to 38 GHz has been demonstrated. The two-stage matrix amplifier described here extends the matrix amplifier to millimeter-wave frequencies. The matrix amplifier topology yields a compact circuit with higher gain per unit area than a conventional distributed amplifier.<<ETX>>