Light sensing device

Abstract

The present application provides a light sensing device, which includes a sensing circuit, a converting circuit, a coupling mode selection circuit and an amplifying circuit. The sensing circuit detects light and generates a corresponding current signal according to the intensity of the light. The converting circuit converts the current signal into a voltage signal, which includes an AC component and a DC component. The coupling mode selection circuit filters the DC component of the voltage signal to output the AC component of the voltage signal, or does not filter the DC component to output the voltage signal including the AC component and the DC component. The amplifying circuit amplifies the voltage signal after filtering the DC component to generate an output signal when the coupling mode selection circuit filters the DC component, and amplifies the voltage signal including the AC component and the DC component to generate another output signal when the coupling mode selection circuit does not filter the DC component.

Description

Technical Field

[0001] The present disclosure relates to a light sensing device, and more particularly to a light sensing device with an AC coupling mode and a DC coupling mode. Background Art

[0002] Conventional light-sensing devices detect ambient light through a light-detecting element, which generates a current. However, the current generated by this element is often too small and contains excessive noise. Directly utilizing the current generated by the light-detecting element for other applications can easily cause the light-sensing device to malfunction.

[0003] Furthermore, the circuit designs of most light-sensing devices utilize non-integrated, independent passive components. However, using too many non-integrated, independent passive components increases the wiring and area required for the circuit board layout and makes it susceptible to noise interference. Furthermore, if a damaged light-sensing element needs to be replaced with a different one—for example, one of a different model or from a different manufacturer—repairers must further adjust the parameter configurations of other passive components and related circuits. Each replacement of a light-sensing element requires a corresponding adjustment of the circuit configuration, making repair difficult and limiting circuit design flexibility. Summary of the Invention

[0004] The present invention provides a light sensing device. The light sensing device includes a sensing circuit, a conversion circuit, a coupling mode selection circuit, and an amplifier circuit. The sensing circuit detects a light and generates a corresponding current signal according to the intensity of the light. The conversion circuit converts the current signal into a voltage signal, and the voltage signal includes an AC component and a DC component. The coupling mode selection circuit filters out the DC component in the voltage signal to output the AC component in the voltage signal, or the coupling mode selection circuit does not filter out the DC component and outputs a voltage signal including both AC and DC components. The amplifier circuit amplifies the voltage signal after filtering out the DC component to generate an output signal when the coupling mode selection circuit filters out the DC component, and amplifies the voltage signal including both AC and DC components to generate another output signal when the coupling mode selection circuit does not filter out the DC component. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1 FIG. 1 is a block diagram of an optical sensing device according to an embodiment of the present invention.

[0006] Figure 2 for Figure 1 A circuit diagram of an embodiment of a light sensing device.

[0007] Figure 3 for Figure 1 A circuit diagram of another embodiment of a light sensing device.

[0008] Figure 4 Figure 1 is a circuit diagram of an embodiment of a light transistor or photodiode comprising a sensing circuit. Figure 1 Figure 2 is a graph of current versus bias voltage for the light transistor or photodiode of Figure 1.

[0009] Figure 5 Figure 3 is a circuit diagram of an embodiment of a light transistor or photodiode comprising a sensing circuit. Figure 4 Figure 4 is a graph of current versus bias voltage for the light transistor or photodiode of Figure 3.

[0010] BRIEF DESCRIPTION OF DRAWINGS

[0011] 1 light sensing device

[0012] 11 sensing circuit

[0013] 12 conversion circuit

[0014] 121 operational amplifier

[0015] 122 resistor

[0016] 123 capacitor

[0017] 13 coupling mode selection circuit

[0018] 131 AC coupling capacitor

[0019] 132 first switching switch

[0020] 133 resistor

[0021] 134 second switching switch

[0022] 135 third switching switch

[0023] 136 fourth switching switch

[0024] 137 fifth switching switch

[0025] 14 amplification circuit

[0026] 141 operational amplifier

[0027] 142 resistor

[0028] 143 resistor

[0029] 144 capacitor

[0030] 15 bias voltage circuit

[0031] 151-153 bias voltage resistors

[0032] 154-155 switches

[0033] 156 capacitor

[0034] 16 control circuit

[0035] 17 analog-to-digital conversion circuit

[0036] P1 input port

[0037] P2 input port

[0038] P3 input port DETAILED DESCRIPTION

[0039] Please refer to Figure 1 and Figure 2 , Figure 1 FIG. 1 is a block diagram of an embodiment of a light sensing device according to the present application, Figure 2 FIG. 2 is a circuit diagram of an embodiment of the light sensing device of Figure 1 The light sensing device 1 comprises a sensing circuit 11, a conversion circuit 12, a coupling mode selection circuit 13, and an amplification circuit 14. The conversion circuit 12 is coupled between the sensing circuit 11 and the coupling mode selection circuit 13, and the coupling mode selection circuit 13 is coupled between the conversion circuit 12 and the amplification circuit 14.

[0040] In an embodiment, the sensing circuit 11 can be implemented by a phototransistor or a photodiode. The sensing circuit 11 detects a light, and generates a corresponding current signal according to the intensity of the light. For example, the intensity of the light is proportional to the current size of the current signal. If the light is stronger, the sensing circuit 11 generates a current signal with a larger current size. If the light is weaker, the sensing circuit 11 generates a current signal with a smaller current size.

[0041] The conversion circuit 12 is coupled to the output of the sensing circuit 11, and receives the current signal generated by the sensing circuit 11. The conversion circuit 12 converts the current signal into a voltage signal. The coupling mode selection circuit 13 is coupled to the output of the conversion circuit 12, and receives the voltage signal generated by the conversion circuit 12. The coupling mode selection circuit 13 selectively filters out the DC component of the voltage signal to output the AC component thereof, i.e. the coupling mode selection circuit 13 can selectively filter out or not filter out the DC component of the voltage signal. In detail, the light sensing device 1 has an AC coupling mode and a DC coupling mode. When the light sensing device 1 is in the AC coupling mode, the coupling mode selection circuit 13 filters out the DC component of the voltage signal and outputs the AC component thereof, so as to reduce the rising slope and noise of the voltage signal. The voltage signal after filtering out the DC component is more stable, but has a lower voltage level. When the light sensing device 1 is in the DC coupling mode, the coupling mode selection circuit 13 does not filter out the DC component of the voltage signal, but outputs the voltage signal containing the AC component and the DC component. The voltage signal containing the AC component and the DC component has a higher voltage level, because it is not attenuated by the coupling mode selection circuit 13.

[0042] The amplification circuit 14 is coupled to the output of the coupling mode selection circuit 13. When the light sensing device 1 is in the AC coupling mode, the amplification circuit 14 receives the voltage signal containing the AC component after filtering out the DC component by the coupling mode selection circuit 13. The amplification circuit 14 amplifies the voltage signal after filtering out the DC component and generates an output signal (hereinafter referred to as a first output signal). The first output signal is less susceptible to noise interference and has better stability. When the light sensing device 1 is in the DC coupling mode, the amplification circuit 14 receives the voltage signal containing the AC component and the DC component. The amplification circuit 14 amplifies the voltage signal without filtering out the DC component and generates an output signal (hereinafter referred to as a second output signal). The second output signal has a higher voltage level than the first output signal. Accordingly, according to the AC coupling mode and the DC coupling mode of the light sensing device 1, the light sensing device 1 converts light into the first output signal which is amplified and less susceptible to noise interference, or converts light into the second output signal which has a higher voltage level. The light sensing device 1 can provide different output signals according to different application products, and has good product compatibility.

[0043] In one embodiment, the light sensing device 1 further comprises a control circuit 16 coupled to the coupling mode selection circuit 13. The control circuit 16 is capable of controlling the coupling mode selection circuit 13 to filter out the DC component in the voltage signal to output the AC component, or to control the coupling mode selection circuit 13 to not filter out the DC component in the voltage signal to output the DC component and the AC component. Thus, the designer of the light sensing device 1 can set the control circuit 16 to generate a corresponding control signal to control the coupling mode selection circuit 13 to filter out or not filter out the DC component in the voltage signal according to the application of the light sensing device 1. For example, if the light sensing device 1 is applied in a high noise environment, or the current signal generated by the phototransistor or photodiode included in the sensing circuit 11 generates a signal containing more noise, the light sensing device 1 can be controlled by the control circuit 16 to operate in the AC coupling mode; if the current signal generated by the phototransistor or photodiode included in the sensing circuit 11 generates a smaller current signal or the light sensing device 1 is applied in a low noise environment, the light sensing device 1 can be controlled by the control circuit 16 to operate in the DC coupling mode.

[0044] In one embodiment, the conversion circuit 12 comprises an operational amplifier 121 and a resistor 122. The operational amplifier 121 comprises an output terminal, a positive input terminal and a negative input terminal. The positive input terminal and the negative input terminal of the operational amplifier 121 are coupled to the sensing circuit 11. The operational amplifier 121 has a negative feedback circuit, and the resistor 122 is coupled between the output terminal of the operational amplifier 121 and the negative input terminal of the operational amplifier 121, that is, the output terminal of the operational amplifier 121 is coupled to the negative input terminal thereof via the resistor 122 to form the aforementioned negative feedback circuit, and the resistance value of the resistor 122 determines the amplification ratio between the input signal and the output signal of the operational amplifier 121. Here, the current signal generated by the sensing circuit 11 flows through the resistor 122, and the operational amplifier 121 generates the aforementioned voltage signal according to the amplification ratio determined by the resistor 122 to convert the current signal into a voltage signal, and the output terminal of the operational amplifier 121 outputs the voltage signal.

[0045] Furthermore, the conversion circuit 12 further comprises a capacitor 123 coupled between the output terminal of the operational amplifier 121 and the negative input terminal of the operational amplifier 121, and the capacitor 123 is connected in parallel to the resistor 122, and the capacitor 123 is capable of filtering out high-frequency noise. In one embodiment, the resistor 122 is a variable resistor with an adjustable resistance value, and the resistance value of the resistor 122 can be controlled by the control circuit 16, and the operational amplifier 121 can generate a corresponding voltage signal according to the resistor 122 with different resistance values.

[0046] In one embodiment, the coupling mode selection circuit 13 comprises an AC coupling capacitor 131 and a switching switch 132 (hereinafter referred to as the first switching switch 132). The two ends of the AC coupling capacitor 131 are respectively coupled to the output end of the operational amplifier 121 and the amplification circuit 14, and the AC coupling capacitor 131 is connected in series between the operational amplifier 121 and the amplification circuit 14. The two ends of the first switching switch 132 are also respectively coupled to the output end of the operational amplifier 121 and the amplification circuit 14, and the first switching switch 132 is connected in parallel to the AC coupling capacitor 131. The first switching switch 132 is controlled by the control circuit 16 to be in an on state or an off state, and the light sensing device 1 is switched between the DC coupling mode or the AC coupling mode through the on state or the off state of the first switching switch 132.

[0047] In detail, when the first switching switch 132 is in the off state, the AC coupling capacitor 131 filters out the DC component in the voltage signal, and the amplification circuit 14 receives the voltage signal containing the AC signal after filtering out the DC component via the AC coupling capacitor 131 to generate the first output signal; when the first switching switch 132 is in the on state, the two ends of the first switching switch 132 are coupled to the output end of the operational amplifier 121 and the amplification circuit 14 to bypass the AC coupling capacitor 131, and the AC coupling capacitor 131 does not filter out the DC component in the voltage signal, and the amplification circuit 14 receives the voltage signal containing the DC component and the AC component output by the operational amplifier 121 via the first switching switch 132 to generate the second output signal.

[0048] In one embodiment, the light sensing device 1 comprises input / output terminals P1, P2, which are respectively located at the two ends of the AC coupling capacitor 131, and the input / output terminals P1, P2 can be respectively connected to an external capacitor, so that the AC coupling capacitor 131 is connected in parallel to the external capacitor, and the AC coupling capacitor 131 can generate a larger equivalent capacitance value after being connected in parallel to the external capacitor, to further reduce the rising slope and noise of the voltage signal transmitted to the amplification circuit 14. Therefore, through the input / output terminals P1, P2, the two ends of the AC coupling capacitor 131 can generate different equivalent capacitance values, and the designer can add external capacitors to the input / output terminals P1, P2 according to different product applications of the light sensing device 1, to further improve the product compatibility of the light sensing device 1.

[0049] In one embodiment, the coupling mode selection circuit 13 further comprises a resistor 133 and switching switches 134-137 (hereinafter referred to as a second switching switch 134, a third switching switch 135, a fourth switching switch 136 and a fifth switching switch 137, respectively). The one end of the resistor 133 is coupled to the AC coupling capacitor 131 and the first switching switch 132, and the other end of the resistor 133 is coupled to the switching switches 134, 135. The second switching switch 134 is coupled between the resistor 133 and the ground, and the third switching switch 135 is coupled between the resistor 133 and the bias voltage source. On the other hand, the amplification circuit 14 comprises an operational amplifier 141 and resistors 142, 143. The resistors 142, 143 determine the amplification ratio between the input signal and the output signal of the operational amplifier 141. The operational amplifier 141 comprises an output terminal, a positive input terminal and a negative input terminal. The positive input terminal of the operational amplifier 141 is coupled to the AC coupling capacitor 131, the first switching switch 132 and the resistor 133. The operational amplifier 141 is an amplification circuit with negative feedback. The output terminal of the operational amplifier 141 is coupled to the negative input terminal of the operational amplifier 141 via the resistor 142, i.e. the resistor 142 is coupled between the output terminal of the operational amplifier 141 and the input terminal of the operational amplifier 141. Moreover, the resistor 143, which determines the amplification ratio together with the resistor 142, is coupled between the negative input terminal of the operational amplifier 141 and the fourth switching switch 136. The fifth switching switch 137 is coupled between the resistor 143 and the ground, and the resistor 143 is coupled between the negative input terminal of the operational amplifier 141 and the fifth switching switch 137. The fourth switching switch 136 is coupled between the resistor 143 and the bias voltage source.

[0050] Accordingly, when the light sensing device 1 is in the AC coupling mode, the control circuit 16 controls the second switching switch 134 to be on and the third switching switch 135 to be off. The resistor 133 is coupled to the ground via the second switching switch 134 but not coupled to the bias voltage source via the third switching switch 135. The control circuit 16 controls the fifth switching switch 137 to be on and the fourth switching switch 136 to be off. The resistor 143 is coupled to the ground via the fifth switching switch 137 but not coupled to the bias voltage source via the fourth switching switch 136. Thus, the positive input terminal of the operational amplifier 141 is coupled to the ground via the resistor 133 and the second switching switch 134, and the negative input terminal of the operational amplifier 141 is coupled to the ground via the resistor 143 and the fifth switching switch 137. Based on the above configuration, the operational amplifier 141 amplifies the voltage signal comprising AC components after the AC coupling capacitor 131 filters out DC components according to the amplification ratio determined by the resistors 142, 143 to generate the first output signal.

[0051] On the other hand, when the light sensing device 1 is in the direct current coupling mode, the control circuit 16 controls the second switch 134 to be off and the third switch 135 to be on, the resistor 133 is coupled to the bias voltage source via the third switch 135 and not coupled to the ground via the second switch 134, and the control circuit 16 controls the fifth switch 137 to be off and the fourth switch 136 to be on, the resistor 143 is coupled to the bias voltage source via the fourth switch 136 and not coupled to the ground via the fifth switch 137. Thus, the positive input of the operational amplifier 141 is coupled to the bias voltage source via the resistor 133 and the third switch 135, the negative input of the operational amplifier 141 is coupled to the bias voltage source via the resistor 143 and the fourth switch 136, and the operational amplifier 141 amplifies the voltage signal containing direct current component and alternating current component transmitted from the first switch 132 according to the amplification ratio determined by the resistors 142, 143 to generate the second output signal. That is, based on the configuration that both the positive input and the negative input of the operational amplifier 141 are coupled to the bias voltage source, the operational amplifier 141 amplifies the current signal generated by the sensing circuit 11 but not the direct current signal contained in the bias voltage source.

[0052] In one embodiment, the amplifying circuit 14 further comprises a capacitor 144 coupled between the negative input of the operational amplifier 141 and the output of the operational amplifier 141, and the capacitor 144 is in parallel with the resistor 142. The capacitor 144 can filter out high frequency noise. Further, the resistors 142, 143 are variable resistors whose resistance values are adjustable, and the resistance values of the resistors 142, 143 are controlled by the control circuit 16, so that the operational amplifier 141 has adjustable amplification ratio to generate the first output signal and the second output signal corresponding to the amplification ratio.

[0053] In one embodiment, the light sensing device 1 further includes a bias circuit 15 coupled to the sensing circuit 11. The bias circuit 15 includes bias resistors 151, 152, and 153. The bias resistors 151 and 152 are coupled between a power source and a ground terminal. The bias resistor 153 is coupled to the connection point between the bias resistors 151 and 152. Through the bias resistors 151, 152, and 153, the bias circuit 15 generates a bias signal for the sensing circuit 11, enabling the sensing circuit 11 to operate and detect light. Furthermore, the bias circuit 15 includes switches 154 and 155. Switch 154 is coupled between the power source and the bias resistor 151, and switch 155 is coupled between the bias resistor 153 and the conversion circuit 12 (switch 155 is coupled between the bias resistor 153 and the positive input terminal of the operational amplifier 121). Switches 154 and 155 can be controlled by control circuit 16 to provide power saving. When light sensing device 1 is not required to detect light, control circuit 16 can control switches 154 and 155 to be off, thereby shutting down bias circuit 15. Furthermore, bias circuit 15 further includes capacitor 156, which is coupled across bias resistor 152. Capacitor 156 can be charged to provide voltage regulation. After capacitor 156 is fully charged, switch 155 ensures that operational amplifier 121 and sensing circuit 11 receive a stable bias signal.

[0054] In one embodiment, the light sensing device 1 may further include an input / output terminal P3, which is located between the bias resistors 151 and 152 of the bias circuit 15. The designer of the light sensing device 1 may add external components to the input / output terminal P3 to connect the bias circuit 15 as needed. Figure 3 As shown, the light sensing device 1 may further include an analog-to-digital conversion circuit (ADC) 17. The analog-to-digital conversion circuit 17 may be coupled to the output end of the operational amplifier 121. The analog-to-digital conversion circuit 17 may convert the voltage signal generated by the operational amplifier 121 into a digital signal for use by other circuits within the light sensing device 1 or other circuits outside the light sensing device 1. Alternatively, the analog-to-digital conversion circuit 17 may also be coupled to the output end of the operational amplifier 141. The analog-to-digital conversion circuit 17 may convert the first output signal and the second output signal generated by the operational amplifier 141 into digital signals for use by other circuits within the light sensing device 1 or other circuits outside the light sensing device 1.

[0055] In one embodiment, the optical sensing device 1 can be used in a fire protection system. The optical sensing device 1 is a smoke sensor. Specifically, the sensing circuit 11 may also include other light-emitting units to generate infrared light. When smoke enters the optical sensing device 1, smoke particles scatter the infrared light beam, causing the phototransistor or photodiode in the sensing circuit 11 to receive the scattered light. The greater the amount of smoke, the more light the phototransistor or photodiode receives. The stronger the light, the greater the reverse current generated by the phototransistor or photodiode.Figure 4 and Figure 5 As the intensity of the light increases, the phototransistor or photodiode generates a greater reverse current. Therefore, when the amount of smoke in the environment is greater, the phototransistor or photodiode generates a greater reverse current, and the sensing circuit 11 can generate a corresponding current signal. Depending on the phototransistor or photodiode produced by different manufacturers, the current value of the current signal generated by the sensing circuit 11 is in the range of 100 pA to 1 uA.

[0056] In summary, according to an embodiment of the light sensing device of the present disclosure, the light sensing device is internally configured with multiple groups of switchable circuits, the light sensing device can be set to a direct current coupling mode or an alternating current coupling mode, and the amplification of the operational amplifier is adjustable. The light sensing device further has a reserved input and output terminal for external connection. The light sensing device can adjust and add elements on the circuit according to the characteristics of different phototransistors or photodiodes on the market, greatly improving the flexibility of its design and maintenance, and meeting most photoelectric smoke detection applications on the market. Moreover, the present disclosure integrates passive elements, filter circuits, and operational amplifiers, thereby reducing the number of passive elements and reducing the wiring and area of the circuit board layout.

[0057] Although the present disclosure has been disclosed as above with embodiments, it is not intended to limit the present disclosure, and any person skilled in the art can make some changes and modifications without departing from the concept and scope of the present disclosure. Therefore, the protection scope of the present disclosure shall be subject to the definition of the claims.

Claims

1. A light sensing device comprising: A sensing circuit for detecting light and generating a corresponding current signal according to the intensity of the light; a conversion circuit for converting the current signal into a voltage signal, wherein the voltage signal includes an AC component and a DC component; a coupling mode selection circuit for filtering out the DC component in the voltage signal to output the AC component, or for not filtering out the DC component and outputting the voltage signal including the AC component and the DC component; an amplifier circuit configured to amplify the filtered voltage signal to generate an output signal when the coupling mode selection circuit filters out the DC component, and to amplify the voltage signal including the AC component and the DC component to generate another output signal when the coupling mode selection circuit does not filter out the DC component; and A bias circuit is coupled to the sensing circuit and the conversion circuit. The bias circuit generates a bias signal. The sensing circuit operates according to the bias signal to detect the light. The bias circuit includes: two bias resistors coupled between the power supply terminal and the ground terminal; and a switch coupled between one of the bias resistors and a power supply terminal, The coupling mode selection circuit includes an AC coupling capacitor connected in series with the conversion circuit and coupled between the conversion circuit and the amplifier circuit to filter out the DC component in the voltage signal and output the AC component; and a first switching switch connected in parallel with the AC coupling capacitor. 2 . The light sensing device as claimed in claim 1 , further comprising an input / output terminal located at a connection point between the two bias resistors.

3. A light sensing device comprising: A sensing circuit for detecting light and generating a corresponding current signal according to the intensity of the light; a conversion circuit for converting the current signal into a voltage signal, wherein the voltage signal includes an AC component and a DC component; a coupling mode selection circuit for filtering out the DC component in the voltage signal to output the AC component, or for not filtering out the DC component and outputting the voltage signal including the AC component and the DC component; an amplifier circuit configured to amplify the filtered voltage signal to generate an output signal when the coupling mode selection circuit filters out the DC component, and to amplify the voltage signal including the AC component and the DC component to generate another output signal when the coupling mode selection circuit does not filter out the DC component; and A bias circuit is coupled to the sensing circuit and the conversion circuit. The bias circuit generates a bias signal. The sensing circuit operates according to the bias signal to detect the light. The bias circuit includes: a first bias resistor coupled to the power supply terminal; a second bias resistor coupled to the first bias resistor and the ground terminal and coupled together with the first bias resistor between the power terminal and the ground terminal; a capacitor connected in parallel to the second bias resistor; a third bias resistor coupled to a connection point between the first bias resistor and the second bias resistor and coupled to one end of the capacitor; and a switch coupled between the third bias resistor and the conversion circuit, The coupling mode selection circuit includes an AC coupling capacitor connected in series with the conversion circuit and coupled between the conversion circuit and the amplifier circuit to filter out the DC component in the voltage signal and output the AC component; and a first switching switch connected in parallel with the AC coupling capacitor.

4. The light sensing device as claimed in claim 1 or 3, wherein the amplifying circuit comprises an operational amplifier having a negative feedback circuit, wherein the coupling mode selection circuit further comprises: a second switch coupled to the AC coupling capacitor and the first switch, and coupled between the positive input terminal of the operational amplifier and the ground terminal; a third switch coupled to the AC coupling capacitor and the first switch, and coupled between the positive input terminal of the operational amplifier and a bias power supply; a fourth switch coupled between the negative input terminal of the operational amplifier and a bias power supply; and A fifth switch is coupled between the negative input terminal of the operational amplifier and the ground terminal. 5 . The light sensing device as claimed in claim 1 , further comprising two input and output terminals respectively located at two ends of the AC coupling capacitor. The light sensing device as claimed in claim 5 , wherein the two input and output terminals are connected to an external capacitor.

7. A light sensing device comprising: A sensing circuit for detecting light and generating a corresponding current signal according to the intensity of the light; a conversion circuit for converting the current signal into a voltage signal, wherein the voltage signal includes an AC component and a DC component; a coupling mode selection circuit for filtering out the DC component in the voltage signal to output the AC component, or for not filtering out the DC component and outputting the voltage signal including the AC component and the DC component; an amplifier circuit configured to amplify the filtered voltage signal to generate an output signal when the coupling mode selection circuit filters out the DC component, and to amplify the voltage signal including the AC component and the DC component to generate another output signal when the coupling mode selection circuit does not filter out the DC component; and a control circuit for controlling the coupling mode selection circuit to filter out the DC component in the voltage signal and output the AC component, or to control the coupling mode selection circuit not to filter out the DC component in the voltage signal and output the voltage signal including the AC component and the DC component; The coupling mode selection circuit includes an AC coupling capacitor connected in series with the conversion circuit and coupled between the conversion circuit and the amplifier circuit to filter out the DC component in the voltage signal and output the AC component; and a first switching switch connected in parallel with the AC coupling capacitor.

8. A light sensing device comprising: A sensing circuit for detecting light and generating a corresponding current signal according to the intensity of the light; a conversion circuit for converting the current signal into a voltage signal, wherein the voltage signal includes an AC component and a DC component; a coupling mode selection circuit for filtering out the DC component in the voltage signal to output the AC component, or for not filtering out the DC component and outputting the voltage signal including the AC component and the DC component; an amplifier circuit configured to amplify the filtered voltage signal to generate an output signal when the coupling mode selection circuit filters out the DC component, and to amplify the voltage signal including the AC component and the DC component to generate another output signal when the coupling mode selection circuit does not filter out the DC component. The amplifier circuit includes an operational amplifier and a plurality of variable resistors. The operational amplifier has a negative feedback circuit. The variable resistors are located on the negative feedback circuit. The coupling mode selection circuit includes an AC coupling capacitor connected in series with the conversion circuit and coupled between the conversion circuit and the amplifier circuit to filter out the DC component in the voltage signal and output the AC component; and a first switching switch connected in parallel with the AC coupling capacitor.

9. A light sensing device comprising: A sensing circuit for detecting light and generating a corresponding current signal according to the intensity of the light; a conversion circuit for converting the current signal into a voltage signal, wherein the voltage signal includes an AC component and a DC component; a coupling mode selection circuit for filtering out the DC component in the voltage signal to output the AC component, or for not filtering out the DC component and outputting the voltage signal including the AC component and the DC component; an amplifier circuit configured to amplify the filtered voltage signal to generate an output signal when the coupling mode selection circuit filters out the DC component, and to amplify the voltage signal including the AC component and the DC component to generate another output signal when the coupling mode selection circuit does not filter out the DC component. The conversion circuit includes an operational amplifier and a variable resistor. The operational amplifier has a negative feedback circuit, and the variable resistor is located on the negative feedback circuit. The coupling mode selection circuit includes an AC coupling capacitor connected in series with the conversion circuit and coupled between the conversion circuit and the amplifier circuit to filter out the DC component in the voltage signal and output the AC component; and a first switching switch connected in parallel with the AC coupling capacitor.

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