CN103457545B - The ultra-low noise analogue amplifier of 3 D resistivity acquisition system - Google Patents

Abstract

An ultra-low noise analog amplifier for a three-dimensional resistivity data acquisition system, including two parts, the first part is a direct-coupled voltage series negative feedback ultra-low noise amplifier composed of six transistors, and the second part is composed of three operational amplifiers low noise amplifier. In the first part, the emitter of the second stage provides a bias current to the base of the first stage. While obtaining the bias current, a DC negative feedback is introduced to make the static operating point of the circuit more stable. Adding to the bias current feedback circuit The capacitance is added, which greatly improves the input impedance of the amplifying circuit; the second part is two non-inverting input universal integrated operational amplifiers with highly consistent performance parameters, with double-ended signal input and only single-ended signal output, common mode rejection ratio Very high, it has a very good effect on electromagnetic field interference suppression, and can make the measurement accuracy below 0.1μV, which can greatly reduce the weight of field sending equipment and receiving equipment, and greatly improve the efficiency of electrical exploration work.

Description

Ultra Low Noise Analog Amplifier for 3D Resistivity Acquisition System

technical field

The invention belongs to the technical field of geophysical exploration, and relates to an ultra-low noise analog amplifier used in a three-dimensional resistivity data acquisition system in the technical field of resource and environmental exploration.

Background technique

The three-dimensional resistivity data acquisition system belongs to the direct current method exploration instrument. The development of direct current prospecting instrument technology is inseparable from the development of electric prospecting theory, electronic technology, signal processing technology and computer technology. Direct current prospecting instruments have gone through a development process similar to other instruments, from mechanical to electronic tube and transistor stage, to integrated circuit and microcomputer control stage.

With the gradual development of mineral resource exploration to the deep, the required exploration depth is getting larger and larger. Therefore, the direct current method exploration instrument has to find a way in the transmitter to increase the transmission power and increase the transmission current. The unavoidable price, of course, is bulkiness of the equipment. Zong’s transmitter GGT-30 has a maximum power of 3OKW, a maximum output voltage of 10O0V, and a maximum current of 45A. Phoenix’s T-200 transmitter has a maximum power of 6OKW, a maximum transmission voltage of 1600V, and a maximum transmission current of 16OA.

The working conditions of direct current prospecting instruments are in the field, especially for mineral resource exploration, which may be in areas with high mountains and dense forests, criss-cross rivers, or desert areas with few people. The heavy transmitter equipment reduces work efficiency and even makes it impossible to carry out work. In the direct current method prospecting instrument system, in order not to make the high-voltage, high-current transmitter power too large and make the equipment too heavy, it is necessary to improve the measurement sensitivity and measurement accuracy of the instrument receiver, and to improve the sensitivity and accuracy of the instrument receiver. Accuracy, the noise of the pre-amplifier in the instrument must be as low as possible, and the current domestic similar product instrument receiver measurement sensitivity and measurement accuracy are in the order of 0.1-0.9mV.

Contents of the invention

The purpose of the present invention is to design an ultra-low noise analog amplifier for a three-dimensional resistivity data acquisition system with ultra-low noise, strong anti-interference and high measurement accuracy.

The ultra-low noise analog amplifier of the three-dimensional resistivity data acquisition system of the present invention includes two parts, the first part is a directly coupled voltage series negative feedback ultra-low noise amplifier composed of six transistors, and the second part is composed of three operational amplifiers The low-noise amplifier; the first part of the ultra-low-noise amplifier, the first stage is composed of four transistors, the four transistors are connected in parallel, the collectors of the four transistors are connected together, and connected in series with the resistor and then connected to the power supply , the emitters of the four transistors are connected together, and then grounded in series with a resistor, the bases of the four transistors are connected together; the bases of the second-stage transistors are connected to the collectors of the first-stage four transistors, and the second-stage The collector of the transistor is connected to the power supply after the resistor is connected in series, the emitter of the second-stage transistor is connected to the ground after the resistor is connected in series, the emitter of the second-stage transistor is connected to the base of the first stage after the resistor is connected in series at the same time, and the emitter of the first stage The capacitor is connected across the emitter of the second-stage transistor, and this stage forms a voltage series negative feedback amplifier; the base of the third-stage transistor is connected to the collector of the second-stage transistor, and the collector of the third-stage transistor is directly connected to the power supply. The emitter is connected to the output terminal through a capacitor; the second part is composed of three operational amplifiers, the output of the first part is connected to the input pin of the first operational amplifier through a capacitor, the input pin of the second operational amplifier is grounded, and the first operational amplifier A resistor is connected in series between the input pins of the amplifier and the second operational amplifier, the output pin of the first operational amplifier is connected in series with the input pin of the third operational amplifier, and the output pin of the second operational amplifier is connected in series with the resistor Then connect the input pin of the third operational amplifier; the output pin of the first operational amplifier and the output pin of the second operational amplifier are sequentially connected symmetrically with resistors and capacitors, and the output of the third operational amplifier is connected to the main amplifier.

In the ultra-low noise analog amplifier of the three-dimensional resistivity data acquisition system of the present invention, the emitter of the second stage in the first part provides a bias current to the base of the first stage. While obtaining the bias current, the whole circuit also introduces DC negative feedback can make the static operating point of the circuit more stable. Adding a capacitor to the bias current feedback circuit can greatly improve the input impedance of the amplifying circuit. At the same time, it can remove the AC negative feedback of the circuit caused by the bias current resistance. Thereby greatly improving the input impedance of the preamplifier stage; the second part is two general-purpose integrated op amps with non-inverting input with highly consistent performance parameters, and the two form a balanced and symmetrical differential amplifier input stage, which is characterized by Double-ended signal input and only single-ended signal output, the common mode rejection ratio is very high, and it has a very good effect on electromagnetic field interference suppression, which can make the signal measurement accuracy of the direct current method exploration instrument less than 0.1μV, which can greatly reduce field transmission. The weight of equipment and receiving equipment can greatly improve the efficiency of electrical prospecting.

Description of drawings

Fig. 1 is the first part ultra-low noise amplifier circuit schematic diagram of the present invention;

FIG. 2 is a schematic diagram of the second part of the low noise amplifier circuit of the present invention.

detailed description

An ultra-low noise analog amplifier for a three-dimensional resistivity data acquisition system, including two parts, the first part is a direct-coupled voltage series negative feedback ultra-low noise amplifier composed of six transistors, and the second part is composed of three operational amplifiers Low noise amplifier; the first part of the ultra-low noise amplifier, the first stage is composed of four transistors T1 ~ T4, the four transistors are connected in parallel, the collectors of the four transistors are connected together, and connected in series with the resistor R1 Then connect the power supply VEE1, the emitters of the four transistors are connected together, and then connected in series with the resistor R6 and grounded, the bases of the four transistors are connected together, and then connected with R4 and C3, and the four transistors T1~T4 are performance parameters The same transistor; the second stage is composed of transistor T5, resistors R3 and R7, the base of transistor T5 is connected to the output of the first stage, that is, the collectors of the four transistors T1~T4, and the collector of transistor T5 is connected in series with resistor R2 and then connected to the power supply VEE1, the emitter of transistor T5 is connected in series with resistors R3 and R7 and then grounded, the emitter of transistor T5 is connected in series with R8 and R4 at the same time and connected to the base of the first stage, one end of capacitor C5 is connected to the emitter of the first stage, and the other end Connected between resistors R8 and R4, this stage forms a voltage series negative feedback amplifier; the third stage is composed of transistor T6, resistors R5, R6, the base of transistor T6 is connected to the output of the second stage, that is, the collector of transistor T5 , the collector of the transistor T6 is directly connected to the power supply VEE1, and the emitter of the transistor T6 is connected to the output U01 through the capacitor C4.

The second part of the ultra-low noise analog amplifier is composed of three operational amplifiers LT1028, respectively denoted as N1, N2, and N3. The output of the first part is connected to the No. 3 pin of N1 through C4, and the No. 3 pin of N2 is grounded. N1, R17 and R11 are connected in series between the No. 3 pins of the two operational amplifiers of N2, the No. 6 output pin of N1 is connected to R9, and then connected to No. 3 pin of N3, and the No. 6 output pin of N2 is connected to R18, and then connected to N3 Resistors R12, R13, R14, R15 are connected in series between the output pin 6 of N1 and the output pin 6 of N2, the capacitor C6 is connected across the two ends of R12, and the capacitor C7 is connected across R15 At both ends, R12 and C6 are connected to the No. 2 pin of the other input end of N1 at the same time, R15 and C7 are connected to the No. 2 pin of the other input end of N2 at the same time, and No. 6 pin of N3 is connected to the output, which is sent to the master of the subsequent stage. amplifier.

At the forefront of the three-dimensional resistivity acquisition system, the weak signal sent by the measuring electrode first enters the first stage of the first part of the ultra-low noise analog amplifier. The first stage amplifier circuit is composed of transistors T1~T4. During the implementation process, special Pay attention to the selection of transistors with low noise and high β value, metal film resistors for resistors, and tantalum capacitors for capacitors.

The second stage consists of T5, R2, R3, and R7. It is a general voltage series negative feedback amplifier. During the implementation, it should be noted that T5 should choose a transistor with a high β value, and R2, R3, and R7 should choose metal film resistors.

The third stage is composed of transistor T6, resistors R3, R5T, etc. It is an emitter follower, and its voltage amplification factor is close to 1.

The first part of the ultra-low noise analog amplifier composed of T1 ~ T6, etc. should take the following measures during the implementation process:

1. There is a multi-core long cable at the input end of the three-dimensional resistivity data acquisition system. The long cable is directly connected to the first stage of the first part of the ultra-low noise analog amplifier composed of T1~T6. One of the most important problems of interference, there are two types of differential mode interference and common mode interference. To reduce the differential mode electromagnetic interference of long cables, twisted pair wires should be used to transmit signals. Twisted pair wires not only provide a smaller differential mode loop area, but also because The currents in the adjacent twisted joints of the twisted pair are opposite, and the magnetic fields they generate are also opposite, and they cancel in space. If the long cable does not use the twisted pair to carry the signal, it is possible that the first part of the ultra-low noise analog amplifier will not work properly.

2. The common-mode electromagnetic interference of long cables is generated by the common-mode current, and the loop of the common-mode current is formed by the cable and the earth (or other adjacent large conductors), which has a large loop area and will generate a strong Common Mode Electromagnetic Interference. In the PCB design of the first part of the ultra-low noise analog amplifier, a "clean ground" should be set at the input port of the long cable. There is no circuit that can generate noise voltage in the "clean ground", and the local potentials on the ground wires are almost equal. If the chassis of the 3D resistivity data acquisition system uses a metal chassis, connect this "clean ground" with the metal chassis with low impedance; if the chassis of the 3D resistivity data acquisition system uses a non-metal chassis, it should Put a metal plate under the PCB of the first part of the amplifier, and connect the "clean ground" and the metal plate with low impedance.

3. A signal line filter is also used at the input port of the long cable. Since there is a long multi-core cable at the input end, an interface often has dozens of wires, and the signal filter should be dominated by capacitors. A ferrite bead is set on the signal line. In order to obtain a better filtering effect, a feedthrough capacitor or other devices with good high-frequency characteristics must also be used.

The installation of the common mode filter capacitor should be connected between the signal line and the metal case of the equipment. If the case of the 3D resistivity data acquisition system is non-metallic, a large metal plate should also be added under the circuit board as a filter capacitor. ground wire.

4. The second part of the ultra-low noise analog amplifier is composed of three operational amplifiers LT1028. In the implementation process, attention should be paid to selecting a high CMRR value of the LT1028 operational amplifier. The parameters of the three operational amplifiers should be the same or similar.

Claims (1)

1. the ultra-low noise analogue amplifier of a 3 D resistivity data collecting system, it is characterized in that: it comprises two parts, Part I is the direct-coupled Voltage Series negative-feedback ultra-low noise amplifier being made up of six transistors, and Part II is the low-noise amplifier of three operational amplifier compositions; Described Part I ultra-low noise amplifier, the first order is made up of four transistor T 1～T4, four transistors are connected into parallel form, four transistorized colelctor electrodes link together, and meet power supply VEE1 after being connected in series with resistance R 1, and four transistorized emitter stages link together, then ground connection after being connected in series with resistance R 6, four transistorized base stages link together, and are then connected with resistance R 4, capacitor C 3, and four transistor T 1～T4 are the transistor that performance parameter is identical; The second level is made up of transistor T 5, two resistance R 3, R7, the base stage of transistor T 5 connects the i.e. colelctor electrode of four transistor T 1～T4 of output of the first order, after transistor T 5 collector series connection resistance R 2, meet power supply VEE1, ground connection after transistor T 5 emitter stages are connected in series with two resistance R 3, R7, transistor T 5 emitter stages are connected with the base stage of the first order after being connected in series another two resistance R 8, R4 simultaneously, the emitter stage of the one termination first order of capacitor C 5, the other end is connected between two resistance R 8, R4; The third level is made up of transistor T 6, two resistance R 5, R6, and the base stage of transistor T 6 is connected with the colelctor electrode that the output of the second level is transistor T 5, and transistor T 6 colelctor electrodes directly meet power supply VEE1, and transistor T 6 emitter stages meet output U01 by capacitor C 4;

Ultra-low noise analogue amplifier Part II is made up of three operational amplifiers, be expressed as operational amplifier N1, operational amplifier N2, operational amplifier N3, the output of Part I is connected to No. 3 pins of operational amplifier N1 by capacitor C 4, No. 3 pin ground connection of operational amplifier N2, N1, between No. 3 pins of N2 two operational amplifier, be connected in series two resistance R 17 and R11, No. 6 pin connecting resistance R9 of output of operational amplifier N1, access again No. 3 pins of operational amplifier N3, No. 6 pin connecting resistance R18 of output of operational amplifier N2, access again No. 2 pins of operational amplifier N3, between No. 6 pins of output of operational amplifier N1 and No. 6 pins of output of operational amplifier N2, be connected in series successively four resistance R 12, R13, R14, R15, capacitor C 6 is connected across resistance R 12 two ends, capacitor C 7 is connected across resistance R 15 two ends, resistance R 12, capacitor C 6 connect No. 2 pins of another input of operational amplifier N1 simultaneously, resistance R 15, capacitor C 7 connect No. 2 pins of another input of operational amplifier N2 simultaneously, No. 6 pins of operational amplifier N3 connect output, deliver to the main amplifier of rear class.