An active signal filter for outputting current signal

Abstract

The present invention provides an active signal filter that outputs a current signal, which can not only output a current signal, but also enable a drone to fly autonomously along a preset route when there is an interference signal, even when a ground control station cannot control it. The filter circuit is connected to an external sensor through a signal filter circuit to filter out clutter from the received signal and then output a filter signal, which is sent to a remote control conversion circuit. The remote control conversion circuit provides an output current signal through a voltage / current conversion circuit according to different working modes and connects to an external servo actuator to control its action. When in autonomous flight mode, the ground control signal can be prevented from being interfered with and the external servo actuator can be directly controlled, so that the drone can fly autonomously along a preset route when the ground control station cannot control it.

Description

Technical Field

[0001] The invention relates to the technical field of filters, and in particular to an active signal filter which outputs a current signal. Background Art

[0002] As one of the important components of micro-UAVs, the sensor needs to process the sensor signal during the execution process. First, the signal needs to be filtered and the clutter signal needs to be removed, that is, signal filtering (commonly known as active signal filter) is performed so that the computer can truly recognize it. However, there are currently two main problems in the process of sensor signal transmission: 1. After receiving the signal, the ground control station needs to analyze, process and calculate the signal, and then issue a control command to the UAV. The time for signal analysis and processing plus the time for signal transmission back and forth takes about several seconds, resulting in a slow response speed. At this time, if there is an interference signal, the transmission signal will be interfered, and the ground control station will not be able to control the UAV, which poses a safety problem; 2. Generally, the output signal of the active signal filter is a voltage signal. In some cases, the servo actuator on the UAV needs a current signal to drive, so there is an incompatibility problem. Summary of the invention

[0003] In view of the problems that the existing active signal filters have long signal transmission time, are easily interfered by external signals, affect safety of use, and can only output voltage signals and are not suitable during use, the present invention provides an active signal filter that outputs current signals, which can not only output current signals, but also enable the UAV to fly autonomously along a pre-set route when there are interference signals and the ground control station cannot control it.

[0004] The technical scheme is as follows: an active signal filter for outputting current signals, characterized in that it comprises a signal filtering circuit, a remote control conversion circuit and a voltage / current conversion circuit, wherein the signal filtering circuit is connected to an external sensor and outputs a filtered signal after filtering the received signal, the input end of the remote control conversion circuit is connected to the output end of the signal filtering circuit, the output end of the remote control conversion circuit is connected to the input end of the voltage / current conversion circuit, the remote control conversion circuit is also externally connected to a base station control signal, and the output end of the voltage / current conversion circuit is connected to an external servo actuator;

[0005] When the control of the ground control station is not required, it is the autonomous flight mode. The remote control conversion circuit directly outputs the filtered signal to the voltage / current conversion circuit, and the current signal directly output by the voltage / current conversion circuit drives the servo actuator to operate. When the control of the ground control station is required, it is the base station controlled flight mode. The remote control conversion circuit outputs the received filtered signal to the ground control station for monitoring, but does not add it to the input end of the voltage / current conversion circuit. At this time, the control signal is sent to the voltage / current conversion circuit through the ground control station to drive the servo actuator to operate.

[0006] Its further feature is that: the signal filtering circuit includes an operational amplifier U1, the pin 1 of the operational amplifier U1 is connected to one end of a resistor R5, the other end of the resistor R5 is connected to the pin 7 of the operational amplifier U1, one end of a resistor R6, one end of a capacitor C4 and a +9V voltage source, the other end of the resistor R6 is connected to the pin 8 of the operational amplifier U1, the other end of the capacitor C4 is connected to one end of a capacitor C3 and grounded, the pin 3 of the operational amplifier U1 is connected to the other end of the capacitor C3 and one end of the resistor R3, the other end of the resistor R3 is connected to one end of a resistor R2 and one end of a capacitor C2, the other end of the resistor R2 is connected to one end of a resistor R1 and one end of a capacitor C1, and the other end of the resistor R1 is connected to the input signal V IN The other end of the capacitor C2 is connected to the 6th pin of the operational amplifier U1, one end of the resistor R15, and the output signal V O1 And the remote control conversion circuit, the 2nd pin of the operational amplifier U1 is connected to one end of the resistor R4 and one end of the resistor R14, the other end of the resistor R4 is connected to the other end of the capacitor C1 and then connected to one end of the capacitor C5 and grounded, the other end of the resistor R14 is connected to the other end of the resistor R15, and the 4th pin of the operational amplifier U1 is connected to the other end of the capacitor C5 and a -9V voltage source;

[0007] The remote control conversion circuit includes a MOS tube optocoupler driver U5, wherein pin 1 of the MOS tube optocoupler driver U5 is connected to the cathode of the diode D2 and one end of the resistor R18, the anode of the diode D2 is grounded, the other end of the resistor R18 is connected to one end of the resistor R21 and a +9V voltage source, the other end of the resistor R21 is connected to one end of the resistor R17, one end of the resistor R22, and the base of the transistor U4, and the other end of the resistor R17 is connected to the base station control signal V ctr1 The other end of the resistor R22 is connected to the collector of the transistor U4 and then grounded. The emitter of the transistor U4 is connected to the 2nd pin of the MOS tube optocoupler driver U5. The 4th pin of the MOS tube optocoupler driver U5 is connected to the source of the MOS tube U6, the cathode of the diode D1, and the input signal V IN2And the voltage / current conversion circuit, the 4th pin of the MOS tube optocoupler driver U5 is connected to the gate of the MOS tube U6 and one end of the resistor R19, and the drain of the MOS tube U6 is connected to the signal filtering circuit;

[0008] The voltage / current conversion circuit includes an operational amplifier U2, wherein pin 1 of the operational amplifier U2 is connected to one end of a resistor R10, pin 5 of the operational amplifier U2 is connected to one end of a resistor R11, pin 2 of the operational amplifier U2 is connected to one end of a resistor R7 and one end of a resistor R12, pin 3 of the operational amplifier U2 is connected to one end of a resistor R8 and one end of a resistor R16, the other end of the resistor R10 is connected to the other end of the resistor R11 and then connected to one end of a resistor C6, pin 7 of the operational amplifier U2, the drain of a MOS tube U3 and a +9V voltage source, pin 6 of the operational amplifier U2 is connected to the gate of the MOS tube U3, pins 4 and 8 of the operational amplifier U2 are grounded respectively, the other end of the resistor R7 is grounded, the other end of the resistor R12 is connected to one end of a resistor R9, the other end of the resistor R8 is connected to the remote control conversion circuit, and the other end of the resistor R16 is connected to one end of a load resistor RL, a sampling resistor R S one end, the load resistor RL is grounded at the other end, and the sampling resistor R S The other end is connected to the source of the MOS tube U3 and the other end of the resistor R9.

[0009] After adopting the above structure, the signal filtering circuit is connected to the external sensor to filter out the clutter from the received signal and output the filtered signal. The output filtered signal is sent to the remote control conversion circuit. The remote control conversion circuit provides an output current signal through the voltage / current conversion circuit according to different working modes and connects to the external servo actuator to control its action. When it is in autonomous flight mode, it can prevent the ground control signal from being interfered with and directly control the external servo actuator, so that the UAV can fly autonomously according to the pre-set route when the ground control station cannot control it. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a circuit schematic diagram of the present invention. DETAILED DESCRIPTION

[0011] like Figure 1 As shown, an active signal filter that outputs a current signal. In addition to the filtering function, the signal filter of the present invention also includes a current output signal. The specific parameters are: filter passband 0~100Hz, filter input signal amplitude 0~50mV, filter output signal amplitude 0~5V, corresponding output current 0~2ADC, voltage / current conversion accuracy better than 1.5%, working environment temperature -45~+85℃, and the volume must be small. In addition, the power consumption indicators are required to be standby time (≥48 hours) and continuous working time (≥4 hours).

[0012] The signal filter of the present invention comprises a signal filtering circuit, a remote control conversion circuit and a voltage / current conversion circuit. The signal filtering circuit is connected to an external sensor and outputs a filtered signal after filtering the received signal. The input end of the remote control conversion circuit is connected to the output end of the signal filtering circuit, and the output end of the remote control conversion circuit is connected to the input end of the voltage / current conversion circuit. The remote control conversion circuit is also externally connected to a base station control signal, and the output end of the voltage / current conversion circuit is connected to an external servo actuator.

[0013] Specifically, the signal filtering circuit includes an operational amplifier U1, peripheral resistors R1, R2, R3, R4, R5, R6, R 14 , R 15 And capacitors C1, C2, C3, C4, C5, the specific circuit connection relationship is: the 1st pin of the operational amplifier U1 is connected to one end of the resistor R5, the other end of the resistor R5 is connected to the 7th pin of the operational amplifier U1, one end of the resistor R6, one end of the capacitor C4 and the +9V voltage source, the other end of the resistor R6 is connected to the 8th pin of the operational amplifier U1, the other end of the capacitor C4 is connected to one end of the capacitor C3 and grounded, the 3rd pin of the operational amplifier U1 is connected to the other end of the capacitor C3 and one end of the resistor R3, the other end of the resistor R3 is connected to one end of the resistor R2 and one end of the capacitor C2, the other end of the resistor R2 is connected to one end of the resistor R1 and one end of the capacitor C1, and the other end of the resistor R1 is connected to the input signal V IN The other end of the capacitor C2 is connected to the 6th pin of the operational amplifier U1, one end of the resistor R15, and the output signal V O1 And the remote control conversion circuit, the 2nd pin of the operational amplifier U1 is connected to one end of the resistor R4 and one end of the resistor R14, the other end of the resistor R4 is connected to the other end of the capacitor C1 and then connected to one end of the capacitor C5 and grounded, the other end of the resistor R14 is connected to the other end of the resistor R15, and the 4th pin of the operational amplifier U1 is connected to the other end of the capacitor C5 and a -9V voltage source.

[0014] The above signal filtering circuit uses an operational amplifier U1 to form a third-order active low-pass filter, which can greatly save volume. Its cut-off frequency is f cp =100Hz, the transition band roll-off rate is 18dB / octave, which can effectively filter out the cut-off band clutter. The circuit design calculation is relatively complicated. To simplify the design, take R1=R2=R3=R, then the transfer function is:

[0015] K1=V O1 / V in =1 / (S 3 A+S 2 B+SC+1) (1)

[0016] Where A=C1C2C3R1R2R3=C1C2C3R 3 , B=C1C2C3(R1+R2)+C1C3R1(R2+R3)=2C1C2C3R+2C1C3R 2 , C=C1R1+C3(R1+R2+R3)=C1R+3C3R.

[0017] Since the isolation amplifier filter passband is 0~100Hz, the cutoff frequency of the active signal filter circuit is taken as f cp =100Hz, normalize (1) to get the normalized capacitance:

[0018] C1'=0.998 / (2πf cp )=1.5×10 -3 ,C2'=1.423 / (2πf cp )=2.26×10 -3 , C3'=0.2538 / (2πf cp )=4.0×10 -4 .

[0019] Take the maximum capacitance C2 = 0.022uf, then: R = C2' ÷ C2 = 102K (take R = R1 = R2 = R3 = 100K), C1 = C1' ÷ R = 0.015uf, C3 = C3' ÷ R = 390pf.

[0020] R 15 As a debugging resistor, fine-tuning its resistance value can fine-tune the DC gain. In order to improve the output voltage accuracy, a zero adjustment circuit is set. When the input voltage is zero, changing the values ​​of R5 and R6 can make the output of the operational amplifier U1 zero. The output signal V O1 To output voltage signal, it can be sent by the UAV to the ground control station or output to the voltage / current conversion circuit.

[0021] Specifically, the voltage / current conversion circuit includes an op amp U2, a MOS tube U3, resistors R7, R8, R9, R10, R11, R12, R13, R16, a capacitor C6, a sampling resistor RS, and a load RL. Pin 1 of the op amp U2 is connected to one end of the resistor R10, pin 5 of the op amp U2 is connected to one end of the resistor R11, pin 2 of the op amp U2 is connected to one end of the resistor R7 and one end of the resistor R12, and pin 3 of the op amp U2 is connected to one end of the resistor R8 and one end of the resistor R16. , the other end of resistor R10 is connected to the other end of resistor R11, and then connected to one end of resistor C6, pin 7 of op amp U2, the drain of MOS tube U3 and +9V voltage source, pin 6 of op amp U2 is connected to the gate of MOS tube U3, pins 4 and 8 of op amp U2 are grounded respectively, the other end of resistor R7 is grounded, the other end of resistor R12 is connected to one end of resistor R9, the other end of resistor R8 is connected to the remote control conversion circuit, the other end of resistor R16 is connected to one end of load resistor RL, sampling resistor R S One end, the load resistor RL, the other end is grounded, and the sampling resistor R S The other end is connected to the source of the MOS tube U3 and the other end of the resistor R9.

[0022] Signal filter output signal V O1 The resistor R8 is added to the non-inverting input terminal of the operational amplifier U2 to control the DS pole voltage of the MOS tube U3, thereby controlling the size of the load current Io, specifically Vo1↑→ V G ↑→V DS ↓→I O ↑; On the contrary, Vo1↓→V G ↓→V DS ↑→I O ↓. Assume the signal filter output V O1 When the load current Io increases, the sampling resistor R S The voltage drop increases, and the voltage added to the inverting terminal of the op amp U2 increases, making V G Decrease, V DS Increase, so that the load current Io decreases, to achieve a steady flow; on the contrary, the load current I O When the sampling resistance R S The voltage drop decreases, and the voltage added to the inverting terminal of the operational amplifier U2 decreases, making V G Increase, V DS Reduce, so that the load current I O Increase to achieve steady flow.

[0023] Specific signal filter output voltage V O1 The relationship with the load current Io should satisfy:

[0024] Io=V O1 ×(R 12 +R9)÷(R7×R S ) (2)

[0025] When V O1 =5V, Io=2A, take R S =0.2Ʊ, R7=10K, substitute the above values ​​into (2), and we get R 12 +R9=0.8K, then R9=750Ʊ, R 12 =51Ʊ.

[0026] At the same time, R 13 +R 16 Should satisfy R 13 +R 16 =R 12 +R9, then R 13 =750Ʊ, R 16 =51Ʊ, R 12 , R 16 As a debugging resistor, correct the sampling resistor R S MOS tube U3 works in Class B working state, by adjusting R 10 , R 11 resistance, outputs a starting voltage to the op amp U2, which is also a static operating point V of the MOS tube. Q =30mV.

[0027] Since the maximum output current is Io=2A, heat dissipation needs to be considered. For this reason, the circuit board of the present invention adopts a ceramic substrate with a length, width and thickness of 18×13×1mm and a thermal resistance of R θ =1.3℃ / W. MOS tube U3 adopts NCEP014AS, and its electrical parameters are: DS extreme withstand voltage V DSS =100V, DS pole maximum current I DSS =14A, maximum power consumption P CMAX =3.5W, on-resistance R ON =13mƱ, thermal resistance R θJA =36℃ / W, maximum operating junction temperature T JMAX =175℃. When the maximum output current is 2A, the maximum power consumption of the product is: P max =P U1 +P U2 +P U3 (3)

[0028] Where P U1 is the power consumed by the operational amplifier U1, P U2 is the power consumed by the operational amplifier U2, P U3 MOS tube U3, sampling resistor R S The maximum power consumed. U1 =0.01×9×2=0.18W, P U2=0.057×9=0.513W, P U3 =I O 2 R ON +I O 2 RS=0.8W, T AMAX =85℃Substituting into (3), we get Pmax=1.5W.

[0029] Therefore, the maximum operating junction temperature of MOS tube U3 is:

[0030] T JMAX =T AMAX +P MAX ×(R θ +R θJC ) = 140 °C <T JMAX =175℃ (3)

[0031] Therefore, the junction temperature of MOS tube U3 is within a safe temperature range.

[0032] Specifically, the remote control conversion circuit includes a transistor U4 (9012), a MOS tube optocoupler driver U5 (TLP590B), a MOS tube U6 (2N7002), a diode D2, and a resistor R 17、 R 18、 R 19、 R 21 , R 22。 Pin 1 of the MOS tube optocoupler driver U5 is connected to the cathode of the diode D2 and one end of the resistor R18. The anode of the diode D2 is grounded. The other end of the resistor R18 is connected to one end of the resistor R21 and the +9V voltage source. The other end of the resistor R21 is connected to one end of the resistor R17, one end of the resistor R22, and the base of the transistor U4. The other end of the resistor R17 is connected to the base station control signal V ctr1 The other end of resistor R22 is connected to the collector of transistor U4 and then grounded. The emitter of transistor U4 is connected to pin 2 of MOS optocoupler driver U5. Pin 4 of MOS optocoupler driver U5 is connected to the source of MOS tube U6, the cathode of diode D1, and the input signal V IN2 And the voltage / current conversion circuit, the 4th pin of the MOS tube optocoupler driver U5 is connected to the gate of the MOS tube U6 and one end of the resistor R19, and the drain of the MOS tube U6 is connected to the signal filtering circuit.

[0033] When the remote control conversion circuit is working, it has two working modes. One is when the ground control station control is not required, this is the autonomous flight mode, the remote control conversion circuit directly outputs the filtered signal to the voltage / current conversion circuit, and the current signal directly output by the voltage / current conversion circuit drives the servo actuator to operate; the other is when the ground control station control is required, this is the base station control flight mode, the remote control conversion circuit outputs the received filtered signal to the ground control station for monitoring, but does not add it to the input end of the voltage / current conversion circuit, at this time the ground control station sends a control signal to the voltage / current conversion circuit to drive the servo actuator to operate.

[0034] The specific working principle is that when the base station control signal V ctr1 When it is low level, it is in autonomous flight mode. At this time, transistor U4 is turned on, optocoupler driver U5 works, driving MOS tube U6 to turn on, and the output voltage V O1 The voltage / current conversion circuit is added through MOS tube U6 to realize autonomous flight of the UAV; when the base station control signal V ctr1 When the level is high, the base station controls the flight mode. At this time, the transistor U4 is turned off, the optocoupler driver U5 does not work, the MOS tube U6 is turned off, and the output voltage V O1 It cannot be added to the voltage / current conversion circuit (through MOS tube U6), and the base station only receives data for real-time monitoring. The input signal V IN2 The base station gives input, and then the voltage / current conversion circuit drives the drone servo actuator to operate, realizing the base station control flight mode. In order to ensure that the present invention reduces energy loss during use, it also provides a third working mode, namely the standby working mode. Since the power of micro drones is very precious, users also have standby time requirements. The voltage / current conversion circuit has a static working point and consumes a certain amount of power. Therefore, the operational amplifier U2 uses the TLC080 with a shutoff function. When the standby control signal V ctr2 When the standby control signal V ctr2 When it is at a high level, the op amp is turned on and enters the working state.

[0035] Since the output signal of the traditional active signal filter is a voltage signal, it cannot drive the servo actuator that requires a current output signal. The present invention adds a special voltage / current conversion circuit and a working mode switching circuit to the output stage of the active signal filter, which can directly drive the current-type servo actuator to operate and greatly reduce energy consumption. Actual tests show that the standby time is 56 hours (the indicator requires ≥48 hours), the continuous working time is 4.9 hours (the indicator requires ≥4 hours), and other indicators also meet the requirements of users. It is suitable for some special requirements of micro-UAVs that require low energy consumption, autonomous flight, and base station-controlled flight modes, and the size and cost are greatly reduced. It is also particularly suitable for rapid, low-cost, and large-scale production during wartime.

[0036] The active signal filter part can sometimes be implemented by using an alternative solution of software filtering. The use of software filtering also requires a corresponding amplifier circuit, which is the same size as the active signal filter part of this patent, but the software filtering sometimes ignores or increases the signal from the sensor. Therefore, in terms of the restoration of the sensor signal, software filtering is not as good as hardware active signal filtering.

[0037] There are two partial alternatives to the voltage / current conversion circuit: the op amp can be replaced by a high-power op amp (output current of more than 3A, such as OPA548), but the size is relatively large. The length and width of the op amp alone are 18.7×13mm, which is very large. Since the static current of the op amp is large, and the output is generally a triode, it is a current-type drive, and a large drive current is required when full power output is required; the other is to use a medium-power op amp (output current greater than 50mA, size is about 5×6mm), and the output pole still uses a medium-power triode (CE pole maximum current is about 3-4A, size is about 6.5×10mm), but the triode is also a current-driven device, and the base of the triode still requires a drive current of about 25mA, and the power consumption is also relatively large. Using the special voltage / current conversion circuit of this patent, the op amp is a low-power op amp (size is 5×3mm), and the output uses a MOS tube (size is 5×6mm). Since the MOS tube is a voltage-type drive, a large drive current is not required when (full power) output. It is estimated that the full power output current of the special voltage / current conversion circuit of this patent is about 30~35mA smaller than that of alternative schemes 1 and 2, and the power consumption is reduced by about 0.27W~0.32W, which is very important for micro-UAVs where electric energy is very precious. In addition, due to the small size of the MOS tube, the active signal filter produced by this patent has a total volume of 20×15×10mm. If the above two alternatives are used, the total volume is estimated to be 25×20×10mm. Therefore, the signal filter produced by this patent is much smaller than the alternatives, and is particularly suitable for use in micro-UAVs and other occasions where device miniaturization is required.

[0038] The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by anyone familiar with the technology within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. An active signal filter for outputting a current signal, characterized in that: It includes a signal filtering circuit, a remote control conversion circuit and a voltage / current conversion circuit. The signal filtering circuit is connected to an external sensor and outputs a filtered signal after filtering the received signal. The input end of the remote control conversion circuit is connected to the output end of the signal filtering circuit. The output end of the remote control conversion circuit is connected to the input end of the voltage / current conversion circuit. The remote control conversion circuit is also externally connected to a base station control signal. The output end of the voltage / current conversion circuit is connected to an external servo actuator. When the control of the ground control station is not required, it is the autonomous flight mode, and the remote control conversion circuit directly outputs the filtered signal to the voltage / current conversion circuit, and the servo actuator is driven by the current signal directly output by the voltage / current conversion circuit; when the control of the ground control station is required, it is the base station controlled flight mode, and the remote control conversion circuit outputs the received filtered signal to the ground control station for monitoring, but does not add it to the input end of the voltage / current conversion circuit. At this time, the control signal is sent to the voltage / current conversion circuit through the ground control station to drive the servo actuator to act; The signal filtering circuit includes an operational amplifier U1, wherein pin 1 of the operational amplifier U1 is connected to one end of a resistor R5, the other end of the resistor R5 is connected to pin 7 of the operational amplifier U1, one end of a resistor R6, one end of a capacitor C4 and a +9V voltage source, the other end of the resistor R6 is connected to pin 8 of the operational amplifier U1, the other end of the capacitor C4 is connected to one end of a capacitor C3 and is grounded, pin 3 of the operational amplifier U1 is connected to the other end of the capacitor C3 and one end of the resistor R3, the other end of the resistor R3 is connected to one end of a resistor R2 and one end of a capacitor C2, the other end of the resistor R2 is connected to one end of a resistor R1 and one end of a capacitor C1, and the other end of the resistor R1 is connected to the input signal V IN The other end of the capacitor C2 is connected to the 6th pin of the operational amplifier U1, one end of the resistor R15, and the output signal V O1 And the remote control conversion circuit, the 2nd pin of the operational amplifier U1 is connected to one end of the resistor R4 and one end of the resistor R14, the other end of the resistor R4 is connected to the other end of the capacitor C1 and then connected to one end of the capacitor C5 and grounded, the other end of the resistor R14 is connected to the other end of the resistor R15, and the 4th pin of the operational amplifier U1 is connected to the other end of the capacitor C5 and a -9V voltage source; The remote control conversion circuit includes a MOS tube optocoupler driver U5, wherein pin 1 of the MOS tube optocoupler driver U5 is connected to the cathode of the diode D2 and one end of the resistor R18, the anode of the diode D2 is grounded, the other end of the resistor R18 is connected to one end of the resistor R21 and a +9V voltage source, the other end of the resistor R21 is connected to one end of the resistor R17, one end of the resistor R22, and the base of the transistor U4, and the other end of the resistor R17 is connected to the base station control signal V ctr1 The other end of the resistor R22 is connected to the collector of the transistor U4 and then grounded. The emitter of the transistor U4 is connected to the 2nd pin of the MOS tube optocoupler driver U5. The 4th pin of the MOS tube optocoupler driver U5 is connected to the source of the MOS tube U6, the cathode of the diode D1, and the input signal V IN2 And the voltage / current conversion circuit, the 4th pin of the MOS tube optocoupler driver U5 is connected to the gate of the MOS tube U6 and one end of the resistor R19, and the drain of the MOS tube U6 is connected to the signal filtering circuit.

2. The active signal filter for outputting a current signal according to claim 1, characterized in that: The voltage / current conversion circuit includes an operational amplifier U2, wherein pin 1 of the operational amplifier U2 is connected to one end of a resistor R10, pin 5 of the operational amplifier U2 is connected to one end of a resistor R11, pin 2 of the operational amplifier U2 is connected to one end of a resistor R7 and one end of a resistor R12, pin 3 of the operational amplifier U2 is connected to one end of a resistor R8 and one end of a resistor R16, the other end of the resistor R10 is connected to the other end of the resistor R11 and then connected to one end of a resistor C6, pin 7 of the operational amplifier U2, the drain of a MOS tube U3 and a +9V voltage source, pin 6 of the operational amplifier U2 is connected to the gate of the MOS tube U3, pins 4 and 8 of the operational amplifier U2 are grounded respectively, the other end of the resistor R7 is grounded, the other end of the resistor R12 is connected to one end of a resistor R9, the other end of the resistor R8 is connected to the remote control conversion circuit, and the other end of the resistor R16 is connected to one end of a load resistor RL, a sampling resistor R S one end, the load resistor RL is grounded at the other end, and the sampling resistor R S The other end is connected to the source of the MOS tube U3 and the other end of the resistor R9.

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