5-6 GHz RFIC Front-End Components in Silicon Germanium HBT Technology
In 1997 the Federal Communications Commission (FCC) released 300 MHz of
spectrum between 5-6 GHz designated the unlicensed national information
infrastructure (U-NII) band. The intention of the FCC was to provide an
unlicensed band of frequencies that would enable high-speed wireless
local area networks (WLANs) and facilitate wireless access to the
national information infrastructure with a minimum interference to other
devices. Currently, there is a lack of cost-effective technologies for
developing U-NII band components. With the commercial market placing
emphasis on low cost, low power, and highly integrated implementations
of RF circuitry, alternatives to the large and expensive distributed
element components historically used at these frequencies are needed.
Silicon Germanium (SiGe) BiCMOS technology represents one possible
solution to this problem. The SiGe BiCMOS process has the potential for
low cost since it leverages mature Si process technologies and can use
existing Si fabrication infrastructure. In addition, SiGe BiCMOS
processes offer excellent high frequency performance through the use of
SiGe heterojunction bipolar transistors (HBTs), while coexisting Si CMOS
offers compatibility with digital circuitry for high level
The work presented in this thesis focuses on the development of a SiGe
RFIC front-end for operation in the U-NII bands. Specifically, three
variants of a packaged low noise amplifier (LNA) and a packaged active
x2 sub-harmonic mixer (SHM) have been designed, simulated and measured.
The fabrication of the Rifts was through the IBM SiGe foundry; the
packaging was performed by RF Micro devices. The mixer and LNA designs
were fabricated on separate die, packaged individually, and on-chip
matched to a 50 ohm system so they could be fully characterized.
Measurements were facilitated in a coaxial system using standard FR4
printed circuit boards.
The LNA designs use a single stage, cascoded topology. The input ports
are impedance matched using inductive emitter degeneration through
bondwires to ground. One version of the LNA uses an shunt
inductor/series capacitor output match while the other two variation use
a series inductor output match. Gain, isolation, match, linearity and
noise figure (NF) were used to characterize the performance of the LNAs
in the 5 - 6 GHz frequency band. The best LNA design has a maximum gain
of 9 dB, an input VSWR between 1.6:1 and 2:1, an output match between
1.7:1 and 3.6:1, a NF better than 3.9 dB and an input intercept point
(IIP3) greater than 5.4 dBm. The LNA operates from a 3.3 V supply
voltage and consumes 4 mA of current.
The SHM is an active, double-balance mixer that achieves x2 sub-harmonic
mixing through two quadrature (I/Q) driven, stacked Gilbert-cell
switching stages. Single-ended-to-differential conversion, buffering
and I/Q phase separation of the LO signal are integrated on-chip.
Measurements were performed to find the optimal operating range for the
mixer, and the mixer was characterized under these sets of conditions.
It was found that the optimal performance of the mixer occurs at an IF
of 250-450 MHz and an LO power of -5 dBm. Under these conditions, the
mixer has a measured conversion gain of 9.3 dB, a P_1-dB of -15.7 dBm
and an 2LO/RF isolation greater than 35 dB at 5.25 GHz. At 5.775 GHz,
the conversion gain is 7.7 dB, the P_1-dB is -15.0 dBm, and the
isolation is greater than 35 dB. The mixer core consumes 9.5 mA from a
5.0 V supply voltage.
This work is sponsored by RF Microdevices (RFMD)through the CWT a liate
program.The author was supported under a Bradley Foundation fellowship.