I describe the implementation of a simple algorithm to optimize the
buffer frequency location to maximize the number of resonators.
Since the spread of resonator frequencies (especially in the upper
band) exceeds the bandwidth (490 MHz) we have available in the SDR
readout, it is important to pick the buffer location so as to maximize
the number of tones that can actually be used.
Method and Results
The algorithm starts with a first-guess for the LO frequency which is
simply the mean of all of the resonator frequencies in the device list
(for either the lower or upper band). It also excludes any resonators
within +/- 10 MHz of the LO frequency. The number of available
resonators is determined. The routine then shifts the buffer both up
and down by 50 MHz spacings (the number of shifts in each direction
depend on how far the initial buffer edges lie from the edges of the
resonator distribution). At each step comparison is made with the
initial number of available resonators; if the new number is larger,
the current parameters are adopted as the new benchmark.
For the lower bands, this isn't too much of an issue, as the resonator
spread is not much larger than the available bandwidth. For the first 6
X 12 devices (Xa and Xb), 36/49 and 37/44 good resonators can be fit
into the buffer in the lower band; these numbers are not improved by
shifting the buffer. For the upper band, the initial values are 25/65
for Xa and 23/54 for Xb; these are improved to 32/65 and 29/54,
The routine also generates plots showing the location of the LO, the
buffer bandwidth edges, and which resonators (both good and bad) fall
within the useable bandwidth.
devXa_part1.pdf devXa_part2.pdf devXb_part1.pdf devXb_part2.pdf
The buffer generation code needs to be adapted to incorporate this.