Hello, I am trying to design and build a basic signal detector using MOSFETs because they are more compact than resistors, capacitors, and conductors. I was wondering if anyone hear has any suggestions on how I can start my approach on this project. The original thought I had was to simply look up a simple Field Strength Meter (attached below) and simply replace the capacitors in the circuit with properly biased MOSFETs so that they can be used effectively as capacitors. This approach seems too naive, if anyone has a more refined approach please feel free to tell me.

 

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http://forum.allaboutcircuits.com/threads/basic-signal-detector-using-mosfets.122976/

 

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Why do you think a MOSFET can replace a capacitor? they are very different components. If anything, a MOSFET can be made to emulate a variable resistor, not a capacitor.

Your question is not clear. What is it you are trying to do? Why is compactness important?

ak

 

I am actually wondering if its even plausible(rational) to design a basic signal detector with only an antenna and MOSFETs. The idea of compactness is so that it can possibly fit on some sort of small chip with a printed antenna.

 

http://theradioboard.com/rb/viewtopic.php?t=5959

 

http://theradioboard.com/rb/viewtopic.php?t=5959

Thanks for the link. This seems very interesting, however, they using huge inductors (coils). Is there a way to replace them with a smaller antenna instead?

 

If you are talking about replacing the traditional detector diode with a MOSFET, I think the FET threshold voltage will be a problem. Note in one of the linked schematics there is a 3 V battery and a pot to bias the FET to the edge of conduction. Are you going for a zero-power radio, or is a battery allowed? Also, note that there already are many single-chip AM radio parts on the market. Most implement the standard super-het method, but there also are strange critters such as the 3-pin ZN414.

ak

 

If you are talking about replacing the traditional detector diode with a MOSFET, I think the FET threshold voltage will be a problem. Note in one of the linked schematics there is a 3 V battery and a pot to bias the FET to the edge of conduction. Are you going for a zero-power radio, or is a battery allowed? Also, note that there already are many single-chip AM radio parts on the market. Most implement the standard super-het method, but there also are strange critters such as the 3-pin ZN414.

ak

Battery is perfectly fine, although no battery is as well.