Tuesday, March 30, 2021

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

Saturday, December 26, 2020

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.

Saturday, November 14, 2020

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

Saturday, November 7, 2020

OCTAVE Functions for Basic Signal Processing

 

In the following entry of this blog, several functions built for OCTAVE will be presented.

The aim of these functions is to serve as basic tools for digital signal processing.

Each function will be tested separately and each test file will be included as part of the information provided for each function.

These functions will be presented in order of complexity, just a way of organizing the information.


The functions will be the following:

  • Bit_Seq_Gen.m: Function for getting a pseudo random bit sequence.

    • Test file: “Test_Bit_Seq_Gen.m

  • Unipolar2Polar.m: Function for transforming an unipolar bit sequence to a bipolar one.

    • Test file: “Test_Unipolar2Polar.m”.

  • NRZ_Sequence2.m: Function for getting a NRZ signal from a pseudo random bit sequence.

    • Test file: “Test_NRZ_sequence2.m”.

  • RZ_Sequence2.m: Function for getting a RZ signal from a pseudo random bit sequence.

    • Test file: “Test_RZ_sequence2.m”.

  • SP_L_Sequence2: Function for getting a SP-L signal from a pseudo random bit sequence.

    • Test file: “Test_SP_L_Sequence2.m”.

  • NRZ_Sequence.m: Function for getting a NRZ signal from a pseudo random bit sequence. In this case it is possible to define the transition time to high value and to low value, being both the same.

    • Test file: “Test_NRZ_Sequence.m”.

  • RZ_Sequence.m: Function for getting a RZ signal from a pseudo random bit sequence. In this case it is possible to define the transition time to high value and to low value, being both the same.

    • Test file: “Test_RZ_Sequence.m”.

  • RCF.m: Function for building the rise cosine filter response.

    • Test file: “Test_Rise_Cosine_filter.m”.


After those functions are presented, several examples of usage will be included as a short of annex.

 The document that presents these functions can be accessed in this link:

OCTAVE Basic functions for signal processing 

All the OCTAVE files that are presented in the document can be accessed in the following link:

OCTAVE Files for signal processing

 

Saturday, October 3, 2020

Non linear Models for Microstrip Basic Elements working in QUCS Studio

 The present work that conforms this new entry of the blog is an on going task which eventually will not be necessary if the progress of QUCS Studio as a CAD tool continues to develop in the manner that it has being doing until now.
QUCS Studio is really alive and its progression is really awsome. Therefore, eventually, the work that is going to be presented in this new entry will be just a mere theoretical, maybe interesting and meaningless exercise.
One of the things that needs to be improved is the way that the microstrip basic models included in the transmission lines tab deal with the non linear analysis.

Transient analysis and harmonic balance do not work if the schematic that is under simulation contains microstrip line models. This is because this elements are designed to work only with linear analysis like the scattering parameters one.

The elements that are going to be introduced in the document linked in this blog entry try to mitigate this situation until a future version of the software make them useless.

A brief presentation of this work in made in the document that is available in the following link:

Non linear models for Microstrip Basic Elements


The models presented are compiled in this QUCS Studio project that can be downloaded in the following link:

Microstrip Non Linear Models for QUCS Studio


As it has been said in the begining of the entry, this is an on going process, and there is some of the elements that needs to be refined. Any improvement or progress in any of them will be updated. And, of course, any suggestion, correction or any form of cooperation will be really wellcome.

Sunday, September 27, 2020

QUCS Studio project files for L-Band Oscillator & L-Band Amplifier tutorials

Some people have asked regarding the files corresponding to the L-Band oscillator design and for the L-Band amplifier design. These are two of the tutorials that you can find in two entries of this website. But, inexplicably, the project files where not available yet.

Let's fix that. Both project files will be now available in the following links:

 

L Band Amplifier design QUCS Studio project files 

 

 L Band Amplifier desing QUCS Studio project files



Saturday, May 16, 2020

QUCS Studio vs ADS2016. Annex Simulation. Microstrip Coupled lines


As a Annex of a previous document in this entry you will find a document where it is included one more comparison between the results obtained when a simple coupled pair of microstrip lines are simulated using QUCS Studio and those obtained using ADS 2016.
In the previous document, that you can also find as one entry of this blog, you will find more examples of simulations comparing different microstrip structures very commonly used in high frequency RF circuits.
This time, the schema simulated is a pair of coupled microstrip lines matched in the isolated port and the coupled port with the characteristic impedance, in this case, 50 ohm, then terminated with the MELF component in ADS comparing it with the MOC from QUCS Studio, and, finally, evaluating only the microstrip coupled lines in both simulators.

The link where the Annex can be accesed is the following:


The link where the S2P files with the results obtained from ADS2016 can be obtained in this link: