User:Jakub.duchon

Low Noise Amplifier Design

Tutorial

Specification

The amplifier is usually part of a system which is composed of many blocks. Such a system can be connected in a cascade and when connecting many blocks together behavior of each block must be described. This description is called specification. The specification is set of parameters specifying behavior of particular block. Parameter in specification care for example an operating point, input and output parameters, extreme working conditions, supply. Specification is a language how engineers communicate between each other. Specification sets a course of the product development.

Specification

Parameter	min	typ	max	unit	Note
Center frequency				Hz
Bandwidth				Hz
Gain				dB
Gain Flatness				dB
RL input				dB
RL output				dB
Noise Figure				dB
OIP3				dBm
Consumption				dBm
Stability				-
Size
Cost				€
Temperature				°C
I/O Impedance				Ω

All parameters should be satisfied within the whole bandwidth.

Transistor Selection

Transistor selection affects the whole process of design. This part is very important and special attention has to be paid. Transistor selection can make whole design procedure succeed or fail. The question is from where and how to start finding the best fitting transistor to the specification. Well, it pretty much depends on the specification. Good start can be making a set of priorities and start from the most demanding parameters. It may be a good practice to be a bit pessimistic. Choosing better performing transistors can pay off during the finalization of the design. Based on the specification a priority list can be made.

Selection

1. Low consumption
2. Low Noise Figure
3. High Gain
4. Price
5. ...

Based on this list a designer knows what to look for. Taking this list as an example, there is still one significant parameter missing. Operating frequency has to be considered in parallel with almost all parameters in the list. Operating frequency prompts technology (BJT, FET, HEMT) and also the bandwidth has to be considered. Once the priorities are set, the selection can start.

Manufacturers

Avago Infineon NXP

Formula

$\Gamma _{S}^{*}=\Gamma _{in}=s11+{\frac {s12\cdot s21\cdot \Gamma _{L}}{1-\left(\Gamma _{L}\cdot s11\right)}}$

$\Gamma _{L}^{*}=\Gamma _{out}=s22+{\frac {s12\cdot s21\cdot \Gamma _{S}}{1-\left(\Gamma _{S}\cdot s22\right)}}$

Transistor Models

Transistor can be represented by a model.