CN114244363A - Microcurrent IV conversion device and method - Google Patents

Abstract

Translated fromChinese

本发明提供一种微电流IV转换装置及方法，该转换装置包括：IV转换器、反相比例放大器和二阶低通滤波器，IV转换器，用于将微电流信号转换为微电压信号；反相比例放大器，用于放大微电压信号；二阶低通滤波器，用于对放大后的微电压信号进行滤波，确定电压信号。本发明通过将微电流信号进行IV转换、反相比例放大和二阶低通滤波处理后，将微电流信号转换为能直接被模数转换器处理的电压信号，同时降低外界环境及自身干扰。

The invention provides a micro-current IV conversion device and method, the conversion device comprises: an IV converter, an inverse proportional amplifier and a second-order low-pass filter, and the IV converter is used for converting a micro-current signal into a micro-voltage signal; The inverse proportional amplifier is used to amplify the micro-voltage signal; the second-order low-pass filter is used to filter the amplified micro-voltage signal to determine the voltage signal. The invention converts the micro-current signal into a voltage signal that can be directly processed by the analog-to-digital converter by performing IV conversion, inverse proportional amplification and second-order low-pass filtering processing on the micro-current signal, and simultaneously reduces external environment and self-interference.

Description

Microcurrent IV conversion device and method

Technical Field

The invention relates to the technical field of electronic circuits, in particular to a micro-current IV conversion device and a method.

Background

In practical application, the sensor converts the acquired signal into an electric signal, so that the conversion from the detected signal to the electric signal is realized, but the converted electric signal is a micro-current signal, generally a nA-level current signal, and the micro-current signal cannot be directly input into the analog-to-digital converter for processing. For example, the dissolved oxygen sensor converts a dissolved oxygen signal into a nA-level current signal, an IV conversion is performed to convert the current signal into a voltage signal, and a suitable amplification ratio is performed to obtain a voltage signal in accordance with an analog-to-digital conversion range.

Therefore, it is a technical problem to be solved at present to convert the micro-current signal into a voltage signal that can be directly processed by the analog-to-digital converter, and simultaneously reduce the external environment and self-interference.

Disclosure of Invention

The invention provides a micro-current IV conversion device and a method, which are used for solving the problems that micro-current signals cannot be converted into voltage signals which can be directly processed by an analog-to-digital converter and the external environment and the self interference are reduced in the prior art.

In a first aspect, the present invention provides a microcurrent IV conversion apparatus comprising: an IV converter, an inverting proportional amplifier and a second-order low-pass filter,

an IV converter for converting the micro-current signal into a micro-voltage signal,

the inverse proportional amplifier is used for amplifying the micro-voltage signal;

and the second-order low-pass filter is used for filtering the amplified micro-voltage signal and determining the voltage signal.

Optionally, a constant voltage source is further included for providing a constant dc voltage source for the IV converter, the inverting proportional amplifier and the second order low pass filter.

Optionally, the micro-current signal is connected to the inverting input of the IV converter via an input resistor, and a feedback resistor is included between the inverting input of the IV converter and the output of the IV converter.

Optionally, the IV converter, inverting proportional amplifier, and second order low pass filter comprise TLV 2764.

Optionally, an instrumentation amplifier is also included, the instrumentation amplifier including the AD 620.

Optionally, the micro-voltage signal processing device further comprises a band-pass filter, wherein the band-pass filter is used for filtering the power frequency interference signals in the micro-voltage signal.

Optionally, the device further comprises a signal detector for converting the signal to be measured into a micro-current signal.

Optionally, the signal to be tested includes one or more paths of signals to be tested.

Optionally, the feedback resistance is 1M Ω.

In another aspect, the present invention provides a method for converting a micro-current IV, comprising: converting the micro-current signal into a micro-voltage signal; amplifying the micro-voltage signal; and filtering the amplified micro-voltage signal to determine a voltage signal.

According to the technical scheme, the invention comprises the following steps: an IV converter, an inverting proportional amplifier and a second-order low-pass filter. After the micro-current signal is subjected to IV conversion, inverse proportion amplification and second-order low-pass filtering, the micro-current signal is converted into a voltage signal which can be directly processed by an analog-to-digital converter, and meanwhile, the external environment and self interference are reduced.

Drawings

Fig. 1 is a schematic structural diagram of a micro-current IV conversion apparatus according to an embodiment of the present invention;

fig. 2 is a circuit diagram of an IV converter according to an embodiment of the present invention;

fig. 3 is a circuit diagram of an inverting proportional amplifier according to an embodiment of the invention;

FIG. 4 is a circuit diagram of a second-order low-pass filter according to an embodiment of the present invention;

fig. 5 is a schematic flow chart of a method for converting a micro-current IV according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without making any creative effort, shall fall within the protection scope of the present invention.

Fig. 1 is a schematic structural diagram of a micro-current IV conversion device according to an embodiment of the present invention, and as shown in fig. 1, the conversion device of the present embodiment includes: an IVconverter 11, an invertingproportional amplifier 12 and a second orderlow pass filter 13.

In a specific embodiment, an IVconverter 11 for converting the micro-current signal into a micro-voltage signal; an invertingproportional amplifier 12 for amplifying the micro-voltage signal; and the second-order low-pass filter 13 is used for filtering the amplified micro-voltage signal and determining the voltage signal.

Specifically, the microcurrent IV conversion apparatus further includes a signal detector, the signal detector is configured to convert a signal to be detected into a microcurrent signal, the signal to be detected includes one or more paths of signals to be detected, for example, the signal detector includes a temperature sensor, the signal to be detected includes one path of temperature signal, the signal detector includes a temperature sensor and a dissolved oxygen sensor, and the signal to be detected includes one path of temperature signal and one path of dissolved oxygen signal. If the signal to be detected only comprises one path of signal to be detected, only one path of signal to be detected is subjected to IV conversion; if the signal source module comprises a plurality of paths of signals to be tested, all the signals to be tested need to be subjected to IV conversion respectively.

The IVconverter 11 converts the micro-current signal transmitted by the signal detector into a micro-voltage signal through a feedback resistor; the inverseproportional amplifier 12 amplifies the micro-voltage signal proportionally by an operational amplifier, for example, amplifies the mV-level voltage signal proportionally to a V-level voltage signal, and determines the amplification factor of the voltage signal by selecting the ratio of the feedback resistance and the input resistance; the second-order low-pass filter 13 filters the high-frequency voltage signal in the amplified voltage signal through a second-order low-pass filter circuit and a voltage follower, and finally outputs a voltage signal meeting the requirement of the analog-to-digital converter, so that the process of converting the micro-current signal into the voltage signal is completed.

Fig. 2 shows a schematic circuit diagram of an IV converter according to an embodiment of the present invention, as shown in fig. 2, the IV converter of this embodiment may use a TLV2764 manufactured by TI, where the TLV2764 is a four-channel low-power single-power-supply operational amplifier and a rail-to-rail output operational amplifier, and it is not necessary to introduce multiple operational amplifiers, so that noise possibly introduced by discrete device connection is reduced, and the performance of the circuit is also improved by using an integrated operational amplifier itself. In this embodiment, one of the TLV2764 four-channel operational amplifiers is used for the IV converter, the other is used for the inverting proportional amplifier, and the other is used for the voltage follower in the second-order low-pass filter. The power supply voltage range of the TLV2764 is 1.8-3.6V, under the condition that loads are the same, the lower the power supply is, the smaller the power consumption is, and the TLV2764 can be powered by a 3.3V power supply provided by a constant voltage source.

In a specific embodiment, the signal detector may include an optical sensor that converts the signal to be measured into a micro-current signal and simultaneously converts the micro-current signal into a micro-voltage signal. For example, fluorescence emitted from the light source is quenched by the signal to be detected, the fluorescence intensity or the fluorescence lifetime changes, and the photodiode receives the quenched fluorescence signal and converts the optical signal into a micro-current signal. The photodiode may comprise an OPT301, and the OPT301 is a basic optical signal detector, and the change of the fluorescence intensity may cause the current generated inside the OPT301, and the generated current signal is very weak, so that the micro-current signal needs to be IV-converted and amplified. In the internal amplifier circuit of OPT301, inverting input and output directly connect 1M omega's feedback resistance, and feedback resistance connects the electric capacity of a 40pF in parallel, increases a zero point for compensate the phase place, improve the operational stability of putting, prevent the auto-excitation, signal detector OPT301 just can realize the IV conversion, converts little current signal into little voltage signal.

In a specific embodiment, the signal detector can only convert a signal to be detected into a micro-current signal, but cannot convert the micro-current signal into a micro-voltage signal, and an external IV converter is required to be connected to the signal detector to convert the micro-current signal into the micro-voltage signal. The micro-current signal output by the signal detector is connected with the inverting input end of the IV converter, a feedback resistor R1 is arranged between the inverting input end of the IV converter and the output end of the IV converter, and the feedback resistor R2 is connected with a feedback capacitor C1 in parallel.

The negative feedback-based IV converter lowers the input impedance by using negative feedback, and can lower the input impedance to a low level by the action of negative feedback even if the value of the current-voltage conversion resistor R1 is increased. Meanwhile, the signal-to-noise ratio of the IV converter is greatly affected by the feedback resistor R1, the current-voltage conversion gain of the IV converter is in direct proportion to the feedback resistance R1, and the noise generated on the feedback resistor R1 is in direct proportion to the square root of the resistance of the feedback resistor R1, so that the increase of the feedback resistance R1 is beneficial to the reduction of the signal-to-noise ratio of the IV converter. However, when the feedback resistance R1 exceeds 100M Ω, the frequency characteristic of the IV converter may change, which affects the stability, in this embodiment, the feedback resistance R1 is 1M Ω, and the relationship between the output voltage and the input current of the IV converter is shown in formula (1):

U_out＝-R₁I_in (1)

as can be seen from the formula (1), the output voltage of the IV converter is proportional to the input current, the proportionality coefficient is R1, the negative sign indicates the inverse phase, and the trickle current signal is converted into the trickle voltage signal through the degeneration resistor R1.

The phase lag caused by the feedback capacitor C1 is added to the phase lag of the IV converter and the feedback resistor R1 is connected in parallel with the feedback capacitor C1 for phase compensation. In the embodiment, a capacitor C2 is added at the input end of the IV converter, so that the high-frequency signal is well filtered. The bypass capacitor C3 is used to filter the ac signal and part of the high frequency signal in the dc signal, and the final output value of the IV converter is a relatively stable dc micro-voltage signal.

Fig. 3 shows a schematic circuit diagram of an inverting proportional amplifier provided by an embodiment of the present invention, and as shown in fig. 3, the inverting proportional amplifier of the present embodiment adopts one way of operational amplifier in TLV2764 manufactured by TI corporation.

In a specific embodiment, a signal output by the IV converter passes through a low-pass filter composed of R3 and C4 to filter an ac signal with a higher frequency in the micro-voltage signal, a cut-off frequency of the low-pass filter circuit is 1/(2 pi R3C4), and after the low-pass filter, a high-frequency signal in the micro-voltage signal can be filtered. Then, negative feedback is introduced through a feedback resistor R4 by passing through the inverting proportional amplifier, and the relation between the output voltage and the input voltage of the inverting proportional amplifier is shown as the formula (2):

as shown in the formula (2), the output voltage of the inverting proportional amplifier is in proportional relation with the input voltage, the proportionality coefficient is-R4/R3, the negative sign represents the inversion, the micro-voltage signal is proportionally amplified through the inverting proportional amplifier, the amplification factor of the inverting proportional amplifier can be adjusted by adjusting the resistance values of R3 and R4, and the amplification ratio of the micro-voltage signal is determined.

In a specific embodiment, the IV conversion device further includes an instrumentation amplifier, the instrumentation amplifier can select AD620, the AD620 is a low-cost and high-precision instrumentation amplifier, the use is simple, the adjustment of the amplification gain of the micro-voltage signal can be realized only by using one adjustable resistor, and the AD620 has the characteristics of low offset voltage, low offset drift and low power consumption, and compared with a three-operational amplifier structure instrumentation amplifier composed of separate elements, the AD620 has the advantages of small volume, low power consumption and high precision. The instrument amplifier is added at the rear end of the inverting proportional amplifier, so that the influence of a load on a micro-current signal and the temperature rise of a device can be reduced, the instrument amplifier has various settable gains, the micro-voltage signal can be further amplified according to the input requirement of the analog-to-digital converter, and the voltage signal output by the instrument amplifier is transmitted to the second-order low-pass filter for low-pass filtering.

In a specific embodiment, the IV conversion apparatus further includes a constant voltage source, and the constant voltage source provides a constant dc voltage source for the IV converter, the inverting proportional amplifier, and the second-order low-pass filter, for example, the constant voltage source may provide a constant dc voltage source of 3.3V for the TLV2764, that is, the constant dc voltage source is provided for the three-way operational amplifiers of the IV converter, the inverting proportional amplifier, and the second-order low-pass filter.

The constant voltage source may also provide a voltage source for the signal detector, e.g., the constant voltage source provides a constant dc voltage source for the dissolved oxygen sensor, which converts the dissolved oxygen signal to be measured into a micro-current signal. If the signal detector is an optical sensor, the constant voltage source can provide a Pulse Width Modulation (PWM) voltage source for the optical sensor, the PWM is a voltage source with a duty ratio of 50%, the signal detector is turned on when the voltage is 3.3V, the signal detector is turned off when the voltage is zero, and the signal detector is controlled to be turned on or turned off by controlling the duty ratio of PWM waves, so that the external interference and the service life of the signal detector can be reduced, energy can be saved, and the service life of the signal detector can be prolonged.

In a specific embodiment, the IV conversion device further comprises a band-pass filter, an output signal of the IV conversion device is easily interfered by a harmonic signal, especially a power frequency of 50Hz, because the power supply frequency adopted in China is 50Hz, the harmonic signal and the power frequency signal cause a large degree of interference on the signal processing of the electronic circuit, and the band-pass filter circuit can filter the power frequency interference and low-frequency and high-frequency interference signals in the voltage signal, thereby meeting the requirements of modulation and demodulation of the signal to be detected.

A band-pass filter refers to a filter that passes frequency components in a certain frequency range, but attenuates frequency components in other ranges to an extremely low level, as opposed to the concept of a band-stop filter. The band pass filter may include a resistor-inductor-capacitor circuit, produced by a combination of a low pass filter and a high pass filter. The four-order band-pass filter MAX7490 can be adopted, and compared with a band-pass filter circuit built by discrete components, the integrated filter chip has the advantages of low cost, low power consumption, small occupied area and simple design, reduces noise possibly introduced by resistance-capacitance connection, and improves the anti-interference performance of the band-pass filter circuit.

The band-pass filter MAX7490 comprises two same second-order filters with low power consumption, low voltage and wide dynamic range, and mainly comprises three parts: the operational amplifier, the MOS switch and the capacitor can realize good filtering effect only by a small amount of external components. The filters that MAX7490 may generate include: the band-pass filter, the low-pass filter, the band-pass filter and the band-stop filter can also be designed into a higher-order filter through the cascade connection of the filter modules. In the embodiment of the invention, a four-order 10kHz band-pass filter circuit is obtained by adopting multi-stage connection, the center frequency is 10kHz, the bandwidth is 2kHZ, the response frequency range is 8-12 kHz, and a 50Hz power frequency interference signal can be basically filtered.

Fig. 4 is a schematic circuit diagram of a second-order low-pass filter according to an embodiment of the present invention, where the second-order low-pass filter shown in fig. 4 is composed of a second-order low-pass filter circuit and a voltage follower, and the voltage follower includes TLV 2764.

In a specific embodiment, a second-order low-pass filter circuit composed of R7, C6, R8 and C7 can effectively filter the influence of a high-frequency signal on an input voltage signal, through multi-order integral filtering, both cosine and sine components in the voltage signal can be well filtered, and the second-order low-pass filter circuit outputs a direct-current component of the voltage signal. A voltage follower is added between the second-order low-pass filter circuit and the analog-to-digital converter, so that impedance conversion, buffering, isolation and driving load capacity improvement can be realized, the conversion precision of the analog-to-digital converter is ensured, an approximately constant voltage signal is output after the voltage signal passes through the second-order low-pass filter, the voltage signal is in direct proportion to a signal to be detected, the voltage signal is subsequently processed by the analog-to-digital converter and the microprocessor and is converted into an engineering value related to the signal to be detected, and the signal to be detected is determined according to the engineering value.

Fig. 5 is a schematic flow chart of a microcurrent IV conversion method according to an embodiment of the present invention, and as shown in fig. 5, the detection method according to the embodiment includes:

501. converting the micro-current signal into a micro-voltage signal;

502. amplifying the micro-voltage signal;

503. and filtering the amplified micro-voltage signal to determine a voltage signal.

Since the method is based on the conversion device, the working principle of the method is the same as that of the conversion device, and the detailed description is omitted here.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps not listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the unit claims enumerating several means, several of these means may be embodied by one and the same item of hardware. The usage of the words first, second and third, etcetera do not indicate any ordering. These words may be interpreted as names.

Those of ordinary skill in the art will understand that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; such modifications and substitutions do not depart from the spirit of the corresponding technical solutions and scope of the present invention as defined in the appended claims.

Claims (10)

Translated fromChinese

1.一种微电流IV转换装置，其特征在于，包括：IV转换器、反相比例放大器和二阶低通滤波器，1. a micro-current IV conversion device, is characterized in that, comprises: IV converter, inverse proportional amplifier and second-order low-pass filter,所述IV转换器，用于将微电流信号转换为微电压信号；The IV converter is used to convert a micro-current signal into a micro-voltage signal;所述反相比例放大器，用于放大所述微电压信号；the inverse proportional amplifier for amplifying the micro-voltage signal;所述二阶低通滤波器，用于对放大后的微电压信号进行滤波，确定电压信号。The second-order low-pass filter is used for filtering the amplified micro-voltage signal to determine the voltage signal.2.根据权利要求1所述的转换装置，其特征在于，还包括恒压源，2. The conversion device according to claim 1, characterized in that, further comprising a constant voltage source,所述恒压源，用于为所述IV转换器、所述反相比例放大器和所述二阶低通滤波器提供恒定直流电压源。The constant voltage source is used to provide a constant DC voltage source for the IV converter, the inverse proportional amplifier and the second-order low-pass filter.3.根据权利要求1所述的转换装置，其特征在于，所述微电流信号经过输入电阻与所述IV转换器的反相输入端连接，所述IV转换器的反相输入端与所述IV转换器的输出端之间包括反馈电阻。3 . The conversion device according to claim 1 , wherein the micro-current signal is connected to the inverting input terminal of the IV converter through an input resistance, and the inverting input terminal of the IV converter is connected to the inverting input terminal of the IV converter. 4 . A feedback resistor is included between the outputs of the IV converter.4.根据权利要求1所述的转换装置，其特征在于，所述IV转换器、所述反相比例放大器和所述二阶低通滤波器包括TLV2764。4 . The conversion device according to claim 1 , wherein the IV converter, the inverse proportional amplifier and the second-order low-pass filter comprise TLV2764. 5 .5.根据权利要求1所述的转换装置，其特征在于，还包括仪表放大器，所述仪表放大器包括AD620。5 . The conversion device according to claim 1 , further comprising an instrumentation amplifier, the instrumentation amplifier comprising an AD620. 6 .6.根据权利要求1所述的转换装置，其特征在于，还包括带通滤波器，6. The conversion device according to claim 1, characterized in that, further comprising a band-pass filter,所述带通滤波器，用于滤除所述电压信号中的工频干扰信号。The band-pass filter is used to filter out the power frequency interference signal in the voltage signal.7.根据权利要求1所述的转换装置，其特征在于，还包括信号检测器，7. The conversion device according to claim 1, further comprising a signal detector,所述信号检测器，用于将待测信号转换为所述微电流信号。The signal detector is used for converting the signal to be measured into the microcurrent signal.8.根据权利要求7所述的转换装置，其特征在于，所述待测信号包括一路或多路待测信号。8 . The conversion device according to claim 7 , wherein the signal to be measured comprises one or more channels of signals to be measured. 9 .9.根据权利要求3所述的转换装置，其特征在于，所述反馈电阻为1MΩ。9 . The conversion device according to claim 3 , wherein the feedback resistance is 1MΩ. 10 .10.一种微电流IV转换方法，其特征在于，包括：10. A micro-current IV conversion method, characterized in that, comprising:将微电流信号转换为微电压信号；Convert micro-current signal to micro-voltage signal;放大所述微电压信号；amplifying the micro-voltage signal;对放大后的微电压信号进行滤波，确定电压信号。Filter the amplified micro-voltage signal to determine the voltage signal.

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