WO2016112720A1

WO2016112720A1 - Low-power-consumption capacitive sensor interface circuit

Info

Publication number: WO2016112720A1
Application number: PCT/CN2015/092249
Authority: WO
Inventors: 何怡刚; 邓芳明; 佐磊; 尹柏强; 李兵; 袁莉芬; 项胜; 何威
Original assignee: 合肥工业大学
Priority date: 2015-01-13
Filing date: 2015-10-20
Publication date: 2016-07-21
Also published as: CN104485938A

Abstract

Provided is a low-power-consumption capacitive sensor interface circuit, constituted by a sensor control oscillator, a multiplexing frequency divider, and a multiplexer; the output terminal of the sensor control oscillator is connected to the input terminal of the multiplexing frequency divider; the output terminal of the multiplexing frequency divider is connected to the input terminal of the multiplexer; the output terminal of the multiplexer is connected to the input terminal of a counter; the other input terminal of the counter is externally connected to a clock signal; the output terminal of the counter is a digital signal output terminal. The interface circuit employs an all-digital architecture to process a sensor signal in a frequency domain; the configuration of the circuit is simple and the circuit can operate at a relatively low power supply voltage, which is advantageous to reducing the overall power consumption of the circuit; the area of the chip is reduced and the effect on the process is minimal.

Description

Low-power capacitive sensor interface circuit

Technical field

The invention belongs to the field of sensor interface circuits, and in particular relates to a low power capacitive sensor interface circuit.

Background technique

Capacitive sensors use the principle of capacitors to convert non-electricity to be measured in the external environment into capacitance, and then convert the change in capacitance into output such as voltage and frequency. It is widely used in pressure, humidity, acceleration, displacement, and gas. Wait for the test. At present, thanks to the development of microelectronics technology, the CMOS process, which is the mainstream process of integrated circuit manufacturing, can integrate capacitive sensors with readout circuits and signal processing circuits on the same chip, which not only greatly reduces system cost, but also greatly reduces system cost. Capacitive sensors can be used in integrated sensor designs.

The Internet of Things has been identified as one of China's strategic emerging industries. The development of wireless sensor network nodes and RFID tags as key modules of the Internet of Things has a large demand for low-power integrated sensors. For capacitive sensors, the sensor is connected to the interface circuit in the form of a capacitor, so the main power consumption of the capacitive sensor comes from the interface circuit. The traditional capacitive sensor interface circuit processes the sensor signal in the voltage amplitude range. First, a capacitance-voltage converter is used to generate a voltage signal proportional to the difference between the sensor capacitance and the reference capacitance, and then the voltage signal is converted into a phase by an analog-to-digital converter. Corresponding digital signal output. This design method can achieve high speed and high resolution performance, but due to the use of operational amplifiers, the circuit structure is complex, requires a higher power supply voltage, and the overall power consumption is very high, which is not suitable for low power applications.

Summary of the invention

The technical problem to be solved by the present invention is to overcome the shortcomings of the existing capacitive sensor interface circuit in low-power design, and provide an oscillator-based low-power capacitive sensor interface circuit, which is processed in the frequency domain. The sensor signal has a simple circuit structure and can work at a lower power supply voltage, which is beneficial to reducing the overall power consumption of the circuit.

The technical solution adopted by the present invention to solve the technical problem thereof:

A low-power capacitive sensor interface circuit consisting of a sensor-controlled oscillator, a multi-way divider, a multiplexer and a counter. The output of the sensor-controlled oscillator is connected to the input of the multi-way divider, multi-channel The output end of the frequency divider is connected to the input end of the multi-way selector. The output end of the multi-channel selector is connected to one input end of the counter, and the other input end of the counter is externally connected with a clock signal; the output end of the counter is a digital signal output end.

The sensor control oscillator is used to perform conversion of the sensor capacitance value to a corresponding oscillation frequency.

The multi-way frequency divider is used to generate a multi-channel oscillation frequency, and the influence of the deviation of the sensor capacitance value and the oscillation frequency of the oscillator due to the process deviation on the stability of the interface circuit is eliminated.

The multiplexer is configured to select an oscillating frequency suitable for the operation of the counter from among the multiple frequencies output by the multiplexer.

The counter is controlled by the clock signal to calculate the number of pulses received by the multiplexer in one cycle, thereby generating a corresponding digital signal output.

The sensor controlled oscillator, demultiplexer, multiplexer and counter can all be designed using digital integrated circuits.

Preferably, the sensor controlled oscillator adopts a ring oscillator structure, and the ring oscillator is composed of an odd number of inverters connected end to end to form a feedback loop, and the sensor capacitor is connected in parallel to the feedback loop.

Preferably, the inverter employs a current-starved inverter, the current of which is limited by a current mirror.

The interface circuit of the invention processes the sensor signal in the frequency domain, adopts an all-digital structure, has a simple circuit structure, can work at a lower power supply voltage, is beneficial to reducing the overall power consumption of the circuit, saves the chip area, and is less affected by the process.

DRAWINGS

1 is a structural diagram of a capacitive sensor interface circuit of the present invention;

2 is a structural diagram of a sensor controlled oscillator of the present invention;

Figure 3 is a schematic diagram of a current limited inverter;

4 is a structural diagram of a multiplexer of the present invention;

Figure 5 is a structural diagram of a multiplexer of the present invention;

Figure 6 is a diagram showing the structure of a counter of the present invention;

Figure 7 is a graph showing the relative humidity of the integrated humidity sensor tested and the interface circuit output.

detailed description

The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. The following preferred embodiments are merely illustrative of the invention and are not to be construed as limiting.

Taking the design and manufacture of integrated humidity sensor chip by TSMC 0.18μm CMOS process, the interface circuit of the chip adopts the low-power capacitive sensor interface circuit of the invention, and the sensor controls the oscillator, multi-way frequency divider and multi-channel. The selector and counter are constructed.

Referring to FIG. 1, the output end of the sensor control oscillator is connected to the input end of the multi-way frequency divider, and the output end of the multi-way frequency divider is connected to the input end of the multi-way selector, and the output end of the multi-way selector is connected to an input of the counter. At the other end, the other input of the counter is externally connected to the clock signal; the output of the counter is the corresponding number of the sensor Word signal output.

Referring to FIG. 2, the sensor-controlled oscillator adopts a ring oscillator structure, and three end-to-end inverters form a feedback loop. The humidity sensor capacitor C _{sens is} connected in parallel to the feedback loop to generate a frequency of f _sens oscillation frequency.

Referring to Figure 3, the inverter employs a current-starved inverter that can use a 1V supply voltage with a current mirror current of 10μA.

The demultiplexer is used to generate a multi-channel oscillation frequency. In this embodiment, two-way, four-, four-, eight-, and sixteen-way divisions are used (see FIG. 1).

The multiplexer is configured to select an oscillating frequency suitable for the counter operation from the multiple frequencies output by the multiplexer. In this embodiment, the 4-to-1 channel mode is selected, and the 4-way channel is selected.

The counter is controlled by the system clock signal to calculate the number of pulses received by the multiplexer in one cycle, thereby generating a corresponding digital signal output. In this embodiment, a 10-bit counter is used, and the frequency of the external clock signal is 1 kHz, and the output of the counter is b _out is the digital signal output corresponding to the sensor.

The sensor-controlled oscillator, multi-way divider (see Figure 4), multiplexer (see Figure 5), and counter (see Figure 6) can all be designed with a basic digital integrated circuit, eliminating the need for an op amp, circuit structure Simple, it can work at lower supply voltages.

7 is a graph showing the relative humidity of the integrated humidity sensor tested and the interface circuit output. As can be seen from FIG. 7, the capacitive sensor interface circuit of the present invention achieves good linearity.

Claims

A low-power capacitive sensor interface circuit, characterized in that it is composed of a sensor-controlled oscillator, a multi-way frequency divider, a multiplexer and a counter, and an output of the sensor-controlled oscillator is connected to an input of a multi-way frequency divider The output end of the multi-way frequency divider is connected to the input end of the multi-way selector. The output end of the multi-way selector is connected to one input end of the counter, and the other input end of the counter is externally connected with a clock signal; the output end of the counter is a digital signal. Output

The sensor control oscillator is configured to perform converting the sensor capacitance value into a corresponding oscillation frequency;

The multi-way frequency divider is configured to generate a multi-channel oscillation frequency, and eliminate the influence of the deviation of the sensor capacitance value and the oscillation frequency of the oscillator on the stability of the interface circuit caused by the process deviation;

The multiplexer is configured to select an oscillating frequency suitable for a counter operation from among multiple frequencies output by the multiplexer;

The counter is controlled by the system clock signal to calculate the number of pulses received by the multiplexer in one cycle, thereby generating a corresponding digital signal output.
The low power capacitive sensor interface circuit of claim 1 wherein said sensor controlled oscillator, demultiplexer, multiplexer and counter are each designed using a digital integrated circuit.
The low-power capacitive sensor interface circuit according to claim 1 or 2, wherein the sensor-controlled oscillator adopts a ring oscillator structure, and an odd-numbered inverters are connected end to end to form a feedback loop, and the sensor capacitors are coupled. Into the feedback loop.
The power consuming capacitive sensor interface circuit according to claim 3, wherein the inverter employs a current limited inverter, and the current of the inverter is limited by the current mirror.