Research on GaAs pHEMT Low Noise Amplifiers for Ka-band Applications
Date Issued
2015
Date
2015
Author(s)
Chen, Kuan-Wei
Abstract
This thesis describes the design of the Ka-band low noise amplifier (LNA) which is applied to the front end of a phase array system for satellite communications. The operation frequencies of the receiver and transmitter are 19.2 GHz and 29 GHz, respectively. In order to select the receiving left-handed or right-handed signal, the LNA design should include the function of switching signal path. According to the system requirements, the center frequency for LNA is 19.2 GHz with a bandwidth of 3 GHz, and the gain and the noise figure should be better than 18 dB and 1.3 dB, respectively. The DC power consumption is less than 21 mW. Because the leakage signal from the output of the PAs may degrade the linearity of LNAs, a 29-GHz resonator is added for the LNA to attenuate the leakage signal from transmitter. For low noise characteristics and flip-chip assembling consideration, 0.15-um GaAs pHEMT process with copper pillar for flip-chip connection, WIN PL15-15 EMR, is selected for this design. Because it is a new process, the data offered from foundry is not complete. To speed up the simulation with reasonable accuracy, the metal without thickness in EM simulation software is used to simulate the passive components, and the simulation results are compared with the measurement data provided by WIN. There are two versions of the LNA design in this thesis. For the first version, in order to select the signal from left-handed or right-handed circular polarization port, a single-pole-double-throw (SPDT) switch is used at the output of two identical LNAs. Since excellent input return loss and very low noise figure cannot be achieved simultaneously, another version of LNA is designed for better input return loss. Because we use a new process to design LNA, a set of test kits including a capacitor, an inductor and TRL calibration kits are designed to check the characteristics of passive components. Besides, we are also taped-out different size transistors used in the LNA and switch, and one-stage amplifier cut from 3-stage LNA is also taped-out to verify the circuit characteristics. Due to the difference between the measurement and simulation results, the debug work is implemented according to the measurement results of the test kits. We found that the metal without thickness in EM simulation software is not good enough, and the completeness of the ground plane also has significant effect to the circuit characteristics. Therefore the EM simulation environment is corrected, and the circuits are re-simulated using the new EM simulation environment. For the second version LNA, in order to save the area, the switch in output of LNA is removed. Instead, two 1-stage LNAs are used for the input stage, and turn off one of the LNA to select left-handed or right-handed circular polarization. To choose the polarized signal which is desired and minimize the effect of the process variation, a bias circuit that could switch path by outer signals and controlled by a reference current is designed on GaAs chip. This bias circuit could get more steady bias in gate terminal of transistor in simulation. When we verify the DC bias conditions in the bias circuit on chip, we find that the measurement result is close to simulation result.
Subjects
Low noise amplifier
Ka band
GaAs pHEMT
Type
thesis
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