6 ACTIVE RF SEMICONDUCTOR DEVICES

ACTIVE RF SEMICONDUCTOR DEVICES.
This are active semiconductors which when measured in a 50ohms terminating impedances at the source and load, the device itself will not be affected by changes in the input or output voltages or currents that may result with the use of other values of impedances at the terminals. This assumption underpins the entire linear design when we represent active device by a matrix formulation such as Y – or S – parameters.
It is assumed that the device is independent of the circuit in which it is embedded.
1) Two-port device models are made of GaAs MESFET
In this device, current is the function of the drain – source voltage.
2) The silicon bipolar transistor .
It is the first two-port device used for solid – state RF-design for RF frequencies lower than 1GHZ.
3) Others are the HBT (Heterojunction Bipolar Transistor). The Gummel-poon model transistor considers the number of additional features:
- Low current effects resulting from additional base current due to combination of a minority carriers in the bass.
- High level injection; occurs with excess majority carriers spill over from the base to collector.
- Base-width modulation – effective width of the base through which the electrons must transit is increased when forward bias on either of the junction increases.
- The Ac model parameters to account for change aggregation within the device.
4) The heterojuction bipolar transistor
­ - Is a high speed transistor; with better high frequency performance
The high-electron mobility transistor (HEMT) made of ALGaAs layers.
With high gain and extended frequency performance 200GHZ range. This excellent low- noise properties result from their high transconductance and good electron mobility. Off-the-shelf HemTs with 0.6dB and associated gain of 12dB at 15GHZ are available.
5) Silicon Ldmos and Cmos technologies
This are Rf intergrated circuits where synchronous digital hierarchy (SDH) operate up to 10Gbps and wireless LANS at 100Mbps.
LDmos are meant for GSM cellular system for its power amplification for upto 2GHZ and can also be used for power switching application at lower frequencies.
6) Others are the schottky diodes.
The pin diodes, which are used for high frequency switches and variable resistors.
Varector diode – Is capacitive under reverse bias.
7) IMPATT-diode – IMPact Avalanche and transistor Time which is a time diode.
8) Tunnel diode
9) TRAPPATT, BARRITT and Gunn diodes Trapped plasma Avalanche Triggered Transit – High efficiency upto 75%
BARRier Injection Transit Time has low efficiency of 5% to less 1 and is commonly used in RADAR mixed and detectors circuits.

Ref: practical RF CIRCUIT DESIGN FOR MODERN WIRELESS SYSTEM. Volume Ii by ROWAN GILMORE & LEE BESSER