Oscillator Design and Verification in MWO AWR

[doha17]

Hello Everyone. I am trying to design a 1 GHz Oscillator using AT 41411. I am following 2 port negative oscillator design. I initially made sure to see negative resistance from both ports collector and Emitter after adding series feedback inductor to base. Then I terminated the collector port and emitter port still sees negative resistance. After that I tried adding the load network and do oscaprobe analysis however it never gives right solution. I have not touched any simulaion parameters. I am confused about where to place the oscaprobe and what changes to make for it to oscillate.

Terminated using inductor.

Port 1 input imedence. The load is added as Re_in/3 and -Xin.

 

[BigBoss]

OSCPORT has been wrongly placed. This element should be placed around Feedback circuit like.

Also,

You make a serious mistake. Z₁₁ is NOT equal to Input Impedance of a Port. Since there are two Ports, Z₁₁ is Input Impedance WHILE second port is open circuited, NOT terminated. You have to use ZIN instead. Oscillator circuits cannot be considered as simple as ordinary amplifiers or mixers. Every termination has an impact heavily on oscillator functionality. You cannot omit this feature. While the oscillator is working with a load condition, it might stop to oscillate with different loading effect.

 

[doha17]

OSCPORT has been wrongly placed. This element should be placed around Feedback circuit like.

View attachment 198990
Also,

You make a serious mistake. Z₁₁ is NOT equal to Input Impedance of a Port. Since there are two Ports, Z₁₁ is Input Impedance WHILE second port is open circuited NOT terminated. Oscillator circuits cannot be considered as simple as ordinary amplifiers or mixers. Every termination has an impact heavily on oscillator functionality. You cannot omit this feature. While the oscillator is working with a load condition, it might stop to oscillate with different loading effect.

Thank you so much for your reply. so the oscaprobe should be place around the series feedback inductor in base terminal? I have plotted the Z11 resistance after adding the termination in port 2. I omit the port and place ground. and look at the input impedance from z11 and find negative resistance.

 

[BigBoss]

Your method is wrong dear doha17.
You have to separate this oscillator as active and passive part then check negative impedance.
You still use Z₁₁, this is NOT correct. Even you terminate the port, the simulator will make it open circuit by definition of Z parameters.
There is an example in AWR installation, open it and follow that method.

 

[doha17]

Thank you very much. I believe you are talking about this example. In my case the tank would be my terminating network and negative resistance portion is as it is without adding the load to it and just have the port looking in. Am I correct? I am trying to use the test bench by replacing the subcircuits with my subcircuit but it is giving me the exact same plot as the example. How are they measuring the conductance and susceptence?

--- Updated Wednesday at 3:06 AM ---

Thank you very much. I believe you are talking about this example. In my case the tank would be my terminating network and negative resistance portion is as it is without adding the load to it and just have the port looking in. Am I correct? I am trying to use the test bench by replacing the subcircuits with my subcircuit but it is giving me the exact same plot as the example. How are they measuring the conductance and susceptence? For the testbench, without editing, I used the Yin equation from to verify and it gives same result as Y(1,1). So, in the test bench the equations for Y_total is different and I am struggling to find what that eqaution is or how the measurement is done.

 

[BigBoss]

In order to test the negative impedance, create a separate schematic like this below. This part is a test circuit for negative impedance of the example in my previous post.

And when I check input impedance this graph is obtained.

As you can see, I have used ZIN instead of Z₁₁. They are different.
Also, you can make Nyquist simulations in a closed loop to predict oscillation frequency.

 

[doha17]

In order to test the negative impedance, create a separate schematic like this below. This part is a test circuit for negative impedance of the example in my previous post.
View attachment 199022
And when I check input impedance this graph is obtained.
View attachment 199024
As you can see, I have used ZIN instead of Z₁₁. They are different.
Also, you can make Nyquist simulations in a closed loop to predict oscillation frequency.

Thank you so much for helping me understand. One more question regarding Oscaprobe placement. I found the following images from your reply to a separate issue.In this case the PORT 1 is at the collector from where the RF output is taken and oscaprobe is placed between negative component and resonating network right?