A Resistive Measurement Readout IC Based On ZCB Integrator

With the continuous development of the Internet of Things technology,more and more different types of sensors are being applied to the latest electronic products.Resistive sensor have attracted much attention in the industry due to its wide application scenarios(such as sensing of temperature,humidity,pressure and other physical quantities).As a bridge between the analog quantity in nature and the digital quantity used for computer data processing,Readout IC(ROIC)has always been an indispensable part of the sensing system.Sigma-Delta Analog to Digital Converter(ADC)which relies on oversampling and noise shaping technology can achieve high precision analog-to-digital conversion with a lower cost,so it is more suitable for the current IoT application scenarios than other types of analog-todigital converters.However,the traditional Sigma-Delta ADC also has some shortcomings that need to be improved: in order to achieve more accurate charge transfer in the sampling/integration phase,the Operational Transconductance Amplifier(OTA)in the ADC modulator's integrator is necessary.However,the use of OTA will cause the problem of loop stability.At the same time,due to the requirements of bandwidth,slew rate and other indicators,Power consumption has always been a problem in practical circuit design.As a result,designing an OTA that meets such performance requirements has considerable challenges.Based on the above discussion,a Sigma-Delta resistive measurement readout IC based on ZCB(Zero-crossing-based)integrator is designed in this paper.By using a switched capacitor integrator designed with ZCB circuit technology,the same charge transfer function as an OTAbased integrator can be achieved,while loop stability issues can be avoided and power consumption can be reduced.The bias current multiplexing of the resistance sensor which embedded in the readout circuit can greatly reduce the static power consumption of the readout chip.In addition,by disassembling the arms of a traditional Wheatstone bridge into two branches and connecting them to the "pseudo-differential" measurement scheme of the measurement path,the chip can still have a good power-supply ratio in the unbalanced state of the bridge-rejection ratio(PSRR),and avoid the static power consumption of the bridge itself.The resistance measurement readout chip designed in this paper is taped out using Global Foundries 0.18?m CMOS process,and tested and verified under different sensor resistance values,temperature,power supply voltage and other conditions.The results show that the single-resistance measurement mode and the bridge measurement mode have achieved an equivalent resolution of 13-bit rms noise at a conversion rate of 8KS /s.In addition,the singleresistance measurement mode has achieved 250 ppm non-linearity and the power consumption is 34.3?W,PSRR is 45 dB,power supply and temperature coefficient are 1%/V and 216 ppm/?,respectively.In contrast,the non-linearity in the bridge mode is 400 ppm,the power consumption is 58.6?W,the PSRR is increased to 65 dB,and the power supply and temperature coefficient are improved to 0.23%/V and 55ppm/?,which is more obvious promotion than the single resistance measurement mode.