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Active Mixer Conversion Gain Calculation Issue with the Ports

Mehdi Nasr

Hi, 

I do have a question about active mixer simulation. I have checked the DC biasing of my active mixer and it is working fine. But whenever I apply "vpulse" as local oscillator to the transistors everything is fine and I can see the corect DC biasing but when I apply port (which is generating the same signal amplitude but sinewave), the DC biasing at the input of the transistors of the gilbert cell is zero. I have tried diferent configurations and also followed the Cadence Tutorial for Mixers but this is a question that I asked after trying to debug the circuit since I have got some meaningless results after the simulation for conversion gain. 

Thanks in advance for your help. 

Regards,

Mehdi

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  • Hi Mehdi,

    You've not really given much information to go on here. Is it just that you've not set the DC level of the sine source appropriately? A sine source would (by default) have a DC voltage of 0, so maybe you need to specify the DC value to offset it to your expected DC bias level?

    Note that there's no requirement to use a port component for RF simulation; you could just use a vsource or vsin component. The port component is really only needed if it's a power-based system where you have a low impedance (e.g. 50ohm) input to the circuit and you want to specify the input signal as a power in dBm. If the circuit has a high impedance input and is voltage-based, then use a sine voltage source. If you use a port with a high impedance input circuit, the signal at the output of the port will be double the specified amplitude because there's an assumption that the port impedance matches the input impedance of the circuit.

    Regards,

    Andrew.

  • in reply to Andrew Beckett

    Dear Andrew, 

    Thanks for your quick reply. Yes, I have checked the DC level in transient simulation and I have applied exactly the same signal specifications except for one of them is square and the other one coming from port is sine wave. But I cannot get the same DC level from DC analysis on my Mixer. (As you know, the positive LO input of mixer should be high and the other one should be low to make sure the switching performance, I can get the same from applying vpulse but not the port). Based on your somments its better to not use the port for the DC simulation in this case. I have to only use ports for the conversion gain and other simulations then. 

    Regards,

    Mehdi

  • in reply to Mehdi Nasr

    Hi Mehdi,

    I'm still not really sure as to what is going on here as there's not much info. I don't see why you'd need to use a port to compute the conversion gain (I'm assuming you'd want voltage convergence gain rather than power conversion gain since this is a high-impedance input). So I'm not sure I can offer that much help - could you contact customer support?

    Regards,

    Andrew.

Reply
  • in reply to Mehdi Nasr

    Hi Mehdi,

    I'm still not really sure as to what is going on here as there's not much info. I don't see why you'd need to use a port to compute the conversion gain (I'm assuming you'd want voltage convergence gain rather than power conversion gain since this is a high-impedance input). So I'm not sure I can offer that much help - could you contact customer support?

    Regards,

    Andrew.

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