Interview with Jeff Crockett

Featured Engineer

Jeff Crockett

Jeff Crockett - Senior Analog/RF Design Engineer at Aubrey Group, Inc.

How did you get into electronics/ engineering and when did you start?

My Father and Grandfather were both very successful Mechanical Engineers (designing mammoth machines that ran with the precision of a well tuned clock while moving tons of material) and they both enjoyed working on electronic projects for a portion of their entertainment at home. This provided my exposure to the engineering mentality and way to look at things. I did tinkering on my own and this was encouraged by my parents. As a senior in high school I was fortunate to have a job at a TV shop and was the beginning of the development of my troubleshooting skills.

In 1975 when I graduated High School there was a large demand for R&D Electronic Technicians. After High School I went through the DeVry Technician program. Started working as an R&D Electronic Technician and discovered that I could do more, and proceeded to study at home Electronic Engineering skills from CIE correspondence course.

The skill sets learned from DeVry and CIE combined with diving head first into solving problems at work (mostly Analog and RF) lead to a career of exciting learning and promotions into the Electronic Engineering role.

What are your favorite hardware tools that you use?

Tektronix Oscilloscope, Tektronix TCP202 Current Probe, HP Network Analyzer, and Spectrum Analyzer.

What are your favorite software tools that you use?

LTspice, Mathcad, Excel

What is one of the harder/trickier bugs you have ever fixed?

Aubrey Group, Inc. is a contract product development and manufacturing company using state-of-the-art technologies to develop new medical devices and biotech instruments. One of the award winning projects is the Osmetech Molecular Diagnostics eSensor XT-8, revolutionary gene detection system. Within this system is a potentiostat stage that drives the chemistry and an analog conditioning/filtering section that processes the analog signal from the chemistry with a flat gain from dc to the upper corner frequency of the system. This signal inherently has a small AC signal superimposed on a varying DC level. The data from the prototype systems were being scrutinized in great detail and it was found that the AC gain was changing by ~1% over the DC sweep range. After careful stage by stage testing the stage that was causing the problem was identified and found to be a potentiostat stage. This is configured as an inverting opamp gain stage that had a feedback capacitor that is intended to provide loop stability, low pass filtering, and should not have a significant effect on the AC gain for the AC frequency range used. However, the intended low value NP0 capacitor inadvertently had a larger value X7R capacitor installed in place of it. This capacitor had a larger nominal capacitance value than the intended capacitor, and as a result reduced the closed loop bandwidth to the point where the capacitance of this capacitor significantly affected the AC gain in the AC frequency range. Also, an X7R capacitor has a significant capacitance change as a function of DC voltage as opposed to the NP0 capacitor. Analysis revealed that the resulting change in gain with DC bias was explained by the incorrect capacitor installation.

What is on your bookshelf?

Electronic Filter Design Handbook (Arthur B. Williams; Fred J. Taylor))
Design of Feedback Control Systems (Gene H. Hostetter; Clement J. Savant, Jr.; Raymond T. Stefani)
RF Design Guide—Systems, Circuits and Equations (Peter Vizmuller)
Oscillator Design & Computer Simulation (Randall W. Rhea)
RF Circuit Design [SAMS]
Phase-Locked Loops (Roland E. Best)
CRC Standard Math Tables
Others

Do you have any tricks up your sleeve?

When analyzing a circuit I typically have a good idea of what to expect with manual calculations before any simulation begins. Otherwise, it is easy to get mislead by a model error or the like.

What has been your favorite project?

Developing RF Surgical Generators contains a set of challenges that exercises my favorite disciplines. This involves creating efficient conversion of DC to the RF frequency controllable from zero to several hundred watts. In some cases cooling fans are not allowed thus making the efficiency a paramount design requirement. Along with the efficient power conversion this system requires accurate voltage and current sensing that is processed and used in adaptive control algorithms that controls constant power to the rapidly changing impedance of the tissue of the patient.

The associated IEC requirements for isolation at the mains frequency as well as the RF frequency presents its own set of challenges.

Do you have any note-worthy engineering experiences?

I suspect that I am not alone in having inadvertently performed minor epidermal ablation while moving my hands into the high voltage section of RF Generator breadboard. The shocking feeling is not present since this frequency is too high to cause electrostimulation of the muscles. It initially presents a warm feeling followed by the unmistakable smell of burning flesh.

What are you currently working on?

Due to the confidential nature of the agreements with our clients, I am not at a liberty to say.

h5. What direction do you see your business heading in the next few years?

With the aging population and rise of life-style devices, Aubrey Group expects to continue to develop innovative solutions for challenging problems that face the medical device industry.

What challenges do you foresee in our industry?

The proposed comparative-effectiveness studies in the US will pose a challenge to the medical device industry in general. Medical device manufacturers already prefer to introduce devices in the European market. The challenge will be for US companies to innovate and introduce new products here.