RECONFIGURABLE POWER AMPLIFIER WITH TUNABLE INTERSTAGE MATCHING NETWORK USING GaAs MMIC AND SURFACE-MOUNT TECHNOLOGY

As the demand of reconfigurable devices increases, the possibility of
exploiting the interstage matching network in a two-stage amplifier to provide center
frequency tuning capability is explored. While placement of tuning elements at the
input and/or output matching network has some disadvantages, placement of tuning
elements in the interstage absorbs the lossy components characteristics into useful
attributes. The circuit design methodology includes graphical method to determine
the bandpass topology that achieves high Q-contour on the Smith chart thus result in
narrow bandwidth. T-section and π-section topologies are used to match reactive
terminations provided by the first and second amplifier stages. The design
methodology also includes utilization of interstage mismatch loss that decreases as
increasing frequency to compensate for amplifier gain roll-off and equalize the gain
at different tuning states.
In prototype realization, three design configurations are discussed in this
thesis: 1) a discrete design for operation between 0.1 – 0.9 GHz with the total layout
area of 7.5 mm x 12.5 mm, 2) a partial monolithic design (Quasi-MMIC) for
operation between 0.9 – 2.4 GHz that is 25 times smaller layout area compared to the
discrete design, and 3) a conceptual design of integrated monolithic reconfigurable
PA for operation between 0.9 – 2.4 GHz that is 130 times smaller layout area
compared to the discrete design. One variant of the fabricated reconfigurable PA
offers advantage of 4-states center frequency tuning from 1.37 GHz to 1.95 GHz
with gain of 21.5 dB (+ 0.7 dB).
The feasibility of interstage matching network as tuning elements in
reconfigurable power amplifier has been explored. The input and output matching
networks are fixed while the interstage impedances are varied using electronic
switching (discrete SP4T and GaAs FET switches). The discrete design is suited for
the operation at low frequency (fo < 1GHz), while monolithic implementation of the
tunable interstage matching network is required for higher frequency operation due
to size limitation and parasitic effects. The reconfigurable PA using MMIC tuner was
designed at higher frequency to possibly cover GSM, CDMA, Bluetooth, and
WiMAX frequency (0.9 – 2.4 GHz).