A Piezo-sensor Readout Integrated Circuit for Multifunctional Electronic Skins

In general, there are two types of integrated circuits for reading piezoresistive and piezoelectric properties of PVDF-rGO: resistance-to-digital converter (RDC) and charge-to-digital converter (QDC). The resistor-to-digital converter is also divided into three types: resistor array-based RDC, current DAC-based RDC, and correlated double-sampling-based RDC. The most common form of charge-to-digital converter can be categorized by the number of amplifiers used, also called single-AMP-based QDC and multi-amps-based QDC, and will be introduced in the paper.

The readout integrated circuits introduced so far in previous papers are insufficient to apply to PVDF-rGO. Property of PVDF-rGO based on bias (a) and incorrect circuit structure without consideration of bias (b). Measured graph of RDC with passive resistance component.s Fig. Measured waveform of RDC for pulse with PVDF-rGO.

The resistance value according to the pressure of PVDF-rGO and tolerance of constant C. a) Specification results of manufactured chips and (b) comparison table. ROIC: Readout Integrated Circuit RDC: Resistor-to-Digital Converter QDC: Charge-to-Digital Converter MCU: Microcontroller.

It shows extremely low power consumption as most of the blocks consist of digital blocks and it can be implemented as a very simple structure. Since the size of the sensor resistance is not known, the amount of current is determined through a process of calibration by the comparator so that a suitable current source must be operated in the current DAC to maximize ADC performance. The gain of the first stage is the same with the single-AMP based charge-to-digital converter, but the signal can be amplified at more time in the second stage by the ratio of the resistors.

All the signals can be detected throughout the readout integrated circuits and the digitized bits can be transferred to microcontroller (MCU). It is designed to adjust the gain of the amplifier according to operating mode using programmable gain amplifier (PGA) before analog signal enters the ADC. However, in this process, the DC offset from the amplifier acts as noise that can distort the signal, and a second chopper and low-pass filter are used at the back to remove it.

The circuit designer must design the chopper's switching frequency high enough so that the low-pass filter does not attenuate the original signal. The proposed new type of differential conversion scheme uses the output signal received from the output stage as the input of an inverse amplifier such as VON and VOP, which is very vulnerable to offset error occurring in the amplifier. Proposed architecture of RDC using chopping technique and its waveform. the advantage of eliminating nearly 50% of the offsets that occur, and eliminating white noise and offsets through a low-pass filter.

However, there is a problem in that the impedance of the output stage is increased while a clock is required to control the switch. This is a way to somewhat solve the problem of passive low-pass filter impedance for analog voltage signal transfer to 12-bit SAR ADC. The voltage α at the ADC output is the basis for ensuring linearity when considering the piezoresistive characteristics of PVDF-rGO.

The linearity of the system including PVDF-rGO sensor material and ROIC has the advantage that pressure can be measured with stable performance and reliability. Therefore, we can see that the linearity of the system is guaranteed to be within the application pressure range we will be using, although this is not guaranteed over the entire range. 29 shows the charge-to-digital converter mode operation when PVDF-rGO acts as a piezoelectric material.

In the transresistance stage, there is a zero bias voltage in the PVDF-rGO due to the common mode voltage at both ends. The amount of charge generated by PVDF-rGO was observed in the form of voltage by varying the intensity and period of the applied vibration. This makes continuous blood pressure measurement difficult and the volume of the device is also inconvenient to carry.

Therefore, there is a tendency to measure users' blood pressure as a minimum limit using ECG and PPG [16].

Fig. 2. Worldwide wearable electronics market share from 2011 to 2018.

Conclusions

Wearable Technology and Wearable Devices: Everything You Need to Know." Wearable Devices Magazine, http://www.wearabledevices.com/what-is-a-wearable-device/, March 2014, Web. 3] “Digitsole smartshoe | The World's First Intelligent Sneaker,” KICKSTARTER, https://www.kickstarter.com/projects/141658446/digitsole-smartshoe-the-worlds-first-intelligent-s, 2017, web. 5] Erich, “The status of Wearable Electronics,” talk2myShirt, http://www.talk2myshirt.com/blog/archives/69, November 2006, Web.

MULTIBRIEFS: EKSKLUZIVNO, http://exclusive.multibriefs.com/content/printed-electronics-allow-technological-leap-in-wearable-devices/science-technology, maj, 2017, splet. 10] Subin Choi, "Multi-Sensor Mobile Interface for Industrial Environment and Healthcare Monitoring," IEEE Transactions on Industrial Electronics, marec 2017. 11] Marco Massarotto, "Two-stage Differential Charge and Transresistance Amplifiers," IEEE Transaction on Instumentation in merjenje, februar 2008.

Hopkins, "High Frequency Amplifiers for Piezoelectric Sensors Noise Analysis and Reduction Techniques", IEEE Instrumentation and Measurement Technology Conference (ICMTC) Proceedings, 2015. Ruedi, “Ultra low power microelectronics for wearable and medical devices”, Design, Automation & Test in Europe Conference & Exhibition (DATE), 2017. 18] Kwangmuk Lee, “Een draadloze ExG-interface voor patch-type ECG-holter en EMG-gestuurde robothand”, Sensors, 16 augustus 2017.

CLK_GEN)

SIGNAL_OUT)

AMP_KSM_FINAL)

VBIAS_AMP_KSM)

VBIAS_KSM_V2)

CONTROL_LOGIC_LMODE)

PGA_V9)

A Piezo-sensor Readout Integrated Circuit for Multifunctional Electronic Skins

Contents

Introduction

Conclusions