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Analog Circuit Design: Introduction to Signals and Return Paths

A controller with analog control pads


I’m sure I’ll upset some with this opinion: true gamers don’t game with a keyboard and mouse. They’ll feel alive when they have a firm grip on the analog pad, and experiencing the force feedback brings gaming alive for them. Unfortunately, I was never a true gamer; I’ve always chosen my trusty keyboard over an analog gamepad. 

Being a fan of everything digital doesn’t mean I’m clueless when it comes to analog design. To deliver the satisfying gaming experience of an analog gamepad, you’ll need to up your game in PCB design. It will be unlike anything you’ve done with digital circuits.

What Are Analog Circuits?

Analog circuits function by transmitting continuous voltage or current as a signaling method. Typically analog circuits are made of basic components like resistors, capacitors, diodes, inductors, transistors and operational amplifiers. However, today’s analog circuits design may involve the use of microcontroller or other intelligent, active components.

What’s essential is the nature of how the signals are being transmitted. In digital circuits, signals are represented by logic 1 or 0, and they have a significant margin of error. For analog circuits, signals are represented by a continual value that must be transmitted precisely to the recipient.

Importance Of Getting Analog Circuit Design Right

Pro gamers are sensitive to the tiniest maneuver on the analog pad or the lack of. They will sense the slightest deviation in the sensitivity that results in erroneous movement. But gaming aside, you’ll want to ensure the analog circuit is functional accordingly as they can be used for critical applications.

Analog circuits that involve sensors can have no room for errors. For example, parametric sensing circuit in medical facilities must provide reliable readings at all times. Also, they must not be easily interfered by surrounding equipment. The same goes for transducer circuits used in food processing plants, that require the right level of humidity level to be relayed to environmental controllers.


Industrial sensors gauging measurements in a warehouse

Analog sensor values are crucial for industrial applications.


Even for non-critical analog applications, a poorly designed circuit will affect the quality of the product and draw negative feedback from consumers. 

Useful Analog Circuit Design Tips

Unlike its digital counterpart, analog circuits are highly susceptible to noise. Noise introduced into an analog signal can affect the integrity of its value. A slight deviation can cause a significantly different outcome in an analog processing module.


Components aligned symmetrically on a circuit board

Keep analog traces short and simple.


What complicates matters is today’s analog design often involves high-speed digital circuits. Here are what you should pay attention to if you’re new to analog circuit designs.

1.  Keep Analog Circuits Clear From High-Speed Signals

High-speed signals can introduce noise into analog circuits if routed adjacent to an analog signal. Always remember that the surrounding area for an analog circuit is a no-go for digital, especially high-speed traces. Common communication circuits like SPI, I2C, CAN, and Ethernet is considered high-speed and may affect the integrity of analog circuits.

2. Proper Ground Separation

In mixed-signal design, proper ground separation is mandatory. Analog circuits should have all its signal referenced to the analog ground and is connected to digital ground by a single point. Failure to abide by this practice may subject the analog circuit to ground noise. 

3.  Keep Analog Traces Short

The longer the analog trace is, the higher the risk it’s affected by sources of electromagnetic interference. Keep it short and simple. 

4. Map Analog Signal Return Path

In fundamental electronics, a complete circuit involves both the signal and the return path. In the case of analog circuits, the return path is the ground connection. Not only you should keep the analog trace short, but you’ll want the return path to be a direct shortest connection back to its source. This prevents unwanted noise coupling onto the return path.

5. Minimize Vias On Analog Traces

When you’re designing with high-frequency analog signals, having vias on copper traces can potentially introduce ground loops when the via holes passes through underlying ground planes. A series of vias also contribute to self-inductance, which lowers the self-resonance frequency and can affect high-speed analog signals. It’s best to keep analog traces via-free.

Even with all these tips, using smart PCB design software like that offered by Cadence ensures that you’re not leaving the design to chances. OrCAD PSpice Simulator allows you to simulate the analog circuit and detect potential integrity issues in the design phase.

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