[Design View / Design Solution]
Analog Simulation Tools Aid Digital-Control-Circuit Designers
Gain a greater intuitive understanding of system operation by transforming your design into its most fundamental elements for simulation.
DESIGN VIEW is the summary of the complete DESIGN SOLUTION contributed article, which begins on Page 2.
Although analog and digital controllers may appear vastly different, their principles of operation are usually quite similar. Therefore, popular analog tools like Spice can still be used to benefit common digital proportional-integral controllers through analysis without spending hours on complex math or a fortune on specialized software.
Merging proven analog and digital technologies may achieve the best of both worlds. Listed are 10 benefits of analog simulation for digital circuits:
Leverage decades of proven analog knowledge.
Enhance intuitive understanding of system dynamics.
Systematic circuit optimization.
Time savings over trial-and-error iterations.
Design validation through multiple-domain operation.
Partition analog and digital circuitry.
Substitute low-cost, high-speed op amps.
Develop valuable education tools.
Share results over multiple platforms.
Free evaluation software is adequate for most circuits.
To give readers a hands-on view of these benefits, a digital infrared controller was developed. The PIC MCU drives current through an infrared emitter with its pulse-width modulator and measures the sensor voltage with its analog-to-digital converter.
The article details the simulation of the IR controller through the use of Spice. Among the topics covered are the voltage-controlled voltage source, which is essentially an ideal op amp that can simulate the controller simply by adding resistors and capacitors. Also discussed is execution of the proportional-integral algorithm in Visual Basic. Detailed Spice results are provided.
HIGHLIGHTS:
A Digital Controller Example
A closed-loop controller's function is to maintain a desired response despite system changes and disturbances. An infrared controller was developed for this article to guide the reader through the analog simulation of a digital circuit.
Analog Simulation Of Digital Controllers
One of the most popular programs for simulating analog circuits is Spice, thanks to decades of validated operation and ease of access. An analog equivalent of the digital infrared controller executing the proportional-integral algorithm is provided to illustrate the simulation. The algorithm is executed through a PC in Visual Basic for development ease because it's faster and easier than generating firmware.
Spice Results
Spice results for various parameters were determined for the example digital controller. For instance, the loop gain showed a 3.25-Hz bandwidth and 72.3° phase margin. The values were calculated automatically by the postprocessor in the evaluation version of Intusoft Spice. Also calculated was the transient step response, which matched the hardware measurement that was reached earlier.
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