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SingularitySurfer 2022-06-23 08:48:28 +00:00
parent 56c59e38f0
commit 24b4ec46bd
1 changed files with 61 additions and 6 deletions

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@ -130,7 +130,8 @@ class Phaser:
Each phaser output channel features a servo to control the RF output amplitude
using feedback from an ADC. The servo consists of a first order IIR (infinite
impulse response) filter fed by the ADC and a multiplier that scales the I
and Q datastreams from the DUC by the IIR output.
and Q datastreams from the DUC by the IIR output. The IIR state is updated at
the 3.788 MHz ADC sampling rate.
Each channel IIR features 4 profiles, each consisting of the [b0, b1, a1] filter
coefficients as well as an output offset. The coefficients and offset can be
@ -1088,8 +1089,8 @@ class PhaserChannel:
:param bypass: 1 to enable bypass (default), 0 to engage servo. If bypassed, hold
is forced since the control loop is broken.
:param hold: 1 to hold the servo IIR filter output constant, 0 for normal operation
:param profile: profile index to select for channel (0 to 3)
:param hold: 1 to hold the servo IIR filter output constant, 0 for normal operation.
:param profile: Profile index to select for channel. (0 to 3)
"""
if (profile < 0) or (profile > 3):
raise ValueError("invalid profile index")
@ -1102,9 +1103,32 @@ class PhaserChannel:
def set_iir_mu(self, profile, b0, b1, a1, offset):
"""Load a servo profile consiting of the three filter coefficients and an output offset.
:param profile: profile to load (0 to 3)
:param ab: 3 entry coefficient vector (16 bit)
:param offset: output offset (16 bit)
Avoid setting the IIR parameters of the currently active profile.
The recurrence relation is (all data signed and MSB aligned):
.. math::
a_0 y_n = a_1 y_{n - 1} + b_0 x_n + b_1 x_{n - 1} + o
Where:
* :math:`y_n` and :math:`y_{n-1}` are the current and previous
filter outputs, clipped to :math:`[0, 1[`.
* :math:`x_n` and :math:`x_{n-1}` are the current and previous
filter inputs in :math:`[-1, 1[`.
* :math:`o` is the offset
* :math:`a_0` is the normalization factor :math:`2^{14}`
* :math:`a_1` is the feedback gain
* :math:`b_0` and :math:`b_1` are the feedforward gains for the two
delays
.. seealso:: :meth:`set_iir`
:param profile: Profile to set (0 to 3)
:param b0: b0 filter coefficient (16 bit signed)
:param b1: b1 filter coefficient (16 bit signed)
:param a1: a1 filter coefficient (16 bit signed)
:param offset: Output offset (16 bit signed)
"""
if (profile < 0) or (profile > 3):
raise ValueError("invalid profile index")
@ -1119,7 +1143,38 @@ class PhaserChannel:
@kernel
def set_iir(self, profile, kp, ki=0., g=0., x_offset=0., y_offset=0.):
"""Set servo profile IIR coefficients.
Avoid setting the IIR parameters of the currently active profile.
Gains are given in units of output full per scale per input full scale.
The transfer function is (up to time discretization and
coefficient quantization errors):
.. math::
H(s) = k_p + \\frac{k_i}{s + \\frac{k_i}{g}}
Where:
* :math:`s = \\sigma + i\\omega` is the complex frequency
* :math:`k_p` is the proportional gain
* :math:`k_i` is the integrator gain
* :math:`g` is the integrator gain limit
:param profile: Profile number (0-3)
:param kp: Proportional gain. This is usually negative (closed
loop, positive ADC voltage, positive setpoint). When 0, this
implements a pure I controller.
:param ki: Integrator gain (rad/s). Equivalent to the gain at 1 Hz.
When 0 (the default) this implements a pure P controller.
Same sign as ``kp``.
:param g: Integrator gain limit (1). When 0 (the default) the
integrator gain limit is infinite. Same sign as ``ki``.
:param x_offset: IIR input offset. Used as the negative
setpoint when stabilizing to a desired input setpoint. Will
be converted to an equivalent output offset and added to y_offset.
:param y_offset: IIR output offset.
"""
NORM = 1 << SERVO_COEFF_SHIFT
COEFF_MAX = 1 << SERVO_COEFF_WIDTH - 1
DATA_MAX = 1 << SERVO_DATA_WIDTH - 1