Beamforming and ADC at 60 GHz

Imec presented several solutions for 60 GHz communication at the recent International Solid State Circuit Conference in the US.

One concerns a programmable analog baseband beamformer for a four-antenna 60 GHz phased-array receiver. A second solution is a fast low-resolution four-way interleaved analog-to-digital converter. Both solutions have been designed in 40 nm digital CMOS.

At the conference, Imec and the Holst Centre have been prominent, unveiling their breakthroughs in ultralow power design for wireless communications, wireless sensor networks, 3D design and organic electronics.

This resulted in contributions including 10 reviewed publications and six contributions to tutorials and workshops.

Radios for 60 GHz standards, such as the IEEE 802.15.3c, often use phased antenna arrays to relax the link budget. Due to the extremely high free-space loss at 60 GHz, getting sufficient signal power at the receiver's antenna is a major challenge.

Beamforming with phased antenna arrays is an indispensable technique to overcome this challenge.

Such a phased-array receiver aligns the phases of the signals coming from several antennas. it first applies a variable phase shift to each antenna path and then combines the signals from the individual paths. It has important advantages compared with radio-frequency beamforming; it reduces the chip area, increases the system's robustness and lowers its power consumption. Therefore, analog baseband beamforming is an important asset for low-cost, low-power 60 GHz consumer electronics.

Imec is believed to be the first organisation to present a programmable analog baseband beamformer for a four-antenna 60 GHz channel and through bonding two channels. The phase shifts are achieved with a resolution better than 20°. The bandwidth is high - 1.7 GHz - thanks to the use of amplifiers with very low input impedance, using shunt feedback.

The circuit is fabricated in a digital 40 nm low-power COMS technology. The chip consumes 35 mW from a 1.1 V VDD. So consumption per phase shifter is 7 mW (including a branch shared with the mixer).