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Phase noise measurement #125

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sotirova opened this issue Mar 1, 2021 · 8 comments
Closed

Phase noise measurement #125

sotirova opened this issue Mar 1, 2021 · 8 comments

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@sotirova
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sotirova commented Mar 1, 2021

Setup

  • EEM0 of a Kasli 2.0 connected to EEM0 of a phaser baseband board
  • Kasli 125 MHz ext ref from CLK SYN of R&S SMA 100A
  • Phaser 125 MHz ext ref from RF output of R&S SMA 100A; output level 0 dB
  • Generate a single tone from RF0 of phaser at 150 MHz, output level -9.1 dBm
  • Connect RF0 of phaser to R&S phase noise analyser

Measurement results

First look at phase noise when phaser is using its internal clock vs when it is given an external 125 MHz clock as described above. For both of these measurements Kasli was connected to an external 125 MHz reference as above.
image

For reference, here is also the phase noise from the Kasli MMCX clock outputs when using the Kasli internal clock vs when Kasli takes an external 125 MHz reference.
image

@hartytp
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hartytp commented Mar 2, 2021

Kasli 125 MHz ext ref from CLK SYN of R&S SMA 100A

Interesting. Do you know/did you ever measure what the phase noise spectrum of that output is? I recall it being significantly worse than the main output, but can't find any info in the spec sheet.

@hartytp
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hartytp commented Mar 2, 2021

Anyway, that's lovely data and generally better than I'd expected. From a physics perspective, that's plenty good enough for everything I want to do, which is great.

In terms of background curiosity/calibrating expectations for what should be doable for this kind of design, the AD9910 noise graphs with and w/o PLL are copied below. My understanding is that DDS chips like the AD9910 are generally about as good as one gets for this kind of digital synthesis so are a pretty good reference.

image

Looks like phaser is within 10dB of the AD9910 at all frequencies, a bit better than the 9910 at higher frequencies and a bit worse at lower frequencies, but broadly comparable throught.

image

Phase with PLL is something like 20dB worse than the AD9910 w/o PLL for close-in noise with less than 10dB between them for broader-band noise.

As a general point of interest, I'd be curious to know what the noise spectrum of phaser looks like without the PLL, but that requires a bit of reconfiguration is is not something we need to worry about.

@hartytp
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hartytp commented Mar 2, 2021

Anyway, good work @sotirova! I don't see anything suspicious here (the DAC data sheet doesn't have phase noise plots so doesn't give us anything to directly compare with, but I don't see anything in the above to suggest we're doing worse than I'd expect).

@hartytp hartytp closed this as completed Mar 2, 2021
@sotirova
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sotirova commented Mar 2, 2021

Thanks for the comments @hartytp!

Interesting. Do you know/did you ever measure what the phase noise spectrum of that output is? I recall it being significantly worse than the main output, but can't find any info in the spec sheet.

Here's the phase noise of the synth RF OUT and CLK SYN for reference - indeed the CLK SYN looks worse than the main RF output
synth

@hartytp
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hartytp commented Mar 2, 2021

Here's the phase noise of the synth RF OUT and CLK SYN for reference - indeed the CLK SYN looks worse than the main RF output

What carrier frequency?

@sotirova
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sotirova commented Mar 2, 2021

What carrier frequency?

125 MHz both, as used in the setup

@hartytp
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hartytp commented Mar 2, 2021

anyway, good to know that the CLK SYN phase noise is not a limitation here (although not by that far)

@pathfinder49
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pathfinder49 commented Apr 14, 2021

I've performed similar measurements for the Phaser-Upconverter variant.

My setup:

  • 10 MHz and 125 MHz reference frequencies generated by R&S SMA 100 A
  • R&S FSWP phase noise analyser (using 10 MHz external reference)
  • Kasli v1.1 (using 125 MHz external reference)
  • Phaser upconverter (this uses the kasli clock distribution or dedicated 125 MHz external reference, see below)
  • For measuring LO:
    • All amplitudes and frequencies set to zero
  • For measuring RF output
    • DAC-NCO at 200 MHz
    • DUC at 130.3 MHz
    • Kasli oscillator at 7 MHz
\ Using external reference distributed by Kasli Using dedicated phaser reference
Phaser Reference Clock Kasli 125MHz ext ref
Phaser 2875 MHz Local Oscillator Lo 2875 MHz LO 2875 MHz ext clock
Phaser 3.2123 GHz output RF 3212-3 MHz with LO 2875 MHz RF 3212-3 MHz with LO 2875 MHz ext clock

At ~3 GHz, the broadband output phase-noise within 1 MHz is dominated by the TRF-LO phase noise. The phase noise can be improved substantially by using a dedicated frequency reference.

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