In Practice: Quick and On-Time Engineering

So I've come to realize today how serious, and easy, it is to miss something when you're designing hardware.  It's amazing how easy it is to miss that small tid-bit of information that normally you wouldn't have to worry about.

For instance, when working with amplifiers in High Frequency applications you have to worry about a lot: Output 3rd Order Intercept (OIP3), 1-dB Compression (P1dB), Gain Flatness, Power Saturation Point, Noise Figure (NF), Input and Output Impedance, etc.

This type of information is all critical when designing a system at high frequencies.  But if you miss one, issues will arise.  For instance, if you don't measure P1dB for your amplifier, you may expect gain to continue for any input power, but once you put the amp in the circuit, you may realize that you don't get the power expected.  If you have a P1dB of 15 dBm and a gain of 10 dB, when you put 10 dBm into the amp, there is a VERY HIGH possibility you won't get 25dBm out, and if you do you'll have plenty of distortion.

So the point of this is to say that it's very important to take your time when engineering.  When setting out to design something, first you need to know where you are going.  I have found this to be the best piece of advice I can give someone in engineering.

How can you go anywhere without the direction.  So learn the direction first.  Then find out what will take you there with metrics.  Know how much power you'll need before hand.  Know how big your circuit can be.  Know everything to make it work before you start, with metrics.

Finally, layout what information you'll need to realize these metrics.  Not all metrics are directly measurable.  So you must find out how to measure it.  For instance, amplifier linearity is not directly measurable.  One way to characterize this is to use an OIP3 measurement.  The common way is to add two signals 1 MHz apart and measure the intermods.

This is what you have to figure out.  So to summarize:

1. Know where you're going.  Know your goal
2. Determine your metric requirements whether measurable or not.
3. Figure out how to measure the objective and subjective metrics and then measure them for your proposed design

That's it.  It's simple and I could go in more detail but this is supposed to be the basics...

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Justin Coulston

justin.coulston@gmail.com