RF design consultancy
RF or Radio Frequency is a class of circuits within electrical engineering operating at frequencies found in wireless equipment, like radios. As radio waves are preferably short these RF frequencies lead to designs in which the wave length matters and to the use of so called distributed elements like transmission lines.
In RFIC design a distinction exist between circuit's completely on chip like VCO's, mixer's and filters on one hand and circuits having an interface to the package pins on the other hand, like PA's and LNA's. The first class of circuits not necessarily uses distributed components and the second does.
The impedance seen by a LNA and PA strongly determines their properties. As such the matching networks of the LNA and PA and the bondwires or package is part of their design.
PA design
The design of Power Amplifiers could be seen as a special kind of circuit design. In this kind of circuits power is the signal instead of voltage or current. Power is available if the current and voltage are in phase, this opposed to many other circuit designs in which only the voltage or current matters.
The design of a PA first comprises several choices
- the class, A, B, C, ...
- the process or technology
- the maximum voltage limits, Vdsmax, BVceo
- device lifetime, aging, ruggedness
- single ended or differential mode
- device size
- operating temperature
- pulsed versus Continuous Wave mode
Basically these choices lead to a loadline at which the PA operates. This loadline must be created by an impedance transformation from the reference impedance (often 50 Ω). The higher harmonics must be properly terminated to make the class of operation (B, C etc) possible.
Creating a matching network that imposes the right load over all frequencies is often a difficult and challenging part of PA design.
LNA design
The design of Low Noise Amplifiers is about amplifying signals with adding as little as possible noise. Noise itself is a power signal instead of a voltage or current therefore the input of LNA's should be seen as a power input. The output signal could be a power, voltage or a current wave.
As the input signal is power the source impedance plays a major role in LNA design. It should be chosen such that the voltage and current waves coming from this source are both minimally polluted by added current and voltage noise from the LNA itself. Therefore scaling the ratio between these current and voltage waves, is important for the (added) noise factor.
A differential LNA design has the advantage of being insensitive to common mode noise. In differential LNA's noise from biasing networks, supply and substrate/crosstalk could be common mode noise and therefore easily be suppressed. However the matching network should now probably also being able to convert unbalanced signals to balanced signals, as a balun does.
It should be clear that LNA design is not only about a smart circuit topology but strongly depends on knowing and controlling the passive input side of the LNA.
RF design is a specialism of electrical engineering. It often strongly depends on knowing and controlling the passive side of the circuits. JTL engineering has experience with many RF circuits like PA's, LNA's and RF modules. If you want help send us an email.