A steady trend towards the design of mostly-digital and digital-friendly analog circuits, suitable to integration in mainstream nanoscale CMOS by a highly automated design flow, has been observed in the last years to address the requirements of the emerging Internet of Things (IoT) applications. In this context, this tutorial brief presents an overview of concepts and design methodologies that emerged in the last decade, aimed to the implementation of analog circuits like Operational Transconductance Amplifiers, Voltage References and Data Converters by digital circuits. The current design challenges and application scenarios as well as the future perspectives and opportunities in the field of digital-based analog processing are finally discussed.

Re-Thinking Analog Integrated Circuits in Digital Terms: A New Design Concept for the IoT Era

{This review paper is taken from the references mentioned below, this is just as assignment to learn how reports are converted into IEEE format and submitted to publications}.
Abstract – Implanted medical devices are very important electronic devices because of their usefulness in monitoring and diagnosis, safety and comfort for patients. Since 1950s, remarkable efforts have been undertaken for the development of bio-medical implanted and wireless telemetry bio-devices. Issues such as design of suitable modulation methods, use of power and monitoring devices, transfer energy from external to internal parts with high efficiency and high data rates and low power consumption all play an important role in the development of implantable devices. This paper provides a comprehensive survey on various modulation and demodulation techniques such as amplitude shift keying (ASK), frequency shift keying (FSK) and phase shift keying (PSK) of the existing wireless implanted devices. The details of specifications, including carrier frequency, CMOS size, data rate, power consumption and supply, chip area and application of the various modulation schemes of the implanted devices are investigated and summarized in the tables along with the corresponding key references. Current challenges and problems of the typical modulation applications of these technologies are illustrated with a brief suggestions and discussion for the progress of implanted device research in the future. It is observed that the prime requisites for the good quality of the implanted devices and their reliability are the energy transformation, data rate, CMOS size, and power consumption and operation frequency. This review will hopefully lead to increasing efforts towards the development of low powered, high efficient, high data rate and reliable implanted devices.

Modulation Techniques for Biomedical Implanted Devices and Their Challenges

CRC Look-up Table Optimization for Single-Bit Error Correction

https://research.aalto.fi/files/38536488/ELEC_Kempi_Resilient_flow_control_MaM.pdf

Resilient flow control for wireless data streaming in inductively coupled medical implants

This paper presents a low power bio-signal acquisition system for sleep apnea, which can measure respiration, heart rate, SpO2, and pulse transit time (PTT). For respiration, a nasal airflow sensor with a thermistor is used. For PTT that can serve as a surrogate for blood pressure during sleep, two photoplethysmogram (PPG) sensors are employed at the upper arm and the finger. For improved comfort during sleep, body channel communication (BCC) is used to remove long wires. To reduce power consumption and circuit complexity, sensor’s analog front-end is implemented by using a current-controlled oscillator which is also shared by BCC transmitter that employs analog frequency modulation. Implemented in $0.18~\mu \text{m}$ CMOS, the proposed IC consumes less than 3.6 mW from a 1.8 V supply, while occupying 0.145 mm2 of active area.

A Sleep Apnea Monitoring IC for Respiration, Heart-Rate, SpO 2 and Pulse-Transit Time Measurement Using Thermistor, PPG and Body-Channel Communication

This paper describes the design of an integrated sensor interface for dopamine detection. The sensor interface circuit fabricated in 65 nm CMOS technology utilizes a time-based analog-to-digital conversion circuit built around a ring oscillator. The circuit supports a wide input current range of $\pm 1.2~\mu \text{A}$ and sampling rate of 1 - 20 kHz, enabling sub-second detection of neurochemicals within the supported current range. Measured results with physiologically relevant dopamine concentration of 500 nM demonstrate the ability of the sensor interface circuit to detect oxidation and reduction current peaks, which provides information about the release times and redox potentials of the neurochemical. This chemical information is essential in neurostimulation treatment of neurological and neurodegenerative diseases.

/pdf/time-based-sensor-interface-for-dopamine-detection-1v0arl1ozt.pdf

Time-Based Sensor Interface for Dopamine Detection

This paper describes a voltage controlled oscillator (VCO) -based ADC for biomedical applications which employs a relaxation oscillator for voltage-to-frequency conversion. The proposed circuit uses a redundant pair of capacitors to mitigate the conversion error resulting from the time required for resetting the capacitor. A switch matrix with feedback helps sustain oscillations. Further, the VCO frequency approaches zero as the input voltage approaches zero unlike a converter with ring oscillator, thereby reducing power consumption. Post-layout simulation of the proposed ADC designed with a 28 nm FDSOI CMOS technology shows an ENOB of 8 and power consumption of $12\ \mu \mathbf{W}$ from a 0.7 V supply.

/pdf/a-vco-based-adc-with-relaxation-oscillator-for-biomedical-wldafknw2r.pdf

A VCO-based ADC with Relaxation Oscillator for Biomedical Applications

This paper presents the design of an integrated current-controlled oscillator (CCO) based readout front-end for neurochemical sensing applications. The readout front-end chip is implemented in 65 nm CMOS technology and occupies an area of 0.059 mm2. The proposed design supports an input current range of 1.2 μA (±600 nA) and can also be configured to support wider current range. The CCO-based structure utilized in this design results in noise averaging of the detected neurochemical input signal due to its inherent ΔΣfirst-order noise shaping and anti-alias filtering characteristics. Thus, the prototype chip achieves a current resolution of 100 pA and can detect dopamine concentrations as small as 10 μMol based on measured data from novel diamond-like carbon electrodes. In addition, the digital codes obtained from the readout front-end attain a signal-to-noise (SNR) of 82 dB and linearity limited effective-number-of-bits (ENOB) of 8 at full current range input, without employing any calibration or linearization techniques. The proposed read-out front-end consumes 33.7 μW of power in continuous operation.

/pdf/a-current-controlled-oscillator-based-readout-front-end-for-395zvpq6a0.pdf

A current controlled oscillator based readout front-end for neurochemical sensing in 65nm CMOS technology

This paper describes the hardware implementation of a custom communication protocol tailored for low-power telemetry data streaming over an inductive link. The application-specific features of typical RFID implementations such as random number generation and variable data rate support are omitted from the proposed implementation, focusing only on the continuous data transfer. The post-synthesis results of proposed communication scheme implemented on 28nm CMOS FDSOI process show power consumption of $3.11 \mu W$ while running from a 845.7 kHz clock and occupying 0.0048 mm2 of die area. The current implementation provides an uplink rate of 8 kbit/s, sufficient for streaming of 1-channel 1 kHz 12-bit sample recording.

/pdf/a-low-power-hardware-stack-for-continuous-data-streaming-1faii5540o.pdf

Olaitan Olabode

Papers

Resilient flow control for wireless data streaming in inductively coupled medical implants

Time-Based Sensor Interface for Dopamine Detection

A VCO-based ADC with Relaxation Oscillator for Biomedical Applications

A current controlled oscillator based readout front-end for neurochemical sensing in 65nm CMOS technology

A Low-Power Hardware Stack for Continuous Data Streaming from Telemetry Implants