The base station ADC supports RF sampling, operates across multiple frequency bands (up to 5GHz), and combines high resolution and high linearity with low power consumption. Complementing this is a single-channel handset ADC that is said to have achieved record-breaking power efficiency through multi-bit pipelined stages and background calibration.
Both ADCs, available for licensing, represent a key step toward scalable, high-performance beyond-5G solutions, such as cloud-based AI and extended reality apps.
Beyond-5G technology will be a key enabler of increasingly bandwidth-intensive mobile services, such as cloud-based AI and extended reality apps. But it also comes with the use of higher frequencies (with mobile operators currently exploring frequencies up to 5GHz), and the deployment of ever more advanced infrastructure equipment – 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 typically achieve multiband operation by assigning a transceiver to each frequency band, increasing the radios’ size and power consumption.
In contrast, imec’s new RF-sampling ADC – which covers all bands below 5GHz and features GHz-level sampling speeds – operates seamlessly across multiple frequency bands.
Additionally, while the large antenna arrays required for massive MIMO are usually equipped with numerous power-hungry, discrete transceivers, imec’s approach allows for a much more efficient system-on-chip implementation.
According to 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 delivers 9/8.2 ENOB at low/Nyquist frequencies with SFDR > 60dB up to a 5GHz bandwidth, all within a power budget of only 350mW. As such, this ADC combines the highest effective resolution with superior linearity at the widest bandwidth and exceptionally low power consumption.
To accommodate beyond-5G connectivity at the user end, imec has introduced a single-channel mobile handset ADC that leverages multi-bit pipelined stages based on ring amplification.
“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,” explained Driessche.
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 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.
