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suservo: document offset range limits 

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 frequency: DDS frequency in Hz
:param offset: IIR offset (negative setpoint) in units of full scale. :param offset: IIR offset (negative setpoint) in units of full scale.
For positive ADC voltages as setpoints, this should be negative. 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 :param phase: DDS phase in turns
""" """
if self.servo_channel < 4: if self.servo_channel < 4:
@ -310,9 +312,9 @@ class Channel:
Where: Where:
* :math:`y_n` and :math:`y_{n-1}` are the current and previous * :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 * :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:`o` is the offset
* :math:`a_0` is the normalization factor :math:`2^{11}` * :math:`a_0` is the normalization factor :math:`2^{11}`
* :math:`a_1` is the feedback gain * :math:`a_1` is the feedback gain