Click here to go to our main page on phase shifters
Go to our download page and get a copy of the MWO file that was used to generate content for this page.
New for March 2024. This is the eighth installment of an article on designing a four-bit phase shifter.
Click here to go to the first installment of a four-bit phase shifter design in MWO
Click here for the second installment of this article on phase shifter design, where we correct the RMS phase error calculation.
Click here for the third installment, where we design a MMIC 22-degree bit
Click here to go to the fourth installment, where we design a MMIC 45-degree bit
Click here to go to the fifth installment, where we design a MMIC 90-degree bit
Click here to go to the sixth installment, where we de
sign a MMIC SPDT switch used in a MMIC 180-degree bit
Click here to go to the seventh installment, where we design a MMIC 180-degree bit
Now that we have four MMIC-compatible phase bits it's time to put them together. Below is the high-level schematic showing the cascade. We left the bits in order, 22 on the left, 180 on the right, but you could play around to see what it does to performance.
Here is a layout generated from the schematic. There are nine transistors and three capacitors. Only seven signals are needed, because Q6 and Q8, and Q7 and Q9 are controlled in pairs.
Here are the amplitude states. Average loss is 2.2 dB at band center. Again, the unexpected low loss is because we used a hypothetical high-figure-of-merit switch FET process (FOM=400 GHz). Sorry about letting the Y axis autoscale to -1 dB, that is pretty annoying.
RMS amplitude error is less than 0.2 dB at band center. Oops, we labelled the Y axis incorrectly.
Here are the return losses. They are not great, which is typical for a MMIC phase shifter. If a lossier process was used, the return losses might improve.
Now let's look at phase states, calculated the Microwaves101 way. Sweet!
And here are the phase errors (calculated the Microwaves101 way).
Here are RMS errors calculated by AWR and also by Microwaves101. Either way, of your circuit measures less than 5 degrees RMS when it comes out of fab, you should get a fat bonus. Or seventy Nectar points if your company is owned by investors...
We probably won't take this design any further any time soon, unless we get a lot of interest in it. We don't have an actual design kit from a foundry, and they usually make you sign a lot of non-disclosure crap. The next step would be to create EM models of the FETs using Axiem, we will get around to that one of these days. Never trust a foundry switch FET model unless you like iterating your design.
Your feedback is always appreciated, drop us an email if you have any comments on our phase shifter tutorial!