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The Benefits and Advantages of Frequency Response Simulation in PCB Design

Collection of types of signals and waveforms 

I often hear the question, does frequency really matter? Whether it is in the context of car audio, home audio, or PCB design, yes, frequency matters. The frequency response of any device that requires a particular resonance is vital to the overall design and performance of the device in question.

For example, I recall redesigning a car audio system for someone a few years ago. The recipient of this redesign was currently suffering from shock-induced anger, after spending $2,000 on a pair of subwoofers and an enclosure. It was not the price that had him up in arms, but rather the fact that his car was still reeking of the smell of burnt coils from an improper install.

Even in car audio, simulation is the key to proper design. Well, in this case, it’s apparent that simulation was not part of the plan. The end result was him being embarrassed while demonstrating his new stereo via an epic YouTube fail. These are the types of situations that simulation can and will effectively help you to avoid. Whether you are tuning a bandpass enclosure or designing circuits for a PCB, frequency simulation is the key.

The Importance of Frequency Response Simulations

As a science fiction fan myself, I have seen my share of time-travel related movies, and they always seem to end the same. However, after viewing these movies, I always find myself asking the proverbial question; what if? The ability to know the outcome before the event even happens is one of the critical advantages of simulation software.

In terms of frequency response, simulations provide you with the ability to accurately predict the response of your circuit before you build it. Another advantage to this is, of course, it saves time, lowers cost, and it perfects your design. Furthermore, it also fosters innovation and advances the design process by allowing you to examine various models and configurations.

The Benefits and Advantages of SPICE Simulation

Across multiple sectors, fields, and disciplines, simulation is having a profound positive effect. Ask any engineer, and they will tell you that simulation software is an invaluable design tool. In terms of PCB design, simulation as a whole is the choice between designing your PCB correctly, and a science experiment that has gone wrong.

One of the primary advantages of using simulation software is the fact that it enables you to obtain valuable feedback when designing real-world circuits. Furthermore, this feedback does not come with the time or expenditure typically required to procure this much-needed design insight. This, in turn, allows the designer to determine the efficiency and correctness of their designs without the need to build the circuit or device first.

As a result, simulation software also allows the designer to explore the worthiness of alternate designs without ever building the actual device or circuit. Moreover, examining the effects of your design decisions during the design phase rather than the construction phase, saves time, money, and increases design quality.

Green representation of digital waveform 

Digital signals mixing with analog signals have unique properties.

SPICE Simulation Software and Frequency Response Simulations

When using SPICE, it allows you to place probes and generate waveform plots for further analysis. This is made possible by its ability to determine intricate branch currents and node voltages at each frequency across your entire design.

Some of the primary functions SPICE can perform are as follows:

  • DC Sweep: Allows for the changing of component values (resistor value, voltage, or current) and graphing the results.

  • AC Sweep: Performs an analysis of the frequency response of a circuit (phase and gain).

  • Transient Analysis: Affords you the ability to set a period of time and analyze the response of your circuit within this timeframe.

  • It is worth noting that PSpice can provide an even more in-depth analysis of your circuits and circuit designs. The previously mentioned functions are only a part of what PSpice can afford you. The following are the other more advance simulation functions PSpice provides.

  • Sensitivity: Variations in manufactured components are natural. Sensitivity analysis lets you test circuit performance across the minimum and maximum tolerances for different component values and identify which elements are critical to your design goals.

  • Monte Carlo: Perform statistical Monte Carlo analysis on multiple components varied across their tolerance ranges to help predict your production yield under different conditions. This can be used to identify which parts can have their tolerances widened, reducing cost without sacrificing performance.

  • Smoke (Stress): Identify increases in junction temperature, secondary break-downs, power dissipation stresses, and voltage/current violations throughout your design.

  • Optimizer: Automatically optimize analog circuits and systems to find the best component values for your performance goals and constraints.

  • Parametric Plotter: Analyze/sweep multiple design and model parameters at once in plot or tabular form.

So, what type of simulation do you typically use for frequency response simulations? Well, the short answer is, a time domain simulation is ideal.

Graphic frequency waveform representation

SPICE can help with many aspects of your circuit design


Using Time Domain Simulations to Simulate Frequency Response

In regards to simulation software, time domain is the standard method for examining the behavior of an output signal for a given input signal (response). There are several reasons for this. First of all, when using time domain, you can calculate the current and voltage numerically across the entire circuit.

Secondly, you can examine the transitory behavior of a circuit to either a step response, like an input voltage switching from off to on or an impulse, such as a delta function input signal.

Finally, it affords you the ability to examine the response of a signal to a random input signal. You also have the option of using any input signal you choose as well as have these signals be a (repeating) waveform such as a triangle wave, digital pulse, or sawtooth wave. Also, you have the option of overlaying the input and output voltages to assess how the circuit influences the input signal. Furthermore, you gain a greater understanding of how a circuit performs when you examine the effects of input signal changes.

Frequency response simulations, like all simulations, are a vital part of PCB design. The use of simulations provide lower costs, saves time, increases design decision accuracy, and improves overall design quality. Having the ability to accurately predict the performance of an electronic circuit or device is an option every designer should utilize.

Alternatively, there are also AC simulations like AC sweep analysis wherein you can measure voltage and current changes with frequency. An AC sweep will enable you to calculate voltage and currents across a range of frequencies. Typically you will use a voltage source with an amplitude of 1V and use probes to generate the plots you need. 

What is PSpice Simulation?

If you are like me, you probably have a couple of breadboards lying around, and believe me; they were once an invaluable tool. In some cases, they still have their uses, but overall, when addressing frequency response, simulation is the way to go.

In PCB design, obtaining an accurate frequency response throughout your circuit design is critical to the overall functionality of the PCB. With that in mind, the advantages and benefits of simulation (PSpice) software is a crucial part of ensuring proper design outcome.

So, what is PSpice? PSpice is an acronym for Personal Simulation Program with Integrated Circuit Emphasis. In a more generalized description, it is an electronic circuit simulation tool (Cadence). During operation, PSpice will typically utilize a netlist generated from an OrCAD Capture. However, there is an option to operate it from MATLAB/Simulink. In summary, PSpice allows you to analyze as well as simulate your mixed-signal and analog circuits within OrCAD.

Cadence’s design and analysis tools, are sure to have your designers and production teams working together towards implementing frequency response simulation solutions for all of your PCB designs. OrCAD PSpice Simulator facilitates the implementation of frequency response simulations for all of your electronic circuit design needs, as well as many other types of simulation to ensure top design security. 

If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.