Extra Class Question of the Day: Bipolar junction transistor characteristics

Perhaps the most popular type of transistor is the bipolar junction transistor (BJT). Bipolar junction transistors are three-terminal devices, called the emitter, base, and collector.  In an NPN transistor, the emitter and collector are N-type material and the base is P-type material. In a PNP transistor, the emitter and collector are P-type, while the base is N-type. The base is sandwiched between the base and emitter, so there is a diode junction between the base and the collector and the base and emitter.

Figure E6-1

Refer to Figure E6-1 above. In Figure E6-1, the schematic symbol for a PNP transistor is #1. (E6A07) #2 is the schematic symbol for an NPN transistor. The arrow in both symbols shows the direction of the current flow.

When the base-emitter diode is forward-biased, a current, called the base current will flow. If there is an appropriate voltage between the collector and emitter, this small base current will cause a much larger current to flow between the collector, through the base to the emitter. The amount of base current controls how much collector current flows. This is how transistors amplify signals.

The change in collector current with respect to base current is the beta of a bipolar junction transistor. (E6A06) This is also sometimes called the hfe or current gain of a transistor. The change of collector current with respect to emitter current is the alpha of a bipolar junction transistor. (E6A05)

Another important characteristic of a bipolar transistor is the alpha cutoff frequency. This is a measure of how high in frequency a transistor will operate. Alpha cutoff frequency is the frequency at which the grounded-base current gain of a transistor has decreased to 0.7 of the gain obtainable at 1 kHz. (E6A08)

Resources

What resources have you used for learning how transistors work?

From the trade mags: modern transceiver design, twisted pairs

Here are a couple more articles from the engineering trade magazines.

High-performance HF transceiver design. This article describes some of the decisions that an engineer must make when designing a modern amateur radio transceiver. It also sheds some light on the test methods used to test today’s receivers.

Use a twist (and other popular wires) to reduce EMI/RFI. Alexander Graham Bell patented twisted pair wires in 1881. We still use them today because they work so well.

 

 

From trade magazines: GE Transistor Manual, analog circuit design, HF op amp filters

This time, I have two items from EE Times and one from MicroWaves&RF…..Dan

 

GE Transistor Manual

Master the first 170 pages of the venerable GE Transistor Manual and you'll be a transistor expert.

The GE Transistor Manual. This editorial by Jack Ganssle reminisces about the old GE Transistor Manual. He notes, “It explains transistor theory in a level of detail that my college classes almost a decade later never approached. Read – and understand – the first 170 pages and you’ll be a transistor expert. But no attempt is made to make the subject easy.” One of the comments contains a link that you can use to download your own copy.

Book excerpt: Analog Circuit Design— A Tutorial Guide to Applications and Solutions, Part 1. Based on the Application Notes of Linear Technology, this book covers the fundamentals of linear/analog circuit and system design to guide engineers with their design challenges. It includes a broad range of topics, including power-management tutorials, switching-regulator design, linear-regulator design, data conversion, signal conditioning, and high-frequency/RF design. VERY good stuff.

Fabricating HF Opamp Filters. Until recently, op amp filters have generally been restricted to circuits operating below 1 MHz. Recent advances, though, are enabling op amps to amplify at frequencies up to 1 GHz.This article explains how to use them for lowpass filters to 150 MHz.

Extra Class question of the day: digital circuits, flip-flops

Digital circuits are used for a variety of functions in modern amateur radio equipment. Unlike analog circuits, the output voltage of an ideal digital circuit can only be one of two values. One of these voltages—normally a positive voltage—represents a digital 1. The other value—normally near 0 V—represents a digital 0.

This type of logic is generally called positive logic. Positive Logic is the name for logic which represents a logic “1″ as a high voltage. (E7A11) The logic may be reversed, though. That is to say that a high voltage may represent a logic 0. Negative logic is the name for logic which represents a logic “0″ as a high voltage. (E7A12)

The microcomputers that control today’s transceivers, for example, are very complex digital circuits. These complex digital circuits are made by combining many smaller building blocks called logic gates. These gates perform basic digital logic functions.

NAND Truth Table

Table E7-1. This two-input NAND truth table show the output (Q) for each combination of inputs (A,B).

One of the most basic digital circuits in the NAND gate. The logical operation that a NAND gate performs is that it produces a logic “0″ at its output only when all inputs are logic “1.” (E7A07)

This logical operation can be described by a truth table. A truth table is a list of inputs and corresponding outputs for a digital device. (E7A10) Table E7-1 shows a truth table that describes the operation of a two-input NAND gate. A and B are the two inputs; Q is the output.

NOR Truth Table

Table E7-2.

Other types of gates perform different logical functions. The logical operation that an OR gate performs is that it produces a logic “1″ at its output if any or all inputs are logic “1.” (E7A08) Table E7-2 shows a truth table that describes the logical operation of an OR gate.

The logical operation that is performed by a two-input exclusive NOR gate is that it produces a logic “0″ at its output if any single input is a logic “1.” (E7A09) Table E7-3 shows a truth table that describes the logical operation of an OR gate.

XNOR Truth Table

Table E7-3.

Flip-flops are circuits that are made from combinations of logic gates. The output of a flip-flop is not entirely dependent on its inputs; it is also dependent on the current value of its output.

As an example, let’s look at the SR or RS flip-flop. An SR or RS flip-flop is a set/reset flip-flop whose output is low when R is high and S is low, high when S is high and R is low, and unchanged when both inputs are low. (E7A13) So, once set to a particular value, the output will not change when both inputs are set to low.

Some flip-flops are clocked. That is to say that they only change states when a clock signal input changes states. A D flip-flop is an example of this type of flip-flop. A D flip-flop is a flip-flop whose output takes on the state of the D input when the clock signal transitions from low to high. (E7A15) A JK flip-flop is a flip-flop similar to an RS except that it toggles when both J and K are high. (E7A14)

Another type of flip-flop is the T flip-flop. The T flip-flop is so called because for each transition from low to high on the flip-flop’s T input, the output “toggles” from 0 to 1 if the output was already at 0, and from 1 to 0 if the output was already at 1. Two output level changes are obtained for every two trigger pulses applied to the input of a T flip-flop circuit. (E7A02) See figure E7-1 below.

T Flip Flop

The output of a T flip-flop changes state every time a clock pulse appears on the T input. This effectively divides the input frequency by a factor of two.

A flip-flop can divide the frequency of a pulse train by 2. (E7A03) Consequently, 2 flip-flops are required to divide a signal frequency by 4. (E7A04)

A flip-flop is a bistable circuit. (E7A01) What that means is that its output is stable in either state. An astable multivibrator is a circuit that continuously alternates between two states without an external clock. (E7A05) In other words, it is an oscillator.

A monostable circuit is one that is stable in one state but not the other. One characteristic of a monostable multivibrator is that it switches momentarily to the opposite binary state and then returns, after a set time, to its original state.(E7A06) A trigger pulse causes the monostable vibrator to switch to the unstable state, and it stays in that state for a set period, no matter how long the trigger pulse.

Resources
Wikipedia: Multivibrator (https://en.wikipedia.org/wiki/Multivibrator)

Extra Class question of the day: semiconductor materials

[[I'm not entirely happy with this section, so please feel free to suggest improvements....Dan]]

While transistor theory is outside the scope of this study guide, I will attempt to at least give you a basic understanding of how transistors are put together and how they work.  Most transistors we use in amateur radio are made of silicon. Silicon is a semiconductor. That is to say, it’s neither a conductor with a very low resistance, like copper, or an insulator with a very high resistance, like plastic or glass.

You can manipulate the electrical characteristics of silicon by adding slight amounts of impurities to a pure silicon crystal. When transistor manufacturers add an impurity that adds free electrons to the silicon crystal, it creates a crystal with a negative charge. We call that type of silicon N-type silicon. N-typeis a semiconductor material that contains excess free electrons. (E6A02) Free electrons are the majority charge carriers in N-type semi-conductor material.

When you add other types of impurities to a pure silicon crystal,  you can create a crystal with a positive charge. We call this type of material P-type semiconductor material. In N-type semiconductor material, the majority charge carriers are the free electrons. (E6A16) The majority charge carriers in P-type semiconductor material are called holes. (E6A03) P-type is the type of semiconductor material that contains an excess of holes in the outer shell of electrons. (E6A15)

You can think of holes as spots in the crystal that accepts free electrons. Because of that, the name given to an impurity atom that adds holes to a semiconductor crystal structure is call an acceptor impurity. (E6A04)

Silicon isn’t the only semiconductor material used to make transistors. At microwave frequencies, gallium arsenide used as a semiconductor material in preference to germanium or silicon. (E6A01)

Resources

More ham radio on Twitter and G+

Three more things I found while Twittering and using Google+.

Stay Connected to Your Broadband – an Improved ADSL Filter. I have a DSL line here, and have never had any RFI problems. In Great Britain, however, their broadband lines  seem to be susceptible. This 2010 article shows you how to build a filter that will fix that right up.

Learn circuits and electronics from MIT. The Massachusetts Institute of Technology is putting a lot of courses online, and you can take them for free!  This course, Circuits and Electronics, is the core course for all undergraduate electrical engineering (EE) and electrical engineering and computer science (EECS) students. Before you jump into this, realize that they say it will require about ten hours per week, and you need to know some basic calculus and linear algebra. This is an academic class, after all.

Open Hardware Journal. From the first page:

Open Hardware means sharing the design of physical or electronic objects with the public, similarly to Open Source software. The right to use, modify, redistribute, and manufacture, commercially or as a non-profit, is granted to everyone without any royalty or fee. Thus, Open Hardware designers hope to enrich society by developing a library of designs for useful objects that everyone can make, use, and improve.

The second issue features an article on the TAPR’s High-Performance Software-Defined Radio (HPSDR) project, which now includes over a dozen building blocks that can be used to assemble a high-grade 100 kHz to 55 MHz software-defined radio.

Things I found while twittering

Just some things I found while twittering. I found them interesting, so I thought you might, too…….Dan

Tworse Key:  a tweeting Morse key. An open design exercise in interface archaeology, that decodes the input from a classic Morse key to send twitter messages. The source code and hardware schematics are available online http://modin.yuri.at/tworsekey/

Design analog chips. According to the website, this freely downloadable book is “a comprehensive introduction to CMOS and bipolar analog IC design. The book presumes no prior knowledge of linear design, making it comprehensible to engineers with a non-analog background. The emphasis is on practical design, covering the entire field with hundreds of examples to explain the choices. Concepts are presented following the history of their discovery.”

DashToons.Com. Jeff, K1Nss presents the illustrated adventures of Dash!, the dog-faced ham.

 

Impedance Matching 101

electronic design magazine has just started a series of articles on impedance matching. They’re being written by ed editor Louis Frenzel, who just happens to also be W5LEF.

Ham Radio on Google +

Google+ has really caught on with hams. There are quite a few of us on this new social network, and I currently have 330 in my ham radio “circle.”  Here are a few links that those hams have shared:

The KC5FM Daily. Paper.li is a website that lets you turn Twitter, Facebook and RSS feeds into online newspapers in just a few clicks. Here’s KC5FM’s paper.

‘UHF’ Connector Test Results. This blog post by John Huggins (I couldn’t find his callsign anywhere on the website) shows the results of his UHF connector tests. He also compares their characteristics to other types of RF connectors. Huggins says,

The stunning result is all the UHF connectors in the test have worse performance than all the other connectors. One immediate conclusion concerning ‘UHF’ connectors is they will function at these higher frequencies, but one must decide if using the PL259 or SO239 is worth it in an age where its deficiencies have been made moot by ALL connector designs since WWII.

Prywatna Wytwórnia Lamp, where DIY meets vacuum electron devices. This blog post describes another guy–this one in Poland–who makes his own vacuum tubes.

Google+ is a lot better site for ham-radio social networking than Facebook.  Give it a try and join us.

 

Webinar to Cover Basics of Digital Signals

Normally, these are for subscribers to EETimes, which is targeted at electronics engineers, but I’m sure they wouldn’t mind if a few hams snuck in……..Dan

Webinar:
Fundamentals of the RF Transmission and Reception of Digital Signals

Date:
Wednesday, September 14, 2011; 1600Z

Duration:
60 min

Overview:
Digital Modulation is an important topic forRF designers because most modern day transceivers transmit and receive digitally modulated data. In this webcast, part of ADI’s continuing FUNDAMENTALS OF DESIGN series we will introduce you to the challenges—and solutions—for digital modulation. This webcast is a great way for beginners to get introduced to this vital communications standard or for veteran RF designers learn what’s new in the field. Some of the topics to be discussed will include:

What is the physical transition that happens to digital modulation when it is transmitted into the air?

What RF components are used for transmitting and receiving digital modulation? What are the key parameters in RF parts used in modern day transceivers and why are they important?

What type of digital modulation is there and how does the type of modulation affect the RF components key parameters?

Who should attend?
Students and engineers new to the field of RF Communications, as well as those more experienced engineers looking for a refresher on this topic.

Presenter:
Larry Hawkins, Business Development Manager, RF Group, ADI

Larry Hawkins works at ADI in the RF Group as a Business Development Manager. He has previously worked as an Applications Engineer and in RF Communications Design. Larry has a B.S. in Electrical Engineering, specializing in RF from the University of Utah. He has authored and presented many technical papers and seminars.