A wideband current divider with gain buffer and adjustment method

Abstract

The present application discloses a broadband shunt with a gain buffer, comprising a resistor unit, a gain buffer, and a voltage output unit connected in sequence. The gain buffer comprises a three-stage amplifier, wherein the input voltage is input in parallel to the negative input terminal of the first amplifier, the positive input terminal of the second amplifier, and the positive input terminal of the third amplifier; the output of the first amplifier is fed back to the positive input terminal, the output of the second amplifier is fed back to the negative input terminal, and the output of the third amplifier is fed back to the negative input terminal; the output of the first amplifier is fed back to the DC power supply common terminal of the second amplifier, and the output of the second amplifier is fed back to the DC power supply common terminal of the third amplifier; a load resistor is connected between the output terminal of the third amplifier and the ground. The gain buffer comprises an unloading circuit, which is connected between the output terminal of the second amplifier and the output terminal of the third amplifier, so that the third amplifier is in a non-loaded state. The present application also proposes an adjustment method for a broadband shunt with a gain buffer. The present application solves the problem that the accuracy of small current measurement is affected by the electromagnetic environment.

Description

Technical Field

[0001] The present application relates to the field of electronic technology, and in particular to a broadband current divider with a gain buffer and an adjustment method. Background Art

[0002] In high-precision current measurement, the role of the shunt is to convert current into voltage, and the error caused by the shunt dominates the measurement error. Wideband gain buffers are mainly used for mA-level AC and DC current measurement. According to Ohm's law, a shunt is connected in series in the circuit, and the current value in the circuit is calculated by dividing the measured voltage by the shunt resistance. The mA-level shunt measurement error is easily affected by external electromagnetic interference, noise and other factors.

[0003] When measuring small currents, the resistance value is large, and the capacitance parameters of the shunt have a greater impact. The influence of the input capacitance of the voltmeter that measures the voltage will further aggravate this impact. Finally, when measuring AC power, the voltage signal obtained from the shunt is required to maintain the phase of the current. When the shunt passes AC current, although the impedance modulus of the shunt may not change much, the voltage at both ends of the shunt is no longer in phase with the phase of the current, resulting in an additional phase shift. This puts higher requirements on the AC parameters of the shunt. How to reduce the additional phase shift of the shunt has become a key technology for measuring AC power. In addition, when designing a shunt, it is also necessary to consider the effects of inductance, thermal effects, and anti-interference. Summary of the invention

[0004] The present application proposes a broadband shunt with gain buffer and an adjustment method to solve the problem that the accuracy of small current measurement is affected by the electromagnetic environment. In order to avoid the above shortcomings of the prior art, the purpose of the present invention is to provide a broadband shunt with the same phase to meet the calibration requirements of high-precision current.

[0005] On the one hand, the embodiment of the present application provides a broadband current divider with a gain buffer, comprising a resistor unit, a gain buffer, and a voltage output unit connected in sequence.

[0006] The shunt resistance value of the resistance unit is the set resistance value; the voltage output unit is a cable with matching connector;

[0007] The gain buffer includes a three-stage amplifier, the input voltage is input in parallel to the negative input terminal of the first amplifier, the positive input terminal of the second amplifier, and the positive input terminal of the third amplifier; the output of the first amplifier is fed back to the positive input terminal, the output of the second amplifier is fed back to the negative input terminal, and the output of the third amplifier is fed back to the negative input terminal; the output of the first amplifier is connected to the DC power supply common terminal of the second amplifier, and the output of the second amplifier is connected to the DC power supply common terminal of the third amplifier; a load resistor R is connected between the output terminal of the third amplifier and the ground L ;

[0008] The gain buffer comprises an unloading circuit connected between the output end of the second amplifier and the output end of the third amplifier, so that the third amplifier is in a non-loaded state.

[0009] Preferably, the unloading circuit includes an unloading resistor R ext , the fourth amplifier, the first voltage-dividing resistor R 1 , the second voltage divider resistor R 2 The unloading resistor is connected between the output terminal of the third amplifier and the output terminal of the fourth amplifier; the output terminal of the second amplifier is connected to the negative input terminal of the fourth amplifier; the second voltage-dividing resistor is connected between the output terminal and the positive input terminal of the fourth amplifier, and the first voltage-dividing resistor is connected between the positive input terminal of the fourth amplifier and the ground.

[0010] Preferably, R ext =R L R 2 / R 1 .

[0011] Preferably, the AC / DC conversion error of the gain buffer is less than 100uV / V at 200kHz; and the phase error is less than 100μrad.

[0012] Preferably, the first amplifier and the second amplifier are high speed amplifiers with external input FET stages. Preferably, the third amplifier is a precision amplifier.

[0013] Preferably, the input resistance unit uses a metal foil resistor with a resistance accuracy of ±0.005%.

[0014] Preferably, the cable of the voltage output unit is an N-type connector.

[0015] On the other hand, the present application further proposes a method for adjusting a broadband current splitter with a gain buffer, which is used for the broadband current splitter with a gain buffer described in any embodiment of the present application, and comprises the following steps:

[0016] Adjusting the parameters of the first amplifier, the second amplifier, and the third amplifier so that the difference in output amplitudes of the first amplifier, the second amplifier, and the third amplifier is less than a set error;

[0017] The resistance value of the unloading circuit is adjusted to put the third amplifier in a non-loaded state.

[0018] When the unloading circuit includes an unloading resistor and a voltage-dividing resistor as described in the embodiment of the present application, the adjustment method proposed in the present application includes the following steps: adjusting the resistance value so that R ext =R L R 2 / R 1 .

[0019] At least one of the above technical solutions adopted in the embodiments of the present application can achieve the following beneficial effects:

[0020] The gain buffer unit of the present invention adopts a three-stage amplification design, and its circuit has the functions of buffering, isolation, and improving load capacity. The three-stage amplification design of the gain buffer can significantly reduce the amplitude error and phase error of the current converter. The shunt of the present invention also has the characteristics of small resistance temperature coefficient, good long-term stability, wide frequency characteristic, low heat generation, etc., and is suitable for use as a standard. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0022] Figure 1 It is a principle block diagram of a broadband current divider;

[0023] Figure 2 is the schematic diagram of the gain buffer circuit;

[0024] Figure 3 The invention is an embodiment of a method for adjusting a wideband shunt with a gain buffer. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the present application clearer, the technical solution of the present application will be clearly and completely described below in combination with the specific embodiments of the present application and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

[0026] The technical solutions provided by various embodiments of the present application are described in detail below in conjunction with the accompanying drawings.

[0027] like Figure 1 The diagram shows a principle block diagram of a wide-band shunt, which includes a shunt resistor unit 11, a gain buffer unit 12, and a voltage output unit (not shown in the diagram).

[0028] The input end of the shunt resistor unit is the input end of the shunt, and the output end of the shunt resistor unit 11 is connected to the input end of the voltage follower gain buffer unit 12. The gain buffer unit is connected to the voltage output unit. The rear end of the voltage output unit is the output end of the shunt.

[0029] In the best embodiment of the broadband shunt implemented in the present application, the resistance value is set to 800Ω, which can be used to test 0.1mA~1mA, DC~100kHz current.

[0030] The working principle of the present invention is as follows: the broadband current signal is converted into a broadband voltage signal through a shunt resistor unit, and then the broadband voltage signal passes through a gain buffer to achieve an amplitude and phase consistent with the front end, and a precision phase voltmeter is used at the back end to measure the voltage and phase, and the accurate current value is calculated.

[0031] The shunt resistor of the shunt of the present invention adopts a metal foil resistor. The metal foil resistor has a small temperature coefficient, good long-term stability, wide frequency characteristics, and low heat generation. For example, the shunt resistor unit uses a metal foil resistor from Vishay in the United States. The resistor is made of alloy foil. Compared with film resistors and wire-wound resistors, it has the following advantages: small temperature coefficient; higher stability and reliability; higher long-term stability (ΔR / R≤0.5%), and through precise resistance adjustment, the resistance accuracy can reach ±0.005%; it can be miniaturized; the residual inductance is small, the frequency characteristics are significantly improved, and the electrical performance is good; the resistor body adopts a metal alloy, which has low heat generation, low power consumption, and low noise when loaded. The shunt resistor has a resistance value of 800Ω, so that 1mA, DC~100kHz current can be converted into 0.8V voltage. When 1mA passes through, the shunt resistor consumes 0.8mW of power, and the resistor can pass the power to meet the requirements.

[0032] The maximum input voltage of the gain buffer circuit is 5V, the load resistance is 50Ω~10MΩ, the maximum load capacitance is 200pF, the AC-DC conversion error is less than 100uV / V at 200kHz, and the phase error is also less than 100μrad at 200kHz. In addition, the circuit input impedance reaches 10MΩ or higher, and the input capacitance is less than 20pF. In order to ensure system stability, the front-end input of the gain buffer is less than 5V.

[0033] The voltage output unit transmission line uses a 50Ω cable and the interface is an N-type connector to reduce transmission errors. The output end is connected to a precision phase voltmeter to measure the voltage and phase, and calculate the accurate current value.

[0034] Figure 2 This is the schematic diagram of the gain buffer circuit.

[0035] The gain buffer has three stages of amplifiers for design and amplification, with very little difference. The gain buffer circuit diagram shows all the parameters of the basic gain buffer circuit diagram. The input voltage Vin of the gain buffer is applied to three unity gain voltage followers A1~A3. The output terminal V of the first amplifier A1 is out1 is the common terminal of the DC power supply of the second amplifier A2. Similarly, the output terminal V out2It is the common terminal of the DC power supply of the third amplifier A3. As shown in the figure, in the circuit connected to amplifiers A2 and A3, the positive and negative bias voltages on both sides of the DC power supply common terminal are respectively supplied to the amplifier power supply terminals. The three-stage amplifiers A1, A2, and A3 of the gain buffer have approximately the same amplitude and decreasing phase error. The second amplifier A2 greatly reduces the phase error of the first amplifier A1. However, due to the phase error factor of the second amplifier A2, the second amplifier A2 does not necessarily have to reduce the amplitude error of the first amplifier A1. The third amplifier A3, whose input voltage is slightly different from that of the second amplifier A2, will significantly reduce the amplitude error of the system, and also reduce the phase error. The DC error and noise performance of the gain buffer are determined by the third amplifier A3. Preferably, the third amplifier is a precision amplifier. The first amplifier A1 and the second opposing region A2 include a high-speed amplifier, which has an external input FET stage that can increase the input impedance and reduce the input current. The system current from A1 and A3 generates a voltage of about 1V at the input resistor Rin.

[0036] The gain buffer comprises an unloading circuit connected between the output end of the second amplifier and the output end of the third amplifier, so that the third amplifier is in a non-loaded state.

[0037] The three-stage amplification design of the gain buffer can greatly reduce the amplitude error and phase error of the 1mA current converter in the DC~100kHz state, meeting higher requirements.

[0038] In the embodiment of the application with a fourth amplifier, the fourth amplifier A4 and the external unloading resistor R ext Used to increase the drive current of the gain buffer. Selecting the appropriate resistor R L , so that R ext =R L R 2 / R 1 to ensure that the third amplifier A3 is in a non-loaded state.

[0039] Figure 3 The invention is an embodiment of a method for adjusting a wideband shunt with a gain buffer.

[0040] The present application also proposes a method for adjusting a broadband current splitter with a gain buffer, which is used for the broadband current splitter with a gain buffer described in any embodiment of the present application, and comprises the following steps:

[0041] Step 41, adjusting the parameters of at least one of the first amplifier, the second amplifier, and the third amplifier so that the difference in output amplitudes of the first amplifier, the second amplifier, and the third amplifier is less than a set error;

[0042] Step 42: Adjust the resistance value of the unloading circuit to put the third amplifier in a non-loaded state.

[0043] When the unloading circuit includes an unloading resistor and a voltage-dividing resistor as described in the embodiment of the present application, the present application also proposes a method for adjusting a broadband shunt with a gain buffer, comprising the following steps:

[0044] Step 51, adjusting the parameters of at least one of the first amplifier, the second amplifier, and the third amplifier so that the output amplitudes of the first amplifier, the second amplifier, and the third amplifier are smaller than a set error;

[0045] Step 52: Adjust the resistance value so that R ext =R L R 2 / R 1 .

[0046] When the fourth amplifier is unloaded, the value of each resistor in the unload circuit is adjusted or the value of the load resistor of the third amplifier is adjusted to put the third amplifier in a non-loaded state.

[0047] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the presence of other identical elements in the process, method, commodity or device including the element.

[0048] The above is only the embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A broadband current divider with a gain buffer, characterized in that: It includes a resistance unit, a gain buffer, and a voltage output unit connected in sequence; The shunt resistance value of the resistance unit is the set resistance value; the voltage output unit is a cable with matching connector; The gain buffer includes a three-stage amplifier, the input voltage is input in parallel to the negative input terminal of the first amplifier, the positive input terminal of the second amplifier, and the positive input terminal of the third amplifier; the output of the first amplifier is fed back to the positive input terminal, the output of the second amplifier is fed back to the negative input terminal, and the output of the third amplifier is fed back to the negative input terminal; the output of the first amplifier is connected to the DC power supply common terminal of the second amplifier, and the output of the second amplifier is connected to the DC power supply common terminal of the third amplifier; a load resistor R is connected between the output terminal of the third amplifier and the ground L ; The gain buffer includes an unloading circuit connected between the output end of the second amplifier and the output end of the third amplifier, so that the third amplifier is in a non-loaded state; The unloading circuit includes an unloading resistor R ext , a fourth amplifier, a first voltage-dividing resistor R1, and a second voltage-dividing resistor R2; the unloading resistor is connected between the output terminal of the third amplifier and the output terminal of the fourth amplifier; the output terminal of the second amplifier is connected to the negative input terminal of the fourth amplifier; the second voltage-dividing resistor is connected between the output terminal and the positive input terminal of the fourth amplifier, and the first voltage-dividing resistor is connected between the positive input terminal of the fourth amplifier and the ground.

2. The broadband current splitter with gain buffer as claimed in claim 1, characterized in that: R ext =R L R2 / R1。 3. The broadband current splitter with gain buffer as claimed in claim 1, characterized in that: The AC / DC conversion error of the gain buffer is less than 100uV / V at 200kHz; and the phase error is less than 100μrad.

4. The broadband current splitter with gain buffer as claimed in claim 1, characterized in that: The first amplifier and the second amplifier are high-speed amplifiers with external input FET stages.

5. The broadband current splitter with gain buffer as claimed in claim 1, characterized in that: The third amplifier is a precision amplifier.

6. The broadband current splitter with gain buffer as claimed in claim 1, characterized in that: The input resistance unit uses a metal foil resistor with a resistance accuracy of ±0.005%.

7. The broadband current splitter with gain buffer as claimed in claim 1, characterized in that: The cable of the voltage output unit is an N-type connector.

8. A method for adjusting a broadband current splitter with a gain buffer, used for the broadband current splitter with a gain buffer as claimed in any one of claims 1 to 7, characterized in that: The following steps are involved: Adjusting the parameters of the first amplifier, the second amplifier, and the third amplifier so that the difference in output amplitudes of the first amplifier, the second amplifier, and the third amplifier is less than a set error; The resistance value of the unloading circuit is adjusted to put the third amplifier in a non-loaded state.

9. A method for adjusting a broadband current splitter with a gain buffer, used for the broadband current splitter with a gain buffer as claimed in any one of claims 1 to 7, characterized in that: The following steps are involved: Adjust the resistor value so that R ext =R L R2 / R1.

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