| In recent years,with the continuous development of the Internet of Things and biomedical technology.People are paying more and more attention to the combination of biological signal detection and Internet of Things.This come up with more requirements for the wireless sensor node,more complex functions,lower cost and lower power consumption.RFID tag are widely used in short-distance wireless sensing nodes due to their low power consumption,easy integration,and could short-distance communication.Using semi-active RFID to realize biological signal detection and transmission has great advantages in area and price.In order to detect biological signals,this paper designs a sensor read-out circuit suitable for wireless sensing nodes based on the principles of biological signal sensors.The read-out circuit is composed of a lossless current detection,a voltage quantization circuit based on TDC,and a low-noise Low Dropout Regulator.Based on the non-destructive current detection technology,from the perspective of low-power and low-cost applications of RF chips,according to the traditional mirror power MOSFET current detection technology,a low-power,high-precision current detection circuit is designed,and the circuit is improved.The process instability of linear region MOS current mirror is alleviated,and the loop gain and current detection accuracy are improved.Based on the TSMC 0.18μm CMOS process,The simulation show that when the current detection range is 30μA--450μA,the current detection accuracy is above98.87%,and the circuit power consumption is 4.5μW.The quantization circuit which is based on TDC is composed of a vltage shift circuit and a voltage controlled oscillator.In order to quantify the signal well,a high-linearity and low-power voltage shift circuit is designed to shift the detection signal to a better linearly input range of the voltage-controlled oscillator.In order to complete the low-voltage shift operation and consider the demand for low power consumption,the traditional shift op amp input stage and the rail-to-rail op amp output stage are combined to complete the low-potential shift function.The simulation shows that the lowest potential of the circuit shift range is 30mV,the circuit system offset voltage is 0.188mV,the noise voltage is0.993mV,and the circuit power consumption is 3.6μW.In order to achieve the high linearity and good process characteristics of the voltage-controlled oscillator,this paper adopts the high linearity characteristic of the flow-controlled ring oscillator and the high-robustness of the voltage-controlled ring oscillator to design a high-linearity voltage-controlled oscillator.The simulation shows that when the voltage input range is0.33V-0.66V,the output frequency is 225kHz--450kHz,the linearity reaches 98.5%,the phase noise of the circuit is-50dBc/Hz,and the typical jitter value at the upper flip threshold is 32ns,and the power consumption It is 2.3μW.In order to achieve a stable voltage supply,this article analyzes the source of noise in a low-noise Low Dropout Regulator.A filter circuit is designed for external noise to filter out the noise from the reference circuit,and active resistors are used to reduce the circuit cost.A high-gain low-noise error amplifier is designed for reducing internal noise,and the loop gain is increased by high gain to reduce power supply noise’s influences.The simulation shows that the output noise voltage of the Low Dropout Regulator is 2.8mV;the power supply rejection ratio is-60dB,and the circuit power consumption is 450nW.The circuits mentioned above have been designed under the TSMC 0.18μm standard COMS process,and the layout is designed and circuit simulated by Cadence.The simulation results show that the circuit can meet the needs of wireless sensor nodes and biosensor port circuits. |
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