Low Power FM-UWB Transmitter for Wireless Body Area
Networks
A thesis submitted in partial fulfilment of the requirements of the degree of
Doctor of Philosophy in Electrical Engineering
By
Supervised By
Prof. Mohamad Abdul-Hassan Sawan
Cairo 2017
Thesis: Low Power FM-UWB Transmitter for Wireless Body Area Networks
Degree: Doctor of Philosophy in Electrical Engineering (Electronics and
Communications Engineering)
Professor, Microelectronics Dept.
Faculty of Engineering - Ain Shams University.
3. Prof. Abdelhalim Abdelnaby Zekry ……………
Faculty of Engineering - Ain Shams University.f. Research In
4. Prof. Mohamad Abdul-Hassan Sawan ……………
Electrical Engineering Dept.
Statement of Original Authorship
This thesis is submitted as a partial fulfilment of Doctor of Philosophy degree in Electrical
Engineering, Faculty of Engineering, Ain shams University.
The author carried out the work included in this thesis, and no part of it has been submitted
for a degree or a qualification at any other scientific entity.
Name: Mohamed Ali Ahmed Ali
Signature:
Date of birth : 07 September 1983.
Place of birth : Qena.
Field of specialization : Electronics and Communications Engineering.
University issued the degree: Ain Shams University.
Date of issued degree : February 2011.
Current job : Research Assistant, Electronics Research Institute.
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Acknowledgment
All my thanks to Allah for the successful completion of this work. I express my
deepest gratitude and thanks to Prof. Abdelhalim Zekry, Ain Shams University, for his
continuous supervision support. Prof. Zekry is behind all analytical, technical and even
spiritual actions throughout this work.
Also, my deepest gratitude and thanks to Prof. Mohamad Sawan, Polytechnique
Montreal, Canada for his warm welcoming in Polystim Lab. I would like to express my
gratitude for his great availability and scientific support.
Special thanks to Dr. Heba Shawkey, Electronics Research Institute, for her great
help and support along the way of my work.
I would also like to thank my examination committee members: Prof. Amal
Zaki and Prof. Hani Ragai, thanks to you for serving as my committee members.
I also thank my colleagues at the Polystim Lab. Our discussions and meetings
allowed me to improve my work, while having a social dimension to our activities in the
laboratory. I wish them continued success in their careers.
Many thanks to my mother, father, and brothers for their great hearts which looked
after me all these years.
I am deeply grateful to my wife, who always encourages me for further progress.
Mohamed Ali Ahmed Ali
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Abstract
Among the most challenging wireless area networks, is the emerging WBAN
(Wireless body area network) which is a network of implanted and/or body-worn sensor
nodes that collect, process, and transmit to base station (or remote receiver) vital signals
such as blood pressure, heart-rate, glucose, and even brain signals. WBAN is used to
monitor the health status of the patient and wirelessly transmit the outcomes to the
physician to reduce the load at hospitals and increase the efficiency of healthcare services.
However, WBAN is a portable network. Successfully implementing such networks faces
many key challenges. Battery lifetime in surgically implanted devices is the biggest
challenge as the network has to last for years. So, establishing an energy efficient wireless
link is strongly required to achieve long-lifetime battery use.
The free use of ultra-wideband (UWB) within 3.1-10.6 GHz frequency band has
received great interest in short-range communications systems. Frequency-modulated
ultra-wideband (FM-UWB) technique produces a constant-envelope UWB waveform with
wideband FM modulation, featuring a flat-spectrum with very steep spectral roll off. This
enhances the coexistence of FM-UWB system with the communications standards
transmitting in near bands. In addition, the FM demodulation is performed by the FM-
UWB receiver without the need for a local oscillator. So, carrier synchronization is not
required which results in simple hardware design. The FM-UWB is proper for short-range
(<10 meters), low and medium data rate applications (up to 1 Mbps). It offers some other
advantages such as low power dissipation, low transmitted power (<–41.3 dBm/MHz), and
robustness to interference and multipath. With the afore-mentioned advantages, the FM-
UWB technique is proper for WBAN in medical applications.
We present in this thesis a new energy efficient FM-UWB transmitter. The
proposed architecture involves a subcarrier generator to produce a triangular waveform
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modulated by the input data. The radio frequency (RF) signal is generated using a voltage-
controlled oscillator (VCO) and modulated by the triangular signal resulting in a constant-
envelope UWB spectrum. A phase-locked loop (PLL) based RF calibration scheme is
employed to calibrate the lower and the upper frequencies of the modulated RF signal. The
purpose of this novel calibration structure is to keep transmitting in a fixed emission band.
The proposed transmitter is designed and implemented in 130 nm CMOS technology and
the experimental measurement of various building blocks as well as the whole transmitter
are presented.
1.2 WBAN applications ......................................................................................................... 3
1.3 Main Challenges of WBAN for Medical Purposes ......................................................... 6
1.4 Powering the Implantable Devices .................................................................................. 8
1.4.1 Inductive Coupling ................................................................................................... 9
1.4.2 Energy Harvesting .................................................................................................. 10
2.1 Introduction ................................................................................................................... 15
2.3.1 UWB for Communication Systems ................................................................... 18
2.3.2 UWB in Radar Systems..................................................................................... 19
2.4 UWB Techniques ....................................................................................................... 20
2.4.2 Multiband OFDM ................................................................................................... 23
3.1 Introduction ................................................................................................................... 26
3.3.2 Relaxation Oscillator .............................................................................................. 31
3.3.4 Fractional-N PLL Based Subcarrier Generation ..................................................... 35
3.4 RF Oscillator ................................................................................................................. 36
3.5.1 Integer N-PLL based RF Calibration ...................................................................... 39
3.5.2 SAR based RF Calibration ...................................................................................... 40
3.5.3 RF Calibration with Quasi-Continuous FLL .......................................................... 41
3.5.4 SAR Automatic Frequency Calibration Based RF Calibration .............................. 42
3.6 Comparison .................................................................................................................... 43
3.7 Conclusion ..................................................................................................................... 44
4.1 Introduction ................................................................................................................... 45
4.2.1 Subcarrier Generation ............................................................................................. 47
4.2.5.1 Frequency Divider ............................................................................................ 52
4.2.5.3 Multiplexer (Mux) ............................................................................................ 54
4.3 Simulation Results ......................................................................................................... 54
4.4 Conclusion ..................................................................................................................... 57
Chapter 5 One Mbps 1 nJ/b 3.5-4 GHz Fully-Integrated FM-UWB Transmitter ...... 58
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5.2.1 Binary Frequency Shift Keying (BFSK) ................................................................ 60
5.2.1.1 Relaxation oscillator ......................................................................................... 61
5.2.2 RF Calibration ......................................................................................................... 64
5.2.3 RF VCO .................................................................................................................. 68
5.2.4 Power Amplifier ..................................................................................................... 71
5.3 Measurement Results ..................................................................................................... 73
6.1 Conclusions ................................................................................................................... 84
References .......................................................................................................................... 84
Figure 1.3 Biofeedback process. ....................................................................................... 5
Figure 1.4 Interference in WBANs ................................................................................... 7
Figure 1.5 Principle of transmission by inductive link. .................................................... 9
Figure 2.1 UWB radiation limits for communication systems : (a) Indoor, (b) Outdoor. ..
....................................................................................................................... 16
Figure 2.2 Application of UWB in intensive care units. ................................................. 20
Figure 2.3 A general architecture of IR-UWB transceiver: (a) Transmitter, (b) Receiver.
....................................................................................................................... 22
Figure 2.5 Pulse shape modulation of IR-UWB system. ................................................ 23
Figure 2.6 WiMedia band plan for MB-OFDM UWB approach ................................... 24
Figure 3.1 FM-UWB transceiver general architecture: (a) Transmitter, (b) Receiver. .. 27
Figure 3.2 FM-UWB transmitter modulation scheme. ................................................... 28
Figure 3.3 Simulated PSD of FM-UWB system for various subcarrier frequencies (a)
FSUB = 1 MHz. (b) FSUB = 10 MHz. (c) FSUB = 30 MHz. ............................... 29
Figure 3.4 Block diagram of DDFS system for subcarrier generation ........................... 31
Figure 3.5 Relaxation oscillators: (a) Circuit using grounded capacitor, (b) Circuit using
floating capacitor, and (c) corresponding waveforms. .................................. 33
Figure 3.6 Relaxation oscillator for better linearity. ....................................................... 33
Figure 3.7 Slew rate controlled FSK subcarrier generator: (a) circuit diagram. (b)
Waveforms..................................................................................................... 34
Figure 3.9 Fractional-N PLL based subcarrier generation .............................................. 36
Figure 3.10 Basic LC-VCO topology. ............................................................................... 37
Figure 3.11 Schematic of the current-starved ring VCO. .................................................. 38
Figure 3.12 Digital pre-compensation based RF calibration. ............................................ 39
Figure 3.13 The SAR frequency-locked loop calibration scheme. .................................... 40
Figure 3.14 SAR-FLL timing diagram. ............................................................................. 41
Figure 3.15 Quasi-continuous FLL for RF VCO calibration. ........................................... 42
Figure 3.16 SAR AFC based RF calibration ..................................................................... 43
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Figure 4.1 Block diagram of the proposed FM-UWB transmitter .................................. 46
Figure 4.2 The schematic of the charge pump. ............................................................... 47
Figure 4.3 A 3-stage current-starved ring VCO. ............................................................. 48
Figure 4.4 Simulated VCO output frequency versus input control voltage. ................... 49
Figure 4.5 Simulated VCO phase noise. ......................................................................... 49
Figure 4.6 A Class-AB power amplifier circuit. ............................................................. 50
Figure 4.7 Block diagram of the 6-stage frequency divider. .......................................... 52
Figure 4.8 Circuit of TSPC divider by two. .................................................................... 52
Figure 4.9 Implementation of positive-edge-triggered D flip-flop. ................................ 53
Figure 4.10 PFD logic diagram. ........................................................................................ 53
Figure 4.11 Multiplexer schematic. ................................................................................... 54
Figure 4.12 Transient simulation for the relaxation oscillator. ......................................... 55
Figure 4.13 System simulation during modulation and calibration modes. ...................... 56
Figure 4.14 Simulated FM-UWB transmitter output spectrum. ........................................ 56
Figure 5.1 Energy efficiency and data rate of several RF transmitters. .......................... 58
Figure 5.2 The proposed FM-UWB transmitter.............................................................. 59
Figure 5.3 BFSK subcarrier generator. ........................................................................... 61
Figure 5.4 Relaxation oscillator. (a) Simplified schematic. (b) The circuit of the
comparator. (c) Layout. ................................................................................. 63
Figure 5.5 Charge pump circuit followed by a passive second-order loop filter. ........... 64
Figure 5.6 Layout view of the BFSK subcarrier generator. ............................................ 64
Figure 5.7 The proposed RF calibration scheme. (a) Block diagram. (b) Layout view. 66
Figure 5.8 Simulation results for the RF calibration section. ......................................... 67
Figure 5.9 Three-stages ring VCO. (a) Schematic view. (b) Layout view. .................... 69
Figure 5.10 The current through MN1 versus Vcont. .......................................................... 70
Figure 5.11 Post-simulated VCO output frequency versus control voltage for different
values of Rvco. ................................................................................................. 70
Figure 5.12 Class-AB power amplifier. (a) Schematic view. (b) Simulated scattering
parameters. (c) Layout view. .......................................................................... 73
Figure 5.13 (a) The transmitter micrograph. (b) Transmitter test bench photograph. ....... 74
Figure 5.14 Relaxation oscillator performance measurements (a) Output waveforms. ...(b)
Output frequency versus tuning voltage Vsub (c) phase noise. ....................... 76
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Figure 5.15 (a) Measured BFSK generator performance. (b) Measured subcarrier
spectrum with 500 kbps BFSK modulation. .................................................. 77
Figure 5.16 (a) Measured BFSK generator performance. (b) Measured subcarrier
spectrum with 1 Mbps BFSK modulation. ..................................................... 78
Figure 5.17 Eight-stage divider output signal at 4 GHz input frequency. ......................... 79
Figure 5.18 Measured RF VCO tuning range. ................................................................... 80
Figure 5.19 Measured RF VCO phase noise. .................................................................... 80
Figure 5.20 Measured FM-UWB transmitter output spectrum. ........................................ 81
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Table 1.1 Characteristics of radio technologies for WBAN. ............................................... 13
Table 2.1 Performance comparison between IR-UWB and MB-OFDM UWB systems. ... 25
Table 3.1 Comparison among various FM-UWB transmitter architectures. ....................... 44
Table 4.1 Operation of the Proposed Transmitter. .............................................................. 46
Table 4.2 Summary of the PLL design parameters. ............................................................ 51
Table 4.3 Summary of FM-UWB Transmitter Performance. .............................................. 57
Table 5.1 Components values for LPF1 and LPF2. ............................................................ 66
Table 5.2 Sizes of the transistors employed in the VCO. .................................................... 70
Table 5.3 FM-UWB transmitter performance summary and comparison. .......................... 82
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AFC Automatic Frequency Calibration
BER Bit Error Rate
BLE Bluetooth Low Energy
ECG Electrocardiography
EMG Electromyography
ICI Intercarrier Interference
ISI Intersymbol Interference
LNA Low-Noise Amplifier