Basic Comparison between Different devices for RF applications

Many different semiconductor technologies are currently being used for power amplifiers (PAs), Low noise amplifiers, Switches, Mixers and Oscillators that include a mix of Silicon and GaAs devices –Silicon Bipolar, Silicon MOSFET, GaAs MESFET, GaAs HBT and GaAs pHEMT.

The main features of GaAs pHEMT technology are the very low noise and the high operation frequencies capabiliteies.HEMT’s have low noise performances much better than other devices, Including HBTs, MESFETs, CMOS and BJTs.Their cut off frequencies are typically around 100GHz or even more. This feature makes HEMT devices very attractive for Monolithic Microwave Integrated circuits (MMIC) application especially for Low Noise Amplifier required in wireless applications.E-pHEMT (enhancement-mode psuedomorphic high-electron mobility transistor) is a semiconductor process optimized for wireless applications that operates from a single positive voltage source

Low-frequency noise is in general smaller in HBTs.With proper circuit design for reduced influence of nonlinearities and thus small noise up conversion, HBToscillators can be designed with very small phase-noise performance.

Power applications and development of small size, high efficiency chips have benefited from the availability of HBTs. These devices although less mature in technology than p-HEMTs, offer higher breakdown voltage, better threshold voltage uniformity and exponential rather than power-law transfer characteristics.

If high frequency operation is required, p-HEMTs offer the best choice due to their high gain up to millimeter-wavelengths and their good noise and power performance HBTs are attractive at cellular radio frequencies for power amplification. This can range from the Watt level for handsets to 150W or more for base stations.

Operation of devices using GaAs MESFET technologies for driver amplifier applications above 0.5 W requires biasing voltages above 8 V. Thus the use of these types of devices can sometimes be undesirable for designers constrained to +5 V regulators in their system. GaAs pHEMT and InGaP HBT devices resolve this problem by operating directly from a low voltage as low as 3V, while offering designers high power-added efficiencies and linearity

Advantages of E-pHEMT

Low battery leakage current consumption
No need for drain switch or negative voltage supply
Low quiescent current consumption (Idq) in CDMA
Applications
High power added efficiency (PAE) for longer talk time
Low Voltage Operation
No Secondary Breakdown Mechanism
Survivability under High Mismatch
No thermal runaway

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