I've done the new 5th order filter with sorted components : +/-1nH inductances and 0.3% capacitors.
I've changed the 50MHz oscillator with this model : Connor-Winfield D75J-050.0M (+/-1ppm)
https://www.digikey.fr/product-detail/fr/connor-winfield/D75J-050.0M/CW657CT-ND/1965865The schematic is highly optimized with the components I have and PCB parasitics inductance/capacitor.
This curve result provides
60dB SPUR with the new 5th filter than 50dB with 11th order filter.
Yellow : New 5th order filter
Magenta : 11th order filter
The lineary between new 5th order filter and 11th order filter
The new 5th order filter provides very good linearity for sine signal (+/-0.3dB 0-30MHz) and multitone signal (+/-0.35dB 0-60MHz)
Yellow : New 5th order filter with sine sweep 1MHz to 30MHz
Magenta : 11th order filter with sine sweep 1MHz to 30MHz
Green : New 5th order filter with multitone sweep 1MHz to 12.45MHz
Blue : 11th order filter with multitone sweep 1MHz to 12.45MHz
The rejection of multiple points of this new 5th order filter
125MHz at -32dB
146MHz at -41dB
250MHz at -58dB
The same curve compared to old 11th order filter
Yellow : New 5th order filter
Magenta : Old 11th order filter
1MHz square signal comparison
Yellow : New 5th order filter
Magenta : Old 11th order filter
5MHz square signal comparison
Yellow : New 5th order filter
Magenta : Old 11th order filter
10MHz square signal comparison
Yellow : New 5th order filter
Magenta : Old 11th order filter
25MHz square signal comparison
Yellow : New 5th order filter
Magenta : Old 11th order filter
Conclusion of this new 5th order filterPro :
- Simple to implement
- Very good SPUR
- Very good rejection
- Very good linearity
Con :
- The square signal is awfull, probably due to lots of phase variations.
Note:
I use the term SPUR for SPUR, harmonics and artefacts (provides by sine sampling/phase error...)
Next ?
I'm going to remove the implemented new 5th order filter using 0805 SMD.
I'm working on a little more complex 7th order filter using 0603 SMD.
The goal is to provide more better features with a quasi-linear phase (useful for square signal).