Mixed-Signal Hardware/PCB Design Tips - Phil's Lab #88

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[TIMESTAMPS]
00:00 Introduction

00:33 Altium Designer Free Trial
00:50 Design Review Competition
01:14 PCBWay

02:09 Hardware Overview

03:30 Tip #1 - Grounding
06:18 Tip #2 - Separation and Placement
09:23 Tip #3 - Crossing Domains (Analogue - Digital)
11:55 Tip #4 - Power Supplies
15:09 Tip #5 - Component Selection

17:48 Outro

[PhilsLab]

The current ratings indicated on the schematic for supplies are the max. capabilities of the LDOs. The actual current draw per rail is significantly lower, e.g. for the analogue rail <50mA @5V (therefore, the series resistor being larger is ok in this case). I typically oversize my LDOs quite considerably.

[nheng]

Nice video Phil. I worked with AD for three years but decades with Cadence/Allegro and Pads. I was very happy to hear your philosophy of a single ground with the qualifier that you need to know what you're doing. One thing that I've found very helpful and used regularly on complex boards is the concept of rooms. Not only for the PCB designer, rooms remind you of where things are and not just components, but voltages, currents and their frequencies, and I/O. Fortunately, AD supports rooms, although not necessarily with the easiest implementation. And your lovely schematics, with sections identified and labeled, lend themselves directly to rooms.

One message that pretty much rules in PCB design, echoed by the gurus like Hartly and Bogatin, is to know where your current flows, know where it returns, and to treat that path with respect. Decoupling capacitors bring the energy for the task to the local area where it's needed. Your high current, whether analog or digital, should have it's transient requirements satisfied by capacitors including bulk, "normal distributed decoupling" and for RF and certain compliance reasons, those caps which are right at the IC pins. Basic boards are important to get your blood flowing, cut your teeth, etc. But when your boards get more complex, contain mixed signals AND may need to pass compliance testing in production, the rules for signal flow and returns will never/seldom fail you.

While AD is a great, powerful, professional packages, I have a voodoo doll and pins out for Altium for their abandonment of Circuit Studio and the evolution of it to CircuitMaker Pro, presumably sharing code base and many feature of the (especially now) very high priced package. There are many developers out there, and hobbyists who cannot afford the full AD seat. Students of course, can get the full package for (I guess) free or at least very cheap. And contractors of course, may also need to support other packages (Cadence/Allegro, Pads, etc.) without full installs.

This ends my jab at Altium for abandoning the low end market. But I fully understand the business decisions regarding a $500 package with perpetual license and a $5000 package (just a 1 year license). While I hate subscriptions, I realize the company needs to survive.

[yaghiyahbrenner]

Phil, your work is just incredible! thanks for sharing these tips.

[TheOleHermit]

Thank you for posting this PCB design and recommendations/tips, Phil.
It is very close to my current, first, and only SMD PCB in Kicad for an ILDA standard, 6 channel analog input -> TL084 op amp conversion circuit -> CS42448 ADC CODEC -> TDM -> Teensy 4.1 laser synth -> TDM -> CS42448 DAC -> 6 channels audio output -> TL084 op amp conversion circuits -> ILDA standard PCB.
I've assembled a working prototype, using a T4.1, an OTC CODEC PCB & my own op amp circuits on a breadboard. but, had the dreaded noisy power rails, of which I've mitigated with some large electrolytic caps.
Full disclosure: I'm only a hobbyist and far from being an EE. (Can't believe how far I've gotten with this project, TBH.)
In Kicad's PCB Editor, I've already placed all of the analog inputs on the left, the T4 & CODEC IC in the center, and all of the analog outputs on the right. So, with everything positioned, I've started laying tracks for a 2 layer PCB.
But, within only 15 minutes, you've already pointed out several of my design/layout errors. Thank you for correcting me and avoiding my wasting $ on garbage.
Try, try, again. 10th time lucky, I hope?
Love your informative, clearly narrated channel... at least the parts that I can understand.
Cheers, Phil!

[burakg]

Yes, please make a video for detailed description of the design. Especially about the analog input/output stages. And thanks for all the valuable content!

[loukayser]

Hey Phil, great video as always! I, for one, would love to see a video focused on the design of this effects board!

Also, I just wanted to say that I appreciate it when you get into tips regarding component selection. I find component selection hugely intimidating, so I always get a lot of value out of those sections. Keep up the good work!

[jeremiahbrunkala]

Ive seen both philosophies on ground plains, on the split between analog and digital. On those designs who decided to split the grounds, i have had more issues troubleshooting EMI issues than those who just combined everything.

[wendellknicely]

FX1_EN_A from the footswitch to the cap directly can cause arcing on your footswitch. This can cause oxidation and premature aging of the contact. All such connections of switch to GND (or VCC) to a capacitor should have a series resistor to to current limit the in rush current. This in rush current can also exceed the peak current of the caps (2.2 ceramic would be ok, but tantalum or electrolytic are subject to maximum currents.) Without seeing the rest of the circuit, FX1_EN should be connected to a Schmitt trigger input because of the slow rise time created by the LP (pi-filter)

[merdogan-ee-engineer]

Hey Phil, thanks for this great content. I also think the same way as you do when it comes to "not splitting ground planes". I learned this reality by watching videos from experts such as Rick Hartley and Eric Bogatin. But, recently I went back to my notes and recognized something. In a training video by Rick Hartley named "How to Achieve Proper Grounding - Rick Hartley - Expert Live Training (US)" at 1:13:30 it says that "... the need to split Analog & Digital Ground is only necessary when the analog section is operating under 20kHz". This is the case for an audio signal conditioning circuit. What are your thoughts on this? Do we need to split planes if we work with audio signals?

[PatrickHoodDaniel]

I like the explanation of digital signals being separated from analog signals. In the Atmel reference for the ATMega32 for instance, it shows a dedicated analog ground plane for the ADC, but it doesn't really specify how this ground plane connects to the common ground plane. Is this different when considering ADC on the microcontroller? I am guessing from your tip, it is best to have the ground plane common but with stitching and traces connected to that portion of the ground plane as long as they are separated from the digital traces, it will be fine. This definitely makes this much more understandable. Thanks.

[PCBWay]

Awesome video with great content and a good cadence as always, Phil 👍 BTW, have a wonderful festive season! ☃⛄🎄🎄

[exprymer]

Hi Phil,
If you can, please do some in depth video of this board! It would help us so much!

[isaacclark]

Thanks again for the great content! I designed an audio board around the TLV320 codec and I had a question about that choice...

Edit. You answered the question about the choice of codecs in the video. I removed it to avoid some personal embarrassment.

[kevalkdn]

Hi Phil,
Thanks again for sharing such useful tips and information. Always been big follower of your teachings.
You have changed my perspective to look at electronic design, bringing excitement and motivation to follow designing as career. I have also decided to participate in your Altium design error finding contest, seeing your photo on it.
Also eagerly waiting for your BGA course. Cutting my lunch cost and saving money. I don't want to miss that course.

- KD Nayar

[bikothewolf]

Yet another great video. Would love a video that goes a little into proper grounding on low frequency analog designs where there can be some use in not using a completely solid ground plane (at least if I have understood Rick Hartley correctly)

[ricardocarrillo]

Thank you very much for this and all the videos. For real have been very teaching and significant. I'm now very exciting for the course you mentioned, I think will be amazing :) Thanks Phil.

[AlejandroGarcia-rklc]

Very helpful video as always. I hope for a boost converter design video one day as it is a block that appears in almost every design and it has several complex and simple things altogether

[huababua]

Great video! One comment; your DSP designs are generally not consuming and power in the analog section.
Would be great to see a video focusing on a mixed signal design with higher current consumptions in the analog section - which would maybe need GND splitting.

[svetoslavasenov]

I love your videos. Thank you for sharing your great work!

[Porco_Utah]

I do mostly RF layout, also use Altium. all manual layout, no automated routing.