As those who are watching the repositories on github have probably noticed, there is now a new high-performance, programmable interpolator available for our 32 channel 2.55 MS/s 16 bit DAC Fastino.
- The filter is a fourth order CIC. It's impulse response is the de la Vallée Poussin/Parzen window also known as cubic (fourth order) B-spline.
- The filter has an excellent first sidelobe attenuation of better than 53 dB. This is crucial in narrowband microwave/rf/optical pulse applications where proper windowing is often neglected. It also limits the effect of intermodulation products due to analog non-linearities and reduces the high frequency spectral content in ion trap electrode waveforms.
- It is linear phase and time-symmetric and has a frequency-independent delay (all three properties are equivalent) which is important for ion transport applications (compare this to analog filters).
- Its purely piecewise-polynomial, well-known analytic response fits directly into existing tooling for trap electrode waveform generation, simulation, and optimization algorithms.
- All integer interpolation rates from 1 (2.55 MS/s) to 2**16 (39 S/s) are supported.
- Each channel can have a different interpolation rate.
- Interpolation rate changes can be synchronized among channels.
- The interpolation rate is programmable at run-time and changing rate takes four input samples.
- All interpolation rates of that are powers of two lead to overall unity gain. Those that are powers of cube roots of two lead to a few percent less than unity gain. All others lead to gains between 0.5 and 1.
- Changing interpolation rate does not lead to any transient response or glitches during settling of the filter. As long as the gain stays constant there is no step in output after settling.
- It is backwards and forwards compatible. Any combination of Fastino gateware and ARTIQ will work. Obviously the CIC interpolator is only supported in current ARTIQ master with current Fastino gateware.
Some more pointers: