Method for measuring broadband electric signal

Abstract

The invention belongs to the field of amplifiers, and relates to a broadband electric signal measuring method, a high-bandwidth low-offset amplifier comprises a composite operational amplifier composed of a precision operational amplifier U1, a radio frequency low-noise amplifier U2 and a current feedback operational amplifier U3; a current signal passes through a high-bandwidth low-offset amplifier by using a shunt, is amplified by an operational amplifier and is collected to an ADC (Analog to Digital Converter), the collected current signal is a sinusoidal signal, and autocorrelation calculation is carried out by using continuous 1 million points collected by the ADC; calculating the squared value of the amplitude by using the peak value of the autocorrelation function of the sine wave superposed with the width noise, and calculating to obtain the amplitude As of the collected sine wave; collecting once according to a standard signal, wherein the amplitude of the standard signal is Aa; the calibration coefficient k is equal to As / Aa, then collected current signal data is Aa ', and Aa' * k is the truth value of the current signal extracted from the noise. The low-offset, high-bandwidth, high-gain and high-slew-rate amplifier can be achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of amplifiers and relates to a method for measuring a broadband electrical signal, which is used for measuring a broadband small signal. Background Art

[0002] With the rapid development of new energy industries such as photovoltaics and electric vehicles, the market demand for high-precision and high-reliability power analyzers is growing. In the photovoltaic production and R&D testing of the photovoltaic industry and the bench testing of new energy vehicle motors, power analysis, standby power consumption and inverter efficiency all need to be accurately and reliably measured. It is necessary to solve the problem of precise measurement of broadband small current signals in power analyzers.

[0003] Most of the current power analyzers use a sampling measurement method with ADC as the core to achieve high-bandwidth and high-precision digital measurement of current signals. The principle is to use an operational amplifier to convert the voltage and current signals to be measured into voltage signals that meet the ADC range after the voltage and current are collected. In the power analyzer, since the collected current signal has a small amplitude and high frequency, it is generally amplified by an operational amplifier. However, it is difficult to achieve high indicators at the same time for the DC characteristics (offset voltage, bias current) of general integrated operational amplifiers and the AC characteristics (gain bandwidth product, slew rate, noise) of operational amplifiers. Therefore, when meeting high bandwidth, the accuracy of the collected data will deteriorate due to the high offset voltage value. If an operational amplifier with a small offset voltage is selected, it will be difficult to increase the bandwidth of the entire acquisition channel. Summary of the invention

[0004] The technical problem to be solved by the present invention is to collect a high-bandwidth small signal in a current signal and realize a high-bandwidth low-offset operational amplifier. The technical solution adopted by the present invention is as follows: A method for measuring a broadband electrical signal, a high-bandwidth low-offset amplifier is designed, the high-bandwidth low-offset amplifier comprises a composite operational amplifier consisting of a precision operational amplifier U1, a radio frequency low-noise amplifier U2 and a current feedback operational amplifier U3, three operational amplifiers connected in series in sequence, and the inner loop gain of the current feedback operational amplifier U3 is set to be smaller than the outer loop gain; The current signal is collected to the ADC by amplifying the high-bandwidth low-offset amplifier and the operational amplifier using a shunt. The collected current signal is a sinusoidal signal. The autocorrelation calculation is performed using the 1 million continuous points collected by the ADC. The square value of the amplitude is calculated using the peak value of the autocorrelation function of the sinusoidal wave superimposed with width noise, and the collected sinusoidal wave amplitude As is calculated. The standard signal is collected once, and the amplitude of the standard signal is Aa; Perform a calibration, the calibration coefficient k = As / Aa, and the current signal data collected thereafter is Aa', then Aa'*k is the true value of the current signal extracted from the noise.

[0005] Preferably, the input end of the high-bandwidth low-offset amplifier includes one end of a capacitor C1 and one end of a resistor R16 in parallel, the other end of the capacitor C1 is electrically connected to one end of the capacitor C2, the other end of the capacitor C2 is electrically connected to one end of the resistor R1, the other end of the resistor R1 and the other end of the resistor R16 are both electrically connected to one end of the capacitor C3, one end of the resistor R17, one end of the capacitor C6 and one end of the resistor R6, the other end of the capacitor C3 is electrically connected to one end of the resistor R2, the other end of the resistor R2 and the other end of the resistor R17 are both electrically connected to one end of the capacitor C4 and one end of the resistor R18, the other end of the capacitor C4 is electrically connected to one end of the resistor R3, the other end of the resistor R3 and the other end of the resistor R18 are both electrically connected to one end of the capacitor C5 and one end of the resistor R19, and the other end of the capacitor C5 is electrically connected to one end of the resistor R4; The other end of capacitor C6 is electrically connected to one end of resistor R5 and one end of resistor R9 respectively, the other end of resistor R5 is grounded, and the other end of resistor R9 is electrically connected to the reverse input end of RF low noise amplifier U2. The other end of resistor R6 is electrically connected to one end of capacitor C7 and the reverse input end of precision operational amplifier U1 respectively, the same-direction input end of precision operational amplifier U1 is grounded, the output end of precision operational amplifier U1 and the other end of capacitor C7 are electrically connected to one end of resistor R7, the other end of resistor R7 is electrically connected to one end of resistor R8 and the same-direction input end of RF low noise amplifier U2 respectively, the other end of resistor R8 is grounded, the output end of RF low noise amplifier U2 is electrically connected to one end of resistor R10, and the other end of resistor R10 is electrically connected to the same-direction input end of current feedback operational amplifier U3. The reverse input terminal of the current feedback operational amplifier U3 is electrically connected to one end of the resistor R12, the other end of the resistor R12 is electrically connected to one end of the resistor R11, one end of the resistor R13 and one end of the resistor R15 respectively, the other end of the resistor R11 is grounded, the other end of the resistor R13 is electrically connected to one end of the resistor R14, the other end of the resistor R15 is electrically connected to one end of the capacitor C8, the other end of the resistor R4, the other end of the resistor R19, the output terminal of the current feedback operational amplifier U3, the other end of the resistor R14 and the other end of the capacitor C8 are connected in parallel as the output terminal of a high-bandwidth, low-offset amplifier.

[0006] Preferably, the precision operational amplifier U1 is of model ADA4522-1ARZ, the RF low noise amplifier U2 is of model AD8021ARZ, and the current feedback operational amplifier U3 is of model OPA694IDR.

[0007] Preferably, the ADC is an ADC of ADI model LTC2386-18.

[0008] Preferably, the resistors R16, R17, R18 and R19 are packaged together using thin film process resistors.

[0009] Preferably, the resistor R11 is a 68.1R resistor, the resistor R12 is a 221R resistor, the resistor R13 is a 1K resistor, the resistor R14 is a 3.32K resistor, the resistor R15 is 100Ω, and the capacitor C8 is 10pF.

[0010] Advantages of the present invention: The invention can realize an amplifier with low offset, high bandwidth, high gain and high slew rate, and can realize 100 times amplification of a 5 MHz signal at most. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings: Figure 1 is a schematic diagram of the circuit structure of a high-bandwidth, low-offset amplifier according to an embodiment of the present invention; Figure 2 Schematic diagram of the principle of a method for measuring a broadband electrical signal according to an embodiment of the present invention; Figure 3 1 is a schematic diagram of an application example of the current feedback operational amplifier U3 according to an embodiment of the present invention. DETAILED DESCRIPTION

[0012] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments.

[0013] A method for measuring broadband electrical signals, firstly designs a high bandwidth low offset amplifier, such as Figure 1 As shown, the high-bandwidth low-offset amplifier is mainly a composite operational amplifier composed of three operational amplifiers, namely, a precision operational amplifier U1, a radio frequency low-noise amplifier U2 and a current feedback operational amplifier U3. The precision operational amplifier U1 is model ADA4522-1ARZ, with specific parameters: 2.7MHz bandwidth, 1.7V / uS slew rate, 1.5uV offset voltage, 50pA bias current; the radio frequency low-noise amplifier U2 is model AD8021ARZ, with specific parameters: 560MHz bandwidth, 460V / uS slew rate, 0.4mV offset voltage, 7.5uA bias current; the current feedback operational amplifier U3 is model OPA694IDR, with specific parameters: 15G bandwidth, 1700V / uS slew rate, 0.5mV offset voltage, 5uA bias current.

[0014] The input end of the high-bandwidth low-offset amplifier includes one end of a capacitor C1 and one end of a resistor R16 in parallel, the other end of the capacitor C1 is electrically connected to one end of the capacitor C2, the other end of the capacitor C2 is electrically connected to one end of the resistor R1, the other end of the resistor R1 and the other end of the resistor R16 are both electrically connected to one end of the capacitor C3, one end of the resistor R17, one end of the capacitor C6 and one end of the resistor R6, the other end of the capacitor C3 is electrically connected to one end of the resistor R2, the other end of the resistor R2 and the other end of the resistor R17 are both electrically connected to one end of the capacitor C4 and one end of the resistor R18, the other end of the capacitor C4 is electrically connected to one end of the resistor R3, the other end of the resistor R3 and the other end of the resistor R18 are both electrically connected to one end of the capacitor C5 and one end of the resistor R19, and the other end of the capacitor C5 is electrically connected to one end of the resistor R4.

[0015] The other end of capacitor C6 is electrically connected to one end of resistor R5 and one end of resistor R9 respectively, the other end of resistor R5 is grounded, and the other end of resistor R9 is electrically connected to the reverse input end of RF low noise amplifier U2. The other end of resistor R6 is electrically connected to one end of capacitor C7 and the reverse input end of precision operational amplifier U1 respectively, the same-direction input end of precision operational amplifier U1 is grounded, the output end of precision operational amplifier U1 and the other end of capacitor C7 are electrically connected to one end of resistor R7, the other end of resistor R7 is electrically connected to one end of resistor R8 and the same-direction input end of RF low noise amplifier U2 respectively, the other end of resistor R8 is grounded, the output end of RF low noise amplifier U2 is electrically connected to one end of resistor R10, and the other end of resistor R10 is electrically connected to the same-direction input end of current feedback operational amplifier U3. The reverse input terminal of the current feedback operational amplifier U3 is electrically connected to one end of the resistor R12, the other end of the resistor R12 is electrically connected to one end of the resistor R11, one end of the resistor R13 and one end of the resistor R15 respectively, the other end of the resistor R11 is grounded, the other end of the resistor R13 is electrically connected to one end of the resistor R14, the other end of the resistor R15 is electrically connected to one end of the capacitor C8, the other end of the resistor R4, the other end of the resistor R19, the output terminal of the current feedback operational amplifier U3, the other end of the resistor R14 and the other end of the capacitor C8 are connected in parallel as the output terminal of a high-bandwidth, low-offset amplifier.

[0016] Resistors R16~R19 are made of thin film technology, that is, these four resistors are packaged together, with an absolute temperature drift of 15ppm, a relative temperature drift of 5ppm, an absolute accuracy of 0.025%, and a relative accuracy of 0.010%. They are selected to meet high-precision requirements such as 0.01%. The resistors and capacitors connected in parallel to this type of resistor are to achieve bandwidth compensation. The bandwidth and offset of the operational amplifier have been adjusted before, and the proportional resistors of the operational amplifier also need bandwidth compensation, because the resistors also have parasitic parameters, such as parasitic capacitance, which will attenuate due to different frequency characteristics.

[0017] First, according to the index requirements for the first-stage current amplification in the power analyzer, it is necessary to amplify the signal with a bandwidth of 5MHz by 100 times, so it is necessary to select an operational amplifier with a gain-bandwidth product of more than 500MHz. In the embodiment of the present invention, a radio frequency low-noise amplifier U2 with model AD8021ARZ is selected. Since the offset voltage of AD8021ARZ is 0.4mV, it cannot meet the index requirements of low offset voltage. Therefore, a precision operational amplifier U1 with model ADA4522-1ARZ is used together with AD8021ARZ to form an automatic zeroing composite operational amplifier.

[0018] In order to further expand the closed-loop bandwidth of AD8021ARZ, OPA694IDR and AD8021ARZ are used to form a series composite operational amplifier. That is, the precision operational amplifier ADA4522-1ARZ is used to improve the DC characteristics (low offset voltage, low bias current) of AD8021ARZ, and OPA694IDR is used to expand the bandwidth of AD8021ARZ.

[0019] Offset voltage: The offset voltage of the entire composite operational amplifier is determined by the offset voltage (1.5uV) of ADA4522-1ARZ and the bias current (50pA) of ADA4522-1ARZ through R410 (3.32K). The maximum offset voltage does not exceed 2uV, Umax=1.5uV+50pA*3.32K=1.666uV<2uV.

[0020] High bandwidth: The AD8021ARZ and OPA694IDR are used to expand the bandwidth by connecting a composite operational amplifier in series. On the basis of ensuring the bandwidth, in order to make the entire loop stable, the gain of the inner loop must not be greater than the gain of the outer loop. Therefore, the inner loop gain (64.4 times) is set to be smaller than the outer loop gain (100 times).

[0021] like Figure 2 As shown, the current signal is collected by the shunt through the high-bandwidth low-offset amplifier to the operational amplifier. After the operational amplifier achieves a 5-fold gain amplification, the current signal enters the ADC. The ADC selects the ADI model LTC2386-18 ADC. The analog bandwidth of this ADC is 200MHz, the sampling rate is 10MHz, and the number of bits is 18bit. In the actual application circuit, in order to measure small signals, in addition to the 100-fold amplification of the first-stage amplifier circuit, in order to meet the input voltage range of the ADC, the latter stage will cooperate with some operational amplifier circuits to amplify it 5 times before entering the ADC.

[0022] The collected current signal is a sinusoidal signal. In practical applications, this sinusoidal signal will be superimposed with noise. Using the 1 million continuous points collected by the ADC, autocorrelation calculation is performed: fs = 10e6; (10M sampling rate) fs represents the sampling frequency. The 10M sampling rate in the brackets is a comment on (fs = 10e6;). The formula fs = 10e6; is written in MATLAB, which is 10 to the sixth power, that is, 10M (10 megabytes), which means that 10 million points can be collected in one second.

[0023] Use the first 500,000 points and the last 500,000 points to perform autocorrelation function calculation, corr_result = xcorr(a1(1:500000), a1(500001:1000000)); Then, the square value of the amplitude is calculated using the peak value of the autocorrelation function of the sine wave superimposed with the width noise (this peak value is equal to the square of the sine wave amplitude), and the collected sine wave amplitude As is calculated; Collect once according to the standard signal, such as the amplitude Aa of the standard signal; At this time, a calibration is required, and the calibration coefficient k=As / Aa. The current signal data collected thereafter is Aa', and Aa'*k is the true value of the current signal extracted from the noise.

[0024] According to the actual example, if the 5mA standard current signal is measured, due to the superposition of noise in the circuit, if the effective value is calculated directly using the collected data, 32.848mA is calculated. If the above algorithm is used for calculation, 5.43mA is calculated, which meets the 10% accuracy requirement.

[0025] Note: The shunt is 5mΩ. If the collected current signal is 5mA, the input of the op amp is 25uV. The high-bandwidth, low-offset op amp offset voltage <2uV in the present invention is prepared for the measurement of small signals, because noise is inevitably present in the measurement environment.

[0026] The measured data of 1A current signal can meet the accuracy requirement of 0.01%.

[0027] like Figure 3 As shown, resistor R11 adopts 68.1R resistor, resistor R12 adopts 221R resistor, resistor R13 adopts 1K resistor, resistor R14 adopts 3.32K resistor, resistor R15 takes a value of 100Ω, capacitor C8 takes a value of 10pF, the present invention uses a high-bandwidth and high-precision operational amplifier implemented by a composite operational amplifier composed of multiple operational amplifiers, and adopts a method of increasing bandwidth by connecting two operational amplifiers in series. This method requires an inner loop (an operational amplifier connected in series, i.e. Figure 3The gain of the OPA694IDR in the circuit is less than the gain of the outer loop. In the present invention, the outer loop gain is 100 times and the inner loop gain is 64.4. The calculation formula is: R11=68.1R, Rf is the feedback resistor of OPA694IDR, Rf=1K+3.32K is equal to 4.32K (4320Ω); G=1+Rf / R11=1+63.4=64.4, G represents the gain of the inner loop.

[0028] Implement a composite op amp consisting of three op amps such as Figure 1 As shown, in order to achieve the stability of the composite op amp, the gain of the inner loop needs to be smaller than the gain of the outer loop, otherwise the composite op amp will have peaking, causing instability in the composite op amp loop. It can also be designed in conjunction with other gains of the composite op amp. In actual products, it is impossible to measure only small signals. Current measurement will measure large signals in addition to small signals. For example, if a shunt is used to measure 30A, the 100-fold amplification of the previous stage will be adjusted to 10 times or 1 times according to the range, and the gain of the inner loop will also be modified accordingly.

[0029] For the precision operational amplifier U1, the radio frequency low noise amplifier U2 and the current feedback operational amplifier U3 in the embodiment of the present invention, other similar product model devices with the same performance as the above product models can be selected.

[0030] In the embodiments of the present invention, technical features that are not described in detail are all existing technologies or conventional technical means and will not be described in detail here.

[0031] Finally, it should be noted that the above embodiments are only specific implementation methods of the present invention, which are used to illustrate the technical solutions of the present invention, rather than to limit them, and the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any technician familiar with the technical field can modify the technical solutions recorded in the above embodiments within the technical scope disclosed by the present invention, or can easily think of changes, or make equivalent replacements for some of the technical features therein; and these modifications, changes or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be covered within the protection scope of the present invention.

Claims

1. A method for measuring a broadband electrical signal, designing a high bandwidth low offset amplifier, characterized in that: The high-bandwidth low-offset amplifier comprises a composite operational amplifier consisting of three operational amplifiers, namely, a precision operational amplifier U1, a radio frequency low-noise amplifier U2 and a current feedback operational amplifier U3, which are connected in series in sequence, and the inner loop gain of the current feedback operational amplifier U3 is set to be smaller than the outer loop gain; The current signal is collected to the ADC by amplifying the high-bandwidth low-offset amplifier and the operational amplifier using a shunt. The collected current signal is a sinusoidal signal. The autocorrelation calculation is performed using the 1 million continuous points collected by the ADC. The square value of the amplitude is calculated using the peak value of the autocorrelation function of the sinusoidal wave superimposed with width noise, and the collected sinusoidal wave amplitude As is calculated. The standard signal is collected once, and the amplitude of the standard signal is Aa; Perform a calibration, the calibration coefficient k = As / Aa, and the current signal data collected thereafter is Aa', then Aa'*k is the true value of the current signal extracted from the noise.

2. A method for measuring a broadband electrical signal according to claim 1, characterized in that: The input end of the high-bandwidth low-offset amplifier includes one end of a capacitor C1 and one end of a resistor R16 connected in parallel, the other end of the capacitor C1 is electrically connected to one end of the capacitor C2, the other end of the capacitor C2 is electrically connected to one end of the resistor R1, the other end of the resistor R1 and the other end of the resistor R16 are both electrically connected to one end of the capacitor C3, one end of the resistor R17, one end of the capacitor C6 and one end of the resistor R6, the other end of the capacitor C3 is electrically connected to one end of the resistor R2, the other end of the resistor R2 and the other end of the resistor R17 are both electrically connected to one end of the capacitor C4 and one end of the resistor R18, the other end of the capacitor C4 is electrically connected to one end of the resistor R3, the other end of the resistor R3 and the other end of the resistor R18 are both electrically connected to one end of the capacitor C5 and one end of the resistor R19, and the other end of the capacitor C5 is electrically connected to one end of the resistor R4; The other end of capacitor C6 is electrically connected to one end of resistor R5 and one end of resistor R9 respectively, the other end of resistor R5 is grounded, and the other end of resistor R9 is electrically connected to the reverse input end of RF low noise amplifier U2. The other end of resistor R6 is electrically connected to one end of capacitor C7 and the reverse input end of precision operational amplifier U1 respectively, the same-direction input end of precision operational amplifier U1 is grounded, the output end of precision operational amplifier U1 and the other end of capacitor C7 are electrically connected to one end of resistor R7, the other end of resistor R7 is electrically connected to one end of resistor R8 and the same-direction input end of RF low noise amplifier U2 respectively, the other end of resistor R8 is grounded, the output end of RF low noise amplifier U2 is electrically connected to one end of resistor R10, and the other end of resistor R10 is electrically connected to the same-direction input end of current feedback operational amplifier U3. The reverse input terminal of the current feedback operational amplifier U3 is electrically connected to one end of the resistor R12, the other end of the resistor R12 is electrically connected to one end of the resistor R11, one end of the resistor R13 and one end of the resistor R15 respectively, the other end of the resistor R11 is grounded, the other end of the resistor R13 is electrically connected to one end of the resistor R14, the other end of the resistor R15 is electrically connected to one end of the capacitor C8, the other end of the resistor R4, the other end of the resistor R19, the output terminal of the current feedback operational amplifier U3, the other end of the resistor R14 and the other end of the capacitor C8 are connected in parallel as the output terminal of a high-bandwidth, low-offset amplifier.

3. A method for measuring a broadband electrical signal according to claim 2, characterized in that: The model of the precision operational amplifier U1 is ADA4522-1ARZ, the model of the radio frequency low noise amplifier U2 is AD8021ARZ, and the model of the current feedback operational amplifier U3 is OPA694IDR.

4. The method for measuring a broadband electrical signal according to claim 2, characterized in that: The ADC selected is ADI's LTC2386-18 ADC.

5. The method for measuring a broadband electrical signal according to claim 2, characterized in that: The resistors R16, R17, R18 and R19 are packaged together using thin film technology resistors.

6. A method for measuring a broadband electrical signal according to claim 5, characterized in that: The resistor R11 is a 68.1R resistor, the resistor R12 is a 221R resistor, the resistor R13 is a 1K resistor, the resistor R14 is a 3.32K resistor, the resistor R15 is 100Ω, and the capacitor C8 is 10pF.

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