Design And Research Of Key Analog Integrated Circuits For Body Area Network

There lies a great potential to construct a body area network(BAN)for human health monitoring using wearable or implantable electronic devices.In the BAN system,the electronic equipment attached to the human body collects various types of biomedical physiological signals,which are fed to the center node of network.Then they are transmitted via mobile phones or other means of communication to the hospital,web cloud servers for monitor or in-depth diagnostic analysis.As our country gradually progresses into the aging society,research of BAN for the medical use is of great scientific and social significance.Analog IC design challenges for BAN include lower power consumption,higher levels of integration,and development for more types of medical applications.Design and research of key analog integrated circuits for body area network are conducted in this paper.Firstly,human Body Communication(HBC)can be served as a wireless communication candidate for BAN.IEEE 802.15.6 protocol HBC physical layer defines the use of human tissue as a medium for wireless transmission.The protocol specifies strict output spectrum specifications: with 21 MHz center frequency and 5.25 MHz bandwidth,a spectral rejection of-120 d Br(d B relative to the center frequency)at 1 MHz.The theoretical analysis is performed to locate the bottleneck of the output spectrum shaping,which turns out to be the second-order intermodulation(IM2)of the buffer at the final stage of HBC transmitter.A spectrum shaping HBC transmitter architecture is proposed.The design method of the 8th-order Gm-C bandpass filter(BPF)is discussed in detail.The relationship between the second-order input intercept point(IIP2)and the spectrum rejection ratio at 1 MHz is quantitatively studied.Then three IM2 cancellation buffers are proposed.Secondly,among IC design for medical BANs,there lacks an ultralow power method to transmit the Electrocardiography(ECG)signals to remote computation nodes after they have been acquired by AFE.A modulator is designed,which directly modulates ECG signals to audio frequency(500 Hz-20 k Hz)without analog-to-digital conversion.Modulated signal is then fed to the smartphone via the built-in 3.5 mm audio Jack,after which subsequent complex signal processing is conducted.Modulation is accomplished by a high linearity upconversion passive mixer.Then a low-power Gm-C 5-order low-pass filter(LPF)is used to reject high-frequency harmonic components of mixer output.Instrumental amplifier(IA)and unity gain amplifier(UGA)are used in the modulator output stage.IA is to ensure the high common mode rejection ratio(CMRR)of the double-ended to single-ended(D2S)conversion.Second stage of the UGA is class AB output buffer to drive the low-resistance 5k? load.The smartphone switches between built-in and external microphones mode through impedance detection.This means the driver has to be loaded with low impedance.Lastly,in order to increase the integration of BAN,power management unit is usually integrated on-chip.An audio signal rectifier is designed,output of which is modulated by a low-dropout regulator(LDO)to produce a stable DC supply voltage with load driving capability.Based on different purposes,designs of two LDOs with output of 1.8 V and 1.2 V,the maximum load current of 50 m A and 2 m A are discussed respectively.In addition,the design methodology for LDO is described in detail,including switching power transistor,buffer,error amplifier,and their corresponding layout design considerations.At the same time,two bandgap designs and the working principle of the two start-up circuits are covered.Based on the challenges described in the above work,several integrated circuit techniques and schemes for BAN are proposed.Firstly,in order to fulfill HBC transmitter spectrum shaping,two novel IM2 cancellation techniques are proposed.The first method is based on a two-step hybrid cancellation.The first stage uses a homogeneous MOS bias technique to initially eliminate the IM2 in the single-ended output current.The second stage uses the complementary feature of NMOS and PMOS to cancel the first-stage residual IM2 components.The second IM2 cancellation technique is based on the deliberate introduction of controlled mismatches.They compensate the slight asymmetry of traditional buffers with active current mirrors.Thus,the single-ended output circuit is equivalent to differential output structure.The deliberate mismatch is realized by the asymmetric gate bias of the NMOS input transistors,or by the body bias of the input transistor.Under XFAB 0.35 ?m CMOS process,a HBC transmitter is designed.The simulations results shown that output spectrum at 1 MHz is suppressed to-122 d Br.Secondly,taking into account the process variation and device mismatch,the aforementioned IM2 elimination technology lacks of robustness.So this paper also proposes two automatic calibration schemes.The first scheme is to inject the calibration stimulus at the input of the HBC transmitter and then to detect the relevant amplitude.The control signal is generated and then the mismatch current injected into the buffer is adjusted to complete the calibration.The second calibration technique is based on measuring the average power of the residual IM2 components,i.e.,the regrown spectral components at the low frequency due to IM2.The average power is estimated by the time-averaging filter.Encoded by Asynchronous delta-sigma delta(ADSM)modulator, reconstructed by the ripple counter,average power is then compared recursively with the help of decision logic.Finally,the control signal corresponding to the minimum residual power is found.Then it adjusts the floating current source in the buffer to eliminate the IM2 component at the output.Designed under GF 0.13 ?m CMOS process,after calibration,output spectrum of HBC transmitter meets the requirement of-120 d Br at 1 MHz.Thirdly,in the design of audio modulator,in order to minimize the power consumption of the modulator,a mixer and filter compact merged circuit structure is proposed,which saves a power consumption of an opamp plus a Gm cell.Designed using XFAB 0.35 ?m CMOS process,final simulation results show that the current consumption is 40.8 ?A,effective number of bits is 11,which meet the design specifications.Finally,in power management circuit design for BAN,an audio harvesting scheme is proposed.The half-wave rectifier is used to convert the sinusoidal audio signal from one output channel of the handset audio interface into a DC voltage.This supply voltage is to power the aforementioned ECG audio modulator.By measuring the output load curve of i Phone5 C,the feasibility of the scheme is verified.Under XFAB 0.35 ?m CMOS and XFAB 0.18 ?m SOI CMOS process,simulation and measurement results of the proposed two LDOs meet the design goals.