TWI485991B - Ghost key detecting circuit and related method - Google Patents

Description

Ghost key detection circuit and related method

The present invention refers to a user interface apparatus, and more particularly to a keyboard having a key matrix structure and related methods.

At present, in order to avoid the use of excessive wiring, the manufacturing cost of the keyboard itself is increased and the inconvenience in actual assembly, the conventional keyboard is mostly designed by means of a key matrix. For a keyboard designed with a key matrix, due to the physical characteristics of the key matrix itself, the occurrence of a ghost key can become a factor that cannot be ignored in conventional keyboard design.

In general, in order to avoid ghost keys, it is often necessary to increase the size of the button matrix, or to have to separate each button with a diode. However, such a method will greatly increase the manufacturing cost of the keyboard itself. .

Therefore, one of the objects of the present invention is to propose a ghost key detection circuit with a novel design to avoid ghost keys, which enjoys lower manufacturing cost.

According to an embodiment of the invention, a ghost key detection circuit is disclosed. The ghost key detection circuit includes a plurality of switching elements with a predetermined resistance value, at least one set of scan lines, at least one set of return lines, and a level detecting circuit, wherein the set of return lines and the set of scan lines are mutually Intersection and respectively coupled to the plurality of switching elements, and the The level detecting circuit is coupled to the set of return lines and configured to detect the measured voltage values on the set of return lines to indicate that at least one of the switching elements on the set of scan lines corresponding to the set of return lines is non-conductive State or conduction state.

According to an embodiment of the invention, a method for using a ghost key detection circuit is further disclosed. The ghost key detection circuit has at least a plurality of switching elements with a predetermined resistance value, at least one set of scan lines and at least one set of return lines, and the set of return lines and the set of scan lines intersect each other and are respectively coupled to the plurality of Switching elements. The method includes the following steps: performing level detection on at least one measured voltage value on the set of return lines; when one of the measured returns on at least one of the set of return lines is greater than or equal to a reference voltage value, Generating a logic level signal to indicate that a switching element corresponding to the return line on the current scan line is in a non-conducting state; and generating a logic level when the measured voltage value on the return line is less than the reference voltage value The bit signal indicates that the switching element corresponding to the return line on the current scan line is in an on state.

In order to clearly understand the technical means of the present invention and the problems that can be solved by the present invention, the cause of the occurrence of ghost keys will be briefly described below. Please refer to FIG. 1. FIG. 1 is a schematic diagram of a standard two by two button matrix 100 of a general keyboard. The key matrix 100 includes four buttons forming a double cross structure, that is, correspondingly corresponding thin film switching elements SW ₁ to SW ₄ . Each of the membrane switching elements SW ₁ -SW ₄ has a first end and a second end. When the key corresponding to a membrane switch element (e.g., SW ₁₎ is pressed, a first end of the second end will be in contact therewith, such that the membrane switch element in a conductive state (ON), leading to a scan line (scan Line) X ₁ will be turned on with the return line Y ₁ . Based on this phenomenon, it is known from the signal on the return line Y ₁ whether the button corresponding to the switching element SW ₁ is currently pressed. Conversely, when the button corresponding to the membrane switching element is not pressed, the first end thereof is not in contact with the second end, and thus the membrane switching element is in a non-conducting state (off), return line (return) Line) There is no signal transmission on Y ₁ .

However, because of the physical characteristics of the key matrix 100, as long as the switching element SW to any key corresponding to three ₁ ~ SW ₄ is pressed, even if the remaining fourth key is not actually pressed, will The fourth button is incorrectly judged to be pressed. This button, which is not actually pressed but has been misjudged and has been pressed, is called a ghost key. Specifically, please refer to FIGS. 2A to 2D, which respectively show the possible causes of the ghost key phenomenon in the key matrix 100 shown in FIG. 1. As shown in FIG. 2A, when the switching elements SW ₁ to SW ₃ are turned on, the scanning line X ₂ and the return line Y ₂ are turned on by another conduction path (ie, a thick black line via the switching elements SW ₁ to SW ₃ ). Therefore, the switching element SW _{4 is} also in an on state, and thus the button corresponding to the switching element SW ₄ is erroneously pressed (ie, a ghost key occurs). In addition, as shown in FIG. 2B, when the switching elements SW ₂ to SW ₄ are pressed by their corresponding buttons, the switching elements SW ₂ to SW ₄ will provide another conduction path, resulting in the scanning line X ₁ and the return. The line Y _{1 is} turned on, and the button corresponding to the misjudgment switching element SW ₁ is pressed. Furthermore, as shown in FIG section 2C, the switching element SW is turned to _1, SW _3, and a second conduction path SW ₄ is provided, will be such that the scanning line X ₁ and the return line Y ₂ is turned on, and thus false switching element SW ₂ Suo The corresponding button is pressed; further, as shown in FIG. 2D, when the scanning line X ₂ and the return line Y ₁ are turned on, it is erroneously determined that the button corresponding to the switching element SW ₃ is pressed.

The novel design proposed by the present invention can avoid the above-mentioned ghost key problem, that is, the present invention can truly distinguish whether the key is actually pressed. Please refer to FIG. 3, which is a schematic diagram of a ghost key detection circuit 300 according to an embodiment of the present invention. In this embodiment, the ghost key detection circuit 300 is a membrane keyboard, and includes at least one set of scan lines (including a first scan line S ₁ and a second scan) respectively having a resistance R _C . a line S ₂ ), at least one set of return lines (including a first return line R ₁ and a second return line R ₂ ), a plurality of switching elements 305a-305d having a predetermined resistance R _B , having a resistance R _A two resistive elements 310a and 310b, is defined with the reference voltage level V _th of the detecting circuit 315 and a processor 320, wherein the first scan line S _1, a second scan line S _2, a first of R ₁ and return line The two return lines R ₂ intersect each other and are respectively coupled to the switching elements 305a to 305d to form a well-shaped structure as shown in FIG. 3, and each of the switching elements 305a to 305d has a first end. And a second end, at least one of the first and second ends (eg, the first end) is coated with a specific conductive material (in this embodiment, for example, a conductive carbon ink), such that each switch based element having a predetermined resistance value R _B, to the first end of the switching elements 305a and 305b line coupled to the first scan line S _1, of which Ends respectively coupled to the first return line R ₁ and the first return line R _2, whereas the switching element 305c and the line 305d of the first end coupled to the second scan line S _2, a second terminal respectively coupled to the The first return line R ₁ and the first return line R ₂ , in addition, the second ends of the switching elements 305a, 305c are coupled to the resistive element 310a via the first return line R ₁ and the second of the switching elements 305b, 305d The end is coupled to the resistive element 310b via the second return line R _{2 ,} and the other end of the resistive element 310 a , 310 b is coupled to a voltage source. As shown in FIG. 3, the level detecting circuit 315 is coupled to the first and second return lines R ₁ and R ₂ , and can detect the measurement on the first and second return lines R ₁ and R ₂ . voltage value to indicate that the corresponding scan lines S1 and S2 on state 305a ~ 305d in the return line R ₁ and R ₂ each switching element (in a non-conductive state or a conductive state).

Briefly, in the embodiment of the present invention, based on 310b, a plurality of switching elements 305a ~ 305d, a first scan line and a second scan line S-value resistor element 310a ₁ S ₂ itself, as long as the switching element 305a ~ 305d conducting state (i.e., opposite the keys depressed state) vary, it will affect the first, second return line R ₁ and the voltage value measured on the ₂ R, such that the level detecting circuit 315 based on the reference voltage The comparison of the value _Vth with the measured voltage value detects the pressed state of the button corresponding to the switching elements 305a-305d. Based on the aforementioned well-word structure, when the switching element corresponding to a button is not turned on because the button is pressed, the relative measured voltage value is more divided by the conduction path through the other three switching elements. Therefore, it is greater than or equal to the reference voltage value V _th , and when the switching element corresponding to a button is turned on because the button is pressed, the relative measured voltage value is less divided due to the difference in the conduction path. Therefore, it is smaller than the reference voltage value V _th . Therefore, by comparing the measured voltage value with the reference voltage value V _th , the pressed state of the button can be known.

In order to correctly determine the actual button state, the level detecting circuit 315 performs a level detecting operation on the measured voltage values on the first and second return lines R ₁ and R ₂ respectively, thereby determining that the corresponding The actual button state of each switching element. Specifically, when the level detecting circuit 315 determines that the measured voltage value on the first return line R ₁ is greater than or equal to a reference voltage value V _th , the level detecting circuit 315 generates the first logic level signal. S _L , to indicate that the switching element 305 a corresponding to the first return line R ₁ on a current scan line (for example, S ₁ ) is in a non-conducting state, that is, the button corresponding to the switching element 305 a is not pressed. On the contrary, when the measured voltage value on the first return line R ₁ is less than the reference voltage value V _th , the level detecting circuit 315 indicates that the switching element 305a is in an on state, that is, the button corresponding to the switching element 305a is Press. Thus, coupled to the level detector circuit 315 to a processor 320 according to the first and second logic level signals S _L and S _L level detector circuit 315 'generated by the switching element corresponding to each determination The actual button state does not occur with ghost keys.

In order to make the level detecting circuit 315 can detect based on a reference voltage value V _th of a first, opposite the second change in the voltage on the return line ₂ R ₁ and R, which can be used outside of the first transistor and the interior, the second The electrical connection relationship between the return lines R ₁ and R ₂ defines a reference voltage value V _th . In detail, the reference voltage value V _th is designed to be coupled to the first transistor Q _{1 of the} first return line R ₁ and the threshold voltage of the third transistor Q ₃ coupled to the first transistor Q ₁ . In the first detecting module composed of the first transistor Q ₁ and the second transistor Q ₂ , when the measured voltage value of the first return line R ₁ is greater than or equal to the threshold voltage of the first transistor Q ₁ (ie, reference voltage value V _th ), the first transistor Q ₁ is turned on and its collector voltage is pulled low, so that the second transistor Q ₂ fails to exceed its threshold voltage due to the base-emitter cross-voltage ( Or turn-on voltage) and not turned on. At this time, the first logic level signal S _L will have a high logic level, and the button corresponding to one of the switching elements 305a and 305c on the first return line R ₁ is not pressed. Conversely, when the measured voltage value of the first return line R ₁ is less than the reference voltage value V _th , the first transistor Q ₁ does not conduct, but the open circuit relationship causes the base of the second transistor Q ₂ - The emitter cross voltage exceeds its turn-on voltage, leaving the second transistor Q ₂ itself turned on. At this time, the first logic level signal S _L will have a low logic level, and the button corresponding to one of the switching elements 305a and 305c on the first return line R ₁ has been pressed. The operation of the second detecting module of the first transistor Q ₃ and the second transistor Q ₄ is similar to that of the first detecting module, and is not described herein. Thus, according to the first transistor Q is turned on or _{not. 1} or Q can output signals having different ₃ logic level to indicate whether the key is pressed. When the level detecting circuit 315 detects the relative change of the voltages on the first and second return lines R ₁ and R ₂ based on the reference voltage value V _th , the relative generated logical level signal S _L can be used to determine Corresponding to the state of the keys of each of the switching elements 305a to 305d.

Please refer to FIG. 4, which is an equivalent circuit diagram of the ghost key detecting circuit 300 shown in FIG. As shown in FIG. 4, when the operation of the first scan lines S _1, which is connected to the voltage lines SCAN ₁ will be a low voltage, while in the present embodiment, this is tantamount to a line coupled to the ground. When the second scan line S _{2 is} activated, the voltage SCAN ₂ connected thereto is also a low voltage, which is also coupled to the ground in the embodiment. As shown in FIG. 4, when the switching elements 305a to 305d are both in a non-conducting state, the supply voltage V _DD is turned on through the resistance elements 310a and 310b when the first and second scanning lines S ₁ and S _{2 are} activated. The first transistors Q ₁ and Q _{3 are} such that the first and second logic level signals S _L , S _L ' have a high logic level as described above. In this manner, the processor 320 determines the state of the button corresponding to each switching element according to which of the first and second scan lines S ₁ , S ₂ is activated and the logic levels of the signals S _L , S _L '.

Fig. 5 to Fig. 8 respectively show equivalent circuits when the keys corresponding to the switching elements 305a to 305d shown in Fig. 3 are respectively pressed. In order to simplify the description, only the fifth figure is illustrated here. Since the circuit operation principle of the remaining 6th to 8th drawings is similar to the circuit operation principle of FIG. 5, it will not be described here.

As shown in FIG. 5, since only the button corresponding to the switching element 305a is pressed and the remaining buttons are not pressed, the supply voltage V _{DD is} still turned on through the resistive element 310b when the second scanning line S _{2 is} activated. The first transistor Q _{3 has a} second logic level signal S _L ' with a high logic level. However, the measured voltage value V _R1 on the first return line R ₁ is determined by the following equation due to the partial pressure when the first scanning line S ₁ is operated: V _R1 =V _DD ×(R _B +R _C ) / ( R _A + R _B + R _C ) based on the above relationship, when only the switching element 305a is not turned on, so that the measured voltage value V _R1 on the first return line R ₁ is smaller than that of the first transistor Q ₁ threshold voltage (i.e., the reference voltage value V _th), therefore, the first transistor Q ₁ will not be turned on, and the first logic level signal S _L will have a low logic level, so that the processor 320 may know the actual The button corresponding to only the switching element 305a is pressed; the relationship between V _R1 and V _th can be expressed as follows: V _R1 = V _DD × (R _B + R _C ) / (R _A + R _B + R _C ) <V _th In general, the resistance value R _A can be designed to be greater than the resistance values R _B and R _C such that the divided voltage value V _R1 will be smaller than the threshold voltage V _{th of the} first transistor Q ₁ .

Please refer to FIG. 9 , which is an equivalent circuit when the buttons corresponding to the switching elements 305 b 305 305 of FIG. 3 are pressed and the buttons corresponding to the remaining switching elements 305 a are not pressed; FIG. 9 The circuit of the equivalent circuit for the resistance values R _A , R _B and R _C can be further reduced to the circuit diagram shown in FIG. 10, and the first and second diagrams are respectively shown in FIGS. 11A to 11B. An equivalent circuit diagram of the circuit shown in FIG. 10 when the scanning lines S ₁ and S ₂ are operated. As shown in FIG. 11B, when the second scan line S ₂ operates, the voltage SCAN ₂ forms the same ground level and the voltage SCAN ₁ forms the same supply voltage level (for example, V _DD ), at which time the voltage value VR ₁ and VR ₂ is equal to V _DD ×(R _B +R _C )/(R _A +R _B +R _C ), as previously described, V _DD ×(R _B +R _C )/(R _A +R _B +R _C ) will be lower than the predetermined threshold voltage _Vth , and by the operation of the above-mentioned level detecting circuit 315, the processor 320 can correctly judge that the buttons corresponding to the switching elements 305c and 305d are pressed. On the other hand, as shown on FIG. 11A, when the operation of the first scan lines S _1, the voltage of the same shape lines SCAN ₁ and a ground level voltage of the same shape then the SCAN ₂ the supply voltage level (e.g., V _DD), when the voltage The value VR ₁ and VR ₂ will be different, wherein the voltage value VR ₂ will be equal to V _DD ×(R _B +R _C )/(R _A +R _B +R _C ), and the voltage value VR ₁ due to the partial pressure relationship will be Determined by the following equation: V _R1 =V _DD ×(3×R _B +R _C )/(R _A +3×R _B +R _C )

From this, it can be seen that the value of the measured voltage value V _R1 at this time is determined by the relationship between the resistance value R _A , the predetermined resistance value R _{B of the} switching elements 305b to 305d, and the resistance value R _C of the scanning line S ₂ . Therefore, when any three buttons in the button matrix are pressed and a remaining button is not pressed, although a switch component corresponding to the remaining button is determined to be in a conductive state due to another conductive path, the conductive The return line measurement voltage value caused by the path is different from the return line measurement voltage value caused by the conductive path when the remaining button is actually pressed. Therefore, in this embodiment, the resistance value R _A can be appropriately designed. R _B and R _C such that the measured voltage value V _R 1 at this time is greater than or equal to the threshold voltage of the transistor Q1 (ie, the reference voltage value V _th ), therefore, the transistor Q ₁ will be turned on, and the first logic The level signal S _L has a high logic level, so the aforementioned processor 320 can know that only the button corresponding to the switching element 305a is not pressed; the relationship between V _R1 and V _th can be expressed as follows: V _R1 =V _DD ×(3×R _B +R _C )/(R _A +3×R _B +R _C )≧V _th

Therefore, by appropriately designing the resistance _values R _A , R _B and R _C and the operation of the transistor stabilization in the level detecting circuit 315, the ghost key detecting circuit 300 of the present embodiment can achieve the following effects: when formed When any one of the buttons of a well font structure is pressed and a remaining button is not pressed, the ghost key detecting circuit 300 can correctly determine that the remaining button is not actually pressed. That is, the design of the ghost key detection circuit 300 does not cause misjudgment due to the physical characteristics of the well-type structure itself, so that ghost keys can be avoided.

In addition, in another embodiment, the transistors Q ₁ -Q ₄ in the level detecting circuit 315 can also be implemented by using a Field Effect Transistor (FET). Furthermore, in other embodiments, part of the operation of the first and second detection modules can also be implemented by using an operational amplifier; please refer to FIG. 12, which is illustrated as the level detection shown in FIG. Another implementation variation of measurement circuit 315. As shown, the first and second detection modules are implemented by operational amplifiers OP ₁ and OP ₂ , respectively, wherein operational amplifiers OP ₁ and OP ₂ are used as comparators to compare comparators OP _{1 .} For example, it has an inverting input coupled to one of the reference voltage values V _th , a non-inverting input for receiving the measured voltage value V _R1 on the first return line R ₁ , and used to generate the first An output terminal of the logic level signal S _L , when the measured voltage value V _R1 on the first return line is greater than the reference voltage value V _th , the comparator OP ₁ outputs a first logic level signal S having a high logic level _L , and when the measured voltage value V _R1 on the first return line is smaller than the reference voltage value V _th , the comparator OP ₁ outputs a first logic level signal S _L having a low logic level, and the comparator OP ₂ The operation is similar to that of the comparator OP ₁ . Therefore, it can be seen from the above that the level detecting circuit 315 is implemented by an operational amplifier, and the subsequent processor 320 can also determine whether the button of the well type structure is actually pressed; this embodiment also belongs to the scope of the present invention. . In addition, in another embodiment, one of the first and second detecting modules may be implemented by the first transistor and the second transistor shown in FIG. 3, and the first, The second detection module is implemented by an operational amplifier. In other words, in the embodiment of the present invention, at least one of the first and second detection modules utilizes the first transistor and the second The transistor and the associated resistor are implemented, and at least one of the first and second detection modules is implemented by an operational amplifier; the foregoing various implementation variations are in accordance with the spirit of the present invention.

The above are only the preferred embodiments of the present invention, and all changes and modifications made to the scope of the present invention should be within the scope of the present invention.

100‧‧‧Key Matrix

300‧‧‧ ghost key detection circuit

305a~305d‧‧‧Switching elements

310a, 310b‧‧‧resistive components

315‧‧ ‧ level detection circuit

320‧‧‧ processor

Figure 1 is a schematic diagram of a standard two by two button matrix with a keyboard.

Fig. 2A to Fig. 2D are schematic diagrams showing a possible situation in which a key matrix of the key matrix shown in Fig. 1 has a ghost key.

FIG. 3 is a schematic diagram of a ghost key detection circuit according to an embodiment of the present invention.

Fig. 4 is a schematic diagram showing an equivalent circuit of the ghost key detecting circuit shown in Fig. 3.

Fig. 5 is a schematic diagram showing an equivalent circuit of the ghost key detecting circuit when the button corresponding to the first switching element shown in Fig. 3 is pressed.

Fig. 6 is a schematic diagram showing an equivalent circuit of the ghost key detecting circuit when the button corresponding to the second switching element shown in Fig. 3 is pressed.

Fig. 7 is a schematic diagram showing an equivalent circuit of the ghost key detecting circuit when the button corresponding to the third switching element shown in Fig. 3 is pressed.

Fig. 8 is a schematic diagram showing an equivalent circuit of the ghost key detecting circuit when the button corresponding to the fourth switching element shown in Fig. 3 is pressed.

Figure 9 is a view corresponding to the second, third, and fourth switching elements shown in Fig. 3. The equivalent circuit diagram of the ghost key detection circuit when the key is pressed and the remaining corresponding switch element is not pressed.

Figure 10 is a simplified circuit diagram of the equivalent circuit shown in Figure 9.

11A to 11B are schematic diagrams showing the operation of the simplified equivalent circuit shown in Fig. 10 when the first and second scanning lines are operated.

Fig. 12 is a view showing another variation of the implementation of the level detecting circuit shown in Fig. 3.

300‧‧‧ ghost key detection circuit

305a~305d‧‧‧Switching elements

310a, 310b‧‧‧resistive components

315‧‧ ‧ level detection circuit

320‧‧‧ processor

Claims (11)

A ghost key detection circuit includes: a plurality of switching elements with a predetermined resistance; at least one set of scan lines; at least one set of return lines, the set of return lines and the set The scan lines are coupled to each other and coupled to the plurality of switching elements; a level detecting circuit is coupled to the set of return lines for detecting the measured voltage values on the set of return lines to indicate the set of scans The at least one switching component on the line corresponding to the set of return lines is in a non-conducting or conducting state, the level detecting circuit includes: a first detecting module coupled to the first return line for receiving the One of the first return lines measures the voltage value to generate the first logic level signal; and a second detection module is coupled to the second return line for receiving one of the second reward lines a voltage value to generate the second logic level signal; wherein at least one of the first and second detection modules includes: a first transistor having a first end coupled to a supply voltage, Coupling to a second end of a grounding level and coupling to a return a control terminal, wherein the reference voltage value is a threshold voltage of the first transistor; and a second transistor having a first end for generating a logic level signal coupled to the ground level A second end is coupled to a control end of the first end of the first transistor. The ghost key detecting circuit of claim 1, wherein the at least one switching component corresponding to the set of return lines on the current scan line when the at least one voltage value on the set of return lines is greater than or equal to the reference voltage value The system is in a non-conducting state. Such as the ghost key detection circuit described in claim 1, wherein the set of return lines When at least one of the voltage values is less than the reference voltage value, the at least one switching element corresponding to the set of return lines on the current scan line is in an on state. The ghost key detection circuit of claim 1, further comprising: a processor coupled to the level detecting circuit for generating the first one according to the level detecting circuit The second logic level signal is used to determine the state of the button corresponding to each switching element. The ghost key detection circuit of claim 1, further comprising: a plurality of resistance elements, each of the resistance elements having a first resistance value and coupled to the set of return lines respectively; At least one end of the first and second ends of a switching element is coated with a specific conductive material such that each switching element has the predetermined resistance value, and the set of scan lines respectively have a third resistance value; When three of the plurality of switching elements are in an on state and one of the remaining switching elements is in a non-conducting state, one of the measured voltage values on one of the return lines corresponding to the remaining switching elements is based on the first resistance of the one of the resistive elements The value, the predetermined resistance of the three switching elements, and the third resistance of the set of scan lines are greater than or equal to the reference voltage value. The ghost key detection circuit of claim 1, further comprising: a plurality of resistance elements each having a first resistance value and coupled to the set of return lines respectively; wherein each of the switching elements is At least one end of the first and second ends is coated with a specific conductive material such that each of the switching elements has the predetermined resistance value, and the set of scan lines respectively have a third resistance value; and when corresponding to the set of return lines When the at least one switching element is in an on state, the measured voltage value on one of the return lines corresponding to the switching element is based on the first resistance value, a predetermined resistance value of the switching element, and a third resistance value of the set of scan lines. Less than the reference voltage value. The ghost key detection circuit of claim 1, wherein at least one of the first and second detection modules comprises: a comparator having a reverse coupled to the reference voltage value An input, a non-inverting input for receiving a measured voltage value on a return line, and an output for generating a logic level signal. A method for detecting a ghost key detecting circuit, the ghost key detecting circuit having at least a plurality of switching elements with a predetermined resistance value and a level detecting circuit, the level detecting circuit comprising: a first The detection module is coupled to the first return line for receiving a measured voltage value on the first return line to generate the first logic level signal; and a second detecting module coupled to the second detecting module The second return line is configured to receive a measured voltage value on the second return line to generate the second logic level signal; at least one of the first and second detecting modules includes: a first The transistor has a first end coupled to a supply voltage, a second end coupled to a ground level, and a control end coupled to a return line; the reference voltage is the first transistor a threshold voltage; and a second transistor having a first end for generating a logic level signal, a second end coupled to the ground level, and the first end coupled to the first transistor a control end of one end, at least one set of scan lines and at least one set of return lines, the set of return lines And the set of scan lines intersect each other and are respectively coupled to the plurality of switch elements, and the method includes: performing level detection on the at least one measured voltage value on the set of return lines; wherein, when the set of return lines is When the measured voltage value of the at least one return line is greater than or equal to a reference voltage value, indicating that the switching element corresponding to the return line on the current scan line is in a non-conducting state; and wherein the measurement is performed on the return line When the voltage value is less than the reference voltage value, the logic level signal is generated to indicate that the current scan line corresponds to the return line The switching element is in an on state. The method of claim 8, further comprising: determining, according to the logic level signal, a state corresponding to a button of the switching element. The method of claim 8, wherein the ghost key detection circuit further comprises a plurality of resistance elements, each of the resistance elements having a first resistance value and coupled to the set of return lines respectively; When three of the plurality of switching elements are in an on state and the remaining ones are in a non-conducting state, a measured voltage value on a return line corresponding to the remaining switching elements is first due to a resistive element The resistance value, the predetermined resistance of the three switching elements, and the third resistance of the set of scan lines are greater than or equal to the reference voltage value. The method of claim 8, wherein the ghost key detection circuit further comprises a plurality of resistance elements, each of the resistance elements having a first resistance value and coupled to the set of return lines respectively; When the switching element corresponding to the return line is in an on state, the measured voltage value on the return line corresponding to the switching element is due to a first resistance value of a resistive element, a predetermined resistance value of the switching element, and the The relationship of the third resistance of the group scan line is smaller than the reference voltage value.