Contact detection circuit and denoising circuit thereof

Abstract

The invention discloses a denoising circuit connected to two pins of a chip. The denoising circuit comprises a shielding shunt, a driving shunt and an intermediate capacitor, the shielding shunt is connected among the first pin of the chip, the ground voltage and the shielding metal. And the driving shunt is connected between the second pin of the chip and a load. And the intermediate capacitor is connected between the shielding shunt and the driving shunt. The first pin and the second pin are respectively used for outputting sine wave signals.

Description

Technical Field

[0001] The present invention relates to a contact detection circuit, and more particularly to a contact detection circuit and a denoising circuit thereof which reduce or even eliminate noise interference when detecting a touch event by configuring an active denoising circuit. Background Art

[0002] By using the capacitance detection device to measure the capacitance change, it can be used to determine whether the user touches the capacitance detection device and perform corresponding control on the electronic device equipped with the capacitance detection device.

[0003] However, when detecting minute capacitance changes, the detection results may be changed due to noise in the system, resulting in misjudgment.

[0004] Therefore, how to eliminate noise interference is one of the issues that the capacitance detection device needs to overcome. Summary of the invention

[0005] In view of this, the present invention provides a contact detection circuit and a denoising circuit thereof which are configured with an active denoising circuit to reduce or even eliminate noise interference.

[0006] The present invention provides a contact detection circuit and a de-noising circuit thereof, in which shielding metal is arranged around a driving line between a de-noising circuit and a load and a sine wave signal is provided to the shielding metal.

[0007] The invention provides a noise removal circuit without using an inductor element and a contact detection circuit using the noise removal circuit.

[0008] The present invention provides a de-noising circuit for connecting between two pins of a chip and a load. The de-noising circuit comprises a first resistor, a first capacitor, a second resistor, a second capacitor, a third resistor, a third capacitor and a shielding metal. The first resistor is connected between the first pin of the chip and a first node. The first capacitor is connected between the first node and a ground voltage. The second resistor is connected between the second pin of the chip and a second node. The second capacitor is connected between the first node and the second node. The third resistor is connected to the second node. The third capacitor is connected between the third resistor and a driving line, wherein the driving line is used to connect to the load. The shielding metal surrounds the driving line.

[0009] The present invention also provides a contact detection circuit for detecting impedance changes of a load. The contact detection circuit includes a chip and a de-noising circuit. The chip includes a first pin and a second pin. The de-noising circuit is connected between the chip and the load and includes a first resistor, a first capacitor, a second resistor, a second capacitor, a third resistor, a third capacitor and a shielding metal. The first resistor is connected between the first pin of the chip and a first node. The first capacitor is connected between the first node and a ground voltage. The second resistor is connected between the second pin of the chip and a second node. The second capacitor is connected between the first node and the second node. The third resistor is connected to the second node. The third capacitor is connected between the third resistor and a driving line, wherein the driving line is used to connect to the load. The shielding metal surrounds the driving line.

[0010] The present invention also provides a contact detection circuit for detecting impedance changes of a load. The contact detection circuit comprises a chip, a shielding metal, a shielding shunt, a driving shunt and an intermediate capacitor. The chip comprises a first pin and a second pin for outputting a sine wave signal respectively. The shielding shunt is connected between the first pin, a ground voltage and the shielding metal, and is used to guide noise to the ground voltage. The driving shunt is connected between the second pin and the load. The intermediate capacitor is connected between the shielding shunt and the driving shunt.

[0011] In order to make the above and other purposes, features and advantages of the present invention more obvious, the following will be described in detail with reference to the accompanying drawings. In addition, in the description of the present invention, the same components are represented by the same symbols, which are hereby described together. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a block diagram of a contact detection circuit according to an embodiment of the present invention;

[0013] Figure 2 is a circuit diagram of a denoising circuit according to an embodiment of the present invention;

[0014] Figure 3 is a cross-sectional view of configuring multiple layers of shielding metal in a circuit board of a contact detection circuit according to an embodiment of the present invention;

[0015] Figure 4 is a circuit diagram of a noise reduction circuit and a shielded metal connection load according to an embodiment of the present invention; and

[0016] Figure 5 Schematic diagram of node voltage and line current of a denoising circuit according to an embodiment of the present invention.

[0017] Description of Reference Numerals

[0018] 200 Circuit Board

[0019] 21 Chip

[0020] 11, 10 pins

[0021] 211 First Signal Source

[0022] 210 Second signal source

[0023] 22 Denoising Circuit

[0024] 23 Drive Line

[0025] 24 Shielding Metal

[0026] 25 Load DETAILED DESCRIPTION

[0027] The object of the present invention is to provide a de-noising circuit having an active shielding metal 24 disposed around a driving line 23 and a contact detection circuit using the de-noising circuit. The de-noising circuit includes a de-noising capacitor C1 for guiding noise to a ground voltage to reduce interference with a read signal, such as Io described later. The de-noising circuit also includes a current limiting resistor R1 for reducing the current flowing to a signal source.

[0028] The contact detection circuit of the present invention is connected to a device having at least one conductive area 25 (such as Figure 1 In an embodiment, the device is a steering wheel for a vehicle. Other components of the steering wheel for a vehicle (such as Figure 1 The operation of the heater 92 shown in the figure will generate noise to the conductive area 25. Conventionally, metal 94 (as a shielding component) is inserted between the conductive area 25 and the noise source (i.e., the heater 92) to block its noise. Since the contact detection circuit of the embodiment of the present invention has a de-noising function, the de-noising circuit can guide the noise generated by the noise source in the vehicle steering wheel to the ground through the de-noising capacitor C1 to further reduce noise interference. That is, the de-noising circuit of the embodiment of the present invention can guide the noise that interferes with the detection signal on the driving line 23 and the conductive area 25 to the ground.

[0029] Please refer to Figure 1 , which is a block diagram of a contact detection circuit according to an embodiment of the present invention. The contact detection circuit includes a chip 21, a de-noising circuit 22, a drive line 23, and a shielding metal 24 configured on a circuit board 200. The contact detection circuit is used to detect the impedance change of a load (e.g., a conductive area) 25 to determine whether the load 25 is touched by a user, that is, the impedance changes when touched. The circuit board 200 is, for example, a printed circuit board (PCB) or a flexible circuit board (flexible circuit board), and there is no specific limitation.

[0030] Before leaving the factory, the circuit board 200 carrying the chip 21, the de-noising circuit 22, the driving line 23 and the shielding metal 24 may form a module or a package, which has a contact point for connecting the load 25. Figure 4 In the example where the circuit board 200 is connected to the vehicle steering wheel 90, the vehicle steering wheel 90 has at least one conductive area 25 (e.g., 8 areas filled with diagonal lines are shown, but not limited to 8 conductive areas) for the user to touch. Therefore, the contact detection circuit of the embodiment of the present invention has at least one drive line 23 connected to the at least one conductive area 25 respectively. In the embodiment where the denoising circuit 22 is connected to multiple conductive areas 25 (each conductive area is shielded by a metal 94), the multiple drive lines 23 are surrounded by a shielding metal 24, and the shielding metal 24 surrounds all of the multiple drive lines 23. In another embodiment, each of the multiple drive lines 23 is surrounded by a corresponding shielding metal 24, that is, the contact detection circuit of the embodiment of the present invention is configured with multiple shielding metals 24.

[0031] The content of configuring the conductive area 25 on the vehicle steering wheel can be referred to, for example, the U.S. patent application No. US17 / 949,232 jointly owned by the same applicant in this case, the application date is September 21, 2022, and the invention name is "Hand-off detection device and vehicle control device", all of which are incorporated herein by reference, so it will not be repeated here.

[0032] The load 25 is, for example, an electrode on a car steering wheel, a capacitive touch panel for a computer, or other electronic devices that can detect impedance changes to determine a user contact event.

[0033] The chip 21 is used to send a driving signal to pass through the de-noising circuit 22 and the driving line 23 to the load 25, and read the current value Io of the de-noising circuit 22, but not limited to. The chip 21, more specifically, the processor therein (such as a specific application integrated circuit, a programmable logic gate array, etc.) calculates the change of the current value Io (or the voltage, the charging and discharging time of the capacitor) to determine whether the load 25 is touched by the user. The way in which the capacitive contact device detects contact based on the change of capacitance is known, and is not the main point of the present invention, so its content is not repeated here.

[0034] Figure 1The display chip 21 includes 24 pins or pads, a first signal source 211 and a second signal source 210. The first signal source 211 includes, for example, an operational amplifier (OP) for outputting a first signal to the de-noising circuit 22 via pin 11. The second signal source 210 includes, for example, another operational amplifier (OP) for outputting a second signal to the de-noising circuit 22 via pin 10. In one embodiment, the first signal and the second signal are the same sine wave signal (e.g. Figure 2 The same here means the same frequency, amplitude and phase. Figure 1 The chip 21 is also shown to be connected to a circuit board (shown as a PCB) 200 via pins 22 , but the connection is not limited to being via the pins 22 .

[0035] It should be noted that the chip 21 is not limited to include 24 pins, and the first signal source 211 and the second signal source 210 are not limited to be respectively connected to the pin 11 and the pin 10. When the first signal source 211 and the second signal source 210 provide driving signals (such as Isin) to the other two pins of the chip 21, the de-noising circuit 22 is also connected to the other two pins.

[0036] That is, in the present invention, the form of the chip 21 is not particularly limited, as long as it includes two pins or pads for connecting to the de-noising circuit 22 .

[0037] Please refer to Figure 2 , which shows a circuit diagram of a de-noising circuit 22 according to an embodiment of the present invention. The de-noising circuit 22 is connected between two pins of the chip 21 and the load 25 to reduce circuit noise and current value Is, so as to improve the accuracy of touch event determination and reduce the load of the first signal source 211.

[0038] The de-noising circuit 22 includes a shielding shunt, a driving shunt, a shielding metal 24, and an intermediate capacitor C0 connected between the shielding shunt and the driving shunt. The shielding shunt is connected to the first pin 11_p1 (eg Figure 1 The driving shunt is connected to the second pin 11_p0 (eg, Figure 1 The connection pin 10 (but not limited to) and the load 25. One end of the shielding metal 24 is connected to the shielding shunt.

[0039] In more detail, the shielding shunt includes a first resistor R1 and a first capacitor C1. The driving shunt includes a second resistor R0, a second capacitor C0, a third resistor R, a third capacitor C and a driving line 23. Capacitors C, C0 and C1 are not stray capacitances of circuit lines but actual capacitors.

[0040] Please refer to Figure 1 and Figure 3 As shown, the shielding metal 24 surrounds the driving line 23 in the length direction of the driving line 23 to shield the noise. Figure 1 As shown, the shielding metal 24 is a hollow rectangular column, and the driving line 23 extends therein. In one embodiment, the shielding metal 24 includes multiple layers respectively configured on different layers of the circuit board 200, such as Figure 3 The shielding metal 24 is shown to be located on the first layer, the second layer and the third layer, and the different layers are electrically connected to each other and have the same potential. Preferably, the shielding metal 24 surrounds the driving line 23 until the connection point of the load 25 (or the contact point of the module or package) to completely cover the driving line 23, but the shielding metal 24 is electrically separated from the load 25. In one embodiment, the cross-sections of the shielding metals 24 located on different layers of the circuit board 200 are respectively rectangular, such as Figure 3 The shielding metal 24 and the driving line 23 are made by, for example, an exposure and development process. In another embodiment, the shielding metal 24 is a hollow circular cylinder or has other cross-sectional shapes, without specific limitation.

[0041] Please refer to Figure 2 As shown, the first resistor R1 is connected between the first pin 11_p1 of the chip 21 and the first node N1. The first capacitor C1 is connected between the first node N1 and the ground voltage GND. The second resistor R0 is connected between the second pin 11_p0 of the chip 21 and the second node N2. The second capacitor C0 is connected between the first node N1 and the second node N2. The third resistor R is connected to the second node N2. The third capacitor C is connected between the third resistor R and the driving line 23, wherein the driving line 23 is used to connect to the load 25. One end of the shielding metal 24 is connected to the first node N1, and the other end thereof is connected to the first node N1. Figure 4 As shown, it is connected to the ground voltage GND through the capacitor C_shd.

[0042] The first resistor R1 is used to match the phase of the drive signal Isin on the shielding branch and the drive branch to improve stability. The first capacitor C1 is used to guide the noise to the ground voltage GND to achieve the effect of absorbing / attenuating the noise. The second resistor R0 is used to form a current low-pass filter to limit the noise. The second capacitor C0 is used to absorb / attenuate the noise current to the operational amplifier or the ground voltage GND. The third resistor R and the third capacitor C are used to form a voltage low-pass filter to limit the noise.

[0043] Please refer to Figure 4 As shown, it shows the circuit diagram of the equal calibration when the noise removal circuit 22 is connected to the load 25 (each load 25 is connected to a driving line 23, and some driving lines have been omitted to simplify the diagram), and the load 25 has a load capacitance C L .also, Figure 4The calibrated resistance R_shd and the calibrated capacitance C_shd of the shielding metal 24 are shown. Figure 4 In the figure, reference numeral 80 indicates that the shielding metal 24 surrounds the driving line 23 .

[0044] Please also refer to Figure 2 , Figure 4 and Figure 5 , Figure 5 The frequency response of the voltage Vx of the second node N2 of the de-noising circuit 12 and the current changes of the currents Is, Io and Isin are shown. After the system frequency (i.e., the operating frequency of the touch sensing device) is determined, the low-pass frequency f can be determined first. LPF and the values ​​of the third resistor R and the third capacitor C, where f LPF =1 / 2πRC. Turn frequency F TO It can be determined according to the frequency fi of the driving signal Isin. After the third resistor R and the third capacitor C are determined, the turning frequency F TO Determine the α value, where f TO =1 / 2π(α+1)RC. Finally, the high-pass frequency f can be determined based on the system frequency. HPF , and with the already determined R, C and α, the β value can be determined, where f LPF =1 / 2παβRC. In the present invention, α and β are positive numbers.

[0045] In the present invention, R, C, α and β are determined according to the frequency of the sine wave signal Isin and the noise frequency (the noise frequency range can be measured in advance). In addition, the load 25 has a load capacitor C L When determining the third resistor R and the third capacitor C, the load capacitance C is also considered. L In other words, R, C, α and β are also determined according to the load capacitance C of the load 25. L Decide.

[0046] After R, C, α and β are determined, the value of the first resistor R1 can be selected as (α+1)R / β, the value of the second resistor R2 can be selected as αR, and the capacitance values ​​of the first capacitor C1 and the second capacitor C2 can be selected as βC. Figure 4 .

[0047] like Figure 5 As shown, by configuring the first capacitor C1, the corner frequency F TO With low pass frequency f LFP The frequency response of the voltage Vx will be increased by two times, for example, from 1 / β to 2 / β. At the same time, by configuring the first resistor R1, the current Is flowing into the first signal source 211 can be reduced by (α+1) times, for example, from 1 / R to 1 / R(α+1), so as to reduce the load of the operational amplifier of the first signal source 211.

[0048] In addition, the current Io flowing into the second signal source 210 also changes accordingly with the frequency response change of the voltage Vx. In the present invention, γfi=1 / 2π(α+1)RC is set, and 1 / αγ / R represents the current value of the driving signal Isin at the frequency fi.

[0049] In the present invention, the chip 21 (more specifically, the processor therein) determines whether the load 25 is touched by the user according to the change of the current Io. In one embodiment, the chip 21 includes a trans-integrated amplifier (TIA) for converting the current Io into a voltage, then filtering the voltage using an anti-aliasing filter (AAF), then converting the filtered voltage into a digital value using an analog-to-digital converter (ADC), and then calculating the change value, and judging whether a touch event occurs, for example, by comparing with a predetermined threshold.

[0050] In summary, conventional capacitive sensing devices are susceptible to noise interference, which reduces detection accuracy. Therefore, the present invention further provides a contact detection circuit (refer to Figure 1 ) and its denoising circuit (refer to Figure 2 ), which provides a driving signal to the shielding metal through a shielding shunt to achieve an active shielding effect. The shielding shunt includes a de-noising capacitor for guiding noise to the ground voltage to avoid transmitting into the chip, and includes a current limiting resistor to reduce the load of the signal source.

[0051] Although the present invention has been disclosed through the above examples, they are not intended to limit the present invention. Any person skilled in the art with ordinary knowledge in the art to which the present invention belongs can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the appended claims.

Claims

1. A denoising circuit, the denoising circuit being used to be connected between two pins of a chip and a load, the denoising circuit comprising: A first resistor, the first resistor is connected between a first pin of the chip and a first node; A first capacitor connected between the first node and a ground voltage; A second resistor connected between a second pin of the chip and a second node; a second capacitor connected between the first node and the second node; a third resistor, the third resistor being connected to the second node; a third capacitor connected between the third resistor and a driving line, wherein the driving line is used to connect to the load; and The shielding metal surrounds the driving line.

2. The denoising circuit according to claim 1, wherein: The de-noising circuit and the driving line are arranged on a circuit board, and The shielding metal is disposed on different layers of the circuit board and surrounds the driving line in the length direction of the driving line until reaching the load.

3. The denoising circuit according to claim 2, wherein: One end of the shielding metal is connected to the first node.

4. The denoising circuit according to claim 2, wherein: The cross sections of the shielding metals located at different layers of the circuit board are respectively rectangular.

5. The denoising circuit according to claim 1, wherein: The load is an electrode of a vehicle steering wheel or a capacitive touch panel for a computer.

6. The denoising circuit according to claim 1, wherein: The resistance value of the third resistor is R, The capacitance value of the third capacitor is C, The resistance value of the first resistor is (α+1)R / β, The capacitance values ​​of the first capacitor and the second capacitor are βC respectively, The resistance value of the second resistor is αR, and The α and β are positive numbers.

7. The denoising circuit according to claim 6, wherein: The R, C, α and β are determined according to the system frequency and noise frequency of the denoising circuit.

8. The denoising circuit according to claim 7, wherein: The R, C, α and β are also determined according to the load capacitance of the load.

9. A contact detection circuit, the contact detection circuit is used to detect the impedance change of a load, and comprises: A chip, the chip comprising a first pin and a second pin; and A denoising circuit, which is connected between the chip and the load and comprises: A first resistor, the first resistor is connected between the first pin of the chip and a first node; A first capacitor connected between the first node and a ground voltage; A second resistor connected between the second pin of the chip and a second node; a second capacitor connected between the first node and the second node; a third resistor, the third resistor being connected to the second node; a third capacitor connected between the third resistor and a driving line, wherein the driving line is used to connect to the load; and The shielding metal surrounds the driving line.

10. The contact detection circuit according to claim 9, wherein: The chip further comprises: A first signal source, configured to output a first signal through the first pin; and The second signal source is used to output a second signal through the second pin.

11. The contact detection circuit according to claim 10, wherein: The first signal and the second signal are the same sine wave signal.

12. The contact detection circuit according to claim 9, wherein: The de-noising circuit and the driving line are arranged on a circuit board, and The shielding metal is disposed on different layers of the circuit board and surrounds the driving line in the length direction of the driving line until reaching the load.

13. The contact detection circuit according to claim 12, wherein: One end of the shielding metal is connected to the first node.

14. The contact detection circuit according to claim 12, wherein: The cross sections of the shielding metals located at different layers of the circuit board are respectively rectangular.

15. The contact detection circuit according to claim 9, wherein: The load is an electrode of a vehicle steering wheel or a capacitive touch panel for a computer.

16. The contact detection circuit according to claim 11, wherein: The resistance value of the third resistor is R, The capacitance value of the third capacitor is C, The resistance value of the first resistor is (α+1)R / β, The capacitance values ​​of the first capacitor and the second capacitor are βC respectively, The resistance value of the second resistor is αR, and The α and β are positive numbers.

17. The contact detection circuit according to claim 16, wherein: The R, C, α and β are determined according to the frequency of the sine wave signal and the noise frequency.

18. The contact detection circuit according to claim 17, wherein: The R, C, α and β are also determined according to the load capacitance of the load.

19. A contact detection circuit, the contact detection circuit being used to detect a change in impedance of a load, and comprising: A chip, the chip comprising a first pin and a second pin respectively used for outputting a sine wave signal; Shielding metal; a shielding shunt connected between the first pin, the ground voltage and the shielding metal, and used for guiding noise to the ground voltage; a driving shunt connected between the second pin and the load; and An intermediate capacitor is connected between the shielding branch and the driving branch.

20. The contact detection circuit according to claim 19, wherein: The load is an electrode of a vehicle steering wheel or a capacitive touch panel for a computer.

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