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Phaser: zero oscillator amplitude after `init()` (close #1651) 

Currently, `init()` leaves a single oscillator at full scale. The phase
accumulator of this oscillator is held continuously cleared. Provided no
upconverting mechanism is active (DUC, CMIX, NCO), this produces a full-scale
DC voltage. The DC voltage is blocked by hardware capacitors. This behaviour
is not mentioned by the `init` documentation.

If one attempts to use any other oscillator without reducing the amplitude
of the oscillator enabled by `init`, there is by significant clipping.

In the case that the NCO or CMIX are configured via the device_db
(suggested in the docs), leaving the osillator at full scale results in
full RF output power after calling `init()`. This may plausibly damage loads
driven by phaser.

Signed-off-by: Marius Weber <marius.weber@physics.ox.ac.uk>
This commit is contained in:
Marius Weber 2021-04-02 21:19:09 +01:00
parent 407fba232d
commit 4f812cc4ed
1 changed files with 3 additions and 0 deletions
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artiq/coredevice/phaser.py
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@ -306,6 +306,9 @@ class Phaser:
self.duc_stb() self.duc_stb()
delay(.1*ms) # settle link, pipeline and impulse response delay(.1*ms) # settle link, pipeline and impulse response
data = channel.get_dac_data() data = channel.get_dac_data()
delay(1*us)
channel.oscillator[0].set_amplitude_phase_mu(asf=0, pow=0xc000,
clr=1)
delay(.1*ms) delay(.1*ms)
sqrt2 = 0x5a81 # 0x7fff/sqrt(2) sqrt2 = 0x5a81 # 0x7fff/sqrt(2)
data_i = data & 0xffff data_i = data & 0xffff