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quartiq / phaser

Phaser AWG DSP design
GNU General Public License v3.0
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spectral inversion between DAC outputs and TRF output #9

Closed jordens closed 3 years ago

jordens commented 4 years ago

With the DAC emitting a nominally positive frequency (doesn't matter whether that's the oscillators on Kasli, the DUC, the NCO on the DAC or the CMIX), the IQ mixer will let that end up as the lower sideband. There are only the three possible well known candidates (-I, -Q, I and Q swapped). The current work around is to swap the IQ DACs (DAC configuration option).

jordens commented 4 years ago

With I-Q not swapped at the DAC outputs, the oscillators, DUC, NCO both have correct frequency sign, only the CMIX in the DAC have the wrong sign. Swapping I-Q reverses that. Let's keep the nominally correct mapping and leave it to debugging the CMIX.

jordens commented 4 years ago

https://github.com/m-labs/artiq/commit/ef65ee18bdd14bbf8c41f8aed401a4b0763c8069

jordens commented 4 years ago

Correction: original assessment correct. All oscillator frequencies are inverted unless the DACs are swapped. Worked around by https://github.com/m-labs/artiq/commit/03d5f985f8032c5ae076c6dad4f6d8801fc6d473

jordens commented 3 years ago

Closing since this is wontfix and efficiently worked around without relevant side effects.