mmWave 5G networks have great potential and are needed to provide capacity beyond the existing LTE and sub-6 GHz networks. The substantial investments made by carriers to license the mmWave spectrum in recent auctions is evidence of this need and carriers’ intentions. However, the effective use of this spectrum is not straightforward. At these frequencies, obstacles in the signal path - trees, rainfall and even a user’s hand - can cause significant attenuation. In addition, initial mmWave deployments have underdelivered due to insufficient output power, resulting in limited range and high thermal budgets, reducing reliability and increasing system costs.
RF-SOI based mmWave phased array systems can help address these challenges, especially compared to existing complementary metal-oxide semiconductor (CMOS) or SiGe solutions. RF-SOI process technology has three key advantages:
1. Transistors, substrate and the back-end provide improved RF performance.
2. SOI’s n-FET has lower parasitics than bulk CMOS, enabling higher performance: GlobalFoundries’ 45RFSOI achieves approximately 40 percent higher fmax than bulk CMOS.
3. Stacked RF-SOI transistors enable 10x higher output power and 2x to 5x higher efficiency.
In March, MixComm announced its first production IC, the SUMMIT 2629™, an eight-channel RF front-end for 28 GHz, 5G phased array antenna systems fabricated in RF-SOI. The SUMMIT 2629 was designed to address the challenges constraining 5G mmWave performance by:
- Extending the link range to decrease infrastructure costs and improve customer satisfaction.
- Reducing power consumption and thermal dissipation.
- Reducing antenna array complexity and overall RF front-end cost.
Operating from 26.5 to 29.5 GHz, the SUMMIT 2629 RFIC integrates power amplifiers (PA), low noise amplifiers, T/R switching, beamformers with beam table memory, calibration, gain control and temperature and power telemetry with a high speed system peripheral interface (SPI) for control. A single SUMMIT 2629 provides two sets of four channels for two antenna polarizations - a total of eight channels per RFIC (see Figure 1).
Combining MixComm’s unique circuit architecture with the RF-SOI process capabilities, the SUMMIT 2629 on-chip PAs achieve high power and high efficiency, more than twice the efficiency of competing CMOS solutions. To maintain efficiency and dynamic range, the T/R switches are very low loss, and the receive amplifier has a low noise figure. Beam steering is accomplished using six-bit phase shifters with 360-degree coverage and 16 dB gain adjustment in 0.5 dB steps.
The SUMMIT 2629 offers additional capabilities to enhance performance, control and reliability:
- Fully calibrated for gain and phase matching among multiple RFICs.
- Extensive on-chip temperature and power sensing.
- On-chip gain control for temperature compensation.
- High speed SPI with large on-chip beam table storage memory.
With its high output power and excellent efficiency, the SUMMIT 2629 is well suited for 5G infrastructure applications, such as gNodeB, customer premises equipment (CPE) and repeaters. The higher output power per PA enables significantly superior link budgets, enabling a 2.7x increase in throughput rate (see Figure 2). The figure compares the median CPE uplink throughput of a CPE array using a bulk CMOS-based front-end with an array using MixComm’s 45 nm RF-SOI RFICs, both with equal numbers of antennas.
The SUMMIT 2629 is fabricated on GlobalFoundries’ 45RFSOI process, a 45 nm, partially-depleted SOI technology codeveloped with DARPA to enable mmWave innovation and commercial applications. Since 2008, the 45RFSOI process has been running in high volume at multiple GlobalFoundries’ fabs, evolving to incorporate enhancements improving RF performance. GlobalFoundries is providing turn-key manufacturing of the SUMMIT 2629, from wafer fab through wafer-level chip-scale packaging (WLCSP) and RF testing at the mmWave operating frequencies. SUMMIT 2629’s WLCSP is compatible with assembly onto low-cost PCBs, which are used for 5G antenna arrays.
The first antenna array to use the SUMMIT 2629 is the Taoglas KHA16.23C smart antenna subsystem (see Figure 3). The KHA16.23C is a proprietary 2D antenna array with 16 elements integrated into a multi-layer PCB that contains four Summit 2629 ICs. The PCB has several layers for power optimization and thermal control, digital control and the RF feed - all in footprint of 53 mm x 84 mm. The antenna subsystem is scalable up to 1024 element arrays, depending on device implementation.
Although a relatively new company, founded in 2017, MixComm has a substantial legacy and head-start in RF-SOI and mmWave solutions. The company’s expertise leverages the pioneering work of Harish Krishnaswamy at Columbia University’s COSMIC lab, who cofounded MixComm and serves as chief technology officer. For more than 10 years, members of the COSMIC lab team were key performers on programs such as DARPA’s Efficient Linearized All-Silicon Transmitter ICs, which proved the unique modeling, circuit design and architectures that MixComm is using to optimize RF-SOI for mmWave applications. The SUMMIT 2629 is the first of family of mmWave devices which will cover the 5G mmWave bands.
Sample quantities of MixComm’s SUMMIT 2629 and Taoglas KHA16.23C will be available through Richardson RFPD.