VLSI Symposium: RF ADCs cover 5GHz

At the IEEE VLSI Symposium this week, Imec revealed two ADCs for 5GHz ‘beyond 5G’ communication, one for base stations and one for phones.

The base station ADC operates over bands up to 5GHz.

It is a 10Gsample/s cmos hierarchical time-interleaved ADC that delivers 9 ENOB (effective number of bits) at low frequencies and 8.2 ENOB at Nyquist. SFDR (spurious-free dynamic range) is >60dB up to 5GHz bandwidth. Consumption is 350mW.

The handset ADC has a multi-bit pipelined architecture with background calibration.

“While the multi-bit approach is known to offer several advantages, such as high linearity, bandwidth and power efficiency, it also presents challenges,” said Imec programme manager Joris Van Driessche: “Our implementation addresses these through the use of background calibration to calibrate DAC mismatch and inter-stage gain.”

It achieves 10.91 ENOB and 81dB SFDR at 1Gsample/s while consuming 17.8mW, “resulting in a Walden figure-of-merit of 9.2fJ/conversion step”, said Imec.

“With these ADCs, both of which are available for licensing, we are introducing two key building blocks for enabling beyond-5G
communications,” said Van Driessche. “Our next goal is to develop basestation ADCs that support FR3 frequencies – 6 to 20GHz -while maintaining linearity, using sub-5nm CMOS nodes.”

Beyond 5G frequencies

At last year’s WRC-23 ITU World Radio Conference, four new bands were were allocated to 6G (and 4G and 5G) mobile comms: 3.3-3.4GHz, 3.6-3.8GHz, 4.8-4.99GHz and 6.425-7.125GHz. At the same event, bands at 2GHz and 2.6GHz were identified for high-altitude flying basestations.

VLSI Symposium, or IEEE Symposium on VLSI Technology & Circuits to give it its full name, is on in Honolulu, Hawaii, ending tomorrow (20 June 2024).