Application Note
GaAs MMIC-Based Control Components With Integral Drivers
By Cobham Sensor Systems
Introduction
This application note describes the fundamental
operation and features of a new series of control
components. These switches comprise a family of
devices that use GaAs FET MMIC technology for the
RF circuitry and incorporate application specific
integrated circuit (ASIC) technology to realize an
integral TTL or CMOS compatible driver. The
circuitry is housed in ceramic surface mount
packages that give repeatable and predictable
performance from DC to 3 GHz.
GaAs MMIC Switch Technology
This family of switches is based on metal
semiconductor field effect transistor (MESFET)
technology. The MESFETs are N-Channel depletion
mode devices with 1 µm Schottky gates. Depletion
mode devices are low resistance at 0 bias. When a
negative voltage is applied to the gate, the electric
field begins to narrow the channel, increasing the
resistance. The voltage that closes off the channel
and creates the highest resistance of the MESFET
device is known as the "pinch-off" voltage. Pinch-off
voltages for M/A-COM MESFETs are typically –2.5
volts.
By varying the gate voltage between 0 volts and some value greater than pinch-off (typically –5 to –8 volts), the MESFET acts as a variable resistor. MESFETs can be arranged into series and/or shunt configurations and biased to provide on and off switching characteristics.
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•Application Note: GaAs MMIC-Based Control Components With Integral Drivers
