How to get Edge Triggering | Simulation using Multisim

Summary

This video explains how edge triggering is derived from level triggering in digital electronics using a differentiator circuit. It begins by distinguishing between level triggering and edge triggering, including positive (rising edge) and negative (falling edge) triggering. The instructor then demonstrates how a clock signal can be converted into edge impulses through a capacitor-resistor differentiator circuit, deriving the output mathematically using Kirchhoff’s Voltage Law and differentiation. To reinforce the concept, the circuit is simulated in Multisim, showing spike outputs from a clock input. Finally, the video explains how adding a diode can eliminate unwanted spikes, enabling selective positive or negative edge triggering.

Takeaways

• 🕹️ There are two main types of triggering in digital circuits: level triggering and edge triggering.
• ⚡ Edge triggering is further classified into positive edge (rising) and negative edge (falling) triggering.
• ⏱️ A clock signal with a 50% duty cycle can be converted from level triggering to edge triggering using a differentiator circuit.
• 🔧 A differentiator circuit uses a capacitor and resistor with small values to generate spikes corresponding to signal edges.
• 📐 Mathematically, the output of the differentiator is proportional to the derivative of the input: V_out = RC * dV_in/dt.
• 💡 Differentiating a step or clock signal produces impulses (positive and negative spikes) representing rising and falling edges.
• ⚠️ The initial differentiator output has both positive and negative spikes, which can be confusing for edge detection.
• 🔌 Using a diode in the circuit allows selective removal of either positive or negative spikes for clean edge triggering.
• 💻 The simulation in Multisim involves placing the capacitor, resistor, clock source, diode, and oscilloscope to observe the input and output waveforms.
• 📊 Observing the oscilloscope confirms the theory: the input step signal is converted into edge pulses, and the diode removes unwanted spikes.
• 🎯 This method is simple yet essential for generating precise edge-triggered signals in digital electronics and clocking applications.
• 🔄 Adjusting resistor and capacitor values affects the sharpness of the output pulses and the efficiency of edge detection.

Q & A

What are the two main types of triggering discussed in the script?

The two main types are level triggering and edge triggering. Level triggering responds when the signal stays at a particular level, while edge triggering responds only at transitions.

What are the two categories of edge triggering?

Edge triggering is divided into positive edge triggering and negative edge triggering.

What is positive edge triggering?

Positive edge triggering occurs at the rising edge of the clock signal, when the signal changes from 0 to 1.

What is negative edge triggering?

Negative edge triggering occurs at the falling edge of the clock signal, when the signal changes from 1 to 0.

Why is a normal clock signal not sufficient for edge triggering?

A normal clock signal represents levels because it remains high and low for fixed durations. Edge triggering requires very short transition events rather than entire high or low intervals.

Which circuit is used to convert a level signal into an edge signal?

A differentiator circuit consisting of a capacitor and a resistor is used to convert a level signal into edge-like impulses.

What assumption is made about the resistor and capacitor values in the differentiator circuit?

The product of resistance and capacitance (RC) is assumed to be very small.

How is the output voltage of the differentiator circuit related to the input voltage?

The output voltage is proportional to the derivative of the input voltage, expressed as Vout = RC(dVi/dt).

What happens when a clock signal is differentiated?

Differentiating a clock signal produces impulse-like spikes: positive spikes at rising edges and negative spikes at falling edges.

Why do both positive and negative spikes create a problem?

Having both spikes can cause ambiguity in circuit operation because many digital circuits require only one specific edge type for triggering.

How can unwanted spikes be removed?

A diode can be added to the circuit to eliminate either positive or negative spikes depending on its orientation.

How does the diode remove the negative spikes in the example?

During a negative spike, the diode becomes reverse biased and acts like an open circuit, preventing the spike from appearing at the output.

What happens during a positive spike when the diode is used?

During a positive spike, the diode becomes forward biased and conducts, allowing the output voltage to appear.

Which simulation software is used in the demonstration?

The circuit is simulated using Multisim.

What components were used in the Multisim simulation example?

The simulation used a capacitor of 1 µF, a resistor of 100 Ω, a clock voltage source, ground connections, and an oscilloscope.

What role does the oscilloscope play in the simulation?

The oscilloscope is used to visualize and compare the input waveform and the output waveform of the differentiator circuit.

What was observed in the simulation results?

The input waveform appeared as a clock/step signal, while the output waveform showed positive and negative spikes as predicted by the differentiation process.