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Product Feature
GaN Switches
Enable Hot
Switching at
Higher Power
R
F power control elements, such as RF
switches, are an integral element of any
RF system and traditionally have been
built using Si PIN diodes for higher power
applications and GaAs FETs for lower power
and higher speed applications. The use of GaN
HEMT-based technology in this application
area promises to be a game changer, as GaN
HEMT-based switches can simultaneously offer higher power handling and ruggedness capability as well as low control current requirements. They also deliver excellent insertion
loss and isolation over an ultrawideband, all
within a very small form factor.
These capabilities are demonstrated by the
family of RF switch products developed by
RFMD. The GaN HEMT-based switches are
attractive for multiple applications — MilCom,
electronic warfare, radar, test and measurement, commercial infrastructure communications, and medical — as they offer unique
advantages over competing technologies.
134
Some examples are silicon-on-sapphire, GaAs
FET, pin diodes and even electromechanical switches, depending on the specific application and market drivers. The RFSW2100
GaN HEMT MMIC switch from RFMD is a
reflective, hot switchable SPDT switch that offers broadband power handling capability from
DC to 6 GHz, with low insertion loss (< 0.4
dB at 2 GHz), excellent isolation ( 39 dB at 2
GHz), fast switching times ( 40 ns), as well as
low drive current capability (< 0.5 mA). These
devices are available both in die form and in a
3×3 mm, 12-pin QFN package, which is well
suited for ease of integration into a variety of
applications. The device is designed to present
50 Ω input/output impedance over a broad DC
to 6 GHz band and can switch 45 W of uncompressed RF power (defined by 0.1 dB com-
RFMD
Greensboro, NC
MICROWAVE JOURNAL n JANUARY 2012
Product Feature
TABLE I
performance specification - rfsw2100
Frequency
DC to 6
GHz
Rated Input Power (P0.1dB)
45
W, CW
Insertion Loss
<1
dB, f < 5.5 GHz
Isolation, Off-state
> 30
dB, f < 4 GHz
> 20
dB, f < 6 GHz
40
ns
Switching Speed
On
22
ns
Control Voltage
(45 W at 3:1 VSWR)
Off
0/-60
V
Control Current
< 0.5
mA
Input/Output Return Loss
dB
72
dBm
Package Type
33 mm, 12 lead air-cavity QFN
INSERTION LOSS (dB)
> 10
IIP3
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0
s Fig. 1
loss.
CONTROL
VOLTAGE
–20 V
–40 V
–60 V
1
2
3
4
5
FREQUENCY (GHz)
6
Frequency dependence of insertion
pression of insertion loss). In addition
to these capabilities, the RFSW2100
offers a very respectable IIP3 of
72 dBm, which offers additional possibilities to designers in need of a rugged, high power, low loss switch for
more linear applications, as summarized in Table 1.
The RFSW2100 is designed within the same 0.5 µm GaN technology
platform as RFMD’s qualified and
production released GaN1C process-technology platform and thus
benefits from the industry-leading
process technology manufacturing
control afforded to power amplifier
products based on the GaN1C technology platform. Among the key attributes of this process are very high
breakdown voltage-per-unit distance
and high current density ( 1 A per
unit mm of gate periphery) that offer the combination of low RON and
the ability to withstand high reverse
voltages. This high breakdown voltage capability enabled operation at
control voltages of negative 60 V, enabling excellent ruggedness (exceeding 3:1 at 45 W) as shown in Figure 1
and survivability without compromis136
ing insertion loss, as the performance
improves at larger negative control
voltages. The low leakage current
(< 1 mA) in the OFF condition leads
to low OFF current drive requirements as well as good power dissipation in the OFF state. This power
handling and VSWR capability represents a 5× improvement in power
handling over a comparable 0.5 µm
GaAs FET-based switch. In addition, as the RFSW2100 is a voltagecontrolled device, turning the switch
ON is achieved by simply biasing
to 0 V, with control current in the
ON state being almost negligible
(< 0.5 mA) up to input powers of 45
W. This offers the RFSW2100 a tremendous advantage over Si PIN diode switches in terms of greatly reduced control circuitry, BOM, board
space, weight and cost.
The key small signal figure of merit (FOM) for a switch technology is
the product of the resistance in the
ON state (RON) and the capacitance
in the OFF state (COFF), expressed
as a frequency [1/(2RON·COFF)]
or a time constant (RON·COFF).
RFMD’s RFSW2100 switch technology offers a figure of merit of 343
GHz, obtained by minimizing COFF
and RON. The low COFF results from
small fringing capacitances obtained
from RFMD’s GaN-on-SiC process
as well as the semi-insulating SiC
substrate material. The benefits of
the thermally conductive semi-insulating SiC substrate are two-fold,
minimized leakage current during
large voltage swings across the device
and maximum heat transfer from the
active channel of the device to the
heat sink. This excellent heat sinking
within the die itself results in very stable high power operation over a wide
temperature range as well as linear
operation over a greater input power
range. Due to the fact that the frequency dependence of the insertion
loss is dominated by the COFF, instead
of RON, the RFSW2100 provides
an industry-leading insertion loss
(< 0.4 dB at 2 GHz) over an extremely wideband while offering
exceptional P0.1dB power handling
(> 45 W) and ruggedness (better than
3:1), rendering it attractive for applications, such as military communication and electronic warfare as well as
infrastructure and communication
applications.
The RFSW2100 SPDT switch
is available both in bare die
(RFSW2100D) and in a 3 × 3 mm,
12 lead� air cavity QFN package, specifically designed for handling higher
power in a compact form factor. This
package offers similar advantages
with regard to handling the power
dissipation in GaN-based devices,
similar to metal flange, ceramic air
cavity packages that house high power RFMD GaN power amplifier products. Due to the excellent current
capability and breakdown voltage
afforded by RFMD’s GaN1 process,
in die form, this RFSW2100D switch
offers an additional power handling
capability up to 75 W, depending on
the capability of the heat sink environment and mounting, as well as an
improvement in insertion loss in the
higher frequency range (maintaining
< 1 dB of insertion loss up to 6 GHz).
In addition to the RFSW2100 SPDT
switch, RFMD is developing a family
of high power, extremely broadband
switches that extend from DC to 18
GHz, enabled by the excellent breakdown voltage and small signal FOM
resulting from RFMD’s GaN-on-SiC
technology. RFMD’s GaN1-based
switch technology also enables development of higher power and multithrow count switches, which are expected to undergo product qualification in 2012.
RFMD,
Greensboro, NC
(336) 664-1233,
www.rfmd.com.
MICROWAVE JOURNAL n JANUARY 2012