Abstract:

Nowadays, the university lecturers provoked to enhance the students’ attention to the issues studied, apply innovative ideas, such as creative teaching, audio, and video tools, “real-world” learning, working in teams on projects, etc., for making the classes more attractive to the students and the learning more effective.

Bachelors of the electrical specialties in the University of Ruse are introduced to the main topics in the field of digital electronics in the courses “Digital Electronics” and “Pulse and Digital Devices”. Various combinational circuits such as encoders and decoders, multiplexers and demultiplexers, code converters, and comparators, as well as arithmetic circuits (half-adders, adders, multistage combinational adders) are studied in these courses.

In the last two academic years, in the conditions of the COVID-19 pandemic, the lecturers in these courses decided to introduce inquiry-based learning (IBL) as one of the trends for future education, known as Education 4.0. IBL is a form of active learning that starts by posing questions, problems, or scenarios. Inquirers will identify and research issues and questions to develop knowledge and solutions. IBL includes problem-based learning and is generally used in small-scale investigations and projects, as well as research.

The inquiry-based instruction is principally very closely related to the development and practice of 21st-century skills, such as:
1) critical thinking;
2) creativity;
3) problem solving;
4) collaboration;
5) perseverance;
6) communication, technology, social, literacy, innovation and thinking skills;
7) information, civic, digital and media literacy;
8) global awareness;
9) self-direction;
10) social responsibility.

The students had to work on different projects, getting acquainted with and implementing different digital devices not included in the curriculum of the course at the moment, for example, BCD adders, binary multipliers, various adders’ circuits for fast addition of binary numbers, etc. One of these topics is “Carry Propagation–Look-Ahead Carry Generator”. The carry propagation delay in the “traditional adders” limits the speed of adding two numbers. The outputs of any such adder arrangement will be correct only if signals are given enough time to propagate through gates connected between input and output. Since subtraction is also a process of addition and operations like multiplication and division are also processes involving successive addition and subtraction, the time taken by an addition process is very critical. One of the possible methods for reducing carry propagation delay time is to use faster logic gates. But then there is a limit below which the gate delay cannot be reduced. There are other hardware-related techniques, the most widely used of which is the concept of look-ahead carry, presented in the paper in detail. This concept attempts to look ahead and generate the carry for a certainly given addition operation that would otherwise have resulted from some previous operation.

The paper presents the application of inquiry-based learning on the topic “Carry Propagation–Look-Ahead Carry Generator” implemented with different computer-based tools, such as MS Excel, Logisim, ISE Project Navigator, LearningApps, as a way of attractive presenting the topic to the students. The applications described in the paper are planned to be included when updating the curriculum in the courses “Digital Electronics” and “Pulse and Digital Devices”.

Keywords:

21st-century skills, inquiry-based learning, arithmetic circuits, digital electronics.