Programming instructions

RF MOS_3TDN
 National Instruments Corporation 14-3 Multisim Component Reference Guide
14.4 RF MOS_3TDN
RF FETs have a different type of carrier than bipolar transistors. Only the majority carriers
selected for FET should have better transport properties (such as high mobility, velocity,
diffusion coefficient). For this reason, RF FETs are fabricated on n-type materials since
electrons have better properties.
The two most important parameters are the gate length and width. A reduction in the gate
length will improve the gain, noise figure and frequency of operation. Increasing the gate
width will increase the RF power capability. That is why typical power FETs have multiple
gate fingers, interconnected via air bridges, with a total width of about 400 to 1000 µm.
The model parameters for RF FET transistors can be obtained using measured data for DC
and RF S-parameters. The equivalent circuit model should have almost identical DC and RF
S-parameters.
14.5 Tunnel Diode
A tunnel diode is a heavily doped diode that is used in high-frequency communications
circuits for applications such as amplifiers, oscillators, modulators, and demodulators. The
unique operating curve of the tunnel diode is a result of the heavy doping used in the
manufacturing of the diode. The tunnel diode is doped about one thousand times as heavily as
standard pn-junction diode.
The tunnel diode is different from any other diode because of its negative-resistance region. In
this area, forward voltage and current are inversely proportional. For example, an increase in
forward voltage would result in a reduction in diode current.
A tunnel diode can also be used to generate a sinusoidal voltage using a DC supply and a few
passive elements.
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