Designing Pulse Circuits to Solve Application Problems

Sampling and Capturing Pulses

- By Wolfgang Matthes

Pulse circuits help digital circuits, such as embedded boards, to process pulse trains or bursts of pulses from the outside. This month, Wolfgang tackles the design of basic circuits to solve application problems, using tiny logic, microcontrollers, Complex Programmable Logic Devices, and Field Programmable Gate Arrays.

Many digital systems process signals from outside, generated by sensors, level translators, and the like. Most of them are essentially pulse trains or bursts of pulses. Typical design tasks concern capturing pulses, detecting edges, filtering out or detecting glitches, and synchronizing the pulses with internal clocks. These are minor but intricate problems most textbooks do not cover.

In a three-part article series in Circuit Cellar Issues #413, 414, and 415 [1] [2] [3], I introduced latches and flip-flops as the basic components, and discussed the problems of synchronization and metastability. These topics are, however, only prerequisites to tackling the design of circuits to solve application problems.

Here, I take the next logical step, introducing some basic application circuits. In the beginning, we should become clear about the specifics of the design tasks. Our means comprise discrete devices, especially tiny logic, microcontrollers, CPLDs, and FPGAs. There are many design ideas for detecting pulses, deglitching, debouncing, and so on. Which principles to select depends on the nature of the incoming pulses, the stipulated requirements, and the means available. I will discuss chiefly principles and alternatives. Selected circuits and design ideas can be found in an Internet addendum.

BASIC DESIGN TASKS