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I'm a new user to ADS (Advanced System design). I'm trying to design a discrete Colpitt oscillator at 100 MHz in ADS. Here's my schematic: enter image description here

Now I wanna check if my circuit works properly. I watched and read some tutorial but it seems like a lot of new stuff to me. Can anyone help me to solve the problem?

Henry Nguyen
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1 Answers1

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Problems in coloured boxes: -

enter image description here

  • \$\color{red}{RED}\$ box - no joining junction at cross over point hence transistor gets no bias
  • \$\color{blue}{BLUE}\$ box - inductor passes DC freely and hence connects collector to ground
  • \$\color{purple}{PURPLE}\$ box lower - Move C4 into vacant space in upper purple box and replace C4 with a short
  • \$\color{purple}{PURPLE}\$ box upper - Move C4 into that position
Andy aka
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  • thank you! By the way, do you know how to use ADS? Which type of simulation should I use? – Henry Nguyen Jun 20 '20 at 21:49
  • Sorry I don’t know how to use it. I use micro cap 12. Did the fix proposals work? BTW if you are looking for a very good sim with tons of library parts, micro cap is now free (as in free beer and just as tasty). Highly recommended. – Andy aka Jun 20 '20 at 21:56
  • yes it helped. Actually I referenced this 100 MHz CB Colpitt Oscillator from the book Discrete oscillator design, Linear, Nonlinear, Transient and Noise Domains by Randall Rhea. Here's the schematic in the book https://drive.google.com/file/d/1N_f_R-uc-O8s287DE5zs4xJFunk1mlHi/view?usp=sharing I don't understand the meaning of CP1, port 1 and port 2. I tried to edit the circuit and made the above mistake. Have you got any idea what those things mean? – Henry Nguyen Jun 20 '20 at 22:35
  • No, I have no idea but I wouldn’t worry. – Andy aka Jun 20 '20 at 23:36
  • I've just read your answer to this question about opamp-based Colpitt oscillator https://electronics.stackexchange.com/questions/196274/colpitts-oscillator-startup-problem?fbclid=IwAR3M3y5T5wdPrZ1zw78EYEbOBG9S-AYpbQCJHVFOX4gOjbBtrHUnqlp2DN8. I'm trying to design an oscillator with some specs so I'm wondering if the value of R3 affects the calculations such as the gain of the opamp amplifier block? – Henry Nguyen Jun 21 '20 at 07:41
  • Sorry I can't comment directly to that post because I don't have enough reputations – Henry Nguyen Jun 21 '20 at 07:42
  • @HenryNguyen [this answer](https://electronics.stackexchange.com/questions/355018/colpitts-oscillators-capacitors/355062#355062) derives the equations for the colpitts oscillator and the resistor in question cancels out of the equation (but that resistor is needed). – Andy aka Jun 21 '20 at 09:18
  • Do you mean the equations for the Colpitts oscillator are wrong if I put a resistor at the output of the amplifier? I'm trying to design a 100 MHz Colpitts oscillator and It would be great if you could give me a educational answer. – Henry Nguyen Jun 21 '20 at 13:16
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    @HenryNguyen I think you should raise this as a new question because others will likely want to contribute. Firstly though, go through a few questions using the search bar above to see if anyone has already answered this. – Andy aka Jun 21 '20 at 14:29