High accuracy capacitive readout circuit with temperature compensation

Abstract

The invention discloses a high accuracy capacitive readout circuit with temperature compensation, belonging to the design field of integrated circuits. The circuit realizes high accuracy capacitive readout owing to the adoption of a chopping modulation technology, and can simultaneously realize temperature compensation by adjusting temperature characteristics of internal voltage reference. The circuit comprises an oscillator, a voltage reference source, a full-differential operational amplification unit, a common-mode operational amplification unit, a low pass filter, a switch device and a digital circuit. The voltage reference source generates a square wave in cooperation with a single-pole double throw switch, and the square wave is applied to an intermediate polar plate of a differential capacitance to be detected in order to implement modulation. The full-differential operational amplification unit and a feedback capacitance constitute a charge integrator to detect a transfer charge formed by the variation of the capacitance to be detected. Demodulation is realized by the switch device and the low pass filter. Both an input end and an output end of the full-differential operational amplification unit are set through a switch cycle. The common-mode operational amplification unit and the feedback capacitance constitute a common-mode feedback loop which is connected with the input end of the full-differential operational amplification unit to play the role of inputting common-mode voltage stably.

Description

technical field [0001] The present invention relates to a capacitance readout circuit, and more particularly to a high-precision readout circuit suitable for capacitive micro-electromechanical sensors. Background technique [0002] With the continuous advancement of micro-electromechanical systems (MEMS) technology, capacitive micro-electromechanical sensors have emerged at the historic moment. It has the advantages of small size, low power consumption, fast response and easy integration. International academic and industrial circles have paid attention to and researched on it. heating up. Products such as pressure sensors, accelerometers and angular velocity meters developed with this technology are widely used in various fields of civil and military use. [0003] This kind of sensor can usually be equivalent to a pair of differential variable capacitors, and the variation of the capacitance directly reflects the size of the external physical quantity to be measured. Howe...

AI Technical Summary

Problems solved by technology

The difficulty of the continuous-time current readout method lies in the realization of the feedback resistor. Usually, the resistor should reach the order of gigaohms to achieve an ideal detection sensitivity. It is necessary to realize such a large resistor in an integrated circuit and have a certain linearity. Extremely difficult, often requiring complex compensation circuits that increase system power consumption [3]

The difficulty in the design of the continuous-time voltage-type capacitance readout circuit lies in the realization of the bias at the connection end of the capacitance to be measured.

One end of this node is usually connected to the capacitor plate, and the other end is connected to the gate of the op amp input MOS transistor. It is a high-impedance node, and it is difficult to establish its DC level.

If the bias is not ideal, it will seriously limit the linear range of the readout circuit, and even cause the circuit to not work properly [4]

[0005] The environment with large temperature changes will inevitably impose strict requirements on the temperature drift performance of high-precision capacitance readout. This is a common problem in many application fields and brings considerable challenges to the design.

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