ELECTRONICS INFO DESK

This article is a tutorial to design a BJT amplifier circuit to acquire a given gain impedances and cut-off frequencies. I wrote an article an year ago about a similar topic. But It only matches gain and impedances and also the gain was a little one. This time the gain will be a higher value. The picture you can see on left side is the oscilloscope observation of the actual PCB of the BJT amplifier I designed.

At that previous post I stated that if we have to design a larger gain it is very simple to use a Voltage Divider Bias with a bypass capacitor at the Emitter resistance.

This was the 1st lab class in 3rd year of my degree for the Electronic Engineering subject. Had to design an amplifier circuit of

gain > 40 dB
input impedence > 1kOhms
output impedence < 100 Ohms

1. The voltage gain of overall circuit is given by the multiplication of the gain of all stages.
2. The load (RL) of the 1st stage becomes the input impedence for the next stage.

So the 1st stage must design as a loaded configuration. The last stage is an unloaded one. Because the stages are independent, we analyze them when drawing the schematic of 1st stage showing the load resistor. But when we consider the schematic of the final design we cant draw it because they are only virtual resistors.

In these designs we can use the assumptions of Vbe = 0.7 V for Silicon transistors & Ic = Ie where Ic and Ie are Collector current and Emitter current respectively.
And the value of re = 26mV/Ie always.

Matching hie and hfe values for the Ic can be collected from the datasheet of the transistor we select. hie is called the input impedence of the transistor.

And the overall gain of the amplifier is the multiplication of all the gains by individual stages.

Lower cut-off frequency of the amplifier is defined by a large capacitor of uF values while the upper cut-off frequency is defined by a very small capacitor (capacitance due to wiring and the capacitors in between the p-n junctions inside the transistor) of the amplifier which has normally pF values. But the higher cut-off will be in MHz region naturally. So if we have to move the higher cut-off into a kHz region like in this case we will have to use a single capacitor in parreral with the configuration. 


Every capacitor which we can see in network has their own cutoff frequencies because of their frequency responses. It is necessary to understand only one capacitor is responsible for the lower cut-off frequency and only one another capacitor is responsible for the higher cut-off frequency. In designs we don't want to analyze each and every capacitor. We can fix the capacitors to meet the worst cases and other capacitors not to meet the worsts.

This configuration can accomadate a medium input impedence like 1k Ohms and its Zout is normaly a medium value but higher than Zin like 2k Ohms.

This is a program and the circuit diagram to create a decimal counter by seven segment display decorder. I'm going to do this using PIC16F877A microcontroller and MikroC.

I'm using the pins of PORTB. Here below is the circuit diagram and the program code I'm going to use. In the code, I'm not going to add comments because I'm going to describe the logic under the images.

For this practical we are going to use common cathode seven segment display. Segments to be on and the segment diagrams are also as follows.























































































Never ending while loop counts from zero to 9 and again from zero to nine. 7 segments are powered by the RB0 -> RB7 of PORTB respectively. ssegments function is used to drive the segments which are match to the decimal numbers. This program is based on a simple logic.

Following is a video of the fixed circuit.

Now I'm going to improve my previous program to a more attractive circuit. MCU is same and the language and softwares are same as in the previous post.

I'm going to program my PIC for a knight rider circuit of 8 LEDs using PORTB pins.

Here below is the circuit diagram and the program code I'm going to use. In the code, I'm not going to add comments because I'm going to describe the logic under the images.

























When program starts it simply drive the port B as outputs.
Then the bit 0 of port B is set to high by PORTB = 1; command.

That command means the decimal number 1 is assigned to the register in it's binary format.

Then the delay of half a second is given. And in the never ending loop it calls the two functions implemented earlier when the simple condition of checking last and 1st bits occurs.

Two functions are left and right.

Moving left in a binary patern is equals to a operation of multiply by 2 in values.

So moving right is the opposite of that.

This is the simple logic of the program and following is a short video when the circuit is fixed.





Next tutorial will be based on the port multiplexing method to display a knight rider circuit for more than 8 LEDs.

This is the simplest Microcontroller programing practical for anyone who is interested. In this practical I'm going to use a PIC16F877A microcontroller and some software tools like WinPIC800, PIC Simulator, MikroC PRO etc.
I'm going to blink a LED with a one second delay using the above tools and code the program by MicroC.

Following is the flowchart and the circuit to blink an LED with a one second delay. Note that this can be done by many ways. This is only a simple one.




















I'm going to blink the LED on PORTB. When PORTA or PORTE  is used there is a problem because if so I have to use ADCON registers. So in this case I'm using pins of PORTB.

Some notes about the circuitry :-


4 MHz crystal oscillator is used. 1K resistor bitween VDD and MCLR' is used to prevent self resetting. L7805 voltage regulator is used to control the voltage in 5Vs.

If you want to learn MikroC language syntaxes refer the ebook from the following link. http://www.mikroe.com/eng/downloads/get/31/c_syntax_v102.pdf

1st download the free software from http://www.mikroe.com/eng/products/view/7/mikroc-pro-for-pic/
When it is installed there you can see some sample examples to test your microcontroller. Just close them and start a new project.


Select device name as PIC16F877A -->> clock device 4.00 MHz -->> project name -->> next --> next --> finish !!

Here is the code I wrote.

When coding is completed build the project.
If everything is done correctly it will show a message " Finished Successfully " at the last row on the message box.

Building here is also known as the compiling.
It will genarate a HEX file. Use that HEX file for the work from here.

Some notes about the coding :-

TRISB = 0; and PORTB = 0; is written to drive prots and pins. By this code all the pins in PORTB
is configured as output pins.

While loop here is a never ending loop as the logic is one. PORTB =~ PORTB; means get the logic value from the bits of PORTB and write it's inversion again on the bits of PORTB. Delay_ms(1000); gives a delay of a one second.

If you wish to use PORTA or PORTE which are used specially for analog to digital conversion, You have to write some additional code for ADCON register like below otherwise it's pins will directly return the supply voltage.

After the code is written you can simulate it on PIC SIMULATOR IDE software to see it works well or not.

Sometimes the programs work well in simulator but not in actual circuitry. Even if the ADCON1 = 0x06; line is not written in  the code simulator simulates it correctly.
But actual circuit it doesn't.

Now to PICSimulator IDE.

Download the free version and open it.

File -->> clear memory -->> load program!!


Load the HEX file. Configure the settings


Tools --> 8 * LED board!!


Simulation -->> start!!


Rate -->> Ultimate!!





Here is a screen shot of once it is blinking.
Following is a small video after circuit is fixed.

This is an unbiased report on the affiliated universities of SLIIT - Sri Lanka Institute of Information Technology.
There are so many misunderstandings in university rankings and their quality even among SLIIT students.
This post may be helpful for the students who started the academic life from SLIIT and going to complete their studies abroad.

There are 13 universities from 5 countries which have partnership degree programs with SLIIT. Students can complete 1st few years of their degree in SLIIT and can transfer to those if like to learn abroad. For some degrees students must go there, and for some degrees it is not a must. These degrees include BSc, MSc, DSc, MEng ... etc. First of all there is something to say about university rankings.

University rankings are lists of universities or equivalent institutions in higher education, an order determined by any combination of factors. Rankings can be based on subjectively perceived "quality," on some combination of empirical statistics, or on surveys of educators, scholars, students, prospective students or others. Some rankings evaluate institutions within a single country, while others attempt to assess major institutions in all countries worldwide.

read more on wiki about rankings - definition

The most notable organizations for world rankings are Academic Ranking of World Universities compiled by the Shanghai Jiao Tong University and now maintained by the Shanghai Rankings Consultancy, QS World University Rankings and Times Higher Education World University Rankings and also The Webometrics Ranking of World Universities produced by the Cybermetrics Lab (CCHS), a unit of the Spanish National Research Council (CSIC), the main public research body in Spain. It offers information about more than 12,000 universities according to their web-presence (a computerised assessment of the scholarly contents and visibility and impact of the whole university webdomain).

Note that webometrices are based on a composite indicator that takes into account both the volume of the Web contents (number of web pages and files) and the visibility and impact of these web publications according to the number of external inlinks (site citations) they received. It can be think as a measurement of popularity.

Following is a map of universities by countries which SLIIT has partnership programs.


Lets start from the left of the picture

University of British Columbia (UBC) - Canada

The University of British Columbia, established in 1908, educates a student population of 50,000 on major campuses in two cities and holds an international reputation for excellence in advanced research and learning. The UBC library, which comprises 5.9 million books and journals, is the second-largest research library in Canada.
Kwantlen Polytechnic University - Canada
Webometrics Ranking of World Universities : world rank 2286
Southeast Missouri State University - USA
As a comprehensive institution, the institution offers over 200 areas of study, including undergraduate degrees as well as master's degrees and a cooperative Ed.D. program with the University of Missouri.

UC has an annual enrollment of over 40,000 students, making it one of the 100 largest universities in the U.S.
The most recent 2010 survey by Times Higher Education (UK) ranks the University of Cincinnati as the 76th in North America (this includes American and Canadian institutions of higher education) and as the 190th in the world. The 2011 US News and World Report rankings place the University of Cincinnati as the 156th best school in the nation. The 2007 rankings from The Center at Arizona State University place the University of Cincinnati as a "Public University Ranking in the Top 20 public research universities in the United States.
The university is the fourth largest in the UK in terms of enrolment, with more than 33,000 students, over 3,200 staff and 572 courses.
Uppsala University - Sweden
In 2009 there were 16,030 students enrolled in Higher education and an estimated 14,748 students enrolled in TAFE, including nearly 7000 international students from over 100 different countries.

In 2009, they ranked RMIT as the fourth most internationalised university in the World - behind the University of London's School of Economics and School of Oriental and African Studies and Cranfield University, according to students, and 15th in the World according to faculty/staff.

RMIT is also ranked as the top entrepreneurial university in Australia, and 12th in the World, according to the GSEA annual Top Entrepreneurial Universities List. It is ranked as the top advertising school of the decade in Australia and 5th in the World, according the YoungGuns International Awards. In Victoria, RMIT is currently ranked as the 3rd most research-intensive university, and 10th in Australia.
University of South Australia was ranked 295th in the 2009 Times Higher Education Supplement Top 400 Universities list.
Academic Ranking of World Universities : world rank 151 - 200
Times Higher Education Rankings : world rank 45
QS World University Rankings : world rank 61
Webometrics Ranking of World Universities : world rank 103


About the partnership with SLIIT                  university website