An Integrated Circuit for Radio Astronomy Correlators Supporting Large Arrays of Antennas

Abstract

Radio telescopes that employ arrays of many antennas are in operation, and ever larger ones are being designed and proposed. Signals from the antennas are combined by cross-correlation. While the cost of most components of the telescope is proportional to the number of antennas N, the cost and power consumption of cross-correlation are proportional to [Formula: see text] and dominate at sufficiently large N. Here, we report the design of an integrated circuit (IC) that performs digital cross-correlations for arbitrarily many antennas in a power-efficient way. It uses an intrinsically low-power architecture in which the movement of data between devices is minimized. In a large system, each IC performs correlations for all pairs of antennas but for a portion of the telescope’s bandwidth (the so-called “FX” structure). In our design, the correlations are performed in an array of 4096 complex multiply-accumulate (CMAC) units. This is sufficient to perform all correlations in parallel for 64 signals (N[Formula: see text]=[Formula: see text]32 antennas with two opposite-polarization signals per antenna). When N is larger, the input data are buffered in an on-chip memory and the CMACs are reused as many times as needed to compute all correlations. The design has been synthesized and simulated so as to obtain accurate estimates of the ICs size and power consumption. It is intended for fabrication in a 32[Formula: see text]nm silicon-on-insulator process, where it will require less than 12[Formula: see text]mm2 of silicon area and achieve an energy efficiency of 1.76–3.3[Formula: see text]pJ per CMAC operation, depending on the number of antennas. Operation has been analyzed in detail up to [Formula: see text]. The system-level energy efficiency, including board-level I/O, power supplies, and controls, is expected to be 5–7[Formula: see text]pJ per CMAC operation. Existing correlators for the JVLA ([Formula: see text]) and ALMA ([Formula: see text]) telescopes achieve about 5000[Formula: see text]pJ and 1000[Formula: see text]pJ, respectively using application-specific ICs (ASICs) in older technologies. To our knowledge, the largest-N existing correlator is LEDA at [Formula: see text]; it uses GPUs built in 28[Formula: see text]nm technology and achieves about 1000[Formula: see text]pJ. Correlators being designed for the SKA telescopes ([Formula: see text] and [Formula: see text]) using FPGAs in 16[Formula: see text]nm technology are predicted to achieve about 100[Formula: see text]pJ.