Bunch by Bunch FIR

TMBF FIR Control

LMBF FIR Control

This screen allows the bunch by bunch filters to be configured. Normally the shape of the filter is automatically configured from the :CYCLES_S, :LENGTH_S, :PHASE_S settings, but the FIR can be written to :TAPS_S instead if :USEWF_S is set to "Waveform".

The following PVs can be set for each of the four available FIRs (each PV is prefixed with $(device):$(axis) and the value n runs from 0 to 3):

Name	PV	Description
FIR freq/size	`:FIR:n:CYCLES_S, :FIR:n:LENGTH_S`	These two determine the fundamental shape of the FIR, which is a sine wave with `:FIR:n:CYCLES_S` cycles in `:FIR:n:LENGTH_S` samples. These two numbers need to be adjusted so that the tune frequency is comfortably close to the ratio `cycles/length.`
Phase	`:FIR:n:PHASE_S`	This adjust the phase of the FIR and so determines the feedback phase.
Setup	`:FIR:n:USEWF_S`	Can be either "Settings" or "Waveform". If this is set to "Waveform" then the settings above are ignored and instead `:FIR:n:TAPS_S` is used to define the filter.

We also have the following controls and indicators. The gain and decimation PVs are not prefixed with :$(axis)

Name	PV	Description
Gain	`:FIR:GAIN_S`	Configures the output gain from the FIR.
Decimation	`:FIR:DECIMATION_S`	This control is only available on LMBF and is used to reduce the data rate for the longitudinal samples to a more practical range.
Overflow	`:FIR:OVF`	If the ADC input level is very high (close to full scale) and the FIR has more than 8 taps then it is numerically possible for overflow to occur during FIR processing. This is independent of overflow that can occur when `:FIR:GAIN_S` is set high. If this occurs, either reduce the ADC input level (this can be done by adjusting the ADC filter taps), or reduce the bunch by bunch FIR gain by reducing the value of the taps.

Finally, the FIR waveforms can be viewed and configured by clicking on the Bunch by Bunch FIR Waveform Control buttons.

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Bunch by Bunch FIR

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