Contact or proximity sensing system and method

Abstract

The present invention discloses a system (100) for sensing contact or proximity, comprising: a first number of input terminals (104) configured to couple one or more capacitance sensors (102); a second number of transfer units (106) configured to transfer charge from the one or more capacitance sensors (102) through the first number of input terminals (104) during a transfer phase of a cycle of the one or more capacitance sensors (102), wherein at least one of the first number and the second number is equal to or greater than two; and a first switching unit (108a) coupled between the first number of input terminals (104a) and the second number of transfer units (106), configured to selectively electrically couple any one of the first number of input terminals (104) to any one of the second number of transfer units (106) during the transfer phase.

Description

Technical Field

[0001] The present disclosure relates to sensing systems, and more particularly to contact or proximity sensing systems based on capacitance changes of capacitance sensors. Background Art

[0002] Capacitance sensors are widely used in various applications, for example, in human-machine interface applications for sensing contact or proximity of the body, and in motor applications for determining the position of a rotatable shaft by determining the proximity of a conductive object to a capacitance sensor mounted on the shaft. Contact or proximity to the capacitance sensor is determined by detecting a change in capacitance between two opposing electrodes of the capacitance sensor. Summary of the Invention

[0003] The present disclosure relates to a contact or proximity sensing system having improved noise immunity, configuration flexibility, and average measurement error. Contact or proximity is determined by detecting a change in capacitance between two opposing electrodes of a capacitance sensor. The capacitance between the two electrodes of the capacitance sensor is measured by charging the capacitance sensor to a predetermined voltage and measuring the amount of charge charged to the capacitance sensor. The measurement includes transferring charge to a sampling capacitor by discharging the capacitance sensor.

[0004] In one example, a system for sensing contact or proximity is described. The system includes: a first number of input terminals configured to couple one or more capacitance sensors; a second number of transfer units configured to transfer charge from the one or more capacitance sensors through the first number of input terminals during a transfer phase of a cycle of the one or more capacitance sensors, wherein at least one of the first number and the second number is equal to or greater than two; and a first switching unit coupled between the first number of input terminals and the second number of transfer units and configured to selectively electrically couple any one of the first number of input terminals to any one of the second number of transfer units during the transfer phase.

[0005] In another example, the present disclosure provides a method of operating a contact or proximity sensing system including a first number of input terminals and a second number of transfer units. The method includes: repeatedly charging the one or more capacitance sensors during a charging phase of a cycle of the one or more capacitance sensors; and selectively configuring any one of the second number of transfer units to transfer charge from any one of the first number of capacitance sensors during the transfer phase of the cycle, wherein at least one of the first number and the second number is equal to or greater than two. Brief Description of the Drawings

[0006] Figure 1 is a schematic block diagram of a sensing system according to a first embodiment of the present disclosure;

[0007] Figure 2is a timing diagram showing the change in the voltage difference across the first capacitive sensor and the second capacitive sensor during the operation of the sensing system according to one example; Figure 1 and

[0008] Figure 3a is a corresponding schematic circuit and block diagram for modeling how input noise affects the sensing system of Figure 3b ; Figure 1 shows sampling the input noise using the sampling clocks of

[0009] Figure 4 in the time domain and the frequency domain; Figure 3a and Figure 3b ;

[0010] Figure 5 shows sampling clocks with different phase shifts relative to the input noise in the time domain;

[0011] Figure 6 is a simulation diagram showing the input current of the transfer unit affected by input noise with different phase shifts relative to the sampling clock;

[0012] Figure 7 is a timing diagram showing the change in the voltage difference across the first capacitive sensor and the second capacitive sensor during the operation of the sensing system according to another example in Figure 1 ;

[0013] Figure 8 is a schematic block diagram of the sensing system according to the second embodiment of the present disclosure;

[0014] Figure 9 is a schematic block diagram of the sensing system according to the third embodiment of the present disclosure;

[0015] Figure 10 is a timing diagram showing the change in the voltage difference across the first capacitive sensor and the second capacitive sensor during the operation of the sensing system according to one example in Figure 9 ;

[0016] Figure 11 is a schematic block diagram of the sensing system according to the fourth embodiment of the present disclosure;

[0017] Figure 12 is a timing diagram showing the change in the voltage at the first input terminal and the second input terminal of the sensing system during the operation of the sensing system according to one example; Figure 11 ;

[0018] Figure 13 is a timing diagram showing the change in the voltage at the first input terminal and the second input terminal of the sensing system during the operation of the sensing system according to another example; Figure 11 ;

[0019] Figure 14 is a flowchart of a method for sensing contact or proximity according to a fifth embodiment of the present disclosure;

[0020] Figure 15 is a flowchart of a method for sensing contact or proximity according to a sixth embodiment of the present disclosure; and

[0021] Figure 16 is a flowchart of a method for sensing contact or proximity according to a seventh embodiment of the present disclosure. Detailed Description

[0022] The present disclosure relates to a contact or proximity sensing system that determines contact or proximity by detecting a change in capacitance between two opposing electrodes of at least one capacitance sensor. The capacitance between the two electrodes of the capacitance sensor is measured by charging and discharging the capacitance sensor, and the discharging includes transferring the charge charged to the capacitance sensor to a sampling capacitor. The capacitance is determined based on a period for charging a voltage difference across the sampling capacitor to a predetermined voltage.

[0023] Now referring to Figure 1 , a schematic block diagram of a sensing system 100 for sensing contact or proximity using at least a first capacitance sensor 102a according to a first embodiment of the present disclosure is shown. The first capacitance sensor 102a includes a first end coupled to a first end of the sensing system 100 and a second end opposite the first end coupled to ground. The sensing system 100 is configured to charge a plurality of charges to the first capacitance sensor 102a through the first end of the first capacitance sensor during a charging phase of consecutive cycles, and transfer the charges to a sampling capacitor by discharging the first capacitance sensor 102a during a transfer phase of consecutive cycles to sense a change in capacitance of the first capacitance sensor 102a.

[0024] The sensing system 100 includes: a first number of input terminals 104 configured to be coupled to one or more capacitance sensors (such as the first capacitance sensor 102a); and a second number of transfer units 106 configured to transfer charges from one or more capacitance sensors through the first number of input terminals 104 during a transfer phase, wherein at least one of the first number and the second number is equal to or greater than two. The sensing system 100 further includes a first switching unit 108a coupled between the first number of input terminals 104 and the second number of transfer units 106 and configured to selectively electrically couple any one of the first number of input terminals 104 to any one of the second number of transfer units 106.

[0025] In a preferred embodiment, the first number of input terminals 104 includes a first input terminal 104a configured to couple to the first capacitive sensor 102a, and the second number of transfer units 106 includes a first transfer unit 106a and a second transfer unit 106b. In a preferred embodiment, each of the first transfer unit 106a and the second transfer unit 106b is a current mirror. In a preferred embodiment, the current mirror is a class AB current mirror. The sensing system 100 further includes a second switching unit 108b coupled to the second number of transfer units 106. In one example, the first switching unit 108a and the second switching unit 108b are configured to alternately electrically couple one of the first transfer unit 106a and the second transfer unit 106b between the first input terminal 104a and the first sampling capacitor 110a during the transfer phase of the first capacitive sensor 102a to transfer the charge charged to the first capacitive sensor 102a to the first sampling capacitor 110a. The first sampling capacitor 110a may be part of the sensing system 100 or separated from the sensing system 100. The contact or proximity to the first capacitive sensor 102a is determined based on the period for charging the voltage difference across the first sampling capacitor 110a to a predetermined voltage. In a preferred embodiment, the first number of input terminals 104 further includes a second input terminal 104b. In a preferred embodiment, the second input terminal 104b is configured to receive charge from the second capacitive sensor 102b. The contact or proximity to the second capacitive sensor 102b is determined in the same or a similar manner.

[0026] In one example, the sensing system 100 includes a first charging switch 112a and a second charging switch 112b respectively coupled between a voltage source V reg 114 and the first input terminal 104a and the second input terminal 104b, which are respectively configured to charge the first capacitive sensor 102a and the second capacitive sensor 102b during the charging phase of the capacitive sensor. The first switching unit 108a includes first transfer switches 116a to fourth transfer switches 116d, which are coupled between the first number of input terminals 104 and the second number of transfer units 106 for selectively electrically coupling either the first input terminal 104a or the second input terminal 104b to either the first transfer unit 106a or the second transfer unit 106b. The second switching unit 108b includes fifth transfer switches 116e to eighth transfer switches 116h, which are coupled between the second number of transfer units 106 and the first sampling capacitor 110a and the second sampling capacitor 110b for selectively electrically coupling either of the second number of transfer units 106 to either the first sampling capacitor 110a or the second sampling capacitor 110b. The first charging switch 112a and the second charging switch 112b may be respectively controlled by corresponding first charging signals S1_A and a second charging signal S 1_B transistors that are controlled to operate between an on state and an off state, the first transfer switch 116a to the fourth transfer switch 116d can be transistors that are respectively controlled by corresponding first transfer signals to fourth transfer signals S 2_A 、S 2_B 、S 3_A and S 3_B to operate between an on state and an off state, and the fifth transfer switch 116e to the eighth transfer switch 116h can be transistors that are respectively controlled by the first transfer signal to the fourth transfer signal S 2_A 、S 2_B 、S 3_A and S 3_B to operate between an on state and an off state. In one embodiment, the charging signal and the transfer signal are generated by a signal generator (not shown) based on a clock signal. The relationship between the clock signal and the charging signal or the transfer signal can be configurable by the user through the signal generator.

[0027] Taking the first capacitance sensor 102a as an example, during operation, the first charging signal S 1_A is asserted during the charging phase of consecutive cycles, and the first transfer signal S 2_A and the second transfer signal S 3_A are alternately asserted during the transfer phase of consecutive cycles so as to alternately configure one of the first transfer unit 106a and the second transfer unit 106b to transfer the charge from the first capacitance sensor 102a to the first sampling capacitor 110a, which averages out the errors caused by, for example, random telegraph signal (RTS) noise, current mirror non-linearity, etc. in the first transfer unit 106a and the second transfer unit 106b. Therefore, the accuracy of capacitance change sensing is improved.

[0028] Figure 2 is a timing diagram 200 showing the variations of voltages V Figure 1 at the first input terminal 104a and the second input terminal 104b during the operation of the sensing system 100 according to one example. The timing diagram 200 shows voltages V X_A and V X_B at 202 and 204 respectively, shows the first charging signal S X_A and the second charging signal S X_B at 206 and 208 respectively, and shows the first transfer signal to the fourth transfer signal S 1_A 、S 1_B 、S 2_A 、S 3_A 、S 2_B and S 3_B。The first charging signal S 1_A and the second charging signal S 1_B configure the first capacitive sensor 102a and the second capacitive sensor 102b to be charged in the first half and the second half of each period, respectively. In one example, the first transfer signal S 2_A and the second transfer signal S 3_A configure the first transfer unit 106a and the second transfer unit 106b to alternately transfer the charge received at the first input terminal 104a to the first sampling capacitor 110a in the second half of each period. The third transfer signal S 2_B and the fourth transfer signal S 3_B configure the first transfer unit 106a and the second transfer unit 106b to alternately transfer the charge received at the second input terminal 104b to the second sampling capacitor 110b in the first half of each period. In a preferred embodiment, a gap time 218 is provided between charging and transfer to ensure a break-then-switch operation.

[0029] Return reference Figure 1 , the sensing system 100 further includes a determination unit 118, which is coupled to at least the first sampling capacitor 110a. In a preferred embodiment, the sensing system 100 performs a first conversion and a second conversion, in each conversion, the voltage difference across the first sampling capacitor 110a is charged to a first trip voltage V trip1 , wherein the charging and transfer phases in the second conversion are phase-shifted by half a period with respect to the corresponding charging and transfer phases in the first conversion, which improves the noise immunity of the sensing system 100 against noise injection. The determination unit 118 generates a first signal N 1x indicating the number of periods in the first conversion and a second signal N 2x indicating the number of periods in the second conversion, wherein based on the final count N x the contact or proximity to the first capacitive sensor 102a is determined, and the final count N x is a combination of the first signal N 1x and the second signal N 2x . In one example, the final count N x is defined according to the following equation:

[0030] N X =2·N 1x ·N 2x / (N 1x +N 2x ) (1)

[0031] Contact or proximity to the second capacitive sensor 102b is determined in the same manner based on two transitions with a half - period phase shift. In one embodiment, the sensing system 100 performs sequential scans on the first capacitive sensor 102a and the second capacitive sensor 102b to determine contact or proximity to the first input terminal 104a of the first capacitive sensor 102a and the second input terminal 104b of the second capacitive sensor 102b, respectively, when the first capacitive sensor 102a and the second capacitive sensor 102b correspond to the first button and the second button, respectively.

[0032] Refer to Figure 2 , at 220 shows the first charging signal (labeled S 1_A’ ) that controls the first charging switch 112a in the second transition, which shows a half - period phase shift relative to the first charging signal S 1_A 206. In the second transition, the remaining signals are also phase - shifted by a half - period in the same manner.

[0033] In a preferred embodiment, the determination unit 118 includes: a first comparator 120a that compares the voltage difference across the first sampling capacitor 110a with the first jump voltage V trip1 ; and a first counter (not shown) coupled to the first comparator 120a. The first counter counts the periods in each of the first transition and the second transition, and generates a first signal N trip1 and a second signal N 1X respectively when the voltage difference across the first sampling capacitor 110a reaches the first jump voltage V 2X . In a preferred embodiment, the first sampling capacitor 110a is coupled between the input terminal of the first comparator 120a and ground, so the voltage difference across the first sampling capacitor 110a is determined by determining the voltage at the input terminal of the first comparator 120a. Similarly, the determination unit 118 also includes: a second comparator 120b that compares the voltage difference across the second sampling capacitor 110b with V trip2 ; and a second counter (not shown) coupled to the second comparator 120b. In a preferred embodiment, the first jump voltage V trip1 and the second jump voltage V trip2 are equal to the same jump voltage V trip .

[0034] Noise injection from the electrode to the system can be modeled as Figure 3a and Figure 3b those in, these figures are respectively about how the input noise 304 injected through the first input terminal 104a affects Figure 1Modeling the sensing system 100 simplifies the equivalent schematic circuit and block diagrams 300 and 302. The noise injection can be extracted as a natural sampling process plus an integration process. The input noise 304 represented by a sine signal can be regarded as an additional current source Inoise and is injected into the sensing system 100 by contacting or approaching the first capacitive sensor 102a during the transfer phase. The input noise is sampled by the sampling clock 306 (e.g., the first transfer signal S2_A) and transmitted to and integrated by the integrator 308 (e.g., the first sampling capacitor 110a). Qs is the noise charge injected into the system. The integrator 308 can be regarded as a low-pass filter, so only the low-frequency components of the input noise are important.

[0035] Figure 4 Illustrates sampling the input noise 304 using Figure 3a and Figure 3b the sampling clock 306. In the time domain, the input noise Inoise 304 is represented by a quasi-sine signal x(t) with a frequency f noise and is represented by X(f) in the frequency domain, and the sampling clock 306 is represented by a square-wave signal s(t) with a frequency f chg in the time domain and is represented by S(f) in the frequency domain. Due to the resistance of the first transfer unit 106a and the controller 108, the sine waveform of the input noise Inoise 304 with some distortion is non-linear, and the maximum current of the input noise Inoise 304 is limited. The sampled Inoise 400 is represented by xs(t) in the time domain and by XS(f) in the frequency domain. As shown in Figure 4 the example, the sampled Inoise is formed by multiplying the input noise Inoise and the sampling clock in the time domain and convolving the input noise Inoise and the sampling clock in the frequency domain.

[0036] In one example, in the frequency domain, the frequency f noise of the input noise Inoise can be in the range of 150 kHz to 80 MHz, and the frequency f chg of the sampling clock is typically in the range of 4 kHz to 4 MHz, and in some cases, both are greater than 100 kHz. Therefore, only the f noise -n· f chg frequency components of the input noise Inoise are important, where n is a natural number. Additionally, if the duty cycle of the sampling clock is approximately 50%, the influence of the frequency components of the input noise Inoise with frequencies equal to the even harmonics of the frequency f chg of the sampling clock is zero.

[0037] In the time domain, the input noise Inoise represented by x(t) is defined according to the following equation:

[0038] x(t)=Asin(ωt) (2)

[0039] where ω = 2πf noise .

[0040] s(t) can be represented by a Fourier series as the following equation:

[0041] (3)

[0042] where and .

[0043] If the duty cycle of the sampling clock is 50%, then τ = 0.5Ts. Therefore, C0 = 1 / 2 and Cn = 0.5sinc(nπ / 2). Thus, the sampled Inoise xs(t) is:

[0044] (4)

[0045] In equation (4), the frequency components of interest are:

[0046] and

[0047] .

[0048] If s(t) is phase-delayed by 180°, then

[0049] (5)

[0050] Therefore, the delayed sampled Inoise is:

[0051] (6)

[0052] In equation (6), the frequency components of interest are:

[0053] and

[0054] .

[0055] Based on the above derivation, it is proven that s(t) and s(t + T s / 2) have opposite magnitudes for those frequency components of interest, so the effects of the input noise in the two cases can cancel each other out.

[0056] Figure 5is a waveform diagram showing the sampling clock 306 and the input noise 304 in FIG. 3 with different phase shifts from each other. In one example, the frequency f of the sampling clock 306 chg and the frequency f of the input noise Inoise 304 noise are equal, and the resistances of the first transfer unit 106a and the controller 108 cause little or no distortion. The input noise Inoise with different phase shifts of the reference sampling clock 306 is shown at 500 to 504.

[0057] In (a) where the sampling clock 306 and the input noise Inoise 500 are in the same phase, the sampled Inoise506 is zero. In (b) where the phase shift between the sampling clock 306 and the input noise Inoise 502 is 90°, the sampled Inoise 508 is positive. In (c) where the phase shift between the sampling clock 306 and the input noise Inoise 504 is 270°, the sampled Inoise is negative. The magnitudes of the sampled Inoise 508 and 510 in (b) and (c) are the same but in opposite directions.

[0058] Figure 6 is a simulation diagram showing how the input noise with different phase shifts affects the input charge of the first transfer unit 106a. The input charge without the influence of the input noise and the input charge affected by the input noise in (b) and (c) of Figure 5 are shown at 600 to 604 respectively. The input noise follows the IEC 61000-4-6 level 3 standard.

[0059] Both mathematical derivation and simulation show that the influence of the input noise can be reduced and / or eliminated by performing two conversions in which the sampling clock is offset by half a period.

[0060] In a preferred embodiment, the determination unit 118 is also coupled to the second sampling capacitor 110b and determines the contact or proximity to the second capacitance sensor 102b in the same manner as determining the contact or proximity to the first capacitance sensor 102a.

[0061] Return reference Figure 1 , different from the sequential scan configuration in which the contact or proximity is determined based on the capacitance change of a single capacitance sensor corresponding to a single button, the sensing system 100 can also operate in a parallel scan configuration, determining the contact or proximity based on the capacitance changes of both the first capacitance sensor 102a and the second capacitance sensor 102b corresponding to a single button.

[0062] The determination unit 118 generates a first signal N indicating the number of cycles for charging the voltage difference across the first sampling capacitor 110a to the first jump voltage V trip1 ofA , and a second signal N indicating the number of periods for charging the voltage difference across the second sampling capacitor 110b to a second jump voltage V trip2 . In a preferred embodiment, the first jump voltage V B and the second jump voltage V trip1 are equal to the same jump voltage V trip2 . Contact or proximity to both the first capacitive sensor 102a and the second capacitive sensor 102b is determined based on a final count N, which is a combination of the first signal N trip and the second signal N A . In one example, the final count N is defined according to the following equation: B

[0063] N = 2 * N A * N B / (N A + N B ) (7)

[0064] Return reference Figure 2 , since the charging and transfer periods of the second capacitive sensor 102b are phase - shifted by a half - period relative to the periods of the first capacitive sensor 102a. As discussed above, the effects of input noise are reduced and / or eliminated.

[0065] Figure 7 is a timing diagram 700 showing the variations in the voltages V Figure 1 at the first input terminal 104a and the second input terminal 104b during operation of the sensing system 100 according to another example. X_A and V X_B . The timing diagram 700 shows the voltages V

[0066] at 702 and 704 respectively, the first charging signal S X_A and the second charging signal S X_B at 706 and 708 respectively, and the first transfer signal to the fourth transfer signal S 1_A , S 1_B , S 2_A , S 3_A , S 2_B , and S 3_B at 710 to 716 respectively. Different from the timing diagram 200 of FIG. 200, the first charging signal S 1_A and the second charging signal S 1_B are synchronous, the first transfer signal S 2_A and the third transfer signal S 2_B are synchronous, and the second transfer signal S 3_A and the fourth transfer signal S 3_B ​is synchronous and is associated with the first transfer signal S 2_A and the third transfer signal S 2_B alternately. In a preferred embodiment, a gap time 718 is provided between charging and transfer to ensure a break-before-make operation.

[0067] Figure 8 is a schematic block diagram of a sensing system 800 according to a second embodiment of the present disclosure.

[0068] System 800 is substantially similar to Figure 1 system 100, except that the first transfer unit 806a and the second transfer unit 806b are directly coupled to the first sampling capacitor 910a and the second sampling capacitor 910b, respectively, and the first switching unit 808a is configured to alternately electrically couple one of the first transfer unit 806a and the second transfer unit 806b to the first input terminal 804a. In a preferred embodiment, each of the first transfer unit 806a and the second transfer unit 806b is a current mirror. In a preferred embodiment, the current mirror is a class-AB current mirror. In a preferred embodiment, the determination unit 818 generates a first signal N1 indicating the number of cycles for charging the voltage difference across the first sampling capacitor 810a to a first jump voltage V trip1 and a second signal N2 indicating the number of cycles for charging the voltage difference across the second sampling capacitor to a second jump voltage V trip2 . In a preferred embodiment, the first jump voltage V trip1 and the second jump voltage V trip2 are equal to the same jump voltage V trip . Contact or proximity to the capacitive sensor 802a is determined based on a final count N that is a combination of the first signal N1 and the second signal N2. In one example, the final count N is defined according to the following equation:

[0069] N = (N1 + N2) / 2 (8)

[0070] In addition, as discussed above, the sensing system 800 can be configured to perform two conversions with a half-cycle phase shift to eliminate the effect of input noise.

[0071] Referring to Figure 9 , a schematic block diagram of a sensing system 900 for sensing contact or proximity to a first capacitive sensor 902a and a second capacitive sensor 902b according to a third embodiment of the present disclosure is shown. Sensing system 900 is substantially similar to Figure 1The sensing system 100 is different in that it is configured to utilize only 2 IOs supported by 1 transfer unit. The sensing system 900 includes a first input terminal 904a and a second input terminal 904b for receiving charges from a first capacitance sensor 902a and a second capacitance sensor 902b, respectively, and a transfer unit 906a for transferring the charges received at the first input terminal 904a and the second input terminal 904b. In a preferred embodiment, the transfer unit 906a is a current mirror. In a preferred embodiment, the current mirror is a class-AB current mirror. The sensing system 900 further includes a first switching unit 908a and a second switching unit 908b, which are configured to alternately electrically couple the transfer unit 906a between the first input terminal 904a and a first sampling capacitor 910a and between the second input terminal 904b and a second sampling capacitor 910b.

[0072] In a preferred embodiment, the sensing system 900 includes a first charging switch 912a and a second charging switch 912b respectively coupled between a voltage source V reg 914 and the first input terminal 904a and the second input terminal 904b. The first switching unit 908a includes a first transfer switch 916a and a second transfer switch 916b respectively coupled between the first input terminal 904a and the second input terminal 904b and the transfer unit 906a, and the second switching unit 908b includes a third transfer switch 916c and a fourth transfer switch 916d respectively coupled between the transfer unit 906a and the first sampling capacitor 910a and the second sampling capacitor 910b. The first charging switch 912a and the second charging switch 912b can be transistors operating between an on state and an off state respectively controlled by a corresponding first charging signal S 1_A and a second charging signal S 1_B . The first transfer switch 916a and the third transfer switch 916c can be transistors operating between an on state and an off state controlled by a first transfer signal S 2_A , and the second transfer switch 916b and the fourth transfer switch 916d can be transistors operating between an on state and an off state controlled by a second transfer signal S 2_B .

[0073] Figure 10 is a timing diagram 1000 showing the variations of voltages V Figure 9 at the first input terminal 904a and the second input terminal 904b during the operation of the sensing system 900 according to an example. X_A and V X_B

[0074] Timing diagram 1200 shows voltages V at the first input terminal 904a and the second input terminal 904b of the sensing system 900 at 1002 and 1004 respectively X_A and V X_B , shows the first charging signal S at 1006 and 1008 respectively 1_A and the second charging signal S 1_B , and shows the first transfer signal S at 1010 and 1012 respectively 2_A and the second transfer signal S 2_B . In one example, the first charging signal S 1_A and the second charging signal S 1_B configure the first capacitive sensor 902a and the second capacitive sensor 902b to charge in the first half and the second half of each cycle respectively. The first transfer signal S 2_A configures the transfer unit 906a to transfer the charge from the first input terminal 904a to the first sampling capacitor 910a in the second half of each cycle, and the second transfer signal S 2_B configures the transfer unit 906a to transfer the charge from the second input terminal 904b to the second sampling capacitor 910b in the first half of each cycle. In a preferred embodiment, a gap time 1014 is provided between charging and transfer to ensure a break-before-make operation

[0075] Similarly, as discussed above, contact or proximity to each of the first capacitive sensor 902a and the second capacitive sensor 902b can be determined based on two transitions with a half-cycle phase shift to eliminate the influence of input noise, and similarly, as discussed above, through a parallel scan configuration, the sensing system 900 can be configured to detect a contact or proximity based on capacitance changes of both the first capacitive sensor 902a and the second capacitive sensor 902b

[0076] Figure 11 is a schematic block diagram of a sensing system 1100 according to a fourth embodiment of the present disclosure. The sensing system 1100 is substantially similar to Figure 1 system 100, except that the system 1100 senses changes in the capacitances of the first capacitive sensor 1102a and the second capacitive sensor 1102b based on a mutual capacitance sensing mode, while Figure 1 the sensing system 100 of regAnd is coupled to the transfer unit during the transfer phase, and the opposite second end of the capacitive sensor is coupled to ground. In the mutual capacitance sensing mode, the first end of the capacitive sensor is coupled to the transfer unit, and the opposite second end is coupled to ground during the charging phase and to the voltage source V during the transfer phase reg .

[0077] As Figure 11 shown, the first end of the first capacitive sensor 1102a is coupled to the first input terminal 1104a of the system 1100. The system 1100 further includes a first charging switch 1112a coupled between the opposite second end of the first capacitive sensor 1102a and ground V GND , and a first pumping switch 1122a coupled between the second end of the first capacitive sensor 1302a and the voltage source V reg 1114, wherein the first charging switch 1112a and the first pumping switch 1122a are reciprocally turned on and off to hold the voltage V of the first input terminal 1104a at a first predetermined voltage V X_A during the charging phase, and pump the voltage V of the first input terminal 1104a to a second predetermined voltage during the transfer phase. The second predetermined voltage is proportional to the combination of the first predetermined voltage and the voltage source V tn . X_A The system 1100 further includes a first hold and sample unit 1124a coupled between the first input terminal 1104a and the input terminal of the first transfer unit 1106a, and a second hold and sample unit 1124b coupled between the second input terminal 1104b and the input terminal of the second transfer unit 1106b. Each of the first hold and sample unit 1124a and the second hold and sample unit 1124b is configured to sample the bias voltage at the input terminal of the corresponding first transfer unit 1306a or second transfer unit 1306b during the transfer phase, wherein the first predetermined voltage V reg is based on the bias voltage, and holds the first predetermined voltage V

[0078] during the charging phase. In a preferred embodiment, each of the first transfer unit 1106a and the second transfer unit 1106b is a current mirror. In a preferred embodiment, the current mirror is a class AB current mirror. The bias voltage V tn is generated by a bias current proportional to the reference voltage V tn . tn ref .

[0079] ​System 1100 also includes a first switching unit 1108a coupled between the first input terminal 1104a and the first hold and sample unit 1124a and the second hold and sample unit 1124b, and a second switching unit 1108b. The first switching unit 1108a is configured to selectively electrically couple the first input terminal 1104a to one of the first hold and sample unit 1124a and the second hold and sample unit 1124b during the charging phase to hold the voltage V X_A at a first predetermined voltage V tn . During the transfer phase, similar to the sensing system 100 of Figure 1 , the first switching unit 1108a and the second switching unit 1108b are configured to alternately electrically couple one of the first transfer unit 1106a and the second transfer unit 1106b between the first input terminal 1104a and the first sampling capacitor 1110a to determine contact or proximity to the first capacitive sensor 1102a. The determination unit 1118 determines contact or proximity to the first capacitive sensor 1102a in the same manner as the determination unit 118 of the system 100 of Figure 1 determines contact or proximity to the first capacitive sensor 102a, or the determination unit 818 of the system 800 of Figure 8 determines contact or proximity to the capacitive sensor 802a.

[0080] In a preferred embodiment, each of the first hold and sample unit 1124a and the second hold and sample unit 1124b includes a hold switch 1326a / 1326b and a sample switch 1328a / 1328b. The sample switch and the hold switch can be transistors operating between an on state and an off state controlled by corresponding hold and sample signals S H_1 , S S_1 , S H_2 , S S_2 generated by the sensing system 1100, respectively. The first charge switch 1112a and the first pumping switch 1122a can also be transistors operating between an on state and an off state controlled by corresponding first charge signal S CH_A and transfer signal S TR_A generated by the sensing system 1100, respectively.

[0081] In a preferred embodiment, contact or proximity to the second capacitive sensor 1102b coupled to the second input terminal 1104b of the system 1100 is determined in the same manner by alternately configuring one of the first hold and sample unit 1124a and the second hold and sample unit 1124b to hold the voltage V at the second input terminal 11304b at a first predetermined voltage V X_B during the charging phase. tn, and reciprocally electrically coupling one of the first transfer unit 1306a and the second transfer unit 1306b between the second input terminal 1104b and the second sampling capacitor 1110b. In a preferred embodiment, the charging phase of the second capacitance sensor 1302b is synchronized with the charging phase of the first capacitance sensor 1302a. In another preferred embodiment, the charging phase of the second capacitance sensor 1302b has a half-cycle phase shift relative to the charging phase of the first capacitance sensor 1302a.

[0082] Similar to Figure 1 the first switching unit 118a and the second switching unit 118b of the system 100, the first switching unit 1118a includes first to fourth coupling switches 1116a to 1116d, which are coupled between a first number of input terminals 1104 and a second number of transfer units 1106 and are configured to selectively electrically couple either the first input terminal 1104a or the second input terminal 1104b to either the first transfer unit 1106a or the second transfer unit 1106b. The second switching unit 1118b includes fifth to eighth coupling switches 1116e to 1116h coupled between the second number of transfer units 1106 and the first sampling capacitor 1110a and the second sampling capacitor 1110b. The first to fourth coupling switches 1116a to 1116d may be transistors operating between an on state and an off state controlled by corresponding first to fourth coupling signals S 1_A 、S 2_A 、S 1_B and S 2_B generated by the sensing system 1100 respectively, and the fifth to eighth coupling switches 1116e to 1116h may be transistors operating between an on state and an off state controlled by corresponding first to fourth coupling signals S 3_A 、S 4_A 、S 3_B and S 4_B generated by the sensing system 1100 respectively. The determination unit 1118 determines contact or proximity to the first capacitance sensor 1102a and / or the second capacitance sensor 1102b in the same manner as the determination unit 118 of the Figure 1 sensing system 100. Alternately configuring one of the first transfer unit 1106a and the second transfer unit 1106b to transfer charges from each of the first capacitance sensor 1102a and the second capacitance sensor 1102b averages the distortion caused by each of the first transfer unit 1106a and the second transfer unit 1106b, thereby improving the accuracy of capacitance change sensing. In addition, as discussed above, the sensing system 1100 may be configured to perform two conversions with a half-cycle phase shift to eliminate the influence of input noise.

[0083] Figure 12 shows the voltage V at the first input terminal 1104a and the second input terminal 1104b during the operation of the sensing system 1100 according to one example Figure 11 and the change of V at X_A and V X_B The timing diagram 1200. The timing diagram 1200 shows the voltages V at 1202 and 1204 respectively X_A and V X_B , shows the first charging signal S at 1206 and 1208 respectively CH_A and the second charging signal S CH_B , shows the first transfer signal S at 1210 and 1212 respectively TR_A and the second transfer signal S TR_B , shows the first coupling signal to the fourth coupling signal S at 1214 to 1220 respectively 1_A 、S 2_A 、S 1_B and S 2_B , shows the first hold signal and the first sample signal S at 1222 and 1224 respectively H_1 and S S_1 , shows the second hold signal and the second sample signal S at 1426 and 1428 respectively H_2 and S S_2 , and shows the fifth coupling signal to the eighth coupling signal S at 1230 to 1236 respectively 3_A 、S 4_A 、S 3_B and S 4_B . The charging phase of the second capacitive sensor 1202b is synchronized with the charging phase of the first capacitive sensor 1102a. A gap time 1438 is provided between charging and transfer to ensure a break-before-make operation.

[0084] Figure 13 shows the timing diagram 1300 of the change of the voltage at the first input terminal 1104a and the second input terminal 1104b of the sensing system 1100 under the control of the controller 1108 according to another example Figure 13 The timing diagram 1300 is substantially similar to the timing diagram 1200, except that the charging phase of the second capacitive sensor 1102b is phase-shifted by half a cycle relative to the charging phase of the first capacitive sensor 1102a.

[0085] Reference Figure 14 , shows a flowchart of a method 1400 for sensing contact or proximity to a first capacitive sensor using a sensing system according to a fifth embodiment of the present disclosure. Reference Figure 1The sensing system 100 includes a first switching unit 108a and a second switching unit 108b, which are configured to selectively electrically couple any one of a second number of transfer units 106 to any one of a first number of input terminals 104 of the sensing system 100, where at least one of the first number and the second number is equal to or greater than two. In Figure 1 In the example shown, the sensing system 100 includes a first input terminal 104a and a second input terminal 104b, as well as a first transfer unit 106a and a second transfer unit 106b.

[0086] Starting from step 1402, where a first conversion is performed. The sensing system 100 will Figure 1 The first capacitive sensor 102a is configured to be repeatedly charged and discharged in consecutive cycles, where when discharging the first capacitive sensor 102a, it includes alternately configuring one of the first transfer unit 106a and the second transfer unit 106b to transfer the charge from the first capacitive sensor 102a to the first sampling capacitor 110a through the first input terminal 104a.

[0087] The charging and transfer cycles are repeated until the determination unit 118 determines at step 1404 that the voltage difference across the first sampling capacitor 110a reaches the jump voltage V trip .

[0088] At step 1406, the determination unit 118 generates a first signal N 1x indicating the number of cycles in the first conversion.

[0089] At step 1408, a second conversion is performed. The second conversion is similar to the first conversion, except that the charging phase and the transfer phase of the second conversion are phase-shifted by a half cycle relative to the charging phase and the transfer phase of the first conversion.

[0090] The charging and transfer cycles are repeated until the determination unit 118 determines at step 1410 that the voltage difference across the first sampling capacitor 110a reaches the jump voltage V trip again.

[0091] At step 1412, the determination unit 118 generates a second signal N 2x indicating the number of cycles in the first conversion.

[0092] At step 1414, the determination unit 118 determines the contact or proximity to the first capacitive sensor 102a based on the final count N x , and the final count N x is a combination of the first signal N 1x and the second signal N 2x . In one example, the final count N is defined according to equation (1)x 。

[0093] In a preferred embodiment, contact or proximity to the second capacitive sensor 102b coupled to the second input terminal 104b of the sensing system 100 is determined based on a combination of a third signal and a fourth signal generated in the same manner, wherein the first switching unit 108a and the second switching unit 108b reciprocally configure each of the first transfer unit 106a and the second transfer unit 106b to alternately transfer charge from the first capacitive sensor 102a to the first sampling capacitor 110a, and transfer charge from the second capacitive sensor 102b to the second sampling capacitor 110b.

[0094] In another preferred embodiment, the determination unit 118 determines contact or proximity to both the first capacitive sensor 102a and the second capacitive sensor 102b based on a combination of the first signal and the third signal.

[0095] Reference Figure 15 , a flowchart of a method 1500 for sensing contact or proximity to a capacitive sensor using a sensing system according to a sixth embodiment of the present disclosure is shown. Referring to Figure 8 the sensing system 800, the sensing system includes a first switching unit 808a configured to selectively electrically couple any one of a second number of transfer units 806 to transfer charge from any one of a first number of input terminals 804 of the sensing system 800, wherein at least one of the first number and the second number is equal to or greater than two. In Figure 9 the example shown, the sensing system 800 includes one input terminal 804a, and a first transfer unit 806a and a second transfer unit 806b.

[0096] Starting from step 1502, where a first conversion is performed. The sensing system 800 configures the capacitive sensor 802a to be repeatedly charged and discharged in consecutive cycles, wherein discharging the first capacitive sensor 802a includes alternately configuring the first transfer unit 806a to transfer charge from the capacitive sensor 802a to the first sampling capacitor 810a, and configuring the second transfer unit 806b to transfer charge from the first capacitive sensor 802a to the second sampling capacitor 810b.

[0097] The charging and transfer cycles are repeated until the determination unit 818 determines at step 1504 that the voltage difference across the first sampling capacitor 810a reaches a first jump voltage V trip1 , and the voltage difference across the second sampling capacitor 810b reaches a second jump voltage V trip2 . In a preferred embodiment, the first jump voltage V trip1 and the second jump voltage V trip2equal to the same predetermined jump voltage V trip .

[0098] At step 1506, determination unit 818 determines a first signal N1 indicating the number of cycles for charging the voltage difference across first sampling capacitor 810a to a first jump voltage V trip1 and a second signal N2 indicating the number of cycles for charging the voltage difference across second sampling capacitor 810b to a second jump voltage V trip2 .

[0099] At step 1508, determination unit 818 determines contact with or proximity to first capacitance sensor 802a based on a final count N, which is a combination of first signal N1 and second signal N2. In one example, the final count N is defined according to equation (8).

[0100] Reference Figure 16 , shows a flowchart of a method 1600 for sensing contact with or proximity to a first capacitance sensor and a second capacitance sensor using a sensing system according to a seventh embodiment of the present disclosure. Reference Figure 9 to sensing system 900, the sensing system includes a first input terminal 904a and a second input terminal 904b respectively coupled to a first capacitance sensor 902a and a second capacitance sensor 902b, and a transfer unit 906a.

[0101] Starting from step 1602, sensing system 900 configures first capacitance sensor 902a and second capacitance sensor 902b to be alternately charged and discharged in consecutive cycles, where discharging first capacitance sensor 902a and second capacitance sensor 902b includes configuring transfer unit 906a to alternately transfer charge from first capacitance sensor 902a through first input terminal 904a to first sampling capacitor 910a, and transfer charge from second capacitance sensor 902b through second input terminal 904b to second sampling capacitor 910b.

[0102] The charging phase and transfer phase of first capacitance sensor 902a and second capacitance sensor 902b are repeated respectively until the determination unit 918 determines at step 1604 that the voltage difference across the corresponding sampling capacitor 910a / 910b reaches the jump voltage V trip .

[0103] At step 1606, determination unit 918 generates a first signal N A and a second signal N B , where the first signal N A indicates the number of cycles for charging the voltage difference across first sampling capacitor 910a to the jump voltage V tripThe number of cycles, and the second signal N B Indicates the number of cycles for charging the voltage difference across the second sampling capacitor 910b to the jump voltage V in the first conversion trip .

[0104] At step 1808, determination unit 918 determines the contact or proximity to the first capacitance sensor 1102a and the second capacitance sensor 1102b respectively based on the first signal N A and the second signal N B . In another example, in a parallel scan configuration, determination unit 918 determines the contact or proximity to both the first capacitance sensor 1102a and the second capacitance sensor 1102b based on the combination of the first signal N A and the second signal N B according to equation (7).

[0105] Similarly, as discussed above, the contact or proximity to each of the first capacitance sensor 902a and the second capacitance sensor 902b can be determined based on two conversions with a half-cycle phase shift to eliminate the influence of input noise.

[0106] The description of the preferred embodiments of the present invention is presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the disclosed form. Many modifications, variations, changes, substitutions, and equivalents will be apparent to those skilled in the art without departing from the spirit and scope of the present disclosure as claimed.

Claims

1. A system for sensing contact or proximity, comprising: A first number of input terminals configured to couple to one or more capacitance sensors, the first number of input terminals including a first input terminal configured to couple to a first capacitance sensor; A second number of transfer units configured to transfer charge from the one or more capacitance sensors through the first number of input terminals during a transfer phase of a cycle of the one or more capacitance sensors, wherein the second number of transfer units includes a first transfer unit and a second transfer unit, and at least one of the first number and the second number is equal to or greater than two; And A first switching unit coupled between the first number of input terminals and the second number of transfer units, configured to alternately electrically couple the first input terminal to one of the first transfer unit and the second transfer unit during each transfer phase of the first capacitance sensor.

2. The system according to claim 1, further comprising a second switching unit coupled to the second number of transfer units, wherein the first switching unit and the second switching unit are configured to alternately electrically couple one of the first transfer unit and the second transfer unit between the first input terminal and a first sampling capacitor during each transfer phase of a cycle of the first capacitance sensor, so as to transfer the charge charged to the first capacitance sensor during the charging phase of the cycle to the first sampling capacitor, and determine the contact or proximity based on the number of cycles for charging the voltage difference across the first sampling capacitor to a first jump voltage.

3. The system according to claim 2, wherein the system performs a first conversion and a second conversion, the cycle of the first capacitance sensor in the second conversion is phase-shifted by a half cycle relative to the cycle of the first capacitance sensor in the first conversion, wherein in each of the first conversion and the second conversion, the voltage difference across the first sampling capacitor is charged to the first jump voltage, and the system further includes a determination unit coupled to the first sampling capacitor, configured to generate a first signal indicating the number of cycles in the first conversion and a second signal indicating the number of cycles in the second conversion, wherein the contact or proximity to the first capacitance sensor is determined based on a combination of the first signal and the second signal.

4. The system according to claim 2, wherein the first number of input terminals further includes a second input terminal configured to couple to a second capacitance sensor, wherein the first switching unit and the second switching unit are configured to alternately electrically couple one of the first transfer unit and the second transfer unit between the second input terminal and a second sampling capacitor during a transfer phase of the second capacitance sensor.

5. The system according to claim 4, wherein the period of the second capacitive sensor is a half-period phase shift relative to the period of the first capacitive sensor.

6. The system according to claim 4, wherein the period of the second capacitive sensor is synchronized with the period of the first capacitive sensor, and the first switching unit and the second switching unit are configured to alternately and reciprocally electrically couple the first transfer unit and the second transfer unit between the first input terminal and the first sampling capacitor and between the second input terminal and the second sampling capacitor.

7. The system according to claim 4, wherein the system further includes a determination unit coupled to the first sampling capacitor and the second sampling capacitor, the determination unit generates a first signal indicating the number of periods for charging the voltage difference across the first sampling capacitor to a first jump voltage, and a second signal indicating the number of periods for charging the voltage difference across the second sampling capacitor to a second jump voltage, wherein the contact or proximity to both the first capacitive sensor and the second capacitive sensor is determined based on a combination of the first signal and the second signal.

8. The system according to claim 4, wherein the first switching unit and the second switching unit are configured to alternately electrically couple the first transfer unit between the first input terminal and the first sampling capacitor and the second transfer unit between the first input terminal and the second sampling capacitor, and the system further includes a determination unit coupled to the first sampling capacitor and the second sampling capacitor, the determination unit generates a first signal indicating the number of periods for charging the voltage difference across the first sampling capacitor to a first jump voltage; and a second signal indicating the number of periods for charging the voltage difference across the second sampling capacitor to a second jump voltage, wherein the contact or proximity to the first capacitive sensor is determined based on a combination of the first signal and the second signal.

9. The system according to claim 1, wherein the first number of input terminals includes a first input terminal and a second input terminal configured to be respectively coupled to a first capacitive sensor and a second capacitive sensor, and the second number of transfer units includes one transfer unit, and the system further includes a second switching unit coupled between the transfer unit and the first sampling capacitor and the second sampling capacitor, and the first switching unit and the second switching unit are configured to alternately electrically couple the transfer unit between the first input terminal and the first sampling capacitor and between the second input terminal and the second sampling capacitor.

10. A method of operating a contact or proximity sensing system including a first number of input terminals and a second number of transfer units, the method comprising: charging one or more capacitive sensors during a charging phase of a plurality of periods of the one or more capacitive sensors; and Optionally, any one of the second quantity of transfer units is configured to transfer charge from the one or more capacitive sensors through any one of the first quantity of input terminals during the transfer phase of each cycle, wherein at least one of the first quantity and the second quantity is equal to or greater than two.

11. The method according to claim 10, wherein the first quantity of input terminals includes a first input terminal configured to couple to a first capacitive sensor, and the second quantity of transfer units includes a first transfer unit and a second transfer unit, the method including alternately configuring one of the first transfer unit and the second transfer unit to transfer the charge from the first capacitive sensor.

12. The method according to claim 11, further comprising: Alternately configuring one of the first transfer unit and the second transfer unit to transfer the charge from the first capacitive sensor to a first sampling capacitor during each transfer phase.

13. The method according to claim 12, further comprising: Charging a voltage difference across the first sampling capacitor to a first jump voltage in a first conversion and generating a first signal indicative of the number of cycles in the first conversion; Charging the voltage difference across the first sampling capacitor to the first jump voltage in a second conversion and generating a second signal indicative of the number of cycles in the second conversion, wherein the cycles in the second conversion are phase-shifted by a half cycle relative to the cycles in the first conversion; and Determining contact with or proximity to the first capacitive sensor based on a combination of the first signal and the second signal.

14. The method according to claim 12, wherein the first quantity of input terminals further includes a second input terminal configured to couple to a second capacitive sensor, the method including: Alternately configuring one of the first transfer unit and the second transfer unit to transfer charge from the second capacitive sensor to a second sampling capacitor during each transfer phase of the second capacitive sensor.

15. The method according to claim 14, further comprising reciprocally and alternately configuring the first transfer unit and the second transfer unit to transfer the charge from the first capacitive sensor to the first sampling capacitor and transfer the charge from the second capacitive sensor to the second sampling capacitor.

16. The method according to claim 15, further comprising: Generating a first signal indicative of the number of cycles for charging a voltage difference across the first sampling capacitor to a first jump voltage, and a second signal indicative of the number of cycles for charging a voltage difference across the second sampling capacitor to a second jump voltage; And Determining contact with or proximity to both the first capacitive sensor and the second capacitive sensor based on a combination of the first signal and the second signal.

17. The method according to claim 11, further comprising: Configure the first transfer unit and the second transfer unit to alternately transfer the charge to a first sampling capacitor and a second sampling capacitor, respectively; Generate a first signal indicative of the number of the periods for charging the voltage difference across the first sampling capacitor to a first jump voltage, and a second signal indicative of the number of the periods for charging the voltage difference across the second sampling capacitor to a second jump voltage; And Determine contact with or proximity to the first capacitance sensor based on a combination of the first signal and the second signal.

18. The method according to claim 10, wherein the first number of input terminals includes a first input terminal and a second input terminal respectively configured to couple to a first capacitance sensor and a second capacitance sensor, and the second number of transfer units includes one transfer unit, wherein the method includes: Configure the transfer unit to alternately transfer the charge from the first capacitance sensor to the first sampling capacitor and transfer the charge from the second capacitance sensor to the second sampling capacitor.

19. The method according to claim 18, further comprising: Charge the voltage difference across the first sampling capacitor to a first jump voltage in a first conversion and generate a first signal indicative of the number of the periods in the first conversion; Charge the voltage difference across the first sampling capacitor to the first jump voltage in a second conversion and generate a second signal indicative of the number of the periods in the second conversion, wherein the periods in the second conversion are phase-shifted by a half period relative to the periods in the first conversion; and Determine contact with or proximity to the first capacitance sensor based on a combination of the first signal and the second signal.

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