Simple broadband mixer without transformers.

[neazoi]

Hello, I would like to construct a mixer for LF-HF without transformers and I have found this circuit.
Can I remove the coil (which is coupled to the next stage coil) and connect a capacitor to extract the IF?
A sharp crystal filter will follow this capacitor.
Any comments are welcome.

 

[mtwieg]

That might work, but what's wrong with the numerous active mixer ICs based on the gilbert cell mixer?

 

[neazoi]

That might work, but what's wrong with the numerous active mixer ICs based on the gilbert cell mixer?

nothing wrong! I would like to do it discrete transformer-free for fun.

 

[betwixt]

Gilbert cell mixers can be made/bought without transformers. They provide the mixing by controlling the current/gain of one signal path with the voltage from another. With care you can use a good Gilbert cell mixer from almost DC up to several GHZ. They may not be optimal at any frequency but they work at all.

Brian.

 

[neazoi]

Gilbert cell mixers can be made/bought without transformers. They provide the mixing by controlling the current/gain of one signal path with the voltage from another. With care you can use a good Gilbert cell mixer from almost DC up to several GHZ. They may not be optimal at any frequency but they work at all.

Brian.

So will designs like this **broken link removed** expected to work much better than the single dual gate mosfer (or composite dual mosfet)?

- - - Updated - - -

By looking closely at the gilbert cell, it is a double balanced mixer, so I should expect better performance than the figure of post #1 (Local oscillator should appear very attenuated at the output).
Am I right?

 

[betwixt]

You are right.
What a wonderful link that is, it's great to see someone experimenting and explaining in such simple terms. I wish I could understand Japanese but the translation makes perfect sense.

Brian.

 

[BigBoss]

Why don't you use dual gate MOS ??They are still used to mix. the signals well..

 

[neazoi]

Why don't you use dual gate MOS ??They are still used to mix. the signals well..

It is not the active device used but the topology that makes the difference. The gilbert cell mixers in the japanese link are doubly ballanced mixers, meaning that the carrier is attenuated at the output.
The author provides a fet version at the end too, but what is the reason of using these usually more expensive fets. (besides the creater number of trimmers used)

 

[mtwieg]

Yes, a BF998 would probably work well as a very simple single balanced mixer. If you have some matched pair transistors lying around then making your own gilbert cell would work well too.