Signal amplification device
The signal amplification device addresses power consumption and noise issues by converting current signals to voltage signals and using capacitive feedback to amplify, achieving smaller, more efficient circuit designs.
Patent Information
- Application Number
- JP2022187886
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2022-11-25
- Publication Date
- 2026-08-26
- Estimated Expiration
- 2042-11-25
AI Technical Summary
Existing signal amplification circuits face issues with increased power consumption and noise due to multiple amplification stages, particularly when amplifying current signals, and require larger circuit sizes to handle DC signal components effectively.
A signal amplification device that converts current signals to voltage signals using a signal conversion unit and employs a multiple feedback amplification unit with capacitive elements to amplify while cutting DC components, reducing the need for additional amplification stages and circuit size.
This approach results in smaller devices with reduced power consumption and noise by minimizing circuit size and the number of amplification cycles, while effectively handling DC signal components.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention mainly relates to a signal amplification device for amplifying a signal.
Background Art
[0002] Patent Document 1 discloses a laser gas analyzer that receives and analyzes laser light that has passed through a sample using a photodiode. The current signal output from the photodiode is amplified by a preamplifier and then input to a signal analysis circuit after unnecessary frequency bands (for example, DC signal components) are cut off by a filter. The signal analysis circuit analyzes the current signal to measure the gas concentration.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] In the circuit configuration of Patent Document 1, in order to increase the current value input to the signal analysis circuit, it is necessary to increase the amplification factor of the preamplifier. However, when the amplification factor of the preamplifier is increased, the DC signal component is also amplified. Therefore, when the current value of the current signal exceeds the allowable value of the circuit, the circuit may not operate normally. To avoid this, generally, after the current signal is amplified by the preamplifier, the DC signal component is cut off by a filter, and then the current signal is amplified again. However, this type of circuit configuration has problems such as an increase in power consumption due to an increase in circuit scale and an increase in noise due to an increase in the number of amplifications. Further, this problem is not limited to the processing of the current signal output from the photodiode and may also exist for other current signals.
[0005] This invention has been made in view of the above circumstances, and its main objective is to provide a configuration that can reduce noise while reducing the circuit size in a signal amplifier that receives an electric current signal. Means and effects for solving the problem
[0006] The problems that this invention aims to solve are as described above, and next, the means for solving these problems and their effects will be explained.
[0007] In view of the present invention, a signal amplification device having the following configuration is provided. That is, the signal amplification device comprises a signal conversion unit and a multiple feedback amplification unit. The signal conversion unit converts a current signal into a voltage signal. The multiple feedback amplification unit is connected downstream of the signal conversion unit and inputs the voltage signal to an amplifier via a first capacitance element, feeds back the output of the amplifier to the amplifier via a resistor element, and feeds back the output of the amplifier to the amplifier via a second capacitance element and the first capacitance element, thereby amplifying the voltage signal while cutting the DC signal component of the voltage signal.
[0008] Compared to a configuration that amplifies the current signal, removes the DC component, and then amplifies it again, this method allows for a smaller circuit size, resulting in smaller devices and reduced power consumption. Furthermore, reducing the number of signal amplification cycles also reduces noise.
[0009] In the aforementioned signal amplification device, it is preferable that the signal conversion unit converts the current signal output by the photodiode into the voltage signal.
[0010] This allows for a reduction in the size of the amplification and DC signal component filtering circuits located downstream of the photodiode.
[0011] In the aforementioned signal amplification device, the following configuration is preferable. That is, the signal amplification device includes a resistance adjustment element arranged in parallel with the resistive element. When it is determined that the cathode voltage of the photodiode has become small, the resistance adjustment element lowers the combined resistance of the resistive element and the resistance adjustment element.
[0012] When a photodiode is irradiated with strong light, the cathode voltage of the photodiode decreases, making oscillation more likely to occur. By incorporating a resistance adjustment element, the cathode voltage of the photodiode increases, thereby suppressing the occurrence of oscillation.
[0013] In the signal amplification device described above, the following configuration is preferable. That is, the resistance adjustment element is an analog switch arranged in parallel with the resistance element. When it is determined that the cathode voltage of the photodiode has decreased, the analog switch is closed, thereby lowering the combined resistance of the resistance element and the analog switch.
[0014] The combined resistance can be lowered as needed with a simple circuit configuration.
[0015] In the signal amplification device described above, it is preferable that the combined resistance of the resistance element and the resistance adjustment element gradually decreases as the cathode voltage of the photodiode decreases.
[0016] This prevents the combined resistance from dropping abruptly, thus suppressing overshoot or undershoot in the voltage value of the output voltage signal.
[0017] In the signal amplification device described above, the following configuration is preferable. That is, the resistance adjustment element is a MOSFET arranged in parallel with the resistance element. The cathode voltage of the photodiode is applied to the MOSFET as the gate voltage, and the combined resistance of the resistance element and the MOSFET gradually decreases in accordance with the decrease in the cathode voltage of the photodiode.
[0018] This allows for a simple circuit configuration that gradually reduces the combined resistance as needed.
[0019] In the above-described signal amplification device, it is preferable to have the following configuration. That is, the amplifier receives the voltage signal and a reference voltage. The cathode voltage of the photodiode is different from the reference voltage.
[0020] Thereby, an appropriate cathode voltage different from the reference voltage can be selected.
[0021] In the above-described signal amplification device, it is preferable that the cathode voltage of the photodiode is a voltage at which the photodiode is reverse-biased.
[0022] Thereby, the junction capacitance of the photodiode can be reduced.
[0023] In the above-described signal amplification device, it is preferable to include an adjustment circuit that raises the lower limit value of the decrease in the cathode voltage of the photodiode due to the irradiation of light to the photodiode from the forward voltage of the photodiode to an adjustment value.
[0024] Thereby, the decrease in the cathode voltage of the photodiode when strong light is input can be reduced, so that the recovery time of the photodiode when strong light is no longer input can be shortened.
[0025] In the above-described signal amplification device, it is preferable to have the following configuration. That is, the adjustment circuit includes a diode. The diode is connected to a voltage higher than the lower limit value of the cathode voltage of the photodiode when the light input is zero. The diode is connected to the cathode side of the photodiode.
[0026] Thereby, the amount of decrease in the lower limit value of the cathode voltage can be suppressed using the diode.
[0027] In the above-described signal amplification device, it is preferable to adopt the following configuration. That is, the adjustment circuit includes a MOSFET. A gate voltage higher than the lower limit value of the cathode voltage of the photodiode when the optical input is zero is supplied to the MOSFET.
[0028] Thereby, by using the MOSFET, it is possible to suppress the decrease amount of the lower limit value of the cathode voltage.
[0029] In the above-described signal amplification device, it is preferable to adopt the following configuration. That is, the signal amplification device includes a resistance adjustment element arranged in parallel with the resistance element. When it is determined that the cathode voltage of the photodiode has become small, the resistance adjustment element decreases the combined resistance of the resistance element and the resistance adjustment element.
[0030] Thereby, it is possible to achieve both suppression of oscillation and shortening of the recovery time when a strong light is irradiated on the photodiode.
[0031] In the above-described signal amplification device, it is preferable that the multiple feedback amplification unit feeds back the output of the amplifier to the amplifier via a T-type feedback circuit including the resistance element.
[0032] Thereby, it is possible to increase the amplification factor while suppressing an increase in the circuit scale.
Brief Description of the Drawings
[0033] [Figure 1] Circuit diagram of the signal amplification device according to an embodiment of the present invention. [Figure 2] Circuit diagrams of the signal amplification devices of the first modification example and the second modification example. [Figure 3] Graph showing the change in the combined resistance of the first modification example and the second modification example. [Figure 4] Circuit diagrams of the signal amplification devices of the third modification example and the fourth modification example. [Figure 5] Graph showing the change trends of the optical input, cathode voltage, and time of the third modification example and the fourth modification example. [Figure 6] Circuit diagrams of the signal amplifier for the 5th and 6th modified examples. [Figure 7] Circuit diagrams of the signal amplifier for the 7th and 8th modified examples. [Figure 8] Circuit diagrams of the signal amplifier for the 9th and 10th modified examples. [Figure 9] Circuit diagram of the signal amplifier for the 11th modified example. [Figure 10] Circuit diagram of the signal amplifier for the 12th modified example. [Figure 11] Circuit diagram of the signal amplifier for the 13th modified example. [Modes for carrying out the invention]
[0034] Next, embodiments of the present invention will be described with reference to the drawings. Figure 1 is a circuit diagram of a signal amplifier 1 according to one embodiment of the present invention.
[0035] The signal amplifier 1 shown in Figure 1 is a device that converts a current signal into a voltage signal, cuts out the DC signal component, amplifies it, and outputs it.
[0036] The signal amplifier 1 of this embodiment processes the current signal output by the photodiode 100. The anode side of the photodiode 100 is connected to ground. The cathode side of the photodiode 100 is connected to the signal amplifier 1. When light is input to the photodiode 100, it outputs a current of a magnitude corresponding to the amount of light. Hereinafter, the current output by the photodiode 100 will be referred to as the current signal. Note that the processing target of the signal amplifier 1 is not limited to the current signal of the photodiode 100. In other words, the signal amplifier 1 can also process current signals output by sensors or computing devices other than the photodiode 100.
[0037] As shown in Figure 1, the signal amplifier 1 comprises a signal conversion unit 11 and a multiple feedback amplifier unit 12.
[0038] The signal conversion unit 11 converts a current signal into a voltage signal. As shown in Figure 1, the signal conversion unit 11 is a resistive element and is connected to the photodiode 100 and the multiple feedback amplifier 12. By arranging the signal conversion unit 11, the current signal is converted into a voltage signal within a range corresponding to the magnitude of the resistance value of the signal conversion unit 11. Therefore, it is preferable to determine the magnitude of the resistance value of the signal conversion unit 11 based on the current value output by the photodiode 100 and the voltage value that can be processed by the multiple feedback amplifier 12.
[0039] The multiple feedback amplifier 12 amplifies the voltage signal while cutting the DC signal component of the voltage signal. As shown in Figure 1, the multiple feedback amplifier 12 comprises a first capacitor element 13, an amplifier 14, a resistor element 15, and a second capacitor element 16.
[0040] The voltage signal is input to the amplifier 14 via the first capacitance element 13. The first capacitance element 13 is a capacitor capable of storing electric charge. By passing through the first capacitance element 13, the DC signal component of the voltage signal is cut off.
[0041] Amplifier 14 is an operational amplifier and inverts and amplifies a voltage signal. Specifically, the non-inverting input terminal of amplifier 14 is connected to ground. The inverting input terminal of amplifier 14 is connected to the first capacitance element 13, and a voltage signal is input to the inverting input terminal. Amplifier 14 inverts the positive and negative signs of the voltage signal, amplifies it, and outputs it. The voltage signal output by amplifier 14 is output to an external device that performs some processing using the voltage signal. Amplifier 14 may also be used in a non-inverting amplification mode.
[0042] Furthermore, the voltage signal output by amplifier 14 is fed back and input to the inverting input terminal of amplifier 14. Hereafter, the circuit connecting the output terminal of amplifier 14 and the inverting input terminal of amplifier 14 will be referred to as the feedback circuit. A resistor 15 is placed in the feedback circuit. The voltage signal output by amplifier 14 is fed back by the resistor 15 placed in the feedback circuit and input to the inverting input terminal of amplifier 14.
[0043] Furthermore, a second capacitance element 16 is placed in the feedback circuit. The second capacitance element 16 is a capacitor that can store electric charge. When a voltage signal passes through the second capacitance element 16, the DC signal component of the voltage signal is cut off. The feedback circuit is also connected to a circuit in which the voltage signal converted by the signal conversion unit 11 is input to the amplifier 14. In other words, the first capacitance element 13 receives the voltage signal output by the amplifier 14 and passed through the second capacitance element 16, and the voltage signal converted by the multiple feedback amplifier unit 12. The first capacitance element 13 cuts the DC signal component of the sum of these two voltage signals and inputs the resulting signal to the inverting input terminal of the amplifier 14.
[0044] As described above, the voltage signal output by amplifier 14 is a signal in which the DC signal component is cut while the signal components other than the DC signal component are amplified. In a typical amplifier circuit that does not include the first capacitor element 13 and the second capacitor element 16, the DC signal component is also amplified, so it is not desirable to increase the amplification factor. In contrast, in this embodiment, the DC signal component can be cut and amplified by the first capacitor element 13 and the second capacitor element 16, so it is permissible to increase the amplification factor. Specifically, the amplification factor is given by the following equation (1).
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[0045] Furthermore, while the signal amplifier 1 of this embodiment shares some commonalities with a general bandpass filter circuit, a general bandpass filter processes voltage signals. In other words, a general bandpass filter circuit cannot process the current signal of the photodiode 100. In this respect, the signal amplifier 1 of this embodiment includes a signal conversion unit 11. Therefore, it can process the current signal of the photodiode 100.
[0046] In this specification, the voltage connected to the non-inverting input terminal of the amplifier 14 (the terminal on which no voltage signal is input), or the voltage connected to the anode side of the photodiode 100, is referred to as the reference voltage. In general circuits, the cathode voltage of the photodiode 100 when no light is input is often matched to the reference voltage. In this embodiment, the cathode voltage of the photodiode 100 when no light is input matches the voltage (Vref) to which the signal conversion unit 11 is connected. In other words, generally, Vref is often matched to the reference voltage (ground in this embodiment). In this embodiment, however, Vref is different from the reference voltage. Specifically, Vref is higher than the reference voltage. As a result, when no light is input, a reverse bias is applied to the photodiode 100. Also, the junction capacitance of the photodiode 100 depends on the applied voltage. Therefore, by determining Vref as in this embodiment, the junction capacitance of the photodiode 100 can be reduced.
[0047] Next, the first and second modified examples of the above embodiment will be described with reference to Figures 2 and 3. Figure 2 is a circuit diagram of the signal amplifier 1 of the first and second modified examples. Figure 3 is a graph showing the change in combined resistance of the first and second modified examples. In the following descriptions of each modified example, the same or similar components as in the above embodiment will be denoted by the same reference numerals in the drawings, and their descriptions may be omitted. Also, in the circuit diagrams of each modified example, the rectangular dashed line indicating the multiple feedback amplifier 12 will be omitted.
[0048] The signal amplifier 1 of the first and second modified examples differs from the signal amplifier 1 of the above embodiment in that it includes a resistance adjustment element. The function and configuration of the resistance adjustment element will be described below. First, the selectivity of the multiple feedback amplifier 12 as a filter can be described by the following equation (2). Generally, high selectivity is undesirable because it makes oscillation more likely.
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[0049] Furthermore, if very strong light is input to the photodiode 100, the cathode voltage of the photodiode 100 may become low, even lower than ground. As a result, the photodiode 100 may behave like a typical diode. In this case, the equivalent resistance of the photodiode 100 can be expressed by the following equation (3).
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[0050] Therefore, when strong light is input, the equivalent resistance of the photodiode 100 becomes smaller than the resistance of the signal conversion unit 11. Also, since the equivalent resistance of the photodiode 100 is arranged in parallel with the signal conversion unit 11, when the equivalent resistance of the photodiode 100 becomes smaller than the resistance of the signal conversion unit 11, the combined resistance becomes smaller than the resistance of the signal conversion unit 11. As a result, Ra, described in equation (2), becomes smaller, so the selectivity increases and oscillation becomes more likely.
[0051] The resistance adjustment element reduces the combined resistance with the resistance element 15 under predetermined conditions. This results in a circuit configuration equivalent to the case where R, described in equation (2), is small, thus lowering the selectivity. Therefore, oscillation can be made less likely.
[0052] As shown in Figure 2(a), the resistance adjustment element in the first modified example is an analog switch 21 arranged in parallel with the resistor element 15. The combined resistance of the internal resistance of the resistor element 15 and the analog switch 21 is lower than the resistance value of the resistor element 15. In other words, the selectivity can be reduced by closing the analog switch 21.
[0053] The analog switch 21 is controlled as follows: When strong light is input, the cathode voltage of the photodiode 100 decreases. Therefore, it is preferable to close the analog switch 21 when the cathode voltage of the photodiode 100 falls below a threshold. Specifically, this configuration can be achieved by placing a voltmeter to measure the cathode voltage of the photodiode 100, and sending a command to the analog switch 21 to close it when the voltage value measured by the voltmeter falls below a threshold. The graph in Figure 3(a) shows that the equivalent resistance decreases when the cathode voltage falls below a threshold.
[0054] As shown in Figure 2(b), the resistance adjustment element in the second modified example is a MOSFET 22 arranged in parallel with the resistor element 15. Although a PMOS is shown in the figure, an NMOS may also be used. The gate of the MOSFET 22 is connected to the cathode side of the photodiode 100. Therefore, as the cathode voltage decreases, the ON resistance of the MOSFET 22 changes gradually. As a result, as shown in Figure 3(b), the combined resistance also changes continuously (gradually) rather than discretely. Consequently, overshoot or undershoot of the voltage signal associated with abrupt changes in resistance is less likely to occur.
[0055] Next, a third and fourth modified example of the above embodiment will be described with reference to Figures 4 and 5. Figure 4 is a circuit diagram of the signal amplifier 1 of the third and fourth modified examples. Figure 5 is a graph showing the trend of change in optical input, cathode voltage, and time for the third and fourth modified examples.
[0056] The signal amplifier 1 of the third and fourth modified examples differs from the signal amplifier 1 of the above embodiment in that it includes an adjustment circuit. The function and configuration of the adjustment circuit will be described below.
[0057] As shown in Figure 5(a), the cathode voltage of the photodiode 100 decreases as the intensity of the light input to the photodiode 100 increases. Also, when the cathode voltage of the photodiode 100 falls below ground, the diode current flows in the opposite direction to the photocurrent (current signal). Furthermore, the lower limit of the cathode voltage is the forward voltage of the photodiode 100 (shown as -VF in the figure). Here, if strong light is input to the photodiode 100 and the cathode voltage reaches the lower limit, and then the light input is suddenly stopped, as shown in Figure 5(a), it takes time for the cathode voltage to rise and return to the original Vref. Therefore, if new light is input before the cathode voltage returns to Vref, it may not be possible to properly detect the next light.
[0058] As shown in Figure 5(b), the adjustment circuits of the third and fourth modified examples are circuits for raising the lower limit of the decrease in the cathode voltage of the photodiode 100 from the forward voltage (-VF) of the photodiode 100 to a predetermined adjustment value. The adjustment value is preferably a positive voltage, but it may also be a negative voltage as long as it is greater than the forward voltage of the photodiode 100.
[0059] As shown in Figure 4(a), the adjustment circuit of the third modified example includes a diode 31. The cathode side of the diode 31 is connected to the photodiode 100 (or the multiple feedback amplifier 12). The anode side of the diode 31 is connected to a predetermined voltage (Va). Preferably, the voltage on the anode side of the diode 31 is greater than, for example, the forward voltage of the photodiode 100 (or greater than ground).
[0060] In this configuration, when the cathode voltage of photodiode 100 becomes low enough to activate diode 31, the cathode voltage of photodiode 100 is connected to the anode voltage of diode 31. As a result, the lower limit of the cathode voltage of photodiode 100 can be raised to the adjusted value.
[0061] As shown in Figure 4(b), the adjustment circuit of the fourth modified example includes a MOSFET 32. The MOSFET 32 is an NMOS, but it may also be a PMOS. A predetermined voltage (Vb) is supplied to the gate of the MOSFET 32. The source of the MOSFET 32 is connected to the cathode side of the photodiode 100. The drain of the MOSFET 32 is connected to a predetermined voltage (Vdd).
[0062] This configuration lowers the cathode voltage of photodiode 100, increasing the voltage difference between the gate and source of MOSFET 32, which in turn causes current to flow from the drain to the source. As a result, the lower limit of the cathode voltage of photodiode 100 can be raised to the adjusted value.
[0063] Next, the fifth and sixth modified examples will be described with reference to Figure 6. Figure 6 is a circuit diagram of the signal amplifier 1 of the fifth and sixth modified examples. The signal amplifier 1 of the fifth and sixth modified examples differs from the signal amplifier 1 of the above embodiment in that it includes both a resistance adjustment element and an adjustment circuit.
[0064] The fifth modified signal amplifier 1 includes an analog switch 21 as a resistance adjustment element. The analog switch 21 in the fifth modified version has the same configuration and function as the analog switch 21 in the first modified version. The fifth modified signal amplifier 1 includes a diode 31 as an adjustment circuit. The diode 31 in the fifth modified version has the same configuration and function as the diode 31 in the third modified version.
[0065] Furthermore, the signal amplifier 1 of the fifth modified example differs from the signal amplifier 1 of the first modified example in that a third capacitance element 41 is arranged in series with the analog switch 21. The third capacitance element 41 is a capacitor that can store electric charge. By arranging the third capacitance element 41, the circuit can be stabilized when the diode 31 operates and diode current flows. Therefore, in the fifth modified example, it is preferable to send a command to close the analog switch 21 at the timing when the diode operates.
[0066] The sixth modified signal amplifier 1 includes a MOSFET 22 as a resistance adjustment element. The MOSFET 22 in the sixth modified version has the same configuration and function as the MOSFET 22 in the second modified version. The sixth modified signal amplifier 1 includes a diode 31 as an adjustment circuit. The diode 31 in the sixth modified version has the same configuration and function as the diode 31 in the third modified version. In addition, the sixth modified signal amplifier 1 has a third capacitance element 41 arranged in series with the MOSFET 22. The third capacitance element 41 in the sixth modified version has the same configuration and function as the third capacitance element 41 in the fifth modified version.
[0067] Next, the seventh and eighth modified examples will be described with reference to Figure 7. Figure 7 is a circuit diagram of the signal amplifier 1 of the seventh and eighth modified examples.
[0068] The signal amplifier 1 of the 7th and 8th modified examples differ from the 5th and 6th modified examples, respectively, in that the adjustment circuit includes a MOSFET 32. The configuration and function of the MOSFET 32 in the 7th and 8th modified examples are the same as those of the MOSFET 32 in the 4th modified example.
[0069] Next, the ninth and tenth modified examples will be described with reference to Figure 8. Figure 8 is a circuit diagram of the signal amplifier 1 of the ninth and tenth modified examples.
[0070] The signal amplifier 1 of the 9th and 10th modified examples differ from the 6th and 8th modified examples, respectively, in that they include a comparator 51. In the 6th and 8th modified examples, the cathode voltage of the photodiode 100 is supplied to the MOSFET 22. Therefore, there is less design flexibility in the timing when the third capacitance element 41 becomes active.
[0071] In contrast, the comparator 51 is connected to the cathode voltage of the photodiode 100 and a predetermined reference voltage (Vc). The comparator 51 compares the cathode voltage of the photodiode 100 with the reference voltage and supplies the difference voltage to the MOSFET 22. Therefore, by changing the voltage value of the reference voltage, the timing at which the third capacitance element 41 becomes active can be changed. In other words, the design flexibility for the timing at which the third capacitance element 41 becomes active can be improved.
[0072] Next, with reference to Figure 9, the 11th modified example will be described. Figure 9 is a circuit diagram of the signal amplifier 1 of the 11th modified example.
[0073] The 11th modified signal amplifier 1 differs from the above embodiment in that it includes a T-type feedback circuit 60 instead of a resistive element 15.
[0074] The T-type feedback circuit 60 comprises a first resistive element 61, a second resistive element 62, and a third resistive element 63. The first resistive element 61 and the second resistive element 62 are arranged in series alongside the feedback circuit described above. The third resistive element 63 is positioned to connect the circuit between the first resistive element 61 and the second resistive element 62 to ground (reference voltage). Since the T-type feedback circuit itself is well known, a detailed explanation is omitted.
[0075] The amplification factor of the above embodiment is as shown in equation (1). To increase the amplification factor, it is necessary to increase the capacitance of the first capacitance element 13 or the resistance of the resistor element 15. In that case, the circuit area will increase slightly. In this respect, by using the T-type feedback circuit 60, the increase in circuit area can be further suppressed for the following reasons. That is, the amplification factor when using the T-type feedback circuit 60 is shown in equation (4) below.
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[0076] Next, with reference to Figure 10, the 12th modified example will be described. Figure 10 is a circuit diagram of the signal amplifier 1 of the 12th modified example.
[0077] The signal amplifier 1 of the 12th modification differs from the signal amplifier 1 of the 11th modification in that it includes a resistance adjustment element and an adjustment circuit. The resistance adjustment element is arranged in parallel with both the first resistance element 61 and the second resistance element 62. As the resistance adjustment element, an analog switch 21 or MOSFET 22 as shown in other modifications can be used. In addition to the resistance adjustment element, a third capacitance element 41 as shown in other modifications may also be provided. As the adjustment circuit, a diode 31 or MOSFET 32 as shown in other modifications can be used. Furthermore, a comparator 51 as shown in other modifications may also be provided.
[0078] Next, with reference to Figure 11, the 13th modified example will be described. Figure 11 is a circuit diagram of the signal amplifier 1 of the 13th modified example.
[0079] The signal amplifier 1 of the 13th modified example differs from the signal amplifier 1 of the 12th modified example in the position where the resistance adjustment element is arranged. In the 13th modified example, the resistance adjustment element is arranged in parallel only with the second resistance element 62 (i.e., not in parallel with the first resistance element 61). Alternatively, the resistance adjustment element may be arranged in parallel only with the first resistance element 61 (i.e., not in parallel with the second resistance element 62). Even with this arrangement of the resistance adjustment element, the same effect as the 12th modified example can be achieved.
[0080] As described above, the signal amplification device 1 of the above embodiment and each of its modifications comprises a signal conversion unit 11 and a multiple feedback amplification unit 12. The signal conversion unit 11 converts a current signal into a voltage signal. The multiple feedback amplification unit 12 is connected downstream of the signal conversion unit 11 and inputs the voltage signal to the amplifier 14 via the first capacitance element 13, feeds back the output of the amplifier 14 to the amplifier 14 via the resistor element 15, and feeds back the output of the amplifier 14 to the amplifier 14 via the second capacitance element 16 and the first capacitance element 13, thereby amplifying the voltage signal while cutting the DC signal component of the voltage signal.
[0081] Compared to a configuration that amplifies the current signal, removes the DC component, and then amplifies it again, this method allows for a smaller circuit size, resulting in smaller devices and reduced power consumption. Furthermore, reducing the number of signal amplification cycles also reduces noise.
[0082] In the above embodiment and each of its modifications, the signal amplification device 1 converts the current signal output by the photodiode 100 into a voltage signal.
[0083] The circuit size for amplification and DC signal component filtering, which are located downstream of the photodiode 100, can be reduced.
[0084] The signal amplifier 1 of the above embodiment and each of its modifications includes a resistance adjustment element arranged in parallel with the resistive element 15. The resistance adjustment element lowers the combined resistance of the resistive element 15 and the resistance adjustment element when it is determined that the cathode voltage of the photodiode 100 has become small.
[0085] When a strong light is shone on a photodiode, oscillation is likely to occur due to a decrease in the photodiode's cathode voltage. By incorporating a resistance adjustment element, the photodiode's cathode voltage is increased, thereby suppressing the occurrence of oscillation.
[0086] In the above embodiment and each of its modifications, the signal amplifier 1 is an analog switch 21 arranged in parallel with the resistor 15. When it is determined that the cathode voltage of the photodiode 100 has decreased, the analog switch 21 is closed, thereby lowering the combined resistance of the resistor 15 and the analog switch 21.
[0087] The combined resistance can be lowered as needed with a simple circuit configuration.
[0088] In the above embodiment and each of its modified versions, the combined resistance of the resistor element 15 and the resistor adjustment element gradually decreases as the cathode voltage of the photodiode 100 decreases.
[0089] This prevents the combined resistance from dropping abruptly, thus suppressing overshoot or undershoot in the voltage value of the output voltage signal.
[0090] In the above embodiment and each of its modifications, the signal amplifier 1 is a MOSFET 22 arranged in parallel with the resistive element 15. The cathode voltage of the photodiode 100 is applied to the MOSFET 22 as the gate voltage, and the combined resistance of the resistive element 15 and the MOSFET 22 gradually decreases as the cathode voltage of the photodiode 100 decreases.
[0091] This allows for a simple circuit configuration that gradually reduces the combined resistance as needed.
[0092] In the above embodiment and each of its modifications, the signal amplification device 1 receives a voltage signal and a reference voltage as inputs to the amplifier 14. The cathode voltage of the photodiode 100 and the reference voltage are different values.
[0093] This allows for the selection of an appropriate cathode voltage that differs from the reference voltage.
[0094] In the above embodiment and each of its modifications, the cathode voltage of the photodiode 100 is the voltage at which a reverse bias is applied to the photodiode 100.
[0095] This makes it possible to reduce the junction capacitance of the photodiode 100.
[0096] In the above embodiment and each of its modifications, the signal amplifier 1 is provided with an adjustment circuit that raises the lower limit of the decrease in the cathode voltage of the photodiode 100 due to the irradiation of light to the photodiode 100 from the forward voltage of the photodiode 100 to an adjustment value.
[0097] This reduces the drop in the cathode voltage of the photodiode 100 when strong light is input, thereby shortening the recovery time of the photodiode when the strong light input is removed.
[0098] In the above embodiment and each of its modifications, the signal amplifier 1 includes a diode 31. The diode 31 is connected to a voltage higher than the lower limit of the cathode voltage of the photodiode 100 when the optical input is zero. The diode 31 is connected to the cathode side of the photodiode 100.
[0099] This allows the diode 31 to suppress the decrease in the lower limit of the cathode voltage.
[0100] In the above embodiment and each of its modifications, the signal amplifier 1 includes a MOSFET 32. The MOSFET 32 is supplied with a gate voltage higher than the lower limit of the cathode voltage of the photodiode 100 when the optical input is zero.
[0101] This allows the MOSFET32 to be used to suppress the decrease in the lower limit of the cathode voltage.
[0102] The signal amplifier 1 of the above embodiment and each of its modifications includes a resistance adjustment element arranged in parallel with the resistive element 15. The resistance adjustment element lowers the combined resistance of the resistive element 15 and the resistance adjustment element when it is determined that the cathode voltage of the photodiode 100 has become small.
[0103] This makes it possible to suppress oscillation and shorten the recovery time when strong light is shone on the photodiode 100.
[0104] In the above embodiment and each of its modified versions of the signal amplification device 1, the multiple feedback amplifier 12 feeds back the output of the amplifier 14 to the amplifier 14 via a T-type feedback circuit 60 including a resistor element 15.
[0105] This allows for a higher amplification factor while keeping the circuit size down.
[0106] Preferred embodiments and modifications of the present invention have been described above, but the above configuration can be modified as follows, for example.
[0107] The circuit of the signal amplifier 1 shown in the above embodiments and each of its modifications is merely an example, and at least a part of the circuit of the signal amplifier 1 may be replaced with an equivalent circuit or a circuit having the same function. Furthermore, the features of the above embodiments and each of its modifications may be combined.
[0108] In the above embodiments and their modifications, the voltage value of Vref is different from that of ground, but the voltage value of Vref may be made to match that of ground. [Explanation of Symbols]
[0109] 1. Signal Amplifier 11 Signal conversion section 12 Multiple Feedback Amplifier 13. First Capacitance Element 14 Amplifier 15 Resistors (Feedback resistor element) 16. Second Capacitance Element 100 photodiodes
Claims
1. A signal conversion unit that converts current signals into voltage signals, A multiple feedback amplifier unit is connected downstream of the signal conversion unit and includes a first path that inputs the voltage signal to the amplifier via a first capacitance element, a second path that feeds back the output of the amplifier to the amplifier via a feedback resistor element and without going through the first capacitance element, and a third path that feeds back the output of the amplifier to the amplifier via the second capacitance element and the first capacitance element, and amplifies the voltage signal while cutting the DC signal component of the voltage signal. Equipped with, The signal conversion unit converts the current signal output by the photodiode into the voltage signal, No resistive elements are placed in the path from the photodiode to the first capacitive element. The amplifier receives the voltage signal and the reference voltage as inputs. The cathode voltage of the photodiode and the reference voltage are different values. A signal amplification device characterized in that the cathode voltage of the photodiode is a voltage at which a reverse bias is applied to the photodiode.
2. A signal amplification device according to claim 1, The feedback resistor element is provided with a resistance adjustment element arranged in parallel with the aforementioned resistance element. The signal amplification device is characterized in that the resistance adjustment element lowers the combined resistance of the feedback resistance element and the resistance adjustment element when it is determined that the cathode voltage of the photodiode has become small.
3. A signal amplification device according to claim 2, The resistance adjustment element is an analog switch arranged in parallel with the feedback resistance element. The signal amplification device is characterized in that, when it is determined that the cathode voltage of the photodiode has decreased, the analog switch is closed, thereby lowering the combined resistance of the feedback resistor and the analog switch.
4. A signal amplification device according to claim 2, The signal amplification device is characterized in that, as the cathode voltage of the photodiode decreases, the combined resistance of the feedback resistor and the resistor adjustment element gradually decreases.
5. A signal amplification device according to claim 4, The resistance adjustment element is a MOSFET arranged in parallel with the feedback resistance element. A signal amplification device characterized in that the cathode voltage of the photodiode is applied to the MOSFET as the gate voltage, and the combined resistance of the feedback resistor and the MOSFET gradually decreases in accordance with the decrease in the cathode voltage of the photodiode.
6. A signal amplification device according to claim 1, A signal amplification device characterized by comprising an adjustment circuit that raises the lower limit of the decrease in the cathode voltage of the photodiode, which occurs when light is irradiated onto the photodiode, from the forward voltage of the photodiode to an adjustment value.
7. A signal amplification device according to claim 6, The adjustment circuit includes a diode, The diode is connected to a voltage higher than the lower limit of the cathode voltage of the photodiode when the light input is zero. The signal amplification device is characterized in that the diode is connected to the cathode side of the photodiode.
8. A signal amplification device according to claim 6, The adjustment circuit comprises a MOSFET, The signal amplification device is characterized in that the MOSFET is supplied with a gate voltage higher than the lower limit of the cathode voltage of the photodiode when the optical input is zero.
9. A signal amplification device according to claim 6, The feedback resistor element is provided with a resistance adjustment element arranged in parallel with the aforementioned resistance element. The signal amplification device is characterized in that the resistance adjustment element lowers the combined resistance of the feedback resistance element and the resistance adjustment element when it is determined that the cathode voltage of the photodiode has become small.
10. A signal amplification device according to any one of claims 1 to 9, The signal amplification device is characterized in that the multiple feedback amplifier section feeds back the output of the amplifier to the amplifier via a T-type feedback circuit including the feedback resistor element.
Citation Information
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