Frequency Generation and Baseband Filters for mm-Wave 5G and 6G Transceivers
Author
Summary, in English
In order to keep up with the constant demand for higher data rates, the fifth
generation of mobile communication (5G) introduced the use of mm-wave carrier frequencies from 24 to 71 GHz. Plenty of new frequency spectrum then became available, which has allowed for channel bandwidths of several hundreds of MHz. 6G is projected to continue this trend with even higher carrier frequencies and wider bandwidths, reaching carrier frequencies above 100 GHz and bandwidths in the multi-GHz range. However, this creates new challenges for circuit designers, as the performance of radio circuits typically degrades with increasing frequency. Two critical components in radio transceivers whose performance are highly affected by the increase in carrier frequency and bandwidth are frequency generators and baseband filters. The former generates a local oscillator (LO) signal required for frequency translating the data signal to/from the baseband from/to the carrier frequency, and the latter is used to separate the desired signal from undesired interference and noise in a receiver and to prevent leakage of undesired spectrum content to nearby channels in a transmitter. The design of the frequency generation is also made much more complicated due to mm-wave 5G and 6G communication relying on beamforming, in which the signals from multiple antennas are combined to overcome the high path loss at these frequencies. The LO signal must then be
distributed to multiple frequency converters while retaining a constant relative
phase shift. If the beamforming is done using so-called LO beamforming, this relative phase shift must also be tunable in a very accurate manner.
In this thesis, five research papers are included; two concern mm-wave frequency generation, two concern multi-GHz integrated baseband filters, and one is about system-level simulations of beamforming receivers. The thesis is divided into two parts, with the first part providing an introduction and context to the conducted research, while the second part consists of the included papers.
Paper I presents a frequency generation circuit for 28-GHz LO beamforming sliding-IF transceivers. An external 7-GHz signal is first phase shifted by an injection-locked oscillator and then fed to an injection-locked frequency tripler. A harmonic mixer is used as a phase detector to measure the applied phase shift, enabling automatic phase tuning. The phase detector can also be used to automatically tune the oscillators to obtain injection lock. Additionally, a sliding-IF receiver is implemented to properly test the frequency generator.
Paper II presents a modular system-level testbench for sub-THz 6G beamforming receivers, implemented in MATLAB/Simulink. The testbench models the analog circuit blocks with high fidelity, and can thus be used to investigate impacts of circuit non-idealities on the performance of the whole system. The effects of beam squint, ADC resolution, phase noise, baseband filter type, and interfering beams are simulated for a 32-element linear array.
Paper III describes a 28-GHz differential-to-quadrature injection-locked frequency tripler, intended for direct-conversion transceivers. A dual-injection scheme is used to maximize the harmonic rejection, and a mixed-signal feedback system minimizes the quadrature error by automatically tuning the frequency tripler so that its free-running oscillation frequency coincides with the third harmonic of the input signal.
In Paper IV, two differential multi-GHz 5th-order integrated baseband filters are presented, one active Gm-C filter and one passive LC filter, intended for 6G applications, fabricated in a 22-nm FD-SOI CMOS process. The active filter is based on Nauta’s transconductor and utilizes back-gate biasing to achieve state-of-the-art performance. The passive filter uses overlapping inductors, resulting in large mutual inductance and reduced footprint. Owing to this technique, the chip area of the passive filter is similar to that of most active filters, while providing clear benefits in power consumption and dynamic range.
In Paper V, the passive filter in Paper IV is further investigated and improved. A lumped model of the overlapping inductors is derived and used to develop a capacitive cancellation method to reduce stopband peaking, which is verified using EM simulations. To further improve the stopband performance, the overlapping inductors are redesigned in an 8-shape to reduce coupling between different inductors in the filter. The new filter reduces the stopband peaking by almost 30 dB compared to the original filter in Paper IV.
generation of mobile communication (5G) introduced the use of mm-wave carrier frequencies from 24 to 71 GHz. Plenty of new frequency spectrum then became available, which has allowed for channel bandwidths of several hundreds of MHz. 6G is projected to continue this trend with even higher carrier frequencies and wider bandwidths, reaching carrier frequencies above 100 GHz and bandwidths in the multi-GHz range. However, this creates new challenges for circuit designers, as the performance of radio circuits typically degrades with increasing frequency. Two critical components in radio transceivers whose performance are highly affected by the increase in carrier frequency and bandwidth are frequency generators and baseband filters. The former generates a local oscillator (LO) signal required for frequency translating the data signal to/from the baseband from/to the carrier frequency, and the latter is used to separate the desired signal from undesired interference and noise in a receiver and to prevent leakage of undesired spectrum content to nearby channels in a transmitter. The design of the frequency generation is also made much more complicated due to mm-wave 5G and 6G communication relying on beamforming, in which the signals from multiple antennas are combined to overcome the high path loss at these frequencies. The LO signal must then be
distributed to multiple frequency converters while retaining a constant relative
phase shift. If the beamforming is done using so-called LO beamforming, this relative phase shift must also be tunable in a very accurate manner.
In this thesis, five research papers are included; two concern mm-wave frequency generation, two concern multi-GHz integrated baseband filters, and one is about system-level simulations of beamforming receivers. The thesis is divided into two parts, with the first part providing an introduction and context to the conducted research, while the second part consists of the included papers.
Paper I presents a frequency generation circuit for 28-GHz LO beamforming sliding-IF transceivers. An external 7-GHz signal is first phase shifted by an injection-locked oscillator and then fed to an injection-locked frequency tripler. A harmonic mixer is used as a phase detector to measure the applied phase shift, enabling automatic phase tuning. The phase detector can also be used to automatically tune the oscillators to obtain injection lock. Additionally, a sliding-IF receiver is implemented to properly test the frequency generator.
Paper II presents a modular system-level testbench for sub-THz 6G beamforming receivers, implemented in MATLAB/Simulink. The testbench models the analog circuit blocks with high fidelity, and can thus be used to investigate impacts of circuit non-idealities on the performance of the whole system. The effects of beam squint, ADC resolution, phase noise, baseband filter type, and interfering beams are simulated for a 32-element linear array.
Paper III describes a 28-GHz differential-to-quadrature injection-locked frequency tripler, intended for direct-conversion transceivers. A dual-injection scheme is used to maximize the harmonic rejection, and a mixed-signal feedback system minimizes the quadrature error by automatically tuning the frequency tripler so that its free-running oscillation frequency coincides with the third harmonic of the input signal.
In Paper IV, two differential multi-GHz 5th-order integrated baseband filters are presented, one active Gm-C filter and one passive LC filter, intended for 6G applications, fabricated in a 22-nm FD-SOI CMOS process. The active filter is based on Nauta’s transconductor and utilizes back-gate biasing to achieve state-of-the-art performance. The passive filter uses overlapping inductors, resulting in large mutual inductance and reduced footprint. Owing to this technique, the chip area of the passive filter is similar to that of most active filters, while providing clear benefits in power consumption and dynamic range.
In Paper V, the passive filter in Paper IV is further investigated and improved. A lumped model of the overlapping inductors is derived and used to develop a capacitive cancellation method to reduce stopband peaking, which is verified using EM simulations. To further improve the stopband performance, the overlapping inductors are redesigned in an 8-shape to reduce coupling between different inductors in the filter. The new filter reduces the stopband peaking by almost 30 dB compared to the original filter in Paper IV.
Department/s
Publishing year
2024
Language
English
Publication/Series
Series of Licentiate and Doctoral theses
Issue
174
Full text
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Document type
Dissertation
Publisher
Department of Electrical and Information Technology, Lund University
Topic
- Embedded Systems
Keywords
- 5G, 6G, CMOS, FD-SOI, mm-Wave, frequency generation, LO, integrated filters
Status
Published
Research group
- Integrated Electronic Systems
Supervisor
ISBN/ISSN/Other
- ISSN: 1654-790X
- ISBN: 978-91-8104-075-3
- ISBN: 978-91-8104-074-6
Defence date
30 May 2024
Defence time
09:15
Defence place
Lecture hall E:1406, building E, John Ericssons väg 2, Faculty of Engineering LTH, Lund University, Lund. The dissertation will be live streamed, but part of the premises is to be excluded from the live stream.
Opponent
- Piet Wambacq (Prof.)