This paper presents an implantable bio-impedance measurement system for cardiac pacemakers. The fully integrated system features a low power analog front-end and pulse width modulated output. The bio-impedance readout benefits from voltage to time conversion to achieve a very low power consumption for wirelessly transmitting the data outside the body. The proposed IC is fabricated in a 0.18 μm CMOS process and is capable of measuring the bio-impedance at 2 kHz over a wide dynamic range from to with accuracy and maximum current injection while consuming just from a 1 V supply.

In this paper, a 3-bit Flash spin-orbit torque analog to digital converter (SOT-ADC) is presented which works based on switching of a perpendicular-anisotropy magnetic tunnel junction (p-MTJ) by spin Hall effect (SHE) assisted by spin-transfer torque (STT). To quantize the input signal into 8 states, a heavy metal (HM) with different cross-sectional areas that is shared with seven MTJs is utilized. To enable the deterministic switching, STT currents are employed. However, such currents make challenges during conversion and sensing phases which are addressed in this work. The SOT-ADC eliminates the (2 n -1)-time duplication of the input current (Iin) in conventional n-bit current mode CMOS Flash ADCs. Each MTJ acts as a comparator that compares the input signal (current) with its own critical current (IC) as a reference current (Iref). Therefore, the power-hungry comparators in CMOS Flash ADCs can be replaced by simple latch-based comparators for sensing the states of MTJs. Moreover, instead of using different sizes of transistors to create various values of Iref i.e., Iref1, 2Iref1 … fixed currents as sensing currents are used which leads to reducing mismatch issue and chip area. Because of the influence of the resistance of HM, each MTJ has an exclusive reference voltage (Vref) that is created by a dummy 3-bit SOT-quantizer. According to simulation results, power consumption and maximum sampling rate (including all conversion, sensing, and reset phases) of the ADC are 416 µW and 102 MS/s in 180 nm CMOS technology, respectively. In addition, the differential nonlinearity (DNL) and integral nonlinearity (INL) are -0.258 least significant bit (LSB) and -0.275 LSB, respectively.Index Terms-Flash analog to digital converter (ADC), spin-orbit torque (SOT), spin-transfer torque (STT), magnetic tunnel junction (MTJ).

Recent research provides examples of neuromorphic systems applied to process biological signals or to interface biological tissues. Usually, in such contexts, the neuromorphic system is used for automatic anomaly detection. The automation of the long-term monitoring of biological signals holds promise for lightening the burden placed on clinicians. At the same time, the adoption of such devices potentially allows processing to be performed locally, without the need to transfer data to an external processor. In turn, on-site signal analysis makes closed-loop intervention feasible, to correct the source of the anomalies. So far, the common approach has been to deploy the network of spiking neurons either on multi-core neuromorphic platforms or on programmable units (field programmable gate array). However, if the aim is to develop wearable or even chronically implantable devices, it is imperative to move in the direction of embedded solutions, tailored and optimized for the specific application. To this end, the present study proposes a neuromorphic device implemented in CMOS technology for the detection of epileptic seizures (ictal events) from local field potential (LFP) signals. The LFP data have been acquired by a multi-electrode array in a slice of mouse hippocampus-cortex. The system includes an analog-to-event converter (AEC) encoding the recorded signals into trains of spikes, and a small spiking neural network (SNN) of 2 × 1 neurons with online biological-plausible learning. The AEC yields two spike-trains: UP spikes that account for the positive slope signal and DOWN spikes that correspond to the negative slope signal. The synapses among the input and output layers are plastic and follow the spike-timing-dependent plasticity rule. Early results show that the SNN module is able to detect ictal events with a delay of 64.98 ± 30.92 ms, consuming < 50 pW. The layout of the entire system occupies 528 µm × 278 µm.

A low-power mixed-signal IC for implantable pacemakers is presented. The proposed system features three independent intracardiac signal readout channels with pulse-width-modulated outputs. Also, the proposed system is capable of measuring the amplitude and phase of the bioimpedance with pulse-width-modulated outputs for use in rate adaptive pacemakers. Moreover, a stimulation system is embedded, offering 16 different amplitudes from 1 to 7.8 V. A backscattering transmitter transfers the output signals outside the body with very little power consumption. The proposed low-power mixed-signal IC is fabricated in a 0.18-μm HV CMOS process and occupies 2.38 mm. The biopotential channels extract the heart signals with 9.2 effective number of bits and the bioimpedance channels measure the amplitude and phase of the heart impedance with 1.35 Ω accuracy. The complete IC consumes only 4.2 μA from a 1-V power supply.

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