check reconstruction filter

[jordens]

For the upconverter variant we should closely follow the relevant eval boards (important for noise floor due to mixing products, bandwidth, flatness, proper matching, proper output power).

• Consider (or exclude) going DC coupled
• Consider the transformer network
• Double check and follow the guidelines and design procedure from the datasheets.

and others from slua647a

from TSW30H84EWM

[jordens]

#4 (comment)

I think the approach may be good, we should just be sure what we want.

[gkasprow]

@hartytp anything to do here?

[hartytp]

I'm happy with the current filter. AFAICT we followed a sensible process to come up with the filter we chose so unless there is a specific issue with it I'm not aware of / a need for change (but maybe @jordens has further thoughts?). We don't have a tight spec for what we're trying to achieve with this, which means that we can't optimize the solution too far.

[jordens]

To close this, the current performance should be measured (power and frequency characteristics, crosstalk, IMD2 and IMD3 due to impedance errors). If that's ok, this can stay. IMO it would be better if someone does this thoroughly instead of later everybody for themselves in just their frequency window of interest.
AFAIK we don't even know the performance in a single window yet and whether it matches the design. I'd hesitate closing this.

[hartytp]

Okay, that's reasonable. If the action here is to measure those things and post here for posterity I agree. I don't have a clear performance target in mind here (beyond having a look at various data sheets and checking we're not miles off what one might expect) so don't have a clear threshold for what performance level would warrant design changes. I also don't want this to be a release blocker. So let's agree to leave this open for now.

[jordens]

Yes. It's not a release blocker.

[pathfinder49]

I've measured the filter attenuation for a range of DAC frequencies. The measurement was made by measuring the single ended power of a DAC output before and after the filter. I used the Keysight N2795A 1GHz, 1pF probe to reduce probe loading.

[pathfinder49]

Note: The DAC output amplitude changes appreciably with frequency. The plot above does not represent the phaser output amplitude change with frequency.

[hartytp]

Assuming I've followed this correctly, the comparison is with #4 (comment) This data looks really quite different to the simulation, so we should check that we have got this right...

[pathfinder49]

@hartytp It's tricky to read of the plot you linked accurately. However, aside from the ~30 dB offset, to me the measurement looks consistent with the 10-300 MHz range from the simulation.

[hartytp]

maybe you're right and I'm misreading it (I wouldn't worry about the 30dB offset until we've thought about units etc).

Can you compare to the SPICE model

[pathfinder49]

Seems like the Spice model is only for for the voltage regulator. The filter simulation requires Tina. I'll take a look at the trial later (unless @gkasprow can easily make a plot for comparison)

[gkasprow]