CN112290899B - Preamplifier of measuring circuit - Google Patents
Preamplifier of measuring circuit Download PDFInfo
- Publication number
- CN112290899B CN112290899B CN202011155707.1A CN202011155707A CN112290899B CN 112290899 B CN112290899 B CN 112290899B CN 202011155707 A CN202011155707 A CN 202011155707A CN 112290899 B CN112290899 B CN 112290899B
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- field effect
- effect tube
- electrode
- supporting seat
- unit
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- 230000005669 field effect Effects 0.000 claims abstract description 74
- 239000003990 capacitor Substances 0.000 claims description 12
- 238000009413 insulation Methods 0.000 claims description 9
- 238000003466 welding Methods 0.000 claims description 6
- 238000005259 measurement Methods 0.000 claims description 5
- 239000012212 insulator Substances 0.000 claims description 3
- 230000003321 amplification Effects 0.000 claims description 2
- 238000003199 nucleic acid amplification method Methods 0.000 claims description 2
- 230000000694 effects Effects 0.000 abstract description 4
- 230000004907 flux Effects 0.000 description 4
- 238000005476 soldering Methods 0.000 description 4
- 230000005540 biological transmission Effects 0.000 description 3
- 239000012535 impurity Substances 0.000 description 3
- 238000000034 method Methods 0.000 description 3
- 230000003071 parasitic effect Effects 0.000 description 3
- 239000002184 metal Substances 0.000 description 2
- -1 polytetrafluoroethylene Polymers 0.000 description 2
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 2
- 239000004810 polytetrafluoroethylene Substances 0.000 description 2
- 230000002411 adverse Effects 0.000 description 1
- 230000002596 correlated effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000007257 malfunction Effects 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000010355 oscillation Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/45—Differential amplifiers
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
- H03F1/26—Modifications of amplifiers to reduce influence of noise generated by amplifying elements
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Amplifiers (AREA)
Abstract
The utility model provides a measuring circuit pre-amplifier, which comprises a shell, a circuit board, a shielding cover, an insulating supporting seat and a spring contact pin, wherein the circuit board is arranged in the shell, the shielding cover, the insulating supporting seat and the spring contact pin are all arranged in the shell, and a circuit on the circuit board comprises a control power supply, a direct current bias unit, an amplifying unit and a feedback unit. The utility model has the following substantial effects: the driving unit formed by the field effect transistor is introduced, so that the technical problems of overhigh noise floor and low input resistance of the existing preamplifier are solved.
Description
Technical Field
The utility model relates to the technical field of electronic measurement, in particular to a measuring circuit preamplifier.
Background
The pre-amplifier is a circuit or electronic equipment arranged between the signal source and the post-amplifier, and is specially designed for matching the signal source with very high internal resistance and very weak output signal. When noise is mixed in the input signal of the amplifier, the output signal of the amplifier is doped with noise signals with the same amplification factor as the required signal, and the operation of the subsequent circuit is seriously affected.
The term "noise" is generally understood to mean noise that is a general term for all signals other than the target signal. Initially, those electronic signals that cause noise from audio devices such as radios were referred to as noise. However, some of the consequences of an unintended electronic signal on the electronic circuit are not all sound-related, and consequently, the noise concept has been gradually expanded by others.
For example, those electronic signals that cause white streaks on television screens are also referred to as noise. It may be said that all signals in the circuit other than the signal of interest, whether or not it has an effect on the circuit, may be referred to as noise. For example, ripple or self-oscillation in the power supply voltage may adversely affect the circuit, causing the acoustic device to make a hum or cause the circuit to malfunction, but may not cause the above-described effects. For such ripple or oscillation, this should be referred to as a noise of the circuit. There is also a radio wave signal of a certain frequency which is a normal destination signal for a receiver that needs to receive such a signal, and which is a non-destination signal, i.e. noise, for another receiver. The prior art of preamplifiers has the technical problem of excessively high noise floor.
When the output capacitance of the signal source is small and the internal resistance is high, the input impedance of the preamplifier needs to be far greater than the internal resistance of the signal source, and is usually more than 1G omega in order to realize better impedance matching. The input impedance is high, the power absorbed by the circuit (or the output of the previous stage circuit) is small, and the power or the previous stage can drive more loads. The prior art of preamplifiers has the technical problem of low input impedance. The prior art solves the technical problem through a high-performance operational amplifier, but the high-performance operational amplifier has high cost and does not have economy.
In order to solve the above technical problem, publication CN206547077U discloses a microphone pre-amplifier, which is a 3-stage split element amplifier with gain control, and the present case adapts a moving coil microphone with 200 to 600 ohm output impedance. The first transistor Q1 is a common base amplifier, in which case the first transistor Q1 is allowed to operate at a low noise level, improving the signal to noise ratio of the signal. The second transistor Q2 and the third transistor Q3 constitute a direct-coupled amplifier. The collector voltage of the first transistor Q1 is set to half the supply voltage, so that a maximum voltage swing is obtained, as well as a highest overload margin. Here, the first transistor Q1 operates at a collector voltage of 2.4V and a collector current of 200 uA. Such low collector currents, ensuring low noise performance, also improves the input impedance of the stage by about 400 ohms. The utility model has reasonable structural design, enough power gain, small noise generated by the utility model and wide working linear range. However, the input impedance of the utility model is only 400 ohms, and when the input impedance is at least 1G ohm, the utility model cannot meet the impedance matching requirement of the amplifier.
Disclosure of Invention
The utility model aims to solve the technical problems that: the prior preamplifier has the technical problems of over high noise floor and low input impedance.
In order to solve the technical problems, the utility model provides a measuring circuit pre-amplifier, which comprises a shell, a circuit board, a shielding cover, an insulating supporting seat and a spring contact nail, wherein the circuit board is arranged in the shell, the shielding cover, the insulating supporting seat and the spring contact nail are all arranged in the shell, a circuit on the circuit board comprises a control power supply, a direct current biasing unit, an amplifying unit and a feedback unit, the amplifying unit is connected with the control power supply, a sensor is connected with the direct current biasing unit through the spring contact nail and is connected with the input end of the amplifying unit, the input end of the feedback unit is connected with the output end of the amplifying unit, the shielding cover is arranged on the periphery of the circuit board and is fixed through the insulating supporting seat, and the spring contact nail is fixed through the insulating supporting seat. The direct current bias unit provides bias conditions for the amplifying unit, the feedback unit collects output signals of the output end of the amplifying unit and adjusts impedance of the amplifying unit according to the output signals, and frequency response of a circuit high-frequency band is improved. The shell is connected with the grounding end of the circuit board.
Preferably, the insulating support base comprises an inner insulating support base and an outer insulating support base, the spring contact pin comprises a fixed part and a movable part, the fixed part is in sliding connection with the movable part, the inner insulating support base is used for fixing the fixed part of the spring contact pin, and a gap matched with the shielding cover is reserved between the inner insulating support base and the outer insulating support base.
Preferably, the control power supply includes a positive electrode v+ and a negative electrode V-.
Preferably, the dc bias unit includes a field effect tube D1 and a field effect tube D2, where a gate of the field effect tube D1 is connected in parallel with a source and a drain of the field effect tube D2 and then connected with the sensor, and a gate of the field effect tube D2 is connected in parallel with the source and the drain of the field effect tube D1 and then connected with an output end of the feedback unit. Because the field effect transistor has extremely high input impedance when being pinched off, the D1 and D2 form the bias circuit of the D3 grid electrode, which is equivalent to a large bias resistor, so that the impedance matching requirement of a high-impedance signal source can be met.
Preferably, the amplifying unit comprises a field effect tube D3, a field effect tube D4, a field effect tube D5 and a resistor R3, wherein one end of the resistor R3 is connected with a source electrode of the field effect tube D4, the other end of the resistor R3 is connected with a grid electrode of the field effect tube D4, a grid electrode of the field effect tube D4 is connected with a negative electrode V-of the control power supply, a drain electrode of the field effect tube D4 is connected with a source electrode of the field effect tube D3, a grid electrode of the field effect tube D5 is connected with a source electrode of the field effect tube D3 to serve as an output end of the amplifying unit, a source electrode of the field effect tube D5 is connected with a positive electrode v+ of the control power supply, a drain electrode of the field effect tube D5 is connected with a drain electrode of the field effect tube D3, and a grid electrode of the field effect tube D3 serves as an input end of the amplifying unit. D4 and R3 form a constant current circuit, and as a constant current load output by the source electrode of D3, the load impedance can be regarded as infinity. The cascaded bootstrap circuit is formed by the D3 and the D5, so that parasitic capacitance of the D3 can be reduced, and frequency response of a high-frequency band of the circuit can be improved. The constant current circuit formed by D4 and R3 can reduce the noise of the circuit and simultaneously reduce the transmission loss. The amplitude of the signal output by the source electrode of D3 is related to the load, and the larger the resistance value of the load is, the more the amplitude of the signal is close to the input signal, but at the same time, the larger the noise is because the noise is positively correlated with the resistance value of the resistor. After the load formed by the constant current circuit is used for replacing the resistor with high resistance, the introduced noise is greatly reduced. Since the equivalent resistance of the constant current load is infinite, the output signal is very close to the input signal, and the transmission loss is basically 0.
Preferably, the feedback unit includes a capacitor C3, one end of which is connected to the drain of the field effect transistor D5, and the other end of which is connected to the gate of the field effect transistor D2. The capacitor C3 is a feedback capacitor, and feeds back signals at the output ends to the field effect transistors D1 and D2, so that the internal parasitic capacitance of the field effect transistors D1 and D2 is reduced, and the frequency response of the circuit high frequency band can be improved.
Preferably, the field effect transistors D1, D2, D3 and the capacitor C1 are connected with pins connected with each other by bonding on an insulator during assembly and welding. For example, the contact between key signal pins and a circuit board is avoided by overlapping an insulating gasket made of polytetrafluoroethylene. The reason is that the soldering flux or other impurities can remain in the production and welding process of the circuit board, and after the soldering flux or other impurities are combined with moisture in the environment for a long time, the insulation performance of the circuit board is affected, and the input impedance is reduced.
The utility model has the following substantial effects: the technical problems of high noise floor and low input impedance of the existing preamplifier are solved.
Drawings
Fig. 1 is a schematic structural view of the first embodiment.
Fig. 2 is a schematic diagram of an embodiment of an electrical principle.
In the figure: 1. the device comprises a shell, a circuit board, a shielding cover, an inner insulation supporting seat, an outer insulation supporting seat and a spring contact pin.
Detailed Description
The following description of the embodiments of the present utility model will be made with reference to the accompanying drawings.
As shown in fig. 1, the first embodiment includes a metal casing 1, a circuit board 2, a shielding case 3, an insulating support seat and a spring contact pin 6, where the circuit board 2, the shielding case 3, the insulating support seat and the spring contact pin 6 are all disposed in the metal casing 1, the insulating support seat includes an inner insulating support seat 4 and an outer insulating support seat 5, the spring contact pin 6 includes a fixed portion and a movable portion, the fixed portion is slidably connected with the movable portion, the inner insulating support seat 4 is fixed on the fixed portion of the spring contact pin 6, and a gap matched with the shielding case 3 is reserved between the inner insulating support seat 4 and the outer insulating support seat 5.
As shown in fig. 2, the circuit on the circuit board 2 includes a filter capacitor C1, a control power source v+ and V-, a field effect tube D1 and a field effect tube D2 form a dc bias unit of the circuit, wherein a gate of the field effect tube D1 is connected in parallel with a source and a drain of the field effect tube D2 and then connected with the sensor, and a gate of the field effect tube D2 is connected in parallel with the source and the drain of the field effect tube D1 and then connected with an output end of the feedback unit; the field effect tube D3, the field effect tube D4, the field effect tube D5 and the resistor R3 form an amplifying unit of the circuit, one end of the resistor R3 is connected with a source electrode of the field effect tube D4, the other end of the resistor R3 is connected with a grid electrode of the field effect tube D4, a grid electrode of the field effect tube D4 is connected with a negative electrode V-of a control power supply, a drain electrode of the field effect tube D4 is connected with a source electrode of the field effect tube D3, a grid electrode of the field effect tube D5 is connected with a source electrode of the field effect tube D3 to serve as an output end of the amplifying unit, a source electrode of the field effect tube D5 is connected with a drain electrode of the field effect tube D3, a grid electrode of the field effect tube D3 serves as an input end of the amplifying unit, a constant current circuit is formed by the grid electrodes of the field effect tube D4 and R3, and load impedance of the constant current load output by the source electrode of the field effect tube D3 can be regarded as infinite load impedance. The cascaded bootstrap circuit is formed by the D3 and the D5, so that parasitic capacitance of the D3 can be reduced, and frequency response of a high-frequency band of the circuit can be improved. The constant current circuit formed by D4 and R3 can reduce the noise of the circuit and simultaneously reduce the transmission loss; one end of the feedback capacitor C3 is connected with the drain electrode of the field effect tube D5, and the other end of the feedback capacitor C is connected with the grid electrode of the field effect tube D2.
The field effect transistors D1, D2 and D3 and the capacitor C1 are connected with pins which are lapped on an insulator composed of polytetrafluoroethylene during assembly and welding. The special assembly welding process can improve the electrical stability of the product. In this way, contact of the critical signal pins with the circuit board 2 is avoided. The reason is that the soldering flux or other impurities remain in the process of producing and welding the circuit board 2, and after a long time, the soldering flux is combined with moisture in the environment, so that the insulating performance of the circuit board 2 is affected, and the input impedance is reduced.
The above embodiment is only a preferred embodiment of the present utility model, and is not limited in any way, and other variations and modifications may be made without departing from the technical aspects set forth in the claims.
Claims (4)
1. The utility model provides a measurement circuit preamplifier for the signal that other signals of amplification sensor collection were converted to, includes shell and circuit board, the circuit board is arranged in the shell, its characterized in that: the circuit board comprises a control power supply, a direct current bias unit, an amplifying unit and a feedback unit, wherein the control power supply comprises an anode V+ and a cathode V-, the direct current bias unit comprises a field effect tube D1 and a field effect tube D2, a grid electrode of the field effect tube D1 is connected with a source electrode and a drain electrode of the field effect tube D2 in parallel and then is connected with the sensor, and a grid electrode of the field effect tube D2 is connected with a source electrode and a drain electrode of the field effect tube D1 in parallel and then is connected with an output end of the feedback unit; the amplifying unit comprises a field effect tube D3, a field effect tube D4, a field effect tube D5 and a resistor R3, wherein one end of the resistor R3 is connected with a source electrode of the field effect tube D4, the other end of the resistor R3 is connected with a grid electrode of the field effect tube D4, a grid electrode of the field effect tube D4 is connected with a negative electrode V-of a control power supply, a drain electrode of the field effect tube D4 is connected with a source electrode of the field effect tube D3, a grid electrode of the field effect tube D5 is connected with a source electrode of the field effect tube D3 to serve as an output end of the amplifying unit, a source electrode of the field effect tube D5 is connected with a positive electrode V+ of the control power supply, a drain electrode of the field effect tube D5 is connected with a drain electrode of the field effect tube D3, and a grid electrode of the field effect tube D3 serves as an input end of the amplifying unit; the amplifying unit is connected with the control power supply, the sensor is connected with the direct current bias unit through the spring contact pin and is connected with the input end of the amplifying unit, the control end of the direct current bias unit is connected with the output end of the feedback unit, the input end of the feedback unit is connected with the output end of the amplifying unit, the shielding cover is installed on the periphery of the circuit board and is fixed through the insulating supporting seat, and the spring contact pin is fixed through the insulating supporting seat.
2. A measurement circuit preamplifier according to claim 1, wherein: the insulation supporting seat comprises an inner insulation supporting seat and an outer insulation supporting seat, the spring contact nail comprises a fixed portion and a movable portion, the fixed portion is in sliding connection with the movable portion, the inner insulation supporting seat is fixed on the fixed portion of the spring contact nail, and a gap matched with the shielding cover is reserved between the inner insulation supporting seat and the outer insulation supporting seat.
3. A measurement circuit preamplifier according to claim 1, wherein: and one end of the feedback unit comprises a capacitor C3, the other end of the capacitor C is connected with the drain electrode of the field effect tube D5, and the other end of the capacitor C is connected with the grid electrode of the field effect tube D2.
4. A measurement circuit preamplifier according to claim 3, wherein: and pins connected with the field effect transistors D1, D2 and D3 and the capacitor C1 are lapped on an insulator during assembly and welding.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202011155707.1A CN112290899B (en) | 2020-10-26 | 2020-10-26 | Preamplifier of measuring circuit |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202011155707.1A CN112290899B (en) | 2020-10-26 | 2020-10-26 | Preamplifier of measuring circuit |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN112290899A CN112290899A (en) | 2021-01-29 |
| CN112290899B true CN112290899B (en) | 2024-02-06 |
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| Application Number | Title | Priority Date | Filing Date |
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| CN202011155707.1A Active CN112290899B (en) | 2020-10-26 | 2020-10-26 | Preamplifier of measuring circuit |
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| CN112290899A (en) | 2021-01-29 |
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