CN112014647B - Capacitance detection method capable of inhibiting temperature drift - Google Patents

Abstract

The invention discloses a capacitance detection method capable of suppressing temperature drift, comprising steps: (1) the signal link is connected to the capacitance sensing unit, the reference link signal chain is similar, and the capacitance sensing unit is not connected; (2) in the In the PH1 phase, charge the capacitor of the signal link to Vcharge, and charge the capacitor of the reference link to alpha*Vcharge; (3) In the PH2 phase, connect the signal link to the positive terminal of the capacitor voltage converter, and charge the reference link Connected to the negative terminal of the capacitor-to-voltage converter, the transferred charge Vcharge*(Cuser+Cpath1)‑Vharge*alpha*Cpath2; (4) The final transferred charge is Vcharge*Cuser, which is quantified by the analog-to-digital conversion circuit to obtain the human body Close to the capacitor Cuser. The capacitance detection method of the present invention sets two signals, one signal is a signal link with a capacitance sensing unit, and the other is a reference link without a sensing unit; by giving the signal link and the reference link an input The weighted difference method is used at the end to match the environmental changes of the signal link and suppress temperature drift.

Description

A capacitive detection method that can suppress temperature drift

technical field

The invention relates to the field of proximity detection, in particular to a capacitance detection method capable of suppressing temperature drift.

Background technique

Capacitive sensors are widely used in electronic products such as mobile phones and watches, and are mainly used to identify the distance between the human body and electronic products. The specific identification principle is to distinguish the distance between the human body and the electronic product by detecting the capacitance value between the human body and the capacitive sensing element in the electronic product.

In practical applications, since the capacitive sensing unit is generally located on the surface of electronic products, and the chip used to collect signals is located on the internal motherboard, the wiring from the chip to the sensing unit will also generate parasitic capacitance, and the wiring The parasitic capacitance on the line is easily affected by the surrounding environment (temperature and humidity), which affects the judgment of the human body approaching the signal.

Contents of the invention

Purpose of the invention: In view of the above problems, the present invention proposes a capacitance detection method that can suppress temperature drift, and suppress temperature drift by weighting the signal link and the reference link at the input end to find the difference.

Technical solution: In order to achieve the purpose of the present invention, the technical solution adopted in the present invention is: a capacitance detection method that can suppress temperature drift, and two signals are set, one signal is a signal link with a capacitance sensing unit, and the other is a signal link with a capacitance sensing unit. It is a reference link without a sensing unit, and the routing of the reference link is similar to that of the signal link; the detection capacitance is obtained by weighting the signal link and the reference link to obtain the difference.

Further, the weighting is to multiply the reference link by a coefficient to amplify or reduce the signal of the reference link in equal proportion.

Further, specifically include steps:

(1) The signal link is connected to the capacitive sensing unit, the signal link of the reference link is similar, and the capacitive sensing unit is not connected;

(2) In the PH1 phase, charge the capacitance of the signal link to Vcharge, and charge the capacitance of the reference link to alpha*Vcharge;

(3) In the PH2 phase, connect the signal link to the positive terminal of the capacitor voltage converter, connect the reference link to the negative terminal of the capacitor voltage converter, and transfer the charge Vcharge*(Cuser+Cpath1)-Vcharge*alpha *Cpath2;

Wherein, Cuser is the human body proximity capacitance signal of the sensing unit, Cpath1 is the parasitic capacitance signal on the signal link, and Cpath2 is the parasitic capacitance signal on the reference link; Cpath1/Cpath2=alpha;

(4) The final transferred charge is Vcharge*Cuser, which is quantified by an analog-to-digital conversion circuit to obtain the human body proximity capacitance Cuser.

Further, the two waveforms of PH1/PH2 have a phase difference of 180 degrees, which is a non-overlapping clock.

Further, the trace length of the reference link is shorter than the trace length of the signal link, Cpath1>=Cpath2.

Beneficial effects: the capacitive detection method capable of suppressing temperature drift in the present invention requires two signals, one signal is a signal link with a capacitive sensing unit, and the other is a reference link without a sensing unit, and the reference link The routing of the road is similar to that of the signal chain. By weighting the difference between the signal link and the reference link at the input end, and multiplying the reference link by a coefficient, the signal of the reference link is amplified or reduced proportionally, so as to match the environmental changes of the signal link.

Description of drawings

Fig. 1 is the schematic diagram of weighted difference between signal link signal and reference link signal of the present invention;

Fig. 2 is the equivalent capacitance circuit diagram of signal link and reference link provided by the present invention;

Fig. 3 is the equivalent circuit diagram that the present invention provides for capacitance detection;

Fig. 4 is the timing diagram of chip operation provided by the present invention;

FIG. 5 is a circuit diagram for generating the voltage Vcharge*alpha.

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

A proximity detection sensor based on a capacitance signal includes a capacitance-to-voltage converter, an analog-to-digital conversion circuit, a digital filter, and a proximity detection algorithm circuit.

Among them, the capacitor-to-voltage converter is used to convert the capacitor signal into a voltage signal; the high-precision analog-to-digital conversion circuit ADC is used to quantify the voltage signal; the digital filter and the proximity detection algorithm circuit are used to convert the output data of the analog-to-digital converter Perform filtering and downsampling, and extract effective proximity signals to judge the distance between the object and the sensor.

Also included are fixed capacitance compensation capacitors to compensate for fixed capacitance on capacitive sensors.

Wherein, the capacitor-to-voltage converter includes a charge amplifier A.

The capacitive detection method that can suppress temperature drift in the present invention uses the above-mentioned proximity detection sensor for detection. This method requires two signals, one signal is a signal link with a capacitive sensing unit, and the other is a signal link without a sensor The reference link of the unit, the routing of the reference link is similar to the signal link.

The method of using the reference link can offset part of the influence of the environment. However, in the actual application process, the traces of the reference link cannot be exactly the same as the traces of the signal link. The changes in the environmental capacitance of the two are not exactly the same, but There is a certain proportion.

By weighting the difference between the signal link and the reference link at the input end, and multiplying the reference link by a coefficient, the signal of the reference link is amplified or reduced proportionally, so as to match the environmental changes of the signal link.

As shown in Figure 1, it is a schematic diagram of the weighted difference between the signal link signal and the reference link signal. The signal link is connected to the capacitive sensing unit through pcb traces, connected to the positive terminal of the capacitor voltage converter, and the reference link The pcb trace of the circuit board is similar to the signal chain, but it is not connected to the capacitive sensing unit, but connected to the negative terminal of the capacitive voltage converter.

As shown in FIG. 2 , it is a circuit diagram of an equivalent capacitance of a signal link and a reference link. Wherein, Cuser is a human body approaching capacitance signal sensed by the capacitance sensing unit, which is an effective signal. Cpath1 is a parasitic capacitance signal on the signal link trace. Cpath2 is the parasitic capacitance signal on the reference link trace. Since there is a certain difference between the traces of the reference link and the traces of the signal link, generally, the length of the traces of the reference link is shorter than that of the signal link, so Cpath1>=Cpath2, Cpath1/Cpath2=alpha.

As shown in Figure 3, it is a schematic diagram of capacitance detection. In the PH1 phase, the capacitance of the signal chain is charged to Vcharge, and the capacitance of the reference chain is charged to alpha*Vcharge. In the PH2 phase, the capacitor of the signal link is connected to the positive terminal of the capacitor-to-voltage converter, and the capacitor of the reference link is connected to the negative terminal of the capacitor-to-voltage converter, so the total amount of charge transferred is Vcharge*(Cuser+Cpath1 )-Vharge*alpha*Cpath2.

Since Cpath1=alpha*Cpath2, the final transferred charge amount is Vcharge*Cuser, and the transferred charge amount has nothing to do with the capacitance on the wiring. Finally, it is quantized by ADC, and the value obtained after quantization is close to the capacitance value of the human body, which has nothing to do with the environmental capacitance on the wiring, so that the environmental drift is well suppressed. Vcharge is the reference voltage, which is generated by the reference source in the chip.

As shown in Figure 4, it is the waveform diagram of PH1/PH2 during the sampling process. The two waveforms are 180 degrees out of phase and are non-overlapping clocks.

As shown in FIG. 5 , it is a circuit diagram for generating a voltage Vcharge*alpha, by adjusting the value of rfb1/rfb2 so that (rfb1+rfb2)/rfb2=alpha, the output voltage can be Vcharge*alpha.

Claims (4)

1. A capacitance detection method that can suppress temperature drift, is characterized in that, specifically comprises steps: (1) The signal link is connected to the capacitive sensing unit, and the reference link is not connected to the capacitive sensing unit; (2) In the PH1 phase, charge the capacitance of the signal link to Vcharge, and charge the capacitance of the reference link to alpha*Vcharge; (3) In the PH2 phase, connect the signal link to the positive terminal of the capacitor voltage converter, connect the reference link to the negative terminal of the capacitor voltage converter, and transfer the charge Vcharge*(Cuser+Cpath1)-Vcharge*alpha *Cpath2; Wherein, Cuser is the human body proximity capacitance signal of the sensing unit, Cpath1 is the parasitic capacitance signal on the signal link, and Cpath2 is the parasitic capacitance signal on the reference link; Cpath1/Cpath2=alpha; (4) The final transferred charge is Vcharge*Cuser, which is quantified by an analog-to-digital conversion circuit to obtain the human body proximity capacitance Cuser. 2. according to the capacitance detection method that temperature drift can be suppressed according to claim 1, two-way signals are set, and one-way signal is the signal link with capacitance sensing unit, and the other way is the reference link without sensing unit, through The detection capacitance is obtained by weighting the signal link and the reference link to obtain the difference. The weighting is to multiply the reference link by a coefficient, and the signal of the reference link is amplified or reduced in proportion. 3. The capacitance detection method capable of suppressing temperature drift according to claim 1, wherein the two waveforms of PH1/PH2 have a phase difference of 180 degrees, and are non-overlapping clocks. 4. The capacitive detection method capable of suppressing temperature drift according to claim 1, characterized in that, the trace length of the reference link is shorter than the trace length of the signal link, and Cpath1>=Cpath2.

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