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Getting a Feel for RF

Comments(3)Filed under: Circuit Design, Custom IC Design, Virtuoso, RF Design, MMSIM, Simulators, Virtuoso Analog Design Environment

It was a delight when I read the blog by Bill Schweber of TechOnline's RF DesignLine titled “Getting some basic RF experience”. I was surprising pleased that somebody took the time to talk about how one might get the feel for RF. That is because what Bob talks about is more or less how I gained some of the experience that lead me to pursue this decades later.

I have always been fascinated by radio in one form or another. It started when I was youngster listening to an AM radio and found that there was a huge difference in the number of radio stations I heard in the daytime versus the number I heard at night.

Without knowing it I was learning about sensitivity, selectivity, propagation, adjacent channel interference, ambient noise, bandwidth, antennas, modulation and the effects of solar radiation. Through my ears I heard the effects of all of these characteristics and hardware. All of this courtesy of a 1960’s vintage Sears Silvertone, ten-transistor desktop radio.

Later on using a pair of crystal controlled citizen band (CB) transistor walkie-talkies in the late 60’s, I discovered more about antennas, range versus power and elevation, jamming other radios (purely by accident and would serve me well later while working on electronic counter measures), power supplies, what small increases in voltage would do to power out and what too much voltage and power would do to a transistor. This would later in life open the door to an education in electrical engineering and amateur radio. What does this have to do with a blog at Cadence? Plenty.

Simulation provides an avenue for engineers to experiment with designs and sharpen expertise by trying various circuit designs and subjecting them to the environment they will eventually be operating in. When I talk about exploring my ideas and designs, I’m talking about using Virtuoso, SpectreRF and Analog Design Environment (ADE).

I’m lucky in the fact that my employment here puts me in close proximity to these tools everyday, and I often take advantage of it. Because my designs are no longer fabricated in silicon, the capabilities may be a bit more than I need.

Through a virtual test bench in ADE and simulation using SpectreRF one can get a feel for how RF circuits work, testing their susceptibility to variations in component values, which elements in the circuit actually changed the performance versus the ones that limited RF leakage back into the power supplies. One could see how the impedance (load) of one stage or block presents to the next block and so-on. The designer could get a feel for the effects of parasitics on the design. While designing an RFIC it is a lot more than what I described, the basic concepts are still the same.

Whether the results are on a PCB or in silicon, to me it still comes down to getting a feel for the RF either at the bench or through an environment where I can control the simulation, and then see the results. Simulation provides insights well in advance of probing the design on the bench.

For me it was not only the math and physics of it all, but experimenting and playing with the designs. It still is.

 

Tom Costas

Comments(3)

By Zhenbo Zhao on May 17, 2009
It is very good for a jackaroo, thanks for your shareing, I hope there will be more veteran to share their experience.

By Iycee Dy on May 19, 2009
Interesting history into engineering decision.  If done correctly simulation of rf circuits is vision into performance.  For tesbench to work well, circuit loads should be as real as possible. Rf circuit loads typically modeled in frequency domain, as in measuring a load over sweep frequencies into s-parameters. Can you use s-parameters as load in SpectreRF?

By TomC on May 20, 2009
As far as using s-parameters in SpectreRF, the answer is yes. You can define the load as an nport element that includes the s-parameter data.  Hope that helps.  - Tom

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