DPO7000: What is the FIR filter file format used in the Tektronix arbitrary waveform math filter function?

Question:

DPO7000: What is the FIR filter file format used in the Tektronix arbitrary waveform math filter function?

Answer:

The following describes the ASCII file format for storing filters for use in the Tektronix oscilloscope waveform math section.  A filter menu function allows the user to specify a disk file name containing the filter.  A single file format allows the user to specify a different set of coefficients for each sample rate at which the filter is allowed to operate.  If the sample rate is not in the file list then the filter will not be applied to the data.  The file format also allows the user to specify that the set of filter coefficients is normalized.  This allows the same set of filter coefficients to operate at all sample rates.

The ASCII file format is specified as follows:

                        # Comments preceded by # symbol

< sampleRate >  coef1, coef2, …. coefN

< sampleRate >  coef1, coef2, …. coefN

                                    |                       |

                                    |                       |

< sampleRate >  coef1, coef2, …. coefN

Each set of filter coefficients in a file are specified in one row preceded by the sample rate value at which that set will operate.   If the user specifies the @ symbol for the sample rate then the filter will operate at all sample rates.    If the @ symbol is specified then there should only be one set of filter coefficients in the file.  However, the user may have other rows with sample rates specified and they will be ignored.    There will be a separate row for each sample rate the filter is to operate at.    Each row may have a different number of coefficients with a maximum of 1000.  The file may contain up to 20 rows.

An example of a filter that is setup to operate at a specific sample rate is given as follows.  This is the contents of a file named 200MHz_mult_sample_rates.flt that is included in the library directory on the oscilloscope.

#This is a 4th order Bessel Thompsen low pass filter.

#200MHz bandwidth, will operate at any of the following sample rates:

# 40 GS/s, 20 GS/s, 10 GS/s, 5 GS/s, 2.5 GS/s, 1 GS/s, 500 MS/s

5e8; 1.968e-007,1.008,-0.00978,0.002267,-0.0002208,1.643e-005,-1.397e-006,1.434e-007

1e9; 9.524e-008,0.3899,0.4877,0.1304,-0.004733,-0.004566,………………………….  

2.5e9; 3.868e-008,0.01885,0.1081,0.1982,0.2284,0.1981,………………………

5e9; 1.935e008,0.0007332, 0.009428, 0.02874, 0.05408, 0.07921, ………………………..

1e10 ; 9.673e-009,3.445e-006,0.0003666,0.001831,0.004714,0.008978,0.01437,0……………….

2e10;4.837e-009, 1.657e-008, 1.723e-006, 4.274e-005, 0.00018334-009, ………………..

4e10 ;2.418e-009, -3.524e-009, 8.284e-009, -1.795e-008,8.613e-007, ……………….

This FAQ Applies to:

Product: DPO7054, DPO7104, DPO7254, DPO7354

FAQ ID : 55446

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