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2 posts from April 2010

04/29/2010

The Mixer 10 Commandments

Christopher Marki headshot3
 





Christopher F. Marki received his B.S.E.E. from Duke University in 2002 and his M.S.E.E. and Ph.D. from University of California, San Diego in 2004 and 2007, respectively. While in graduate school, Christopher studied high speed fiber optics and consulted for San Diego start-up Ziva Corporation. Following graduate school, Christopher decided to forego a life in Photonics and opted, instead, to work with his father at Marki Microwave and learn the “family business” of microwave mixers. While at Marki Microwave, Christopher has served as Director of Research and has been responsible for the design and commercialization of many of Marki’s fastest growing product lines including filters, couplers and power dividers. Dr. Marki has authored and co-authored numerous journal and conference publications and frequently serves as an IEEE reviewer for Photonics Technology Letters and Journal of Lightwave Technology.   MarkiMicrowave.com

To comment or ask Christopher a question, use the comment link at the bottom of the entry.

 

April 29, 2010


Marki 

I’m the first person to admit that mixers are confusing. Even drawing a mixer schematic can be challenging—what with all the crossing over of lines and the 4 and sometimes 8 diodes configurations. For better or worse, the complexity of mixers means (a) most companies don’t want to design mixers, and (b) Marki Microwave’s customers sometimes need a lot of coaching and advice. To put things in perspective, there are literally hundreds of texts relating to RF and microwave amplifier design, and about 3 relating to mixer design. It is not your fault you are confused!

   

To help you, I have come up with a list of “The Mixer 10 Commandments”. If you can follow these simple rules, I promise they’ll help to make your life a little easier when it comes to using mixers.

1.    Thou shalt not starve the mixer of LO drive.

2.    Thou shalt not blame conversion loss ripple on VSWR problems when reflective filtering is present at the IF and/or RF ports.

3.    Thou shall carefully follow the recommended solder reflow temperature profile when mounting surface mount mixers.

4.    Thou shalt not measure phase noise using mixers made using GaAs devices (FETs, diodes, or otherwise). Silicon schottky diodes are preferred for phase noise measurements.

5.    Thou shall phase lock your synthesizers to a reference oscillator when making mixer measurements.

6.    Thou shall test mixer performance in a broadband 50 Ohm system.

7.    Thou shall place the LO driver amplifier as close to the mixer as possible when laying out a PCB.

8.    Thou shalt not provide attenuation on the LO port unless it is absolutely necessary.

9.    Thou shall assume mixer simulations are always wrong, unless corroborated with measured data. This is especially true when simulating mixer nonlinear performance (i.e. single tone and multi-tone IMD). (This is subject to change as nonlinear modeling matures in the coming years).

10.   Thou shalt not starve the mixer of LO drive.

Here’s a hint, #1 and #10 are by far the most important. Too often engineers believe they are saving board space, power and money by under-driving the mixer, only to find later in development that they have unintentionally caused catastrophic penalties in terms of conversion loss, isolation and IMD. If you add up all the time and money wasted in order to correct this relatively straightforward mistake, you quickly find that the safest, fastest, most economical approach is to drive the mixer at the recommended LO level. Think of it this way: you wouldn’t expect an amplifier to work properly if you don’t bias it to the manufacturer’s recommended DC levels, so why should you expect the mixer to “turn on” with too little LO drive?

To learn more about how mixers work and how to use them, check out our Mixer Tutorial.

 

 

04/19/2010

Engineering Tips and Tricks – Episode 1: Your first slide needs work!

Christopher Marki headshot3
 





Christopher F. Marki received his B.S.E.E. from Duke University in 2002 and his M.S.E.E. and Ph.D. from University of California, San Diego in 2004 and 2007, respectively. While in graduate school, Christopher studied high speed fiber optics and consulted for San Diego start-up Ziva Corporation. Following graduate school, Christopher decided to forego a life in Photonics and opted, instead, to work with his father at Marki Microwave and learn the “family business” of microwave mixers. While at Marki Microwave, Christopher has served as Director of Research and has been responsible for the design and commercialization of many of Marki’s fastest growing product lines including filters, couplers and power dividers. Dr. Marki has authored and co-authored numerous journal and conference publications and frequently serves as an IEEE reviewer for Photonics Technology Letters and Journal of Lightwave Technology.   MarkiMicrowave.com

To comment or ask Christopher a question, use the comment link at the bottom of the entry.

 

April 20, 2010


Marki 

In my experience, practical engineering knowledge cannot be found in a textbook. Truth is, textbook understanding is antiquated. Technology inevitably moves too fast to be accurately captured in a textbook snapshot. In fact, most of the course-work covered in universities is at least 5 years old (more like 20) and renders any newly minted college graduate effectively useless in the real engineering trenches. In an effort to help my fellow engineers gain some practical knowledge (and help them justify reading my blog on the company dime!), I will share some of my favorite engineering tips and tricks in the coming months to help you bridge the gap between what you already know, and what you need to know. For the first “Tips and Tricks” entry, I want to share with you the best advice I was ever given: Your first slide needs work!

 

During my grad school days, I made a lot of presentations. I made presentations for my advisor, I made presentations for conferences, I made presentations for DARPA, I even made presentations about my presentations. For the first 3 years of grad school, my advisor insisted I send him the draft of my slides for him to edit. I would spend days upon days making very detailed slides focusing on the nitty-gritty of my research. By the time I sent the draft to my advisor, my presentation was, literally, a technical roadmap of all the work I had accomplished since the last presentation. Every measurement, success, and failure was cataloged to demonstrate my superlative scientific rigor. Like any good engineer or scientist, I was proud of my work, and darn-it, I was going to prove why others should be in awe of my accomplishments. Inevitably, my professor would send back the presentation within minutes with one simple comment: “Your first slide needs work”. Based on the comment (and his superhuman response time), it was clear that he hadn’t actually read the presentation. He simply opened it, read the first slide or two, and rejected it! I was furious.

   

This algorithm—I make a detailed technical presentation, and my advisor bounced it back with “your first slide needs work”—repeated itself for about 3 years. Until one day, I let him know of my displeasure for his disrespect of my glorious work. With a brash calmness, he explained to me, “Chris, I have no doubt that the technical details of your presentation are fine. Your problem is that you don’t see the big picture. You don’t understand that no one cares about your work! You need to justify to doubters, in the first slide, why they are going to spend their valuable time listening to you. Whether you like it or not, an engineer must always be their own best spokesperson. My best advice is: whenever you are making a presentation of your work, make the presentation for your boss’ boss. Your boss’ boss doesn’t want the details (and probably wouldn’t understand them anyway), he wants to understand why your work matters.”

   

My advisor was a wise man, and had clearly had this conversation with students before. Looking back, this advice was pivotal in developing in me the ability to keep my work relevant. Instead of just keeping my head down and solving problem after problem, I finally began asking harder questions. Why should anyone care? What is the impact of my work? Would someone actually buy this solution? When I freed myself of the arrogant approach of showing off my technical prowess, I began to learn how to sell my work to my boss’ boss. This was the single greatest lesson I learned in grad school…and now I’m giving it to you for free.

 
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