Ryo Ishikawa

Group Delay Equalized UWB InGaP/GaAs HBT MMIC Amplifier Using Negative Group Delay Circuits

A negative group delay (NGD) circuit has been employed to equalize a group delay variation in a broadband ultra-wideband (UWB) InGaP/GaAs heterojunction bipolar transistor (HBT) monolithic microwave integrated circuit (MMIC) amplifier. Using the NGD circuit, a part of a salient group delay characteristic in the operation band of broadband amplifiers can be suppressed without an increase of the entire group delay. The MMIC amplifier has a steep group delay increase in the lower frequency region of the full-band UWB band (3.1-10.6 GHz) due to the sum of phase variations near the cutoff frequencies of the HBTs. The NGD circuit has been inserted to reduce this increase of the group delay in the UWB band. By adding a three-cell NGD circuit while considering input and output matching at the input side of the MMIC amplifier, the group delay variation is decreased by 78%. However, gain was also decreased by insertion of the multistage NGD circuit. In an attempt to avoid this decrease in gain, a one-cell NGD circuit was inserted into the feedback loop of the MMIC amplifier, and as a result, we were able to decrease the group delay variation by 79%, with minimal gain deterioration.

5.65 GHz High-Efficiency GaN HEMT Power Amplifier With Harmonics Treatment up to Fourth Order

A high-efficiency GaN HEMT power amplifier with harmonics treatment up to the fourth order has been developed at the 5.8 GHz band. The harmonics treatment was applied by considering the influence of feedback and shunt capacitance in the GaN HEMT, to reduce the average power consumption in a GaN HEMT including parasitic elements. The fabricated GaN HEMT amplifier delivered a maximum power-added efficiency of 79% and a maximum drain efficiency of 90% at 5.65 GHz, and the saturated output power was 33.3 dBm. This value represents state-of-the-art C-band performance efficiency.

Inverse Class-F AlGaN/GaN HEMT Microwave Amplifier Based on Lumped Element Circuit Synthesis Method

A lumped element design method considering more than third-order higher harmonic frequencies for a microwave AlGaN/GaN HEMT inverse class-F amplifier has been developed. The load circuit consists of a series reactance network having zero impedance at the odd order harmonic frequencies and poles at the even order higher harmonic frequencies as well as a shunt reactance network having zero impedance at the odd order harmonic frequencies. A fabricated AlGaN/GaN HEMT inverse class-F amplifier delivered a power-added efficiency of 76.3% and a drain efficiency of 78.3% at 879 MHz.

A High-Efficiency Low-Distortion GaN HEMT Doherty Power Amplifier With a Series-Connected Load

A distortion reduction method for a newly developed GaN HEMT Doherty amplifier (DA) with a series-connected load operating at 1.8 GHz is presented. Differing from conventional DAs with shunt-connected loads, the newly developed DA with a series-connected load has high input impedance, resulting in low-loss impedance matching and high-efficiency power combining. A distortion cancellation mechanism and its condition are derived, where odd-order nonlinear factors of transistors are considered, so as to retain inherent distortion cancellation between a peaking amplifier and a carrier amplifier. The validity of the design method is demonstrated using the developed 1.8-GHz GaN HEMT DA with a series-connected load. The third-order intermodulation distortion of the DA is improved by more than 15 dB at output powers from 5 to 20 dBm, compared to the case giving priority to power efficiency. The developed amplifier delivers a power-added efficiency (PAE) of 31% at an output power of 24 dBm, corresponding to 10-dB input backoff from a saturated output power of 31 dBm with a PAE of 58%. The proposed distortion reduction method can also be applied to shunt-connected-load-type amplifiers of other devices.

A GaN HEMT Doherty amplifier with a series connected load

Doherty introduced two types of concepts for high-efficiency amplifiers in 1936. One involved a shunt connected load and the other involved a series connected load. The first one is well known. We propose a microwave Doherty power amplifier with a series connected load using baluns. A 1.9 GHz GaN HEMT Doherty power amplifier was designed and fabricated. At 24 dBm middle and 31 dBm saturated output powers, the amplifier realized improved power efficiencies of 31 % and 56 %, respectively, compared to power efficiencies of 15 % at 24 dBm output power and 57 % at 34 dBm saturated power, respectively, obtained with a reference push-pull amplifier.

High-Efficiency GaN-HEMT Class-F Amplifier Operating at 5.7 GHz

We report on the design, fabrication, and measurement results of a high-efficiency class-F amplifier using an AlGaN/GaN HEMT at 5.7 GHz. Because of their higher operating voltage, GaN devices are expected to have higher operating efficiency as compared to GaAs devices. The fabricated amplifier using a low-loss resin microstrip substrate validated high efficiency expectations with a maximum drain efficiency of 77.1%, maximum power added efficiency of 68.7%, and output power of up to 34.5 dBm at 5.69 GHz.

Group delay compensation technique for UWB MMIC using composite right/left-handed circuit

A group delay equalizer consisting of a composite right/left handed (CRLH) circuit in parallel with a right handed (RH) circuit is proposed for UWB RF components. Dispersion characteristics and group delay characteristics for the proposed circuit are described. A group delay compensation circuit was designed for the developed InGaP/GaAs HBT MMIC amplifier with an active balun. It is demonstrated that the measured standard deviations of group delay can be reduced from 16.5 psec in S21 and 12.4 psec in S31 to 4.4 psec in S21 and 7.7 psec in S31, respectively, in a circuit simulation.

A broadband Doherty power amplifier without a quarter-wave impedance inverting network

A new Doherty power amplifier topology without a quarter-wave impedance inverting network is proposed. This topology enables the enhancement of amplifier bandwidth and achieves a more compact amplifier size. In order to remove an inverting network, the output matching network of the carrier amplifier is designed to realize high performance both at a low-RF level in the off-state of a peaking amplifier and at the RF saturation level. A 1.9-GHz Doherty amplifier without a quarter-wave impedance inverting network was designed and fabricated using GaN HEMTs. A series-connection-type amplifier using an output-combining balun was realized in a lumped-element circuit configuration. The amplifier achieved a power-added efficiency (PAE) of 51% at an output power of 29 dBm under an 11-dB input back-off from a 34-dBm saturated output power with a power-added efficiency of 59%. A maximum PAE higher than 48% was obtained over a frequency range of 1.67 to 1.97 GHz.

A Miniature Broadband Doherty Power Amplifier With a Series-Connected Load

A microwave Doherty power amplifier (DPA) consists of a carrier amplifier (CA), a peaking amplifier (PA), and an impedance inverting network. In this paper, a novel DPA topology with neither the impedance inverting network nor offset lines is proposed. This topology enables the enhancement of amplifier bandwidth and achieves a more compact amplifier size. To remove the impedance inverting network and to realize high efficiency at large back-off power level, the output-matching network of the CA is designed to realize high performance both at a low signal power level in the off-state of the PA and at the saturated signal power level. A 1.9-GHz series-connected load Doherty power amplifier without an impedance inverting network is designed and fabricated using GaN HEMTs. The amplifier achieves a power-added efficiency (PAE) of 50% under a 6-dB output back-off from a 34-dBm saturated output power with a PAE of 59%. A maximum PAE higher than 44% is obtained over a frequency range of 1.63-1.98 GHz.

Doppler frequency up conversion of electromagnetic waves in a slotline on an optically excited silicon substrate

The Doppler frequency up conversion of microwaves in a slotline on an optically excited silicon substrate was experimentally observed. An array of 24 optical fibers with different lengths was used to effectively tilt the wave front of a 532 nm neodymium-doped yttrium aluminum garnet laser beam with a pulse duration of 33 ps. The tilted laser beam produced electron-hole surface plasma whose boundary moved at a relativistic velocity of about c/3.4 (c is the speed of light) along the slotline. The experiments showed that microwaves reflected at the moving boundary of the plasma in the slotline are converted to millimeter waves with a frequency up conversion ratio of 3.82.