# Next step electronics 3; A simple BJT transistor bias circuit

The first step in every transistor based amplifier design is to define its bias circuitry. Perhaps the most important parameter in the schematic is the DC current in the collector of the transistor, because it is directly proportional to its small-signal gain. In this post a simple bias method for bipolar junction transistors (BJT) is being shown, where the collector current is being set with relative accuracy.

# Next step electronics 2; A simple sinusoidal oscillator

The most bizarre and mysterious circuits for beginners are probably the oscillators. You plug them to a power supply and they produce a periodic signal without being sure why. Along the years, huge amounts of research and effort has been invested by engineers in an attempt to fully understand how they function with whole books having been written about them.

Today, oscillators can been considered as a well understood electronic building block. However, there is still a debate about their fundamental properties. I read a recently published paper called “The Barkhausen Criterion (Observation ?)” written by a professor at DTU, where I am currently studying for my MSc, stating that the famous Barkhausen criterion is a necessary but not sufficient condition for oscillations to occur.

At any case, this is not a theoretical post. I am going to show you an easy way to design a 10 MHz sine wave Colpitts oscillator using only simple algebra and circuit theory.

# Next step electronics 1; Transistor-based thermometer

Throughout the years of my occupation with analog electronics I have realized that there is a considerable gap between intermediate and advanced analog knowledge. That is, even if you have read every known book regarding analog electronics, either for undergraduate students (The Art of Electronics, Microelectronic Circuits) or for graduate students (Analysis and Design of Analog Integrated Circuits), you will probably have no idea how to analyze monstrous circuits like the LM10 or an fm receiver. It’s not easy to analyze even the LM101 that got out decades ago.

The purpose of this line of posts is just that. To introduce and explain circuits relatively unknown to the average electronics enthusiast. Some of them will be simple (like the one that is going to be presented in this post) and some of them will be a little bit more complicated. But all of them have one common trace; when I stumbled across them for the first time, I felt like making a step towards advancing my expertise on the subject of analog electronics.

Ok, enough with the talking. Let’s find out how we can make a thermometer using off the shelf transistors.

# VLSI Design; 4-bit Up/Down Counter with Parallel Input

Last semester, I took a VLSI class. The class included a project and a written examination. The project was on VLSI Design (duh?) and, to be specific, we had to implement a 4-bit Up/Down Counter with Parallel Input from scratch. Yes, that means we designed our own gates from discrete transistors and built our final circuit one block at a time.

Back in the 60s, communications were not as widespread as they are today. People had the radio and some early form of the television, but this is a one-way information link. If they wanted to send a message across the globe, they had to use the expensive and unreliable telephone. This is why the hobby of Amateur Radio was then, what the Internet is today.

# Open Circuit Time Constants

Besides Miller’s Theorem, there is another technique we can use to determine the 3db frequency of an amplifier. It is known as Open Circuit Time Constants method and it is just as powerful and useful as Miller’s counterpart.

# The standar current source and an improved version

This is an actual implementation of a current source, the current mirror. The left resistor (R1) determines the current of the right resistor (R2). In this post, we discuss and analyze the current source and an improved version of it.

# Welcome 2012-2013

It’s been almost 2 months and plenty university exams, but I am back. So, let’s see what bothered me in the past months, besides equations and circuits.