8.8 22FDX - the superior technology for IoT, RF, Automotive and Mobility: Best-in Class RF, 5G and mmWave designs

This talk presents an overview of the ongoing circuit design activities in cooperation with GLOBALFOUNDRIES. Several RF integrated circuits for multi-Gbps communication have been demonstrated in 22FDX. Two examples will be presented in details: a Travelling Wave Amplifier (TWA) and a Mach-Zehnder Modulator (MZM) driver.

The gain cell employed for the TWAs is based on a conventional cascode topology and its layout is optimized to avoid performance degradation and instability. The TWA delivers a maximum gain of 10 dB over a 3-dB band of 110 GHz. The measured output power at 1 dB compression of the gain (o1dBcp) is 12.5 dBm at 20 GHz. Compared against the state of the art for TWAs, the presented design achieves the highest frequency of operation, as well as the broadest frequency band, and the highest o1dBcp. This circuit was awarded the best student paper award at the 2017 IEEE Asia Pacific Microwave Conference (APMC).

The high-voltage MZM driver is realized with stacked, low-impedance and low-loss switches which allow a voltage swing significantly larger than the breakdown voltage of individual devices. To enable this topology the signal is transferred to different voltage domains with level shifters, then amplified and conditioned to the rail-to-rail swing which ultimately drives the output power-stage. The bandwidth of the driver is increased with shunt and series inductive peaking. Stacking and coupling inductors result in only 0.018 mm² of active area, which is the most compact reported for MZM drivers. Measurements show a 3.75 V_pp swing on a 50 Ω load. Error-free (BER< 10 ⁻¹²) transmission at 30 Gbit/s is demonstrated. By using a switched output stage, only a small static dc-power is consumed, resulting in the most energy-efficient MZM driver with only 2.2 pJ/bit.

High-performance, high-precision, energy-efficient data converters are indispensable in mixed-signal and RF ICs that enable next generation wireless, mobile computing, automotive, medical, and IoT applications. These applications demand the development of data conversion including mixed-signal calibration techniques that emphasize performance, accuracy, robustness, and energy efficiency with reduced silicon area / cost.

In this presentation, we will discuss the latest ADC and DAC architectures and their respective design challenges required for 5G RF systems, optical communication and automotive systems using 22FDX. The stringent performance requirements in terms of noise and linearity demand smart mixed-signal calibration techniques in order to meet the performance targets at minimum power consumption and smallest silicon area. In addition we highlight technological benefits of 22FDX, which enable power savings on both system and circuit level.

FDSOI technology offers both power-efficient and high-performance digital, amongst others because SOI-MOSFET switches have lower parasitic capacitances compared to bulk-technologies. These benefits are not only relevant for digital signal processing, but can also benefit analog radio frequency circuits. For "Software Defined Radios", very selective Radio Frequency bandpass-filters are wanted with a flexibly programmable center frequency to choose the channel. Also, highly linear mixers for frequency down-conversion to baseband before A/D conversion are needed. It turns out that these functions can both be implemented exploiting switches, combined with linear capacitors and resistors, realizing so called "N-path filters" or "Frequency Translated filters". Moreover, the reception frequency is defined by the frequency of a digital clock, which can be implemented using digital dividers and logic. The resulting N-path filters benefit from CMOS scaling as switch parasitics improve, and increasingly higher digital clock frequencies are feasible. This contribution will review the developments in CMOS N-path filters over the last decade, highlighting promising achieved results, while also discussing some implementation aspects and simulation results in 22nm FDSOI.

Co-authors: Janne P. Aikio¹ , Mikko Hietanen² , Henri Hurskainen² , Timo Rahkonen¹ , Aarno Pärssinen²
1. Circuits and systems Research unit, University of Oulu; 2. Center for Wireless Communication - Radio Technologies, University of Oulu

Design complexity is increasing in all aspects when moving towards 5G wireless systems. Enhanced mobile broadband (eMBB) communications require increased bandwidth and thus also higher carrier frequencies starting from lower mmW regime. Solutions call for increased speed of transistors and better passives that are not easily available in bulk CMOS technologies. 22FDX has many potential features to support complete transceiver implementation from mmW antenna interface down to baseband processing.

22FDX provides several enhancements such as wide variety of devices: fast devices for PA and LNA circuits and slower devices for static switches, for example. Another interesting feature is the back-gating option, which we used to decrease the knee voltage of the transistors of a divider circuit. The circuit library is extensive and devices for mm-wave application contain modelling and layout up to fifth metal layer of the stack. This approach simplifies routing and reduces the extraction and simulation time significantly.

We will provide design experience from the first time access to this technology and how we used different modelling approaches precharacterized from library cells to EM simulations with Momentum, and designed test structures including active and passive devices for verification as well as complete amplifiers (LNA & PA) at 28 GHz based mostly on standard cells provided by foundry.

By the time of writing the chip fabrication is still on-going and thus we cannot guarantee if initial measurement results would be available by the time of the conference.