Keysight M8194A 120 GSa/s Arbitrary Waveform Generator User Guide 165
Appendix 7
• Interpolation filter and anti-alias filters are exactly the same although
the filter parameters will depend on the resampling parameters.
• The implemented algorithm does perform filtering and interpolation
simultaneously so the number of calculations is greatly reduced.
Additionally, filters are implemented as look-up tables so those are
calculated only once during the process.
• Timing parameters are based in double precision floating-point
numbers while amplitude related parameters are single precision
numbers. Most calculations consist in multiplication/addition
operations required by convolution processes and only involve
amplitude related variables (input samples and filter coefficients).
Single precision numbers will minimize calculation time while offering
more than enough dynamic range.
Interpolators and anti-aliasing filters share most characteristics as they are
required to be low-pass with good flatness, linear phase, fast roll-off, and
high stop-band rejections ratio. Ideal interpolator filters show a
“brick-wall” response. However, such filters require a very long “sinc-like”
impulse response to obtain good-enough performance. Impulse response
length has a direct effect on calculation times resulting of applying the
filter. Roll-off characteristics are especially important when applying the
filter as the anti-alias filter required for down-sampling. The filter
implemented in these algorithms has been designed with the following
objectives:
• Pass band flatness better than 0.01 dB
• Stop band attenuation better than 80 dB
• F80dB/F3dB ratio better than 1.15
The final filter consists in a sinc signal with a 41 sample periods length
after applying a Blackman-Harris time-domain window.
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