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sawg: expand documentation

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Robert Jördens 2017-06-13 18:51:48 +02:00
parent 3f37870e25
commit 858c1be381
1 changed files with 32 additions and 12 deletions
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44
artiq/coredevice/sawg.py
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@ -121,7 +121,8 @@ class Config:
"""Set the digital up-converter (DUC) I data summing junction upper
limit. In machine units.
The default limits are the full range of signed 16 bit data.
The default limits are chosen to reach maximum and minimum DAC output
amplitude.
For a description of the limiter functions in normalized units see:
@ -163,11 +164,9 @@ class Config:
configurable upper and lower limits. The three summing junctions are:
* At the in-phase input to the ``phase0``/``frequency0`` fast DUC,
where the in-phase outputs of the two slow DDS (1 and 2) are
added together.
after the anti-aliasing FIR filter.
* At the quadrature input to the ``phase0``/``frequency0``
fast DUC, where the quadrature outputs of the two slow DDS
(1 and 2) are added together.
fast DUC, after the anti-aliasing FIR filter.
* Before the DAC, where the following three data streams
are added together:
@ -238,12 +237,32 @@ class SAWG:
q_enable*Im(buddy_oscillators))
This parametrization can be viewed as two complex (quadrature) oscillators
(``frequency1``/``phase1`` and ``frequency2``/``phase2``) followed by
a complex digital up-converter (DUC, ``frequency0``/``phase0``) on top of a
(real/in-phase) ``offset``. The ``i_enable``/``q_enable`` switches
enable emission of quadrature signals for later analog quadrature mixing
distinguishing upper and lower sidebands and thus doubling the bandwidth.
They can also be used to emit four-tone signals.
(``frequency1``/``phase1`` and ``frequency2``/``phase2``) that are
executing and sampling at the coarse RTIO frequency. They can represent
frequencies within their first Nyquist zone from ``-f_RTIO/2`` to
``f_RTIO/2``.
The sum of their outputs is then interpolated by a factor of
:attr:`parallelism` (2, 4, 8 depending on the bitstream) using a
finite-impulse-response (FIR) anti-aliasing filter (more accurately
a half-band filter).
The filter is followed by a configurable saturating limiter.
After the limiter, the data is shifted in frequency using a complex
digital up-converter (DUC, ``frequency0``/``phase0``) running at
:attr:`parallelism` times the coarse RTIO frequency. The first Nyquist zone
of the DUC extends from ``-f_RTIO*parallelism/2`` to
``f_RTIO*parallelism/2``. Other Nyquist zones are usable depending on the
interpolation/modulation options configured in the DAC.
The real/in-phase data after digital up-conversion can be offset using
another spline interpolator ``offset``.
The ``i_enable``/``q_enable`` switches enable emission of quadrature
signals for later analog quadrature mixing distinguishing upper and lower
sidebands and thus doubling the bandwidth. They can also be used to emit
four-tone signals.
.. note:: Quadrature data from the buddy channel is currently
ignored in the SAWG gateware and not added to the DAC output.
@ -266,7 +285,7 @@ class SAWG:
:param parallelism: Number of output samples per coarse RTIO clock cycle.
:param core_device: Name of the core device that this SAWG is on.
"""
kernel_invariants = {"channel_base", "core",
kernel_invariants = {"channel_base", "core", "parallelism",
"amplitude1", "frequency1", "phase1",
"amplitude2", "frequency2", "phase2",
"frequency0", "phase0", "offset"}
@ -274,6 +293,7 @@ class SAWG:
def __init__(self, dmgr, channel_base, parallelism, core_device="core"):
self.core = dmgr.get(core_device)
self.channel_base = channel_base
self.parallelism = parallelism
width = 16
time_width = 16
cordic_gain = 1.646760258057163 # Cordic(width=16, guard=None).gain