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suservo: document offset range limits

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close #1034
This commit is contained in:
Robert Jördens 2018-05-31 16:53:01 +00:00
parent 36dcea3edf
commit a42f774440
1 changed files with 4 additions and 2 deletions
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6
artiq/coredevice/suservo.py
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@ -287,6 +287,8 @@ class Channel:
:param frequency: DDS frequency in Hz
:param offset: IIR offset (negative setpoint) in units of full scale.
For positive ADC voltages as setpoints, this should be negative.
Due to rounding and representation as two's complement,
``offset=1`` can not be represented while ``offset=-1`` can.
:param phase: DDS phase in turns
"""
if self.servo_channel < 4:
@ -310,9 +312,9 @@ class Channel:
Where:
* :math:`y_n` and :math:`y_{n-1}` are the current and previous
filter outputs, clipped to :math:`[0, 1]`.
filter outputs, clipped to :math:`[0, 1[`.
* :math:`x_n` and :math:`x_{n-1}` are the current and previous
filter inputs
filter inputs in :math:`[-1, 1[`.
* :math:`o` is the offset
* :math:`a_0` is the normalization factor :math:`2^{11}`
* :math:`a_1` is the feedback gain