modified 12 years ago

Supposed to be a VCO. Scope looks pretty anyway

01:06:46

I have been informed that EC as it stands at the moment doesn't have varicaps (see below) so simulation will not work as intended although circuit is good, though I forgot to mention that output from the 5.6pf capacitor should be taken using a 50 ohm load to ground in reality. 
This is where annotation would be useful.

published 12 years ago

hurz

12 years ago

EC does not have varicaps so far. So it cant work this way. Taken as documentation for the schematic.

skylight

12 years ago

Thanks for that, hope that is on the wishlist for the future then. One thing I believe may be coming in the future is annotation of circuits according to the authors who are looking to incorporate it in a future release.

waynewec

12 years ago

I found two issues with your circuit: The signal source your using to drive the varactor (which can be implemented with a diode like you did) is dragging the simulation speed too low for EC to simulate the 1.23GHz I got out of it. 2. You forgot the feedback capacitor network between base, emitter and ground. I'll post a corrected VCO in my circuits for you :)

waynewec

12 years ago

Oooohhhh, different topology. It works fine as soon as you remove that 80kHz signal source and manually set the simulation speed and inject some noise at the transistor base. 1GHz almost exactly

waynewec

12 years ago

Seems that diode junction capacitance doesn't simulate like real life. A 1n4148 is commonly used as a "poor mans varactor" and has a pretty wide capacitance range actually. Also, realistically to take output into a 50 ohm load you need a buffer and impedance transformation. So a class A amplifier with collector transformer is commonly used.

hurz

12 years ago

I also tried it and it is oscillating on about 900MHz and i sweeped the varicap voltage as well without any effect but didn't expected its working from past EC expiriences :-(

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