High Power Amplifier design, step by step ... (Part Two)

 

The following presentation shows the second part, following the previous one posted a while ago, of a longer one where the basic steps for designing a power amplifier chain are presented.

This second part of the presentation ends when the medium power amplifier stage, one of the two parts that compose the power chain, is fully designed and the layout is available.
All the basic componentes chosen are presented and a brief explanation of why they where chosen is also included.

The following parts will complete the overall view of the design.

 

 

 High Power Amplifier Design. Part 2

High Power Amplifier design, step by step ... (Part One)

 

The following presentation shows the first part of a longer one where the basic steps for designing a power amplifier chain are presented.

The basic idea of this new entry is to show (in several parts) what are all the basic considerations that must be taken into account for designing a high power amplifier, from the selection of all the materials, to the final manufacturing of one prototype.

This first part of the presentation ends when the architecture of the power chain is finally evaluated and the main components are chosen.

The following parts will complete the overall view of the design.

 

High Power Amplifier Design 

Extracting the lumped elements model for the SMA connector in QUCS Studio

 

Many times, after a thorough and, some times, exhausting design process staring the simulator in the computer, it happens that the results obtained in the laboratory from the first bread boards manufactured are rather far from the theoretical analysis.

Almost of all the times, this miscorrelation of the results compared to the simulations are due to lack of accuracy in the models used.

One of the most significant details normally underestimated by the designers is the effect of connectors used for testing the PCBs.

SMA connectors are one of the most used connectors type in RF designs, because of the quality and its, general speaking, low cost.

But they are not transparent to the actual measurements once the are introduced in the testing PCB.

The effect is clear, even when the most simple structures are remarkable. In the present document it is presented a simple method to obtain the electrical model for SMA connectors that can improve the results of the circuits design.

Extracting the lumped elements model for the SMA connector in QUCS Studio

Simple way of getting S2P file from a simulation in QUCS Studio

 

The scattering parameters file is one of the most useful information the designer can handle, once it is involved in the analysis of a new RF circuit working in the small signal domain.

Normally the scattering parameter file is part of the inputs used for designing, but it is common to face the necessity of extracting S2P file for an intermediate simulation, to be later used in a following step of the design.

By the time of the publication of this document, QUCS Studio offers the option of exporting in a CSV file type one trace plotted in a diagram as a result of one simulation.

It is important to take note that the information contained in the CSV file is just the trace selected in the diagram. So, in order to get the 8 traces that compose the whole information archived in the S2P file as it is defined, this process should be repeated eight times.

In the document linked in this entry, it is presented a quite simple way of getting the whole S2P into one file in one single time. It is based on the usage of the OCTAVE capabilities included as nominal in QUCS Studio.

Simple way of getting S2P parameter file in QUCS Studio

OCTAVE Functions for Basic Signal Processing (II)

 

In the following entry of the blog, another OCTAVE function is included to the set published previously in this blog. In this case is the Root raised consine filter function, which allows to simulate one of the most used filter for pulse shaping purposes used in digital communications.

The filter is described in terms of its time equations, according to the following expression published by NASA:

"Root Raised Cosine Filters & Pulse Shaping in Communication Systems" by Erkin Cubukcu.

A brief description of the function performances is summarized in the document that is accessible in the following link:

OCTAVE Functions for Basic Signal Processing (II)

The files referred in the document can be downloaded in the following link:

OCTAVE Functions for Basic Signal Processing (II) FILES

RF Passive Components Models for QUCS Studio (Part I)

 In the following entry of this blog, several models for passive componets suitable to build high frequency circuits in QUCS Studio are presented. It is delivered in a qucs project file that is accesible in the "Spice and Models" section of this site.
The models contained are the following:

1.- High frequency 0603 resistor
2.- High frequency 0402 resistor
3.- High frequency 0402, type wrap, resistor
4.- High frequency 0201 resistor
 

All of them, from VISHAY manufacturer and based in a technical note issued and downloadable in the following link: 

VISHAY Technical Note. Frequency Response of Thin Film Resistors

In the file it is include also a kit of inductor values, 0603 geometry, from COILCRAFT

COILCRAFT 0606 Inductor Modelling of Type CS elements 

 
This is an open activity. There will be another updates that will include more models for RF components from other manufacturers.

Microstrip coupled lines simulation anomaly in QUCS Studio

In this new entry of the blog, I will share the results of several simulations that prove there is some sort of bug in the equations of the microstrip coupled lines model in QUCS Studio, that produces wrong results in the simulations, once several parameters of the microstrip substrate are set in a determined manner.

This bug has been discovered by Margeride48. She brought to my attention several strange results simulating microstrip coupled lines. She wanted me to try to reproduce her results, just to confirm the wrong ones that she was getting from the simulator.

The following lines explain the anomaly in her words:

Focusing on coupled microstrips lines, have you tried thinner dielectrics ?
I'm simulating a 0.254mm I-Tera MT RF material.
S-parameter simulation values are going suddenly totally wrong when thickness is lower than 0.44 mm (eg 0.435mm).

Same for the Coupled Microstrip Line Calculator !
Impedances, losses, etc, become suddenly wrong.

On the opposite, the 'single' Microstrip Line Calculator leads to good results for 0.254mm thickness.

An EM simulation performed on the auto-generated PCB give good results with 0.254mm thickness for coupled microstrips.

We made a little investigation and I think that the best way of describing the findings is to consult the document linked to this entry that summarizes the results we got.

Microstrip Coupled lines simulation anomaly