Filter circuit of FD-600 low-noise fetus-voice meter

Abstract

The utility model discloses an FD-600 low-noise fetus-voice meter filter circuit. The FD-600 low-noise fetus-voice meter filter circuit comprises a passive band-pass filter circuit, three groups of active low-pass filter circuits, a logarithmic amplifier circuit, two groups of proportional amplifier circuits and an audio signal amplifying and shaping circuit. According to the utility model, the input audio signal is filtered and amplified for many times, so that clutter interference in the audio signal is filtered, and the signal is amplified between the filter circuits, so that the condition that the filtered signal is weak and difficult to capture and further causes distortion is avoided, noise is effectively reduced, and meanwhile, the noise is reduced. The clarity of fetal heart audio signals is improved, and medical staff can conveniently recognize and judge the audio signals detected by the fetal heart meter.

Description

Technical Field

[0001] The utility model relates to the technical field of electronic instruments and meters, in particular to an FD-600 low-noise fetal heart rate monitor filter circuit. Background Art

[0002] Fetal heart rate monitors, also known as fetal heart rate monitors, can obtain fetal heart movement information from the abdomen of pregnant women based on the Doppler principle. They are not used for continuous monitoring, but only for obtaining fetal heart movement information to monitor whether the fetal movement is abnormal. Based on the fetal heart condition, it is convenient for medical staff to make corresponding treatments according to the fetal heart condition. However, since the fetal heart rate monitor needs to detect and judge the fetal heart condition, other noises in the mother's body and the surrounding environment will have a certain impact and interference on the fetal heart condition information, and have an adverse effect on the clarity of the fetal heart rate monitor detection.

[0003] See also Figure 1 , Figure 2 In the prior art, the filter circuit of the fetal heart monitor only has a second-order active low-pass filter function, which is characterized by a simple circuit, but the low noise and anti-interference capabilities of the fetal heart sound are poor. At the same time, in terms of volume control, the prior art mostly uses multi-channel triode voltage division control, and the control gradient is small, so the user experience is poor. In the prior art, the power amplifier in the fetal heart monitor circuit uses a Class D amplifier, so when the audio signal is large, crossover distortion is prone to occur, and the power supply range is required to be high.

[0004] Therefore, the prior art has defects and needs to be improved. Utility Model Content

[0005] The utility model aims to overcome the deficiencies of the prior art and provide a FD-600 low-noise fetal heart rate filter circuit.

[0006] The technical solution of the utility model is as follows: a FD-600 low-noise fetal heart rate monitor filter circuit is provided, comprising: a passive bandpass filter circuit, three groups of active low-pass filter circuits, a logarithmic amplifier circuit, two groups of proportional amplifier circuits, and an audio signal amplification and shaping circuit;

[0007] The output end of the passive band-pass filter circuit is electrically connected to the input end of the first active low-pass filter circuit, the input end and the output end of the logarithmic amplifier circuit are electrically connected to the output end of the first active low-pass filter circuit and the output end of the second active filter circuit respectively, the output end of the second active filter circuit is electrically connected to the input end of the first proportional amplifier circuit, and the input end and the output end of the third active low-pass filter circuit are electrically connected to the output end of the first proportional amplifier circuit and the input end of the second proportional amplifier circuit respectively; the input end of the audio signal amplification and shaping circuit is connected in parallel to the input end of the passive band-pass filter circuit, and the output end of the audio signal amplification and shaping circuit is connected to the ADC sampling circuit of the single-chip microcomputer.

[0008] Furthermore, the passive bandpass filter circuit includes: a resistor R69, a resistor R68, a capacitor C48, a capacitor C49 and a capacitor C51, one end of the resistor R69 is connected in parallel with the input end of the audio signal amplification and shaping circuit with an interface module J2, the other end of the resistor R69 is electrically connected to one end of the capacitor C48 and one end of the capacitor C51, the other end of the capacitor C48 is connected to one end of the capacitor C49 and one end of the resistor R68, the other end of the capacitor C49 is connected to the input end of the first active low-pass filter circuit, and the other end of the capacitor C51 and the other end of the resistor R68 are connected to the ground.

[0009] Furthermore, the first active low-pass filter circuit includes: a resistor R43, a resistor R48, a resistor R39, a capacitor C37, a capacitor C50, and an operational amplifier chip U4A, one end of the resistor R43 is connected to the passive band-pass filter circuit, the other end of the resistor R43 is connected to one end of the resistor R39, one end of the resistor R48 and one end of the capacitor C50, the other end of the resistor R48 is connected to one end of the capacitor C37 and the second pin of the operational amplifier chip U4A, the other end of the resistor R39 is connected to the other end of the capacitor C37 and the first pin of the operational amplifier chip U4A and is connected to the input end of the logarithmic amplifier circuit, and the other end of the capacitor C50 and the 11th pin of the power amplifier chip U4A are grounded respectively.

[0010] Furthermore, the logarithmic amplifier circuit includes: an operational amplifier chip U4D, a resistor R40, a resistor R45, a resistor R63, a diode D1, and a diode D2, one end of the resistor R45 is connected to the output end of the first active low-pass filter circuit, and the other end of the resistor R45 is connected to one end of the resistor R63, the output end of the diode D2, the input end of the diode D1, and the 13th pin of the operational amplifier chip U4D.

[0011] Furthermore, the second active low-pass filter circuit includes: an operational amplifier chip U4B, a resistor R41, a resistor R42, a resistor R33, a capacitor C45, and a capacitor C56, one end of the resistor R41 is connected to the logarithmic amplifier circuit, the other end of the resistor R41 is connected to one end of the resistor R33, one end of the resistor R42 and one end of the capacitor C56, the other end of the resistor R42 is connected to one end of the capacitor C45 and the 6th pin of the operational amplifier chip U4B, the other end of the resistor R33 is connected to the other end of the capacitor C45 and the 1st pin of the operational amplifier chip U4B and is connected to the input end of the first proportional amplifier circuit, and the other end of the capacitor C56 and the 11th pin of the power amplifier chip U4B are grounded respectively.

[0012] Further, the first proportional amplifier circuit includes: an operational amplifier chip U4C, a resistor R44, a resistor R37, a capacitor C46, ​​and a capacitor C53; the third active low-pass filter circuit includes: an operational amplifier chip U6A, a resistor R65, a resistor R62, a resistor R53, a capacitor C68, a capacitor C79, and a capacitor C78; the second proportional amplifier circuit includes: an operational amplifier chip U6B, a resistor R66, a resistor R60, a resistor R67, a capacitor C71, and a capacitor C80;

[0013] One end of the resistor R44 is connected to the output end of the second active low-pass filter circuit, the other end of the resistor R44 is connected to one end of the resistor R37, one end of the capacitor C37, and the 9th pin of the operational amplifier chip U4C, the other end of the resistor R37, the other end of the capacitor C46, ​​the 8th pin of the operational amplifier chip U4C and one end of the capacitor C53 are connected, and the other end of the capacitor C53 is connected to one end of the resistor R65;

[0014] The other end of the resistor R65 is connected to one end of the resistor R53, one end of the resistor R62 and one end of the capacitor C79, the other end of the resistor R62 is connected to one end of the capacitor C68 and the second pin of the operational amplifier chip U6A, the other end of the resistor R53 is connected to the other end of the capacitor C68, the first pin of the operational amplifier chip U6A, and one end of the capacitor C78, ​​the other end of the capacitor C79 and the fourth pin of the power amplifier chip U4B are grounded respectively, and the other end of the capacitor C78 is connected to one end of the resistor R66;

[0015] The other end of the resistor R66 is connected to one end of the resistor R60, one end of the capacitor C71, and the 6th pin of the operational amplifier chip U6B. The other end of the resistor R60, the other end of the capacitor C71, the 7th pin of the operational amplifier chip U6B, and one end of the resistor R67 are connected. The other end of the resistor R67 is connected to one end of the capacitor C80. The other end of the capacitor C80 is connected to the sound signal port VCL.

[0016] Furthermore, the audio signal amplification and shaping circuit includes: an op amp chip U10A, an op amp chip U10B, a capacitor C92, a capacitor C94, a capacitor C95, a resistor R86, a resistor R88, a resistor R89, a resistor R79, a resistor R81, and a diode D8, one end of the capacitor C92 is connected to the fhr_signal port, one end of the capacitor C94 is connected to the passive bandpass filter circuit in parallel to the doppler port, the other end of the capacitor C92 and the other end of the capacitor C94 are connected in parallel to one end of the resistor R86, the other end of the resistor R86 is connected to one end of the resistor R82 and the op amp chip U10A, and the other end of the capacitor C94 is connected to one end of the resistor R86 and the other end of the resistor R86 is connected to one end of the resistor R82 and the op amp chip U10B. The first pin of the operational amplifier chip U10A is connected to the other end of the resistor R82 and one end of the resistor R88, the other end of the resistor R88 is connected to one end of the capacitor C95, the other end of the capacitor C95 is connected to one end of the resistor R89, the other end of the resistor R89 ​​is connected to one end of the resistor R79, one end of the resistor R81 and the sixth pin of the operational amplifier circuit U10B, the other end of the resistor R79 is connected to the output end of the diode D8, the input end of the diode D8 is connected in parallel with the other end of the resistor R81 and the seventh pin of the operational amplifier circuit U10B to the ADC sampling circuit of the single-chip microcomputer.

[0017] Furthermore, the output end of the second proportional amplifier circuit is connected to a digital volume potentiometer circuit, and the digital volume potentiometer circuit includes: a potentiometer U8, a capacitor C76 and a capacitor C81, the 8th pin of the potentiometer U8 is connected to one end of the capacitor C76 and connected to a 5V power supply, the other end of the capacitor C76 is grounded, the 4th pin and the 6th pin of the potentiometer U8 are grounded in parallel, the 1st pin of the potentiometer U8 is connected to the INC_V port, the 2nd pin of the potentiometer U8 is connected to the U / D port, the 7th pin of the potentiometer U8 is connected to the CS_V port, and the 5th pin of the potentiometer U8 is connected to an audio power amplifier circuit.

[0018] Furthermore, the audio power amplifier circuit includes: polar capacitor C72, polar capacitor C73, polar capacitor C82, polar capacitor C86, polar capacitor C85, polar capacitor C7, capacitor C75, capacitor C88, resistor R71, resistor R58, resistor R74, resistor R76, audio power amplifier chip U9, headphone jack J5 and speaker jack J4, the third pin of the audio power amplifier chip U9 is connected to the digital volume potentiometer circuit, and the first pin of the audio power amplifier chip U9 is connected to the digital volume potentiometer circuit. The pin is connected to the positive terminal of the polarity capacitor C85, the negative terminal of the polarity capacitor C85 is connected to one end of the resistor R76, the other end of the resistor R76 is connected to the 8th pin of the audio power amplifier chip U9, the 7th pin of the audio power amplifier chip U9 is connected to the positive terminal of the polarity capacitor C87, the 2nd pin of the audio power amplifier chip U9 and the negative terminal of the polarity capacitor C87 are connected to the ground in parallel, the 6th pin of the audio power amplifier chip U9 is connected to one end of the resistor R58, one end of the resistor R140, and the One end of the capacitor C75, the positive end of the polarity capacitor C73, and the positive end of the polarity capacitor C72 are connected, the other end of the resistor R58 is connected to a 12V power supply, the other end of the resistor R140 is connected to the VTCC port, the other end of the capacitor C75, the negative end of the polarity capacitor C72, and the negative end of the polarity capacitor C73 are connected to the ground in parallel, the 5th pin of the audio power amplifier chip U9 is connected to one end of the resistor R71, the positive end of the polarity capacitor C82, and the positive end of the polarity capacitor C86, the other end of the resistor R71 is connected to one end of the capacitor C88, the negative end of the polarity capacitor C82 and the negative end of the polarity capacitor C86 are connected in parallel to the 2nd pin and the 4th pin of the headphone jack J5, the 1st pin of the headphone jack J5 is connected to one end of the resistor R74, the 3rd pin of the headphone jack J5 is connected to one end of the speaker jack J4, and the other end of the speaker jack J4, the other end of the resistor R74, and the other end of the capacitor C88 are grounded respectively.

[0019] Adopting the above scheme, the utility model BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic diagram of a circuit of the prior art Figure 1 .

[0021] Figure 2 A schematic diagram of a circuit of the prior art Figure 2 .

[0022] Figure 3 Schematic diagram of the circuit module of the passive bandpass filter circuit.

[0023] Figure 4 It is a circuit module schematic diagram of a first active low-pass filter circuit.

[0024] Figure 5 Schematic diagram of the circuit module of the logarithmic amplifier circuit.

[0025] Figure 6 Schematic diagram of a circuit module of a second active low-pass filter circuit.

[0026] Figure 7 It is a circuit module schematic diagram of a proportional amplifier circuit and a third active low-pass filter circuit.

[0027] Figure 8 It is a circuit module diagram of the audio signal amplification and shaping circuit.

[0028] Fig. 9 Figure 2 is a circuit module diagram of a digital volume potentiometer circuit.

[0029] Fig.10 Schematic diagram of the circuit module of the audio power amplifier circuit. DETAILED DESCRIPTION

[0030] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0031] The utility model provides an FD-600 low-noise fetal heart rate monitor filter circuit, comprising: a passive bandpass filter circuit, three groups of active low-pass filter circuits, a logarithmic amplifier circuit, two groups of proportional amplifier circuits, and an audio signal amplification and shaping circuit.

[0032] The output end of the passive band-pass filter circuit is electrically connected to the input end of the first active low-pass filter circuit, the input end and the output end of the logarithmic amplifier circuit are electrically connected to the output end of the first active low-pass filter circuit and the output end of the second active filter circuit respectively, the output end of the second active filter circuit is electrically connected to the input end of the first proportional amplifier circuit, and the input end and the output end of the third active low-pass filter circuit are electrically connected to the output end of the first proportional amplifier circuit and the input end of the second proportional amplifier circuit respectively; the input end of the audio signal amplification and shaping circuit is connected in parallel to the input end of the passive band-pass filter circuit, and the output end of the audio signal amplification and shaping circuit is connected to the ADC sampling circuit of the single-chip microcomputer.

[0033] The utility model filters and amplifies the input audio signal multiple times, thereby filtering out the clutter interference in the audio signal and amplifying the signal between the filter circuits, so as to avoid the situation where the signal is weak after filtering and difficult to capture, thereby causing distortion. In this way, the noise is effectively reduced while improving the clarity of the fetal heart audio signal, making it easier for medical personnel to identify and judge the audio signal detected by the fetal heart monitor.

[0034] See also Figure 3The passive bandpass filter circuit includes: resistor R69, resistor R68, capacitor C48, capacitor C49 and capacitor C51. One end of the resistor R69 is connected in parallel with the input end of the audio signal amplification and shaping circuit to an interface module J2. The other end of the resistor R69 is electrically connected to one end of the capacitor C48 and one end of the capacitor C51. The other end of the capacitor C48 is connected to one end of the capacitor C49 and one end of the resistor R68. The other end of the capacitor C49 is connected to the input end of the first active low-pass filter circuit. The other end of the capacitor C51 and the other end of the resistor R68 are connected to the ground. The fetal heart audio signal is input from the resistor R69. The resistor R69 and the capacitor C51 are low-pass filter circuits with a design frequency of 10KHz. The capacitor C48 and the resistor R68 are high-pass circuits with a design frequency of 100Hz. The passive filter is used as a pre-filter. Its Q value is small, the difference between the theoretical progress and the actual value is large, and the signal attenuation is large. Therefore, the back end needs to compensate and gain the signal attenuation.

[0035] See also Figure 4 The first active low-pass filter circuit includes: a resistor R43, a resistor R48, a resistor R39, a capacitor C37, a capacitor C50, and an operational amplifier chip U4A, one end of the resistor R43 is connected to the passive band-pass filter circuit, the other end of the resistor R43 is connected to one end of the resistor R39, one end of the resistor R48 and one end of the capacitor C50, the other end of the resistor R48 is connected to one end of the capacitor C37 and the second pin of the operational amplifier chip U4A, the other end of the resistor R39 is connected to the other end of the capacitor C37 and the first pin of the operational amplifier chip U4A and is connected to the input end of the logarithmic amplifier circuit, and the other end of the capacitor C50 and the 11th pin of the power amplifier chip U4A are grounded respectively. The signal is input from the passive bandpass filter circuit to the first active low-pass filter circuit. The filter circuit is a 1.5KHz second-order low-pass filter. As the back end connected to the passive bandpass filter circuit, in order to compensate for the attenuation of the signal by the passive bandpass filter circuit, a gain value of nearly 20 times is adopted to avoid the final output of the fetal heart information being weak due to signal attenuation, which makes it inconvenient for medical staff to judge the fetal heart status.

[0036] See also Figure 5, the logarithmic amplifier circuit includes: an operational amplifier chip U4D, a resistor R40, a resistor R45, a resistor R63, a diode D1, and a diode D2, one end of the resistor R45 is connected to the output end of the first active low-pass filter circuit, and the other end of the resistor R45 is connected to one end of the resistor R63, the output end of the diode D2, the input end of the diode D1, and the 13th pin of the operational amplifier chip U4D. The electrical signal is input from the first active low-pass filter circuit to the logarithmic amplifier circuit and transmitted in the direction of the second active low-pass filter circuit. After the audio signal is processed by the logarithmic amplifier circuit, it can meet the human ear's receiving comfort for the sound effect and improve the user experience.

[0037] See also Figure 6 The second active low-pass filter circuit includes: an operational amplifier chip U4B, a resistor R41, a resistor R42, a resistor R33, a capacitor C45, and a capacitor C56. One end of the resistor R41 is connected to the logarithmic amplifier circuit, and the other end of the resistor R41 is connected to one end of the resistor R33, one end of the resistor R42, and one end of the capacitor C56. The other end of the resistor R42 is connected to one end of the capacitor C45 and the 6th pin of the operational amplifier chip U4B. The other end of the resistor R33 is connected to the other end of the capacitor C45 and the 1st pin of the operational amplifier chip U4B and connected to the input end of the first proportional amplifier circuit. The other end of the capacitor C56 and the 11th pin of the power amplifier chip U4B are grounded respectively. The fetal heart audio signal is input from the logarithmic amplifier circuit to the second active low-pass filter circuit, and a 500H second-order low-pass filter is used to further filter the required fetal heart audio in a closer frequency band.

[0038] See also Figure 7 The first proportional amplifier circuit includes: an operational amplifier chip U4C, a resistor R44, a resistor R37, a capacitor C46, ​​and a capacitor C53; the third active low-pass filter circuit includes: an operational amplifier chip U6A, a resistor R65, a resistor R62, a resistor R53, a capacitor C68, a capacitor C79, and a capacitor C78; the second proportional amplifier circuit includes: an operational amplifier chip U6B, a resistor R66, a resistor R60, a resistor R67, a capacitor C71, and a capacitor C80.

[0039] One end of the resistor R44 is connected to the output end of the second active low-pass filter circuit, the other end of the resistor R44 is connected to one end of the resistor R37, one end of the capacitor C37, and the 9th pin of the operational amplifier chip U4C, the other end of the resistor R37, the other end of the capacitor C46, ​​the 8th pin of the operational amplifier chip U4C and one end of the capacitor C53 are connected, and the other end of the capacitor C53 is connected to one end of the resistor R65.

[0040] The other end of the resistor R65 is connected to one end of the resistor R53, one end of the resistor R62 and one end of the capacitor C79, the other end of the resistor R62 is connected to one end of the capacitor C68 and the second pin of the operational amplifier chip U6A, the other end of the resistor R53 is connected to the other end of the capacitor C68, the first pin of the operational amplifier chip U6A, and one end of the capacitor C78, ​​the other end of the capacitor C79 and the fourth pin of the power amplifier chip U4B are grounded respectively, and the other end of the capacitor C78 is connected to one end of the resistor R66.

[0041] The other end of the resistor R66 is connected to one end of the resistor R60, one end of the capacitor C71, and the 6th pin of the operational amplifier chip U6B. The other end of the resistor R60, the other end of the capacitor C71, the 7th pin of the operational amplifier chip U6B, and one end of the resistor R67 are connected. The other end of the resistor R67 is connected to one end of the capacitor C80. The other end of the capacitor C80 is connected to the sound signal port VCL.

[0042] The fetal heart audio signal is input from the second active low-pass filter circuit to the first proportional amplifier circuit for processing, and then passes through the third active low-pass filter circuit and the second proportional amplifier circuit in sequence to compensate the signal. Because the second active low-pass filter circuit will cause a certain attenuation to the useful signal, before entering the third active low-pass filter circuit, the signal is amplified and compensated by the first proportional amplifier circuit, and then further noise reduction is performed by the third active low-pass filter circuit. After the second proportional amplifier circuit provides signal compensation, it is output to the sound signal port VCL, so as to achieve a more ideal filtering effect, amplify and compensate the signal, and improve the medical staff's judgment of the fetal heart audio signal.

[0043] See also Figure 8The audio signal amplification and shaping circuit includes: an op amp chip U10A, an op amp chip U10B, a capacitor C92, a capacitor C94, a capacitor C95, a resistor R86, a resistor R88, a resistor R89, a resistor R79, a resistor R81, and a diode D8. One end of the capacitor C92 is connected to the fhr_signal port, one end of the capacitor C94 is connected to the passive bandpass filter circuit in parallel to the doppler port, the other end of the capacitor C92 and the other end of the capacitor C94 are connected in parallel to one end of the resistor R86, the other end of the resistor R86 is connected to one end of the resistor R82 and the op amp chip U10A The first pin of the operational amplifier chip U10A is connected to the other end of the resistor R82 and one end of the resistor R88, the other end of the resistor R88 is connected to one end of the capacitor C95, the other end of the capacitor C95 is connected to one end of the resistor R89, the other end of the resistor R89 ​​is connected to one end of the resistor R79, one end of the resistor R81 and the sixth pin of the operational amplifier circuit U10B, the other end of the resistor R79 is connected to the output end of the diode D8, the input end of the diode D8 is connected in parallel with the other end of the resistor R81 and the seventh pin of the operational amplifier circuit U10B to the ADC sampling circuit of the single-chip microcomputer.

[0044] The operational amplifier chip U10A is a simple first-stage proportional operational amplifier circuit. Its function is to amplify the audio signal before shaping it. The positive half-axis part of the audio information centered on the programmed voltage is then completely removed through the operational amplifier chip U10B, leaving only the negative half-axis part. Finally, it is input into the ADC sampling circuit of the microcontroller, making full use of the dynamic range of the power supply, which is beneficial to the calculation and recognition of small signals.

[0045] See also Fig. 9 The output end of the second proportional amplifier circuit is connected to a digital volume potentiometer circuit, which includes a potentiometer U8, a capacitor C76 and a capacitor C81. The 8th pin of the potentiometer U8 is connected to one end of the capacitor C76 and connected to a 5V power supply. The other end of the capacitor C76 is grounded. The 4th and 6th pins of the potentiometer U8 are connected to the ground in parallel. The 1st pin of the potentiometer U8 is connected to the INC_V port. The 2nd pin of the potentiometer U8 is connected to the U / D port. The 7th pin of the potentiometer U8 is connected to the CS_V port. The 5th pin of the potentiometer U8 is connected to an audio power amplifier circuit. The chip model used by the potentiometer U8 of the digital volume potentiometer circuit is X93156 / TSOP, which has a high-resolution adjustment of 32 gears. Therefore, compared with the circuit grading in the prior art, it can bring customers a more delicate volume adjustment experience.

[0046] See also Fig.10The audio power amplifier circuit includes: polar capacitor C72, polar capacitor C73, polar capacitor C82, polar capacitor C86, polar capacitor C85, polar capacitor C7, capacitor C75, capacitor C88, resistor R71, resistor R58, resistor R74, resistor R76, audio power amplifier chip U9, headphone jack J5 and speaker jack J4, the third pin of the audio power amplifier chip U9 is connected to the digital volume potentiometer circuit, the first pin of the audio power amplifier chip U9 is connected to the polar The positive terminal of the polar capacitor C85 is connected, the negative terminal of the polar capacitor C85 is connected to one end of the resistor R76, the other end of the resistor R76 is connected to the 8th pin of the audio power amplifier chip U9, the 7th pin of the audio power amplifier chip U9 is connected to the positive terminal of the polar capacitor C87, the 2nd pin of the audio power amplifier chip U9 and the negative terminal of the polar capacitor C87 are connected to the ground in parallel, the 6th pin of the audio power amplifier chip U9 is connected to one end of the resistor R58, one end of the resistor R140, and the capacitor C The first end of the audio power amplifier chip U9 is connected to one end of the resistor R71, the positive end of the polarity capacitor C82, and the positive end of the polarity capacitor C86, the other end of the resistor R71 is connected to one end of the capacitor C88, the negative end of the polarity capacitor C82 and the negative end of the polarity capacitor C86 are connected in parallel to the second pin and the fourth pin of the headphone jack J5, the first pin of the headphone jack J5 is connected to one end of the resistor R74, the third pin of the headphone jack J5 is connected to one end of the speaker jack J4, and the other end of the speaker jack J4, the other end of the resistor R74 and the other end of the capacitor C88 are grounded respectively. In this embodiment, a class AB power amplifier is used. Compared with a class D power amplifier, since the signal coupling is in a capacitive manner, coupling is performed by polarized capacitor C82 and polarized capacitor C86, which can solve the problem of clipping due to crossover distortion and meet the requirement that the signal waveform can be processed by charging and discharging the coupling capacitor when the audio input signal is large.

[0047] To sum up, the utility model filters and amplifies the input audio signal multiple times, thereby filtering out the noise interference in the audio signal and amplifying the signal between the filter circuits, so as to avoid the situation where the signal is weak after filtering and difficult to capture, resulting in distortion. In this way, the noise is effectively reduced while improving the clarity of the fetal heart audio signal, making it easier for medical staff to identify and judge the audio signal detected by the fetal heart monitor.

[0048] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A FD-600 low noise fetal heart rate filter circuit, characterized in that: include: Passive bandpass filter circuit, three sets of active lowpass filter circuits, logarithmic amplifier circuit, two sets of proportional amplifier circuits, and audio signal amplification and shaping circuit; The output end of the passive band-pass filter circuit is electrically connected to the input end of the first active low-pass filter circuit, the input end and the output end of the logarithmic amplifier circuit are electrically connected to the output end of the first active low-pass filter circuit and the output end of the second active filter circuit respectively, the output end of the second active filter circuit is electrically connected to the input end of the first proportional amplifier circuit, and the input end and the output end of the third active low-pass filter circuit are electrically connected to the output end of the first proportional amplifier circuit and the input end of the second proportional amplifier circuit respectively; the input end of the audio signal amplification and shaping circuit is connected in parallel to the input end of the passive band-pass filter circuit, and the output end of the audio signal amplification and shaping circuit is connected to the ADC sampling circuit of the single-chip microcomputer.

2. The FD-600 low noise fetal heart rate filter circuit according to claim 1 is characterized in that: The passive band-pass filter circuit includes: a resistor R69, a resistor R68, a capacitor C48, a capacitor C49 and a capacitor C51, one end of the resistor R69 is connected in parallel with the input end of the audio signal amplification and shaping circuit to an interface module J2, the other end of the resistor R69 is electrically connected to one end of the capacitor C48 and one end of the capacitor C51, the other end of the capacitor C48 is connected to one end of the capacitor C49 and one end of the resistor R68, the other end of the capacitor C49 is connected to the input end of the first active low-pass filter circuit, and the other end of the capacitor C51 and the other end of the resistor R68 are connected to the ground.

3. The FD-600 low noise fetal heart rate filter circuit according to claim 1, characterized in that: The first active low-pass filter circuit includes: a resistor R43, a resistor R48, a resistor R39, a capacitor C37, a capacitor C50, and an operational amplifier chip U4A, one end of the resistor R43 is connected to the passive band-pass filter circuit, the other end of the resistor R43 is connected to one end of the resistor R39, one end of the resistor R48, and one end of the capacitor C50, the other end of the resistor R48 is connected to one end of the capacitor C37 and the second pin of the operational amplifier chip U4A, the other end of the resistor R39 is connected to the other end of the capacitor C37 and the first pin of the operational amplifier chip U4A and is connected to the input end of the logarithmic amplifier circuit, and the other end of the capacitor C50 and the 11th pin of the power amplifier chip U4A are grounded respectively.

4. The FD-600 low noise fetal heart rate filter circuit according to claim 1, characterized in that: The logarithmic amplifier circuit includes: an operational amplifier chip U4D, a resistor R40, a resistor R45, a resistor R63, a diode D1, and a diode D2, one end of the resistor R45 is connected to the output end of the first active low-pass filter circuit, and the other end of the resistor R45 is connected to one end of the resistor R63, the output end of the diode D2, the input end of the diode D1, and the 13th pin of the operational amplifier chip U4D.

5. The FD-600 low noise fetal heart rate filter circuit according to claim 1, characterized in that: The second active low-pass filter circuit includes: an operational amplifier chip U4B, a resistor R41, a resistor R42, a resistor R33, a capacitor C45, and a capacitor C56. One end of the resistor R41 is connected to the logarithmic amplifier circuit, the other end of the resistor R41 is connected to one end of the resistor R33, one end of the resistor R42, and one end of the capacitor C56, the other end of the resistor R42 is connected to one end of the capacitor C45 and the 6th pin of the operational amplifier chip U4B, the other end of the resistor R33 is connected to the other end of the capacitor C45 and the 1st pin of the operational amplifier chip U4B and is connected to the input end of the first proportional amplifier circuit, and the other end of the capacitor C56 and the 11th pin of the power amplifier chip U4B are grounded respectively.

6. The FD-600 low noise fetal heart rate filter circuit according to claim 1, characterized in that: The first proportional amplifier circuit includes: an operational amplifier chip U4C, a resistor R44, a resistor R37, a capacitor C46, ​​and a capacitor C53; the third active low-pass filter circuit includes: an operational amplifier chip U6A, a resistor R65, a resistor R62, a resistor R53, a capacitor C68, a capacitor C79, and a capacitor C78; the second proportional amplifier circuit includes: an operational amplifier chip U6B, a resistor R66, a resistor R60, a resistor R67, a capacitor C71, and a capacitor C80; One end of the resistor R44 is connected to the output end of the second active low-pass filter circuit, the other end of the resistor R44 is connected to one end of the resistor R37, one end of the capacitor C37, and the 9th pin of the operational amplifier chip U4C, the other end of the resistor R37, the other end of the capacitor C46, ​​the 8th pin of the operational amplifier chip U4C and one end of the capacitor C53 are connected, and the other end of the capacitor C53 is connected to one end of the resistor R65; The other end of the resistor R65 is connected to one end of the resistor R53, one end of the resistor R62 and one end of the capacitor C79, the other end of the resistor R62 is connected to one end of the capacitor C68 and the second pin of the operational amplifier chip U6A, the other end of the resistor R53 is connected to the other end of the capacitor C68, the first pin of the operational amplifier chip U6A, and one end of the capacitor C78, ​​the other end of the capacitor C79 and the fourth pin of the power amplifier chip U4B are grounded respectively, and the other end of the capacitor C78 is connected to one end of the resistor R66; The other end of the resistor R66 is connected to one end of the resistor R60, one end of the capacitor C71, and the 6th pin of the operational amplifier chip U6B. The other end of the resistor R60, the other end of the capacitor C71, the 7th pin of the operational amplifier chip U6B, and one end of the resistor R67 are connected. The other end of the resistor R67 is connected to one end of the capacitor C80. The other end of the capacitor C80 is connected to the sound signal port VCL.

7. The FD-600 low noise fetal heart rate filter circuit according to claim 1, characterized in that: The audio signal amplification and shaping circuit includes: an operational amplifier chip U10A, an operational amplifier chip U10B, a capacitor C92, a capacitor C94, a capacitor C95, a resistor R86, a resistor R88, a resistor R89, a resistor R79, a resistor R81, and a diode D8, one end of the capacitor C92 is connected to the fhr_signal port, one end of the capacitor C94 is connected to the passive bandpass filter circuit in parallel to the doppler port, the other end of the capacitor C92 and the other end of the capacitor C94 are connected in parallel to one end of the resistor R86, the other end of the resistor R86 is connected to one end of the resistor R82 and the operational amplifier chip U10A The first pin of the operational amplifier chip U10A is connected to the other end of the resistor R82 and one end of the resistor R88, the other end of the resistor R88 is connected to one end of the capacitor C95, the other end of the capacitor C95 is connected to one end of the resistor R89, the other end of the resistor R89 ​​is connected to one end of the resistor R79, one end of the resistor R81 and the sixth pin of the operational amplifier circuit U10B, the other end of the resistor R79 is connected to the output end of the diode D8, the input end of the diode D8 is connected in parallel with the other end of the resistor R81 and the seventh pin of the operational amplifier circuit U10B to the ADC sampling circuit of the single-chip microcomputer.

8. The FD-600 low noise fetal heart rate filter circuit according to claim 1, characterized in that: The output end of the second proportional amplifier circuit is connected to a digital volume potentiometer circuit, which includes: a potentiometer U8, a capacitor C76 and a capacitor C81. The 8th pin of the potentiometer U8 is connected to one end of the capacitor C76 and connected to a 5V power supply, the other end of the capacitor C76 is grounded, the 4th pin and the 6th pin of the potentiometer U8 are grounded in parallel, the 1st pin of the potentiometer U8 is connected to the INC_V port, the 2nd pin of the potentiometer U8 is connected to the U / D port, the 7th pin of the potentiometer U8 is connected to the CS_V port, and the 5th pin of the potentiometer U8 is connected to an audio power amplifier circuit.

9. The FD-600 low noise fetal heart rate filter circuit according to claim 8, characterized in that: The audio power amplifier circuit includes: polar capacitor C72, polar capacitor C73, polar capacitor C82, polar capacitor C86, polar capacitor C85, polar capacitor C7, capacitor C75, capacitor C88, resistor R71, resistor R58, resistor R74, resistor R76, audio power amplifier chip U9, headphone jack J5 and speaker jack J4, the third pin of the audio power amplifier chip U9 is connected to the digital volume potentiometer circuit, the first pin of the audio power amplifier chip U9 is connected to the polarity The positive terminal of the capacitor C85 is connected, the negative terminal of the polar capacitor C85 is connected to one end of the resistor R76, the other end of the resistor R76 is connected to the 8th pin of the audio power amplifier chip U9, the 7th pin of the audio power amplifier chip U9 is connected to the positive terminal of the polar capacitor C87, the 2nd pin of the audio power amplifier chip U9 and the negative terminal of the polar capacitor C87 are connected to the ground in parallel, the 6th pin of the audio power amplifier chip U9 is connected to one end of the resistor R58, one end of the resistor R140, and the capacitor C The first end of the audio power amplifier chip U9 is connected to one end of the resistor R71, the positive end of the polarity capacitor C82, and the positive end of the polarity capacitor C86, the other end of the resistor R71 is connected to one end of the capacitor C88, the negative end of the polarity capacitor C82 and the negative end of the polarity capacitor C86 are connected in parallel to the second pin and the fourth pin of the headphone jack J5, the first pin of the headphone jack J5 is connected to one end of the resistor R74, the third pin of the headphone jack J5 is connected to one end of the speaker jack J4, and the other end of the speaker jack J4, the other end of the resistor R74 and the other end of the capacitor C88 are grounded respectively.

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