UPC EETAC Bachelor's Degree in Telecommunications Systems and in Network Engineering EEL

Content

P1: Analysis of simple circuits based on logic gates

P1 design


Resources in lectures and labs: L1.1, L1.2, L1.3, Lab1.1, Lab1.2 Project objectives

Highlighted analysis project: Circuit_C 

1. Specifications (What do I have to do?)

Analysis: deduce the truth table of Circuit_C in Fig. 1 using the four analysis methods proposed in Fig. 3 and compare solutions.

Circuit_C sketch

Fig. 1. Example Circuit_C to analyse.

Each analysis method is an independent project with all four sections.

Fig. 2. Organise your analysis project following this sequence.

Fig 3 shows the general concept map including up to four methods for analysing simple combinational circuits.

Analysis methods

Fig. 3. Proposed analysis methods (Visio). The concept map combining analysis and design (Visio).


Other tutorial analysis circuits and assignments.


NOTEdesigning equivalent circuits is discussed and proposed in the next complementary P1 design page.


2. Method I planning

 Analytical method using Boolean algebra and pen & paper.

planning method 3

Fig. 4. Planning method I subdividing the circuit in sections.

- Find the circuit equation.

- Simplify equations until simple SoP or PoS equations are obtained.

- Add missing variables to convert SoP into sum of minterms or PoS into product of maxterms.

 Project location for saving pictures, scanned sheets of paper, etc... 

C:\CSD\P1\Circuit_C\algebra\(files)

 

3. Method I development

- Handwritten analysis of Circuit_C and rec.

Circuit
equations
equation

Fig. 5. Deducing the circuit's equation.

From circuit equation, we can apply algebra to try to obtain a simple equation.

equations_3

Fig. 6. Simplification. 

Term Z is complicated, because is not a simple sum or a product. Thus, we can imagine the equation as another independent subcircuit Z = f(D0, A, B):

new problem
equations

Fig. 7. Analysis of Circuit Z = f(D0, A, B).

equation product of maxterms
Equation sum of minterms

Fig. 8. Final equations that we have to compare with results from other methods.

 


2. Method II planning

Planning means organising and discussing how to proceed to reach solutions. A flow chart of sequential operations will be necessary to explain what to do, how to do it and when.

- Choose Proteus as circuit simulator: draw/capture the circuit schematic in Proteus and run a simulation.

- In CSD we never start a project or a simulation from scratch, but we copy and adapt from similar exercises found here in this digsys web. For example, use files to copy and adapt from Lab 1.1.

- Select a library of a classic technology, for instance LS-TTL or CMOS series 4000.

- Try all the possible input combinations to fill in and complete the truth table.

Project location:

C:\CSD\P1\Circuit_C\Proteus\(files)

 

3. Method II development

Developing means executing a given plan to achieve a circuit solution. Fig. 4 shows an example of Proteus capture for Circuit_C.pdsprj

Circuit_C captured in Proteus

Fig. 9. Circuit_C captured in Proteus ready for running simulations.

Pictures in Fig. 10 show results for given combinations.

Running the simulation

Fig. 10. Simulation results when applying input binary combinations "0101" and "1100". We can observe that "0101" generates minterm m5 and "1100" generates maxterm M12.

In this way, trying all 16 combinations we reach the final truth table:

truth table


2. Method III planning

 VHDL synthesis and simulation project.

- Translate to VHDL Circuit_C algebraic equation in Fig. 5 using a similar file to copy and adapt.

- Choose a target chip, for instance CPLD MAX II EPM2210F324C3, and start a VHDL synthesis project using an EDA tool, for instance Quartus Prime. 

- Examine and print the RTL and technology schematics.

- Start a VHDL simulation project, for instance in ModelSim-Intel FPGA Starter Edition, using a testbench to input signal stimulus .

 Project location:

C:\CSD\P1\Circuit_C\VHDL\(files)

 

3. Method III development

This is an example of Circuit_C.vhd translated to VHDL to synthesise the circuit.

This is an example Circuit_C_tb.vhd VHDL testbench to obtain the circuit's truth table.

RTL

Fig. 11. Example RTL (register transfer level) ideal schematic from Quartus Prime shynthesiser.

 

Wave

Fig. 12. Truth table deduced from the simulation of all the input test vectors.

 


2. Method IV planning

Numerical engine WolframAlpha to be used for inferring the truth table from the circuit's algebraic equation.

plannning method 2

Fig. 13. Planning the method IV as a bullet list of operations.

- Write the circuit equation in Fig. 5 in a text file step-by-step.

- Use files to copy and adapt them from Lab 1.1. or WolframAlpha.

- Reorder input variables if such is the case before annotating maxterms and minterms.

- Draw the truth table.

- Project location:

C:\CSD\P1\Circuit_C\wolfram\(files)

 

3. Method IV development

Circuit and equation are at the same conceptual level.

             circuit and equation 

Fig. 14.  Circuit equation.

equation

This is an example Circuit_C_equation.txt file to be pasted in WolframAlpha window.

results

Fig. 15. Results representing the truth table.

 


4. Testing (let us verify whether the results are correct)

Testing means to check or verify that the solution is correct and agrees with the initial specifications.

In this analysis section, the simplest way to check the truth table is by comparison with the truth table obtained by other methods.

 

5. Report

Project report: sheets of paper, scanned and annotated figures, file listings, notes or any other resources. In CSD follow this rubric of indications for writing reports.

 

6. Prototyping

Any of our circuits can be built as a prototype for laboratory experimentation, measurements and characterisation. We will use for instance DE10-Lite boards.