Differential closed-loop negative feedback amplification circuit based on JFET pair transistors

Abstract

The invention discloses a differential closed-loop negative feedback amplification circuit based on JFET geminate transistors, a low-noise amplifier is used for measuring weak voltage signals, discrete JFET field-effect transistors are used for forming an input stage of the low-noise amplifier, noise interference is reduced, meanwhile, extremely high input impedance can be provided by using the characteristic that the grid current of the JFET field-effect transistors is basically zero, and the differential closed-loop negative feedback amplification circuit based on the JFET geminate transistors is obtained. Mirror current is provided for a pair of JFET field effect transistors in the low-noise amplifier module through a current mirror of the low-noise amplifier, a closed-loop feedback structure of the low-noise amplifier can save one path of input for the JFET field effect transistors, so that the amplifying circuit can realize dual-channel input, and a dual-channel input structure can enable an accessed signal to be a differential signal, so that common-mode interference is effectively inhibited, and the reliability of the amplifying circuit is improved. Overall closed-loop negative feedback can achieve high gain stability, reduce nonlinear distortion, increase input impedance, reduce output impedance and improve the performance of the amplifier, and solves the problem of precise amplification and measurement of weak voltage signals in the aviation electromagnetic field.

Description

Technical Field

[0001] The invention relates to the field of low noise amplifiers, and in particular to a differential closed-loop negative feedback amplifier circuit based on a JFET pair of tubes. Background Art

[0002] The amplifier is mainly used for receiving systems in the field of airborne electromagnetics and is used for high-precision amplification of voltage signals. The Z-axis tilting electromagnetic measurement system belongs to the field of deep geophysical exploration in the frequency domain and is usually used to detect and analyze electromagnetic signals in the Z-axis direction. The system is widely used in geological exploration, earthquake early warning, underground resource detection and other fields. These applications are very sensitive to weak changes in signals, so accurate capture and amplification of signals are crucial.

[0003] There are currently two main research directions for amplifying weak voltage signals: one is to use integrated operational amplifiers for preamplification, and the other is to use JFET discrete devices to build amplifiers. The preamplifier circuit in the traditional Z-axis tilting electromagnetic measurement system mostly uses Figure 1 The instrument amplifier shown in the figure, however, because the input stage of the instrument amplifier uses an integrated operational amplifier, its noise is mainly determined by the amplifier model used in the first stage. However, the noise performance of the integrated operational amplifier is not ideal, and it is difficult to meet the needs of effectively amplifying and receiving the signals collected by the Z-axis tilting electromagnetic measurement system.

[0004] Existing patent documents, CN118508892A discloses a broadband high-gain low-noise amplifier, which adopts a source degeneration inductor structure and a common source and common gate structure based on Darlington topology, but its input stage is a single-ended input, and it cannot amplify the signal of a differential structure sensor. CN115765641A discloses a multi-discrete current source low-noise JFET differential parallel amplifier, including a JFET first-stage amplifier circuit and an IOA second-stage amplifier circuit, but there is no closed-loop feedback between the two-stage amplifier circuits, and it is impossible to achieve amplification stability and high linearity.

[0005] At present, another research direction of weak voltage signal amplification is as follows Figure 2 The amplifiers shown are made of discrete components. These circuits have simple structures and certain gain effects, but the feedback loop of the amplifiers made of discrete components occupies one input end of the differential pair tube, which makes it impossible for the sensor signal to be input differentially. They are greatly affected by environmental noise, temperature drift, and signal distortion. In this case, the measurement accuracy will be significantly reduced. Summary of the invention

[0006] The present invention aims to solve the problem that in the existing voltage measurement in the field of aviation electromagnetics, the common mode noise cannot be reduced and the linearity cannot be improved simultaneously because the differential input and the closed-loop feedback cannot be realized simultaneously; a differential closed-loop negative feedback amplifier circuit based on a JFET pair tube is provided.

[0007] A differential closed-loop negative feedback amplifier circuit based on a JFET pair, the amplifier circuit comprising a low-noise amplifier; the low-noise amplifier comprising a first-stage amplifier, a second-stage amplifier, a feedback loop and a current mirror;

[0008] The first stage amplifier uses a discrete JFET pair structure as the input stage of the amplifier module.

[0009] The first stage amplifier is connected to a current mirror, the current mirror is connected to a second stage amplifier, and the second stage amplifier is connected to the first stage amplifier via a feedback loop;

[0010] The first-stage amplifier includes a JFET field effect transistor Q1, a JFET field effect transistor Q2, a triode Q7, a triode Q8 and a VI conversion current source;

[0011] The feedback loop is composed of a resistor R3, a resistor R4, a resistor R10, a resistor R11, a resistor R12 and a resistor R13;

[0012] The drain of the JFET field effect transistor Q1 is connected to the emitter of the transistor Q7, and the drain of the JFET field effect transistor Q2 is connected to the emitter of the transistor Q8;

[0013] The base and collector of the transistor Q7, and the base and collector of the transistor Q8 are all connected to the current mirror;

[0014] The gate of the JFET field effect transistor Q1 is connected to the VI conversion current source through the resistor R3, and the gate of the JFET field effect transistor Q2 is connected to the VI conversion current source through the resistor R4;

[0015] The current mirror is connected to the second-stage amplifier, which is respectively connected to the gate of the JFET field effect transistor Q1 and the resistor R3 through the resistor R10, and is respectively connected to the gate of the JFET field effect transistor Q2 and the resistor R4 through the resistor R11. The resistor R10 is grounded through the resistor R12, and the resistor R11 is grounded through the resistor R13.

[0016] Furthermore, it also includes a power management circuit, which is used to provide power with a rated voltage value to the first-stage amplifier, the second-stage amplifier, the feedback loop and the current mirror.

[0017] Furthermore, the current mirror is used to connect to the low noise amplifier to provide a stable current thereto; the current mirror comprises a resistor R1, a resistor R2, a transistor Q4, a transistor Q5 and a transistor Q6;

[0018] The collector of the transistor Q7 is connected to the collector of the transistor Q4, and the emitter of the transistor Q4 is connected to the resistor R1 and then connected to the power supply VCC;

[0019] The collector of the transistor Q8 is connected to the collector of the transistor Q5, and the emitter of the transistor Q5 is connected to the resistor R2 and then connected to the power supply VCC;

[0020] The base of the transistor Q7 is connected to the base of the transistor Q8 and then connected to the collector of the transistor Q6; the base of the transistor Q4 is connected to the base of the transistor Q5 and then connected to the emitter of the transistor Q6, and the base of the transistor Q6 is connected to the second stage amplifier.

[0021] Further, the second stage amplifier includes an amplifier U2, a resistor R6, a resistor R7, a resistor R8 and a resistor R9;

[0022] The collector of the transistor Q5 is connected to the inverting input terminal of the amplifier U2 through the resistor R6, and the collector of the transistor Q4 is connected to the non-inverting input terminal of the amplifier U2 through the resistor R7;

[0023] The in-phase output terminal of the amplifier U2 is connected to the in-phase input terminal of the amplifier U2 through a resistor R8, the in-phase output terminal of the amplifier U2 is connected to the in-phase input terminal of the amplifier U2 through a resistor R9, the in-phase output terminal of the amplifier U2 is connected to the gate of the JFET field effect tube Q1 through a resistor R10, and the in-phase output terminal of the amplifier U2 is connected to the gate of the JFET field effect tube Q2 through a resistor R11.

[0024] Furthermore, the VI conversion current source is composed of a diode D1, an amplifier U1, a JFET field effect tube Q3 and a resistor R5;

[0025] The gate of the JFET field effect transistor Q1 is connected to the drain of the JFET field effect transistor Q3 through the resistor R3, the gate of the JFET field effect transistor Q2 is connected to the drain of the JFET field effect transistor Q3 through the resistor R4, the gate of the JFET field effect transistor Q3 is connected to the output end of the amplifier U1, the non-inverting input end of the amplifier U1 is grounded through the diode D1, and the inverting input end of the amplifier U1 is connected to the source of the JFET field effect transistor Q3 and then grounded through the resistor R5.

[0026] Effects of the invention: The amplifier circuit of the present invention not only has the characteristics of high gain stability, but also can meet the requirements of differential input in the case of overall closed loop, and has low noise and good linearity. Specifically, it has the following advantages:

[0027] 1. In the amplifier circuit described in the present invention, a differential amplifier circuit is formed by a JFET pair and a current mirror. JFET has the characteristics of high input impedance, small voltage noise, and extremely low current noise (generally in the order of fA / √Hz). Combined with the differential structure, the influence of zero drift and common mode interference can be suppressed. When the source impedance of the induction coil at the front end of the circuit is large, the first-stage amplifier can have better noise performance.

[0028] 2. The second-stage amplifier is composed of a fully differential amplifier, which forms a closed-loop negative feedback with the first-stage amplifier through a feedback loop. The fully differential amplifier uses a true fully differential signal path from input to output. This design brings excellent common-mode noise suppression and total harmonic distortion. The high-voltage differential signal chain can improve the margin and dynamic range through a wide power supply voltage range without adding a separate amplifier for each polarity of the differential signal. This topology can form negative feedback with the first-stage amplifier without occupying the differential input of the first-stage amplifier, which can achieve the effects of low common-mode noise and high linearity at the same time.

[0029] 3. In order to make the amplifier composed of JFET achieve signal amplification without distortion, the amplifier circuit of the present invention needs to set a bias circuit to ensure that the JFET working state is in the saturation region. In the amplifier circuit, the bias circuit mainly includes a DC bias structure and a current source as a load function. In order to make a pair of JFET field effect tubes of the first stage amplifier pass the same current, a proportional buffer current mirror is used instead of a traditional resistor. The proportional buffer current mirror has a small error when copying the current, which is conducive to the design of precision circuits.

[0030] 4. In order to improve the common mode rejection ratio of the JFET field effect tube differential circuit, the amplifier circuit of the present invention adopts a VI conversion current source and adjusts the current by adjusting the resistor R5.

[0031] 5. According to the amplifier circuit described in the present invention, the signal of the front-end sensor can be input into the amplifier in a differential form, and its input noise is substantially equal to the noise of the JFET field effect tube of the first-stage amplifier; due to the closed-loop feedback, the voltage gain of the amplifier is independent of the first-stage and second-stage devices. If R10=R11, R12=R13, and R3=R4, the voltage gain AV of the present invention is 1+(R10 / (R3 / / R12)). BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1A circuit diagram of an existing amplifier circuit as an instrument amplifier circuit;

[0033] Figure 2 A circuit diagram of an existing amplifier as a discrete component amplification circuit;

[0034] Figure 3 A circuit diagram of a differential closed-loop negative feedback amplifier circuit based on a JFET pair of tubes according to the present invention;

[0035] Figure 4 The invention discloses a block diagram of an electromagnetic measurement receiving system of a Z-axis tilt meter in a differential closed-loop negative feedback amplifier circuit based on a JFET pair of tubes.

[0036] Figure 5 The physical structure diagram of the hollow coil of the electromagnetic measurement receiving system of the Z-axis tilt meter in the differential closed-loop negative feedback amplifier circuit based on the JFET pair tube described in the present invention. DETAILED DESCRIPTION

[0037] Specific implementation method 1. Combination Figure 3 The present embodiment is described as a differential closed-loop negative feedback amplifier circuit based on a JFET pair, comprising a power management circuit, a first-stage amplifier, a second-stage amplifier, a feedback loop and a current mirror; the first-stage amplifier uses a discrete JFET pair structure as the input stage of the amplifier module, the first-stage amplifier is connected to the current mirror, the current mirror is connected to the second-stage amplifier, and the second-stage amplifier is connected to the first-stage amplifier through a feedback loop;

[0038] The power management circuit is used to provide power with a rated voltage value to the first-stage amplifier, the second-stage amplifier, the feedback loop and the current mirror module;

[0039] The low noise amplifier is used to perform low noise amplification on weak voltage signals;

[0040] The feedback loop is used to form a closed-loop negative feedback loop with the two-pole amplifier circuit of the low-noise amplifier circuit to improve the gain stability and linearity of the amplifier circuit;

[0041] The current mirror module is used to connect to the low noise amplifier to provide a stable current to it;

[0042] The first-stage amplifier includes a JFET field effect transistor Q1, a JFET field effect transistor Q2, a triode Q7, a triode Q8 and a VI conversion current source;

[0043] The feedback loop is composed of a resistor R3, a resistor R4, a resistor R10, a resistor R11, a resistor R12 and a resistor R13;

[0044] The current mirror includes a resistor R1, a resistor R2, a transistor Q4, a transistor Q5 and a transistor Q6;

[0045] The second stage amplifier includes an amplifier U2, a resistor R6, a resistor R7, a resistor R8 and a resistor R9;

[0046] The drain of the JFET field effect transistor Q1 is connected to the emitter of the transistor Q7, the collector of the transistor Q7 is connected to the collector of the transistor Q4, and the emitter of the transistor Q4 is connected to the resistor R1 and then connected to the positive power supply;

[0047] The drain of the JFET field effect transistor Q2 is connected to the emitter of the transistor Q8, the collector of the transistor Q8 is connected to the collector of the transistor Q5, and the emitter of the transistor Q5 is connected to the resistor R2 and then connected to the positive power supply;

[0048] The gate of the JFET field effect transistor Q1 is connected to the drain of the JFET field effect transistor Q3 through the resistor R3, the gate of the JFET field effect transistor Q2 is connected to the drain of the JFET field effect transistor Q3 through the resistor R4, the gate of the JFET field effect transistor Q3 is connected to the output of the amplifier U1, the non-inverting input terminal of the amplifier U1 is connected to the ground through the diode D1, the inverting input terminal of the amplifier U1 is connected to the source of the JFET field effect transistor Q3 and then connected to the resistor R5 and then grounded;

[0049] The base of transistor Q4 is connected to the emitter of transistor Q6, the collector of transistor Q6 is connected to the base of transistor Q7, and the base of transistor Q7 is connected to the base of transistor Q8; the collector of transistor Q5 is connected to the inverting input terminal of amplifier U2 through resistor R6, and the collector of transistor Q4 is connected to the non-inverting input terminal of amplifier U2 through resistor R7;

[0050] The in-phase output terminal of the amplifier U2 is connected to the in-phase input terminal of the amplifier U2 through a resistor R8, the in-phase output terminal of the amplifier U2 is connected to the in-phase input terminal of the amplifier U2 through a resistor R9, the in-phase output terminal of the amplifier U2 is connected to the gate of the JFET field effect transistor Q1 through a resistor R10, and the in-phase output terminal of the amplifier U2 is connected to the gate of the JFET field effect transistor Q2 through a resistor R11; the resistor R10 is grounded through a resistor R12, and the resistor R11 is grounded through a resistor R13.

[0051] Specific implementation method 2: Combination Figure 4 and Figure 5This embodiment is described. This embodiment is an electromagnetic measurement receiving system for the Z-axis tilt meter composed of a differential closed-loop negative feedback amplifier circuit based on a JFET pair tube described in the specific embodiment 1. The receiving system includes the amplifier circuit, air-core coil and receiver described in the specific embodiment 1; the input end of the amplifier circuit is connected to the air-core coil as a sensor to receive the electromagnetic signal of the earth's magnetic field; the output end of the amplifier circuit is connected to the receiver for data acquisition and storage. In this system, the amplifier circuit can amplify the sensor signal, effectively suppress common-mode interference, and improve linearity.

[0052] In this embodiment, first, according to Faraday's law of electromagnetic induction, the induced electromotive force generated by the hollow coil is:

[0053]

[0054] Among them, the negative sign represents the directional relationship, n is the number of turns of the coil, Φ is the magnetic flux passing through the cross section of the coil, S is the average cross-sectional area of ​​the coil, B is the magnetic induction intensity, and q=n*S, which is called the effective area of ​​the hollow coil.

[0055] Secondly, the differential input of the air-core coil is connected to a low-noise amplifier. After being amplified, the weak voltage signal is connected to the receiver chassis along a coaxial transmission line of about 100m in length for collection and storage.

[0056] According to the characteristics of the existing system, we first determine to use a helicopter as a carrier, and design a hollow coil with a diameter of 8m. The number of coil turns is selected as 37*4 turns. To avoid interference, the hollow coil is often kept at a certain distance from the amplifier circuit, and the two are connected by a long-distance coaxial signal transmission line. In order to suppress common-mode interference during transmission, differential amplifiers are often used in amplifier circuits. Accordingly, hollow coils are often designed as differential structures. The differential hollow coil is essentially two coils wound in the same direction in series, with the center point tapped as the common end, which is connected to the ground potential of the amplifier circuit. Its physical model is as follows: Figure 5 As shown. And fixed with a skeleton of uniform fixed shape.

[0057] After connecting the entire system, first power the receiver and confirm that the system is working properly by observing the ground static data displayed on the receiver.

[0058] Again, power the amplifier circuit and confirm that the signal amplification factor is normal by observing the data displayed on the receiver.

[0059] Finally, after the system completes the detection task, it first turns off the power of the amplifier circuit, then turns off the data acquisition of the receiver, ejects the disk, turns off the power of the receiver, and then performs data processing.

[0060] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0061] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A differential closed-loop negative feedback amplifier circuit based on a JFET pair, the amplifier circuit comprising a low noise amplifier; wherein: The low noise amplifier comprises a first stage amplifier, a second stage amplifier, a feedback loop and a current mirror; The first stage amplifier uses a discrete JFET pair structure as the input stage of the amplifier module. The first stage amplifier is connected to a current mirror, the current mirror is connected to a second stage amplifier, and the second stage amplifier is connected to the first stage amplifier via a feedback loop; The first-stage amplifier includes a JFET field effect transistor Q1, a JFET field effect transistor Q2, a triode Q7, a triode Q8 and a VI conversion current source; The feedback loop is composed of a resistor R3, a resistor R4, a resistor R10, a resistor R11, a resistor R12 and a resistor R13; The drain of the JFET field effect transistor Q1 is connected to the emitter of the transistor Q7, and the drain of the JFET field effect transistor Q2 is connected to the emitter of the transistor Q8; The base and collector of the transistor Q7, and the base and collector of the transistor Q8 are all connected to the current mirror; The gate of the JFET field effect transistor Q1 is connected to the VI conversion current source through the resistor R3, and the gate of the JFET field effect transistor Q2 is connected to the VI conversion current source through the resistor R4; The current mirror is connected to the second-stage amplifier, which is respectively connected to the gate of the JFET field effect transistor Q1 and the resistor R3 through the resistor R10, and is respectively connected to the gate of the JFET field effect transistor Q2 and the resistor R4 through the resistor R11. The resistor R10 is grounded through the resistor R12, and the resistor R11 is grounded through the resistor R13.

2. The differential closed-loop negative feedback amplifier circuit based on JFET pair tubes according to claim 1, characterized in that: The system also includes a power management circuit, which is used to provide a power supply with a rated voltage value to the first-stage amplifier, the second-stage amplifier, the feedback loop and the current mirror.

3. The differential closed-loop negative feedback amplifier circuit based on JFET pair tubes according to claim 1, characterized in that: The current mirror is used to connect to the low noise amplifier to provide a stable current to it; the current mirror includes a resistor R1, a resistor R2, a transistor Q4, a transistor Q5 and a transistor Q6; The collector of the transistor Q7 is connected to the collector of the transistor Q4, and the emitter of the transistor Q4 is connected to the resistor R1 and then connected to the power supply VCC; The collector of the transistor Q8 is connected to the collector of the transistor Q5, and the emitter of the transistor Q5 is connected to the resistor R2 and then connected to the power supply VCC; The base of the transistor Q7 is connected to the base of the transistor Q8 and then connected to the collector of the transistor Q6; the base of the transistor Q4 is connected to the base of the transistor Q5 and then connected to the emitter of the transistor Q6, and the base of the transistor Q6 is connected to the second stage amplifier.

4. The differential closed-loop negative feedback amplifier circuit based on JFET pair tubes according to claim 3, characterized in that: The second stage amplifier includes an amplifier U2, a resistor R6, a resistor R7, a resistor R8 and a resistor R9; The collector of the transistor Q5 is connected to the inverting input terminal of the amplifier U2 through the resistor R6, and the collector of the transistor Q4 is connected to the non-inverting input terminal of the amplifier U2 through the resistor R7; The in-phase output terminal of the amplifier U2 is connected to the in-phase input terminal of the amplifier U2 through a resistor R8, the in-phase output terminal of the amplifier U2 is connected to the in-phase input terminal of the amplifier U2 through a resistor R9, the in-phase output terminal of the amplifier U2 is connected to the gate of the JFET field effect tube Q1 through a resistor R10, and the in-phase output terminal of the amplifier U2 is connected to the gate of the JFET field effect tube Q2 through a resistor R11.

5. The differential closed-loop negative feedback amplifier circuit based on JFET pair tubes according to claim 1, characterized in that: The VI conversion current source is composed of a diode D1, an amplifier U1, a JFET field effect tube Q3 and a resistor R5; The gate of the JFET field effect transistor Q1 is connected to the drain of the JFET field effect transistor Q3 through the resistor R3, the gate of the JFET field effect transistor Q2 is connected to the drain of the JFET field effect transistor Q3 through the resistor R4, the gate of the JFET field effect transistor Q3 is connected to the output end of the amplifier U1, the non-inverting input end of the amplifier U1 is grounded through the diode D1, and the inverting input end of the amplifier U1 is connected to the source of the JFET field effect transistor Q3 and then grounded through the resistor R5.

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