CN112014647A - Capacitance detection method capable of restraining temperature drift - Google Patents

Abstract

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

Description

A Capacitance 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 the electronic product, and the chip used for signal acquisition is located on the internal motherboard, the wiring from the chip to the sensing unit will also generate parasitic capacitance, and The parasitic capacitance on the line is easily affected by the surrounding environment (temperature and humidity), which affects the judgment of the human body's proximity signal.

SUMMARY 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 suppresses temperature drift by weighting the signal link and the reference link at the input end to obtain a 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, setting two signals, one signal is a signal link with a capacitive sensing unit, and the other is a signal link with a capacitive sensing unit. For the reference link without the sensing unit, the wiring of the reference link is similar to the signal link; the detection capacitance is obtained by weighting the signal link and the reference link to calculate the difference.

Further, the weighting is to multiply the reference link by a coefficient, and the signal of the reference link is proportionally enlarged or reduced.

Further, it specifically includes the steps:

(1) The signal link is connected to the capacitive sensing unit, the reference link signal 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 amount Vcharge*(Cuser+Cpath1)-Vharge*alpha *Cpath2;

Among them, 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 transfer charge is Vcharge*Cuser, which is quantified by the 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 less than the trace length of the signal link, Cpath1>=Cpath2.

Beneficial effects: The capacitance detection method that can suppress temperature drift according to 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. The routing of the circuit is similar to that of the signal link. By weighting the signal link and the reference link at the input to find the difference, multiplying the reference link by a coefficient, the signal of the reference link is proportionally enlarged or reduced, so as to match the environmental changes of the signal link.

Description of drawings

1 is a schematic diagram of the weighted difference between a signal link signal and a reference link signal according to the present invention;

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

3 is an equivalent circuit diagram provided by the present invention for capacitance detection;

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

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

Detailed ways

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

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

Among them, the capacitance-to-voltage converter is used to convert the capacitance 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 an effective proximity signal to determine the distance between the object and the sensor.

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

Among them, a charge amplifier A is included in the capacitor-to-voltage converter.

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

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

By weighting the signal link and the reference link at the input to find the difference, multiplying the reference link by a coefficient, the signal of the reference link is proportionally enlarged or reduced, 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 capacitance sensing unit through the pcb trace, connected to the positive terminal of the capacitance-voltage converter, and the reference link The pcb trace is similar to the signal link, but it is not connected to the capacitive sensing unit, but is connected to the negative terminal of the capacitive voltage converter.

As shown in Figure 2, it is the equivalent capacitance circuit diagram of the signal link and the reference link. Among them, Cuser is the human body proximity capacitive signal sensed by the capacitive sensing unit, which is an effective signal. Cpath1 is the parasitic capacitance signal on the signal link trace. Cpath2 is the parasitic capacitance signal on the reference link trace. Because there are certain differences between the traces of the reference link and the traces of the signal link, in general, the traces of the reference link are shorter than the traces 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 link is charged to Vcharge and the capacitance of the reference link is charged to alpha*Vcharge. In the PH2 phase, the capacitance of the signal link is connected to the positive terminal of the capacitor-voltage converter, and the capacitance of the reference link is connected to the negative terminal of the capacitance-voltage converter, so the total transferred charge is Vcharge*(Cuser+Cpath1 )-Vharge*alpha*Cpath2.

Since Cpath1=alpha*Cpath2, the final amount of charge transferred is Vcharge*Cuser, and the amount of transferred charge has nothing to do with the capacitance on the trace. Finally, through ADC quantization, the value obtained after quantization is close to the capacitance value of the human body, and has nothing to do with the environmental capacitance on the trace, so 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 in the sampling process. The two waveforms are 180 degrees out of phase and are non-overlapping clocks.

As shown in FIG. 5 , in order to generate the circuit diagram of the voltage Vharge*alpha, by adjusting the value of rfb1/rfb2 to make (rfb1+rfb2)/rfb2=alpha, the output voltage can be Vcharge*alpha.

Claims (5)

1. A capacitance detection method capable of suppressing temperature drift is characterized in that, two signals are set, one signal is a signal link with a capacitive sensing unit, and the other is a reference link without a sensing unit, the reference link The routing of the circuit is similar to that of the signal link; the detection capacitance is obtained by weighting the difference between the signal link and the reference link. 2 . The capacitance detection method capable of suppressing temperature drift according to claim 1 , wherein the weighting is to multiply the reference link by a coefficient, and the signal of the reference link is proportionally enlarged or reduced. 3 . 3. The capacitance detection method capable of suppressing temperature drift according to claim 1, wherein the method specifically comprises the steps: (1) The signal link is connected to the capacitive sensing unit, the reference link signal 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 amount Vcharge*(Cuser+Cpath1)-Vharge*alpha *Cpath2; Among them, 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 transfer charge is Vcharge*Cuser, which is quantified by the analog-to-digital conversion circuit to obtain the human body proximity capacitance Cuser. 4 . The capacitance detection method capable of suppressing temperature drift according to claim 3 , wherein the two waveforms of PH1 and PH2 have a phase difference of 180 degrees and are non-overlapping clocks. 5 . 5 . The capacitance detection method capable of suppressing temperature drift according to claim 3 , wherein the trace length of the reference link is smaller than the trace length of the signal link, Cpath1 >= Cpath2 . 6 .

Images