Frequency Domain Multiplexing for Microwave Kinetic Inductance Detectors: Comparing the Xilinx ZCU111 RFSoC with the New 2x2 RFSoC Board

Abstract

The Xilinx ZCU111 Radio Frequency System on Chip (RFSoC) is a promising solution for reading out large arrays of microwave kinetic inductance detectors (MKIDs). The board boasts eight on-chip 12-bit / 4.096 giga samples-per-second (GSPS) analogue-to-digital converters (ADCs) and eight 14-bit / 6.554 GSPS digital-to-analogue converters (DACs), as well as field programmable gate array (FPGA) resources of 930,000 logic cells and 4,272 digital signal processing (DSP) slices. While this is sufficient data converter bandwidth for the readout of 8,000 MKIDs, with a 2 MHz channel-spacing and a 1 MHz sampling rate (per channel), additional FPGA resources are required to perform the DSP needed to process this large number of MKIDs, due to a mismatch between the data converter bandwidth relative to the FPGA resources of the ZCU111. A solution to this problem is the new Xilinx RFSoC 2x2 board. This board costs only one fifth of the ZCU111 while still providing the same logic resources, albeit with only a quarter of the data converter resources. Thus, using multiple RFSoC 2x2 boards would provide a better balance between FPGA resources and data converters, allowing the full utilization of the RF bandwidth provided by the data converters, while also lowering the cost per pixel value of the readout system; from approximately €2.50 per pixel with the ZCU111 to €1 per pixel with the 2x2.