Digital Data to Analog Signal: Communication Methods and Design Tips

December 11, 2019 Cadence PCB Solutions

Digital-to-analog converters plugged into an electronic device

 

When digital cameras started taking over their analog counterparts in the early 2000s, I thought the era of analog photography for the typical consumers were gone for good. At least that seemed to be the case until Fujifilm’s Instax proved to be a hit with teenagers who were looking for a more vintage or retro aesthetic for their photographs (and certainly didn’t have to deal with the hassle of an analog camera back in the day). 

The return of consumer analog cameras proved that it’s too early to write off any technologies, and both analog and digital can coexist in a synergistic balance. The same applies if you’re a PCB designer. If you’ve been working with digital modules all this while, you ought to know that the analog part of electronics is a totally different world.

What’s more important is to pick up skills interfacing between both digital and analog electronics. In some applications, digital data needs to be converted to analog signals for the system or product to serve its purpose. 

Digital Data To Analog Signal Conversion Basics

Despite living in a digital world, analog applications are still prevalent in our daily life. The smartphone still relies on analog signals for getting sound out of your favorite tracks. Graphic controllers take digital video signals and convert them to analog R, G, B for external display interface. 

Digital data to analog signal conversion is also common for industrial applications. For example, the 4-20 mA involves turning digital parameters into corresponding analog value current. 

The theory of digital data to analog signal conversion is generating an equivalent voltage that corresponds to the binary value. As for the underlying hardware, the most operational and straightforward digital to analog conversion circuit can be reduced to the R-2R binary ladder circuit.

 

R-2R Binary ladder circuit diagram

 

The R-2R binary circuit is an improvised version of the weighted-resistor circuit connected to a summing amplifier. The voltage generated is based on the resistance value, which is weighted according to the binary value. A logic 1 results in the switch connecting to the reference voltage while a logic 0 connects the switch gto ground. 

Important Parameters For Digital Data To Analog Signal Conversion

In PCB design, you’re more likely to use a DAC chip than the basic R-2R circuit. DAC chips are more sophisticated as they support features like multi-channel, high resolutions, power-optimization, and choice of communication interfaces.

When choosing a DAC chip, you’ll want to consider the following:

  • Resolution - At its strictest sense, the analog signal produced by a DAC could never be as smooth as those generated by a mechanical knob switch. However, choosing a DAC with high-resolution produces smaller steps in the varying analog voltage or current.

  • Refresh Rate - If you’re working on audio applications, you’ll want to go for DACs with a higher refresh rate. The parameter indicates how frequent the DAC will alter its analog output in correspondence to its internal register. 

  • Number of Channels - The beauty of a DAC chip is that you could have multiple channels within a single semiconductor IC. A useful feature if you’re tight on space on the PCB.

  • SNR - The Signal-to-Noise ratio gives you a good idea of the performance of the DAC. For audio applications, the rule-of-thumb is sticking to a DAC above 100 SNR. 

PCB Design Tips With Digital to Analog Converters

The precision of converting digital data to analog signals lie not only on the DAC chip but also on the PCB layout. Analog signals are sensitive to interference, and you’ll need to adhere to certain best practices.

Proper ground separation on a printed circuit board

Ground separation is key in ensuring analog signal integrity.

 

Top of the list is to have proper separation between digital and analog components. Even if you’re having a DAC with a single analog trace heading to a connector, other digital components and traces must be kept away from it.

Ground separations are also crucial in preventing digital noises from coupling into the analog signal. It’s vital that you plan the return path of the analog signal by having a ground plane adjacent to the trace. You’ll also want to ensure a stable power supply for the DAC chip. Place bypass capacitors near the power pins of the DAC and avoid using the sample voltage supply with digital components. 

Cadence's suite of design and analysis tools are paramount for helping any designer work through their digital and analog signal dilemmas. Especially when working through component placement and layout, OrCAD is more than capable of providing you the design experience you need. 

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

About the Author

Cadence PCB solutions is a complete front to back design tool to enable fast and efficient product creation. Cadence enables users accurately shorten design cycles to hand off to manufacturing through modern, IPC-2581 industry standard.

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