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Oscaprobe placement and result

SU202408293314

Hello,

I am designing a 2-port negative oscillator and trying to verify the oscillation frequency by looking at pharm after placing oscaprobe. I have two questions.

1) In my 2-port design I am placing oscaprobe between the collector and the load network as I take output from my collector of bjt. The connection is made after the decoupling capacitor, and the transistor is already biased. Since, the help says place it between active and resonator, I am placing it after the decoupling capacitor of dc biased bjt as I am thinking the whole circuit as active. Is that the correct placement?

2) In theory, after designing the network when I look at the rf output port and plot ZIN I should see 0 im and -30~40 real impedance at my oscillation frequency. I have seen correct results matching my understanding however, in a lot of scenarios I find oscillation frequency even when the Zin dont provide these results or anywhere near it. I am now worried about the accuracy of simulation and if I should trust the results. If Oscaprobe provides oscillation does that mean it is taking into account everything and providing correct results?

3) The transkick is No as I want the noise starting analysis. Thank you.

  • OscPn
    0

    1. Regarding correct setting and placement of OSCAPROBE, check the following link:

    support.cadence.com/.../techpubDocViewerPage

    2. i. OSCAPROBE is designed to initiate large-signal oscillator simulations accurately.
    ii. It operates as an ideal source in series with an ideal impedance element, ensuring precise measurements at the fundamental frequency of oscillation.
    iii. The accuracy of the OSCAPROBE is influenced by several parameters, including the initial guess at oscillation frequency and the maximum number of iterations for analysis.
    iv. Proper placement of the OSCAPROBE in the circuit is crucial for reliable results.
    v. Users are advised to verify oscillator behavior thoroughly before utilizing the OSCAPROBE to ensure accurate oscillation conditions.

  • SU202408293314
    0 in reply to OscPn

    Thank you. I am attaching my design procedure. it would be great if u could take a look at to see if I am doing anything wrong as I am not getting correct impedance values when its oscillating,

  • OscPn
    0 in reply to SU202408293314

    Correct impedance value at the load side? If you see the graph, resistance appears negative, which is required in this condition. As per the last graph, the oscillator is simulating. Regarding the impedance value, ensure that the negative resistance component cancels out the positive resistance of the resonant circuit, thereby generating steady oscillations.

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