Switched capacitor touch detection circuit with current compensation and detection method

Abstract

The invention provides a switched capacitor touch detection circuit with current compensation and a detection method. The switched capacitor touch detection circuit comprises an operational amplifier, and a negative end input port of the operational amplifier is connected with a first end of an internal adjusting capacitor CF; the second end of the internal adjusting capacitor CF is connected with the output port of the operational amplifier; the second end of the stray capacitor Cp is grounded, and the first end of the stray capacitor Cp is connected with the negative end input port of the operational amplifier; and the compensation current source Ic is connected with the second end of the parasitic capacitor Cp. Through multiple times of charging and discharging, the voltage increment caused by finger touch is amplified, so that the sensitivity of touch detection is greatly improved.

Description

Technical Field

[0001] The present invention relates to touch detection technology, and in particular to a switch capacitor touch detection circuit with current compensation and a detection method. Background Art

[0002] In the prior art, the touch detection circuit converts the detection capacitance into output voltage through the principle of charge conservation, and then quantifies the output voltage through ADC. There are two main methods for this operation: one is pure charge transfer, which requires an external large capacitor; the other is through PGA switching capacitor, which requires a compensation capacitor, and excessive external key parasitic capacitance will cause output saturation.

[0003] Since there is a large parasitic capacitance between the touch button and the button wiring and the ground, the existence of this parasitic capacitance makes it easy to cause the PGA output voltage to saturate when using the PGA switch capacitor for touch detection, thus failing to effectively identify the finger. In order to avoid PGA output saturation, a certain compensation circuit is required to eliminate the influence of the parasitic capacitance between the touch button and the ground. Summary of the invention

[0004] In order to overcome the defects of the prior art, the present invention proposes a switched capacitor touch detection circuit and a detection method with current compensation, which effectively prevents PGA output saturation by adopting current compensation.

[0005] The present invention provides a switched capacitor touch detection circuit with current compensation, which is characterized by comprising:

[0006] Operational amplifier, the negative input port of the operational amplifier is connected to the internal adjustment capacitor C F The first end of

[0007] Internal adjustment capacitor C F , the internal regulating capacitor C F The second end is connected to the output port of the operational amplifier;

[0008] Parasitic capacitance C p , the parasitic capacitance C p The second end is grounded, and the first end is connected to the negative input port of the operational amplifier;

[0009] Compensation current source I c , connect the parasitic capacitor C p The second end.

[0010] In one embodiment of the present invention, the touch detection circuit further includes an analog-to-digital converter, a first switch S1, a second switch S2, a third switch S3, a fourth switch S4 and a fifth switch S5;

[0011] The first switch S1 and the parasitic capacitor C p in parallel;

[0012] The first end of the second switch S2 is connected to the compensation current source I c , the second end is connected to the parasitic capacitor C p The first end of

[0013] The first end of the third switch S3 is connected to the second end of the second switch S2, and the second end is connected to the negative input terminal V A connect;

[0014] A first end of the fourth switch S4 is connected to the output end of the operational amplifier, and a second end is connected to the analog-to-digital converter;

[0015] The first end of the fifth switch S5 is connected to the negative input terminal of the operational amplifier, and the second end is connected to the internal adjustment capacitor C F The second end.

[0016] In another embodiment of the present invention, the circuit further has a touch capacitor C finger , the C finger With the parasitic capacitance C p in parallel.

[0017] The present invention also provides a switch capacitance touch detection method with current compensation, characterized in that the method comprises:

[0018] (1) Providing an adjustable constant compensation current source I in the touch detection circuit c , by adjusting I c The conduction time eliminates the parasitic capacitance C between the touch button and the ground. p The impact of

[0019] (2) Providing an internal adjustment capacitor C with a flippable plate between the negative input terminal and the output terminal of the operational amplifier of the touch detection circuit F , used to accumulate charges obtained from the outside;

[0020] (3) For parasitic capacitance C p Perform charging and discharging;

[0021] (4) Comparison voltage V B The positive input terminal of the operational amplifier V ref The voltage relationship between them is used to determine the internal adjustment capacitor C according to the comparison result. F To charge or discharge, the parasitic capacitance C p The charge gained or lost is transferred to the internal regulating capacitor C F superior;

[0022] (5) Repeat the process of (3)-(4) multiple times to achieve the accumulation of multiple charge and discharge charges to improve the touch sensitivity.

[0023] In one embodiment of the present invention, steps (3) to (4) further include:

[0024] Step 1: S5 is closed, S1, S2, S3, and S4 are opened. In this stage, C F The voltage at both ends remains the same, V A =V out =V ref ;

[0025] Step 2: S1 is closed, S2, S3, S4, and S5 are opened. In this stage, C p Charging;

[0026] Step 3: S2 is closed, S1, S3, S4, S5 are opened, and C p Discharge is performed;

[0027] Step 4: S3 is closed, S1, S2, S4, and S5 are opened. In this stage, V A =V B1 =V ref , the voltage at the negative input and output of the operational amplifier is equal, where V A is the voltage at the negative input terminal of the operational amplifier, V ref is the voltage at the positive input terminal of the operational amplifier, V B1 For this stage, the parasitic capacitance C p The first terminal voltage;

[0028] Step 5: Repeat steps 2-3 N times.

[0029] In another embodiment of the present invention, during step 3, V B0 =I c *T s2 / C p =I c *n*T sys / C p , where the conduction time Ts2 of S2 is represented by the number of cycles of the system clock, and the cycle of the system clock is T sys , Ts2=n*T sys , V B0 For this stage, the parasitic capacitance C p The first terminal voltage.

[0030] In another embodiment of the present invention, during step 5:

[0031] ΔV out1 *C F =N*(VB1 -V B0 )*C p

[0032] ΔV out1 =N*(V ref -n*I c *T sys / C p )*C p / C F =N*(V ref *C p / C F -n*I c *I sys / C F )

[0033] The algorithm automatically adjusts the number of cycles n of the compensation current source to make

[0034] V ref =n*I c *T sys / C p ,ΔV out1 =0, V out =V ref .

[0035] In another embodiment of the present invention, when a finger touches a key, there is a C finger With the parasitic capacitance C p When connected in parallel:

[0036] V B2 =I c *T s2 / (C p +C finger )=I c *n*T sys / (C p +C finger ), where C finger is the touch capacitance, V B2 For this stage, the parasitic capacitance C p The voltage at the first terminal.

[0037] In another embodiment of the present invention, when a finger touches a key, there is a C finger With the parasitic capacitance C p in parallel:

[0038] ΔV out2 *C F =N*(V B1 -V B2 )*C p

[0039] ΔVout1 =N*(V ref -n*I c *T sys / (C p +C finger ))*(C p +C finger ) / C F =N*(V ref *(C p +C finger

[0040] ) / C F -n*I c *T sys / C F )

[0041] Voltage increment caused by finger:

[0042] ΔV out =ΔV out2 -ΔV out1 =N*V ref *C finger / C F .

[0043] The present invention adopts the current compensation method to effectively reduce the chip area. At the same time, a constant current is used to continuously charge the key parasitic capacitance, which is faster, can speed up the speed of finger recognition of touch keys and expand the number of keys supported by the touch chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A schematic diagram of a touch detection circuit in an embodiment of the present invention is shown;

[0045] Figure 2 A diagram showing the connection state of the detection circuit in step 1 of an embodiment of the present invention is shown;

[0046] Figure 3 A diagram showing the connection state of the detection circuit in step 2 of an embodiment of the present invention is shown;

[0047] Figure 4A A diagram showing the connection state of the detection circuit in step 3 of an embodiment of the present invention is shown;

[0048] Figure 4B It shows a connection state diagram of the detection circuit after touching the key in step 3 of an embodiment of the present invention;

[0049] Figure 5A A diagram showing the connection state of the detection circuit in step 4 of an embodiment of the present invention is shown;

[0050] Figure 5BIt shows a connection state diagram of the detection circuit after touching the key in step 4 of an embodiment of the present invention; DETAILED DESCRIPTION

[0051] The detailed features and advantages of the present invention are described in detail in the specific embodiments below, and the content is sufficient to enable any person skilled in the art to understand the technical content of the present invention and implement it accordingly, and according to the description, claims and drawings disclosed in this specification, those skilled in the art can easily understand the relevant purposes and advantages of the present invention. Although the description of the present invention will be introduced in conjunction with the preferred embodiment, this does not mean that the features of this invention are limited to this embodiment. On the contrary, the purpose of introducing the invention in conjunction with the embodiment is to cover other options or modifications that may be extended based on the claims of the present invention. In order to provide a deep understanding of the present invention, many specific details will be included in the following description. The present invention can also be implemented without using these details. In addition, in order to avoid confusion or blurring the focus of the present invention, some specific details will be omitted in the description.

[0052] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0053] It is understood that although the terms "first", "second", "third", etc. may be used herein to describe various components, channels, components, regions, layers and / or parts, these components, channels, components, regions, layers and / or parts should not be limited by these terms, and these terms are only used to distinguish different components, channels, components, regions, layers and / or parts. In addition, the terms "first", "second", "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0054] As shown in this application and claims, unless the context clearly indicates an exception, the words "a", "an", "an" and / or "the" do not refer to the singular and may also include the plural. Generally speaking, the terms "include" and "comprise" only indicate the inclusion of the steps and elements that have been clearly identified, and these steps and elements do not constitute an exclusive list. The method or device may also include other steps or elements.

[0055] In some embodiments, numbers describing the number of components and attributes are used. It should be understood that such numbers used in the description of the embodiments are modified by the modifiers "about", "approximately" or "substantially" in some examples. Unless otherwise specified, "about", "approximately" or "substantially" indicate that the numbers are allowed to vary by ±20%. Accordingly, in some embodiments, the numerical parameters used in the specification and claims are approximate values, which may change according to the required features of individual embodiments. In some embodiments, the numerical parameters should take into account the specified significant digits and adopt the general method of retaining digits. Although the numerical domains and parameters used to confirm the breadth of their range in some embodiments of the present application are approximate values, in specific embodiments, the setting of such numerical values ​​is as accurate as possible within the feasible range.

[0056] At the same time, the present application uses specific words to describe the embodiments of the present application. For example, "one embodiment", "an embodiment", and / or "some embodiments" refer to a certain feature, structure or characteristic related to at least one embodiment of the present application. Therefore, it should be emphasized and noted that "one embodiment" or "an embodiment" or "an alternative embodiment" mentioned twice or more in different positions in this specification does not necessarily refer to the same embodiment. In addition, some features, structures or characteristics in one or more embodiments of the present application can be appropriately combined.

[0057] The present invention provides a switch capacitance touch detection method with current compensation, characterized in that the method comprises:

[0058] (1) Providing an adjustable constant compensation current source I in the touch detection circuit c , by adjusting I c The conduction time eliminates the parasitic capacitance C between the touch button and the ground. p The impact of

[0059] (2) Providing an internal adjustment capacitor C with a flippable plate between the negative input terminal and the output terminal of the operational amplifier of the touch detection circuit F , used to accumulate charges obtained from the outside;

[0060] (3) For parasitic capacitance C p Perform charging and discharging;

[0061] (4) Comparison voltage V B The positive input terminal of the operational amplifier V ref The voltage relationship between them is used to determine the internal adjustment capacitor C according to the comparison result. F To charge or discharge, the parasitic capacitance C p The charge gained or lost is transferred to the internal regulating capacitor C F superior;

[0062] (5) Repeat the process of (3)-(4) multiple times to achieve the accumulation of multiple charge and discharge charges to improve the touch sensitivity.

[0063] Figure 1 FIG. 1 is a schematic diagram of a touch detection circuit in an embodiment of the present invention. By detecting the change of the parasitic capacitance associated with the touch button, a touch event can be identified. Figure 1 As shown, C p is the parasitic capacitance, C finger It is the equivalent self-capacitance of the touch button. It amplifies the change of finger touch through multiple charging and discharging, thereby improving the sensitivity of touch detection.

[0064] according to Figure 1 As shown, the touch detection circuit includes a touch capacitor C finger , compensation current source I c , internal adjustment capacitor C F , parasitic capacitance C p , an analog-to-digital converter, a first switch S1, a second switch S2, a third switch S3, a fourth switch S4 and a fifth switch S5;

[0065] The first switch S1 and the parasitic capacitor C p in parallel;

[0066] Touch capacitance C finger With parasitic capacitance C p in parallel;

[0067] The first end of the second switch S2 is connected to the compensation current source I c , the second end is connected to the parasitic capacitor C p The first end of

[0068] Parasitic capacitance C p The second end of is grounded;

[0069] The first end of the third switch S3 is connected to the second end of the second switch S2, and the second end is connected to the negative input terminal V A connect;

[0070] A first end of the fourth switch S4 is connected to the output end of the operational amplifier, and a second end is connected to the analog-to-digital converter;

[0071] The first end of the fifth switch S5 is connected to the negative input terminal of the operational amplifier, and the second end is connected to the internal adjustment capacitor C F The second end of

[0072] Internal adjustment capacitor C F The first end is connected to the negative input terminal of the operational amplifier.

[0073] The steps (3) to (4) of the present invention further include:

[0074] Step 1: S5 is closed, S1, S2, S3, and S4 are disconnected. F The voltage at both ends remains the same, V A =V out =V ref , Figure 2 The connection diagram of the detection circuit in this stage is shown.

[0075] Step 2: S1 is closed, S2, S3, S4, and S5 are opened. In this stage, C p To charge, Figure 3 The connection diagram of the detection circuit in this stage is shown.

[0076] Step 3: S2 is closed, S1, S3, S4, and S5 are disconnected. In this stage, Cp is discharged. During this stage, V B0 =I c *T s2 / C p =I c *n*T sys / C p , Figure 4A The connection diagram of the detection circuit in this stage is shown, where the conduction time Ts2 of S2 is represented by the number of cycles of the system clock, and the cycle of the system clock is T sys , Ts2=n*T sys , V B0 For this stage, the parasitic capacitance C p The first terminal voltage.

[0077] Step 4: S3 is closed, S1, S2, S4, and S5 are opened. In this stage, V A =V B1 =V ref , the voltage at the negative input and output of the operational amplifier is equal, where V A is the voltage at the negative input terminal of the operational amplifier, V ref is the voltage at the positive input terminal of the operational amplifier, V B1 For this stage, the parasitic capacitance C p The first terminal voltage, FIG5 shows the connection diagram of the detection circuit in this stage.

[0078] Step 5: Repeat steps 2-3 N times.

[0079] ΔV out1 *C F =N*(V B1 -V B0 )*C p

[0080] ΔV out1 =N*(V ref -n*I c*T sys / C p )*C p / C F =N*(V ref *C p / C F -n*I c *I sys / C F )

[0081] The algorithm automatically adjusts the number of cycles n of the compensation current source to make

[0082] V ref =n*I c *T sys / C p ,ΔV out1 =0, V out =V ref .

[0083] When a finger touches a key, there is C finger With the parasitic capacitance C p When connected in parallel,

[0084] In step 3, V B2 =I c *T s2 / (C p +C finger )=I c *n*T sys / (C p +C finger ), Figure 4B The connection diagram of the detection circuit in this stage is shown.

[0085] In step 5, ΔV out2 *C F =N*(V B1 -V B2 )*C p

[0086] ΔV out1 =N*(V ref -n*I c *T sys / (C p +C finger ))*(C p +C finger ) / C F =N*(V ref *(C p +C finger

[0087] ) / C F -n*Ic *T sys / C F )

[0088] Voltage increment caused by finger:

[0089] ΔV out =ΔV out2 -ΔV out1 =N*V ref *C finger / C F

[0090] It can be seen that the change in the finger touch is amplified N times through multiple charging, thereby greatly improving the sensitivity of touch detection.

[0091] In summary, compared with the traditional touch detection method, the touch detection method of the present invention has high sensitivity and can amplify the touch change amount by N times by multiple charging according to the actual application needs.

[0092] The terms and expressions used herein are for descriptive purposes only, and the present invention should not be limited to these terms and expressions. The use of these terms and expressions does not mean to exclude any equivalent features of the illustrations and descriptions (or parts thereof), and it should be recognized that various modifications that may exist should also be included in the scope of the claims. Other modifications, variations and substitutions may also exist. Accordingly, the claims should be deemed to cover all such equivalents.

[0093] Similarly, it should be pointed out that although the present invention has been described with reference to the current specific embodiments, ordinary technicians in this technical field should realize that the above embodiments are only used to illustrate the present invention, and various equivalent changes or substitutions may be made without departing from the spirit of the present invention. Therefore, as long as the changes and modifications to the above embodiments are within the scope of the essential spirit of the present invention, they will fall within the scope of the claims of this application.

Claims

1. A switched capacitor touch detection circuit with current compensation, characterized in that: include: Operational amplifier, the negative input port of the operational amplifier is connected to the internal adjustment capacitor C F The first end of Internal adjustment capacitor C F , the internal regulating capacitor C F The second end is connected to the output port of the operational amplifier; Parasitic capacitance C p , the parasitic capacitance C p The second end is grounded, and the first end is connected to the negative input port of the operational amplifier; Compensation current source I c , connect the parasitic capacitor C p The second end.

2. The switched capacitor touch detection circuit with current compensation according to claim 1, characterized in that: The touch detection circuit also includes an analog-to-digital converter, a first switch S1, a second switch S2, a third switch S3, a fourth switch S4 and a fifth switch S5; The first switch S1 and the parasitic capacitor C p in parallel; The first end of the second switch S2 is connected to the compensation current source I c , the second end is connected to the parasitic capacitor C p The first end of The first end of the third switch S3 is connected to the second end of the second switch S2, and the second end is connected to the negative input terminal V A connect; A first end of the fourth switch S4 is connected to the output end of the operational amplifier, and a second end is connected to the analog-to-digital converter; The first end of the fifth switch S5 is connected to the negative input terminal of the operational amplifier, and the second end is connected to the internal adjustment capacitor C F The second end.

3. The switched capacitor touch detection circuit with current compensation according to claim 3, characterized in that: The circuit also has a touch capacitor C finger , the C finger With the parasitic capacitance C p in parallel.

4. A switch capacitance touch detection method with current compensation, characterized in that: The method includes: (1) Providing an adjustable constant compensation current source I in the touch detection circuit c , by adjusting I c The conduction time eliminates the parasitic capacitance C between the touch button and the ground. p The impact of (2) Providing an internal adjustment capacitor C with a flippable plate between the negative input terminal and the output terminal of the operational amplifier of the touch detection circuit F , used to accumulate charges obtained from the outside; (3) For parasitic capacitance C p Perform charging and discharging; (4) Comparison voltage V B The positive input terminal of the operational amplifier V ref The voltage relationship between them is used to determine the internal adjustment capacitor C according to the comparison result. F to charge or discharge, and the parasitic capacitance C p The charge gained or lost is transferred to the internal regulating capacitor C F superior; (5) Repeat the process of (3)-(4) multiple times to achieve the accumulation of multiple charge and discharge charges to improve the touch sensitivity.

5. The switch capacitance touch detection method with current compensation according to claim 4, characterized in that: The steps (3) to (4) further include: Step 1: S5 is closed, S1, S2, S3, and S4 are disconnected. F The voltage at both ends remains the same, V A =V out =V ref ; Step 2: S1 is closed, S2, S3, S4, and S5 are opened. In this stage, C p Charging; Step 3: S2 is closed, S1, S3, S4, S5 are opened, and C p Discharge is performed; Step 4: S3 is closed, S1, S2, S4, and S5 are opened. In this stage, V A =V B1 =V ref , the voltage at the negative input and output of the operational amplifier is equal, where V A is the voltage at the negative input terminal of the operational amplifier, V ref is the voltage at the positive input terminal of the operational amplifier, V B1 For this stage, the parasitic capacitance C p The first terminal voltage; Step 5: Repeat steps 2-3 N times.

6. The switch capacitance touch detection method with current compensation according to claim 5, characterized in that: During step 3, V B0 =I c *T s2 / C p =I c *n*T sys / C p , where the conduction time Ts2 of S2 is represented by the number of cycles of the system clock, and the cycle of the system clock is T sys , Ts2=n*T sys , V B0 For this stage, the parasitic capacitance C p The first terminal voltage.

7. The switch capacitance touch detection method with current compensation according to claim 6, characterized in that: During step 5: ΔV out1 *C F =N*(V B1 -V B0 )*C p ΔV out1 =N*(V ref -n*I c *T sys / C p )*C p / C F =N*(V ref *C p / C F -n*I c *I sys / C F ) The algorithm automatically adjusts the number of cycles n of the compensation current source to make V ref =n*I c *T sys / C p ,ΔV out1 =0,V out =V ref 。 8. The switch capacitance touch detection method with current compensation according to claim 6, characterized in that: When a finger touches a key, there is C finger With the parasitic capacitance C p When connected in parallel: V B2 =I c *T s2 / (C p +C finger )=I c *n*T sys / (C p +C finger ), where C finger is the touch capacitance, V B2 For this stage, the parasitic capacitance C p The voltage at the first terminal.

9. The switch capacitance touch detection method with current compensation according to claim 8, characterized in that: When a finger touches a key, there is C finger With the parasitic capacitance C p in parallel: ΔV out2 *C F =N*(V B1 -V B2 )*C p ΔV out1 =N*(V ref -n*I c *T sys / (C p +C finger ))*(C p +C finger ) / C F =N*(V ref *(C p +C finger ) / C F -n*I c *T sys / C F ) Voltage increment caused by finger: ΔV out =ΔV out2 -ΔV out1 =N*V ref *C finger / C F 。

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