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Fmax setting in nport cell of analogLib

Hi,

I am running simulation with s-parameter file generated in momentum tool for frequency range 0-10GHz. The file is in touchstone format. I have instantiated an nport cell from analogLib. I have done 2 test cases with fmax set to 10GHz in case 1 and 100GHz in case2. My ac simulation shows same result in both test cases but transient simulation shows unexpected result in case1(10GHz) whereas expected result in case2(100GHz).

Could you please help me understand which setting is correct? I read somewhere that fmax must be greater than 2*(max frequency in s-parameter file). Is this true?

Thanks,

Akshay

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Andrew Beckett over 7 years ago

Hi Akshay,

Which version of spectre are you using? What have you set the "interpolation method" to on the nport? In general nowadays we'd recommend leaving the fmax parameter blank, and ideally using "bbspice" as the choice for interpolation method. I'd also suggest you look at this excellent presentation from my colleague Tawna Wilsey: 7 Habits of Highly Successful S-Parameters

Regards,

Andrew.
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akshay91 over 7 years ago in reply to Andrew Beckett

Hi Andrew,

I am using spectre version 16.1.0.354.isr5. I have set interpolation method to spline. When I use bbspice I am getting the following error - Error found by spectre during initial setup.
ERROR (NPORT-1019): `broadbandspice` not found, exit the rational fitting process.

Thanks and regards,

Akshay
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akshay91 over 7 years ago in reply to Andrew Beckett

Hi Andrew,

I am using spectre version 16.1.0.354.isr5. I have set interpolation method to spline. When I use bbspice I am getting the following error - Error found by spectre during initial setup.
ERROR (NPORT-1019): `broadbandspice` not found, exit the rational fitting process.

Thanks and regards,

Akshay
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Andrew Beckett over 7 years ago in reply to akshay91

Hi Akshay,

There was an issue, fixed in SPECTRE16.1 ISR7 (so a little after the version you're using) where some errors from broadband spice were misreported - for example, if the $HOME dir was out of disk space (or quota). Can you check if you have enough space in your home directory? Also, can you try a later subversion of spectre?

In general if not using bbspice, I'd follow Tawna's recommendations on sampling points, frequency range and so on, and then if using spline or linear (probably I'd pick linear) I'd leave all the other parameters alone (not setting fmax). But bbspice is almost certainly a better choice if you can get that to work.

Regards,

Andrew.
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