μblog: engineering from the trenches

I recently read a statement somewhere along the lines of “you always want low equivalent series resistance (ESR) capacitors in your design” which got me thinking about ESR and capacitors in general. The truth of the matter is that you do often want capacitors with moderate ESR (>10 Ohms) for bypass applications, especially in voltage regulation circuits. The main reason is that the capacitor introduces filtering (a zero) into the circuit just through its own capacitance and series resistance, and this filtering can be used to stabelize the feedback of a voltage regulator and prevent ringing/oscillations. AN-1148 is a great application note from National semiconductor that gives an overview of feedback in voltage regulation and frequency domain analysis.

Once the concept of adding a zero to the frequency response of a circuit is clear (see this app note if it is not), it should be apparent that this is exactly the reason why designers put several bypass capacitors in parallel when decoupling a complicated integrated circuit. The IC injects a known set of frequencies into the power system and the designer tries to use each of the capacitors, with a unique zero, to try to filter out each frequency individually. This works well for circuits with precise clocks, however, an RC oscillator can have plenty of drift so it would be advantageous to use capacitors with higher ESR which lead to lower Q values and broaden the range of frequencies which they filter out most effectively. This follows the notion that you should not use high quality components to filter a low quality circuit, all components should be of the same quality.

( an-1148 )

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Penn State University has decided to roll out an ebook reader program by making the PRS-505 portable reader from Sony available for checkout. The program became quite popular and I was unable to get one myself, however, a colleague managed to secure one so I was still able to play around with it for a few weeks. My main goal was to test the reader’s capability of displaying datasheets and scholarly journals.

In short, I was a bit disappointed when I could not clearly read either without converting each page to an image first. It was pretty clear that copying a simple PDF to the device, although it does have some basic PDF viewing capability, was not going to result in something readable. In the case of the journal article, the device would split text in a strange way which sometimes resulted in fragments of words alone on a page. Scaling some datasheets to make them readable crashed the device requiring a hardware reset. Two positive notes are that the ebooks that were loaded on the device displayed really well and that the device was able to reproduce color JPEGs as fairly detailed grayscale images.

I hate to end this review on a negative note, however, this device is pretty useless for my needs so I will wait for the next model and hope.

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I have been doing a lot of signal processing/statistics lately, however, I still design PCBs using the Orcad suite from time to time. PCB Editor is both powerful and feature rich leading to massive frustration every time I forget the exact steps for generating the necessary artwork to submit for manufacturing. In an effort to combat this overhead, I documented the specific steps and am publishing them online in the hope of saving someone else the same frustration. These were noted down fairly quickly so please let me know of any errors.

allegro-gerber

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It took me a few months to finally read this book, but it was well worth it. I have been reading it prior to sleep as it was so full of information that it was difficult to read more than ten pages without taking a break to think about all of the new ideas. Furthermore, the information was presented in such an accessible manner that even those who are not specialists in relativity, topology or physics can appreciate the message.

I selected this book because I figured the topic was far away from electrical engineering that it could give a new perspective on understanding what is implied by measuring time and distance. Sure enough, this book provided many insights into the nature of our universe through the relation of time and space measurement. I will avoid summarizing the book, however, I will mention that it would be a pleasant read for those interested in non-Eucledian coordinates and the effects of gravitational fields. The book is extremely well written and reads much like a lecture series where the audience does not need to be able to carry out all of the steps of each operation, but acquires a taste for the process and a deeper appreceation. From the point of view of technical written English, this was one of the most understandable books on a physical subject that I have read in some time.

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I have many AS and LS series logic gates lying around, so I figured that I would image some as they would be more instructive than looking at the latest CPUs coming out of Intel. I have a few more lined up so please comment if you want me to follow this reasoning. Today’s subject is a hex-inverter, the 74AS04. Below are images of the whole chip and a blowup of the top-right inverter gate.

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As a final follow up, here my paper that was accepted for a slide presentation at the IEEE EMBS meeting:

nchernyy-embs2008i

I am working on a more thorough paper which also covers harmonic/non-linear analysis and does statistical validation of the results, so hopefully that will be forthcoming in the next year. Any questions or comments are always welcome.

As for the image, this advertisement was on many of the bus stops in Vancouver. I guess Intel lost their trademark in Canada.

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