Low Noise Amplifiers

Low noise amplifiers are the amplifiers which are carefully designed to minimize the noise contribution of the amplifier at the output.

Design

A Super Heterodyne Receiver signal chain

The noise added by the amplifier comes from the passive elements (Resistors) and from the active components such as BJTs and FETs which provide the gain. The use of resistor can be avoided and thus the choice of the active component becomes very important.

Bipolar Junction Transistors or BJTs based LNAs

BJTs are the favourite choice for LNAs but the bipolar semiconductor fabrication process is not costlier than the counter part CMOS process.

Metal Oxide Semiconductor (MOS) Field Effect Transistors or MOSFETs based LNAs

The need of integrating the LNAs and infact all other blocks (except the antenna) in the signal path on to the same die of silicon along with the processor or other blocks required for building the complete system, has driven interest in using MOSFETs for LNA design.

Micrograph of a CMOS LNA

Applications

Low Noise Amplifiers or LNAs are mostly used in telecommunication sytems, audio electronics and analog to digital converters.