Best-in-class ADCs for base stations and smartphones

The base station ADC supports RF sampling, operates across multiple frequency bands up to 5GHz, and combines high resolution and linearity with low power consumption. Alongside it, a single-channel handset ADC achieves quality power efficiency through multi-bit pipelined stages and background calibration. Both ADCs, available for licensing, mark an advancement toward scalable, high-performance beyond-5G solutions, including Cloud-based AI and extended reality applications.

Beyond-5G technology is set to enable increasingly bandwidth-intensive mobile services, such as cloud-based AI and extended reality applications. However, it also necessitates the use of higher frequencies, with mobile operators currently exploring frequencies up to 5GHz, and the deployment of more advanced infrastructure, including large antenna arrays.

“This will require a transformation of operators’ mobile networks, particularly in the design of transceivers – and the underlying ADCs – at both the base station and handset ends. Key transceiver requirements will include a small footprint and low power consumption, along with support for features that enhance network capacity, such as multiband operation and Massive MIMO. We are addressing these needs with the introduction of two new ADCs at this year’s VLSI Symposium,” said Joris Van Driessche, Program Manager at imec.

Base station radios usually achieve multiband operation by dedicating a transceiver to each frequency band, which increases the size and power consumption of the radios. In contrast, imec’s new RF-sampling ADC, covering all bands below 5GHz with GHz-level sampling speeds, operates smoothly across multiple frequency bands. Furthermore, the large antenna arrays necessary for massive MIMO typically involve numerous power-hungry, discrete transceivers. However, imec’s approach enables a much more efficient system-on-chip implementation.

Driessche: “To help base station radios cope with interference from other wireless signals, our ADC leverages built-in wideband-linear signal buffering to provide higher Effective Number of Bits (ENOB) than comparable systems – without the need for digital nonlinear distortion correction engines. In addition, its design incorporates a novel hierarchical interleaver architecture that further enhances the ADC’s linearity and speed.”

Imec’s CMOS-based 10GS/s hierarchical time-interleaved ADC for RF-sampling applications achieves 9/8.2 ENOB at low/Nyquist frequencies with SFDR over 60dB up to a 5GHz bandwidth, all within a power budget of just 350mW. This ADC offers the highest effective resolution, superior linearity, the broadest bandwidth, and remarkably low power consumption.

For beyond-5G connectivity at the user end, imec introduced a single-channel mobile handset ADC that utilises multi-bit pipelined stages with background calibration, ensuring high linearity, bandwidth, and record power efficiency. This advanced design leverages ring amplification for optimal performance.

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

Imec’s handset ADC achieves a 10.91 ENOB and 81dB SFDR at 1GS/s, while consuming only 17.8mW – resulting in a Walden FoM of 9.2 fJ/conv.-step.

With these specifications, it sets a new standard for power efficiency.

“With these ADCs, both of which are available for licensing, we are introducing two key building blocks for enabling beyond-5G communications. Our next goal is to develop base station ADCs that support FR3 frequencies (6 to 20GHz) while maintaining high linearity and low power consumption, using advanced sub-5nm CMOS nodes,” concluded Driessche.