CN102790589B - Amplifier for measuring 1MHz common mode rejection ratios of high-resistance high-voltage differential probe - Google Patents

Abstract

An amplifier for measuring the 1MHz common-mode rejection ratio of a high-impedance high-voltage differential probe, comprising a preamplifier unit, a frequency-selective amplifier unit, and two independent DC power supply voltages, wherein the two independent DC power supply voltages are respectively connected to The pre-amplification unit and the frequency-selective amplifying unit are used to independently power the pre-amplifier unit and the frequency-selective amplifying unit; the pre-amplifying unit is used to provide a pre-set range The pre-stage amplification factor amplifies the signal and noise buried in the noise together; the frequency-selective amplifying unit: connected to the pre-amplifying unit, including an amplifying unit composed of an LC frequency-selecting network designed to have a resonance center frequency of 1MHz and a triode, It is used to further amplify the filtered 1MHz useful signal. The invention solves the technical problem in the prior art that the high-attenuation level 1MHz common-mode output voltage of a high-resistance high-voltage differential probe cannot be directly measured.

Description

An amplifier for measuring 1MHz common-mode rejection ratio of high-impedance high-voltage differential probes

technical field

The invention relates to an amplifier, in particular to an amplifier for measuring the 1MHz common-mode rejection ratio of a high-resistance high-voltage differential probe.

Background technique

Common mode rejection ratio is one of the key parameters reflecting the performance of high-impedance high-voltage differential probes. , ×1000), according to the requirements of the technical specification, it is necessary to give the measurement results of the common mode rejection ratio of the high-impedance high-voltage differential probe at 50Hz (60Hz), 1kHz, 10kHz, 100kHz, and 1MHz frequency points. At present, the high-impedance standard source can output sine wave frequency up to 1MHz and the output amplitude is the largest, only FLUKE5700A, and its output level capabilities at different frequency points are shown in Table 1. When measuring the common-mode rejection ratio of the high-impedance high-voltage differential probe at the high-attenuation level of the 1MHz frequency point, the output amplitude of the high-impedance standard source is not large enough, so the common-mode output voltage amplitude after passing through the high-impedance high-voltage differential probe is only tens of microvolts To hundreds of microvolts, it is buried in the noise and appears as a line on the oscilloscope, so it is impossible to obtain the common mode rejection ratio measurement value of the high-impedance high-voltage differential probe high-attenuation level 1MHz frequency point.

Table 1 Output level capability table of high-impedance standard source FLUKE 5700A at different frequency points

frequency point 50Hz(60Hz), 1kHz 10kHz, 100kHz 1MHz The maximum level that can be output 1000V 200V 20V

There is currently no amplifier capable of achieving a 1MHz common-mode output signal of a high-impedance high-voltage differential probe buried in noise. The existing amplifier can amplify the 1MHz common-mode signal, but it also amplifies the noise, and the result is still buried in the noise. Existing filters include high-frequency filters, intermediate-frequency filters, and low-pass filters. There are no off-the-shelf filters with a center frequency of 1MHz.

Due to the differences in input impedance, operating frequency band, and amplification capability among existing amplifier products, there is no amplifier suitable for amplifying an effective signal buried in noise with an amplitude of about several hundred microvolts and a frequency of 1MHz. Such as radios, walkie-talkies, etc., first of all, their matching impedance is 50 ohms, and they receive weak high-frequency signals from antennas, etc., because the common-mode output signal of high-impedance high-voltage differential probes has high impedance characteristics, so the existing solutions cannot be applied to high-impedance high-voltage Amplification of the common-mode signal of the differential probe; secondly, the center frequency of the frequency selection of the existing implementation scheme is in the high-frequency band, and the frequency selection effect of the common-mode signal with the center frequency of 1MHz is not good.

Contents of the invention

The purpose of the present invention is to provide an amplifier for measuring the 1MHz common-mode rejection ratio of a high-impedance high-voltage differential probe, so as to solve the technical problem in the prior art that the high-attenuation level 1MHz common-mode output voltage of a high-impedance high-voltage differential probe cannot be directly measured .

The present invention aims at the above-mentioned deficiencies existing in the prior art, designs an amplifier for measuring the 1MHz common-mode rejection ratio of high-resistance high-voltage differential probes, and develops an amplifier that can amplify the 1MHz common-mode output signal buried in the noise in a targeted manner , so as to successfully realize the measurement of the common mode rejection ratio of the high-impedance high-voltage differential probe at 1MHz frequency.

The present invention is realized through the following technical solutions:

An amplifier for measuring the 1MHz common-mode rejection ratio of a high-impedance high-voltage differential probe, including a preamplifier unit, a frequency-selective amplifier unit, and two independent DC power supply voltages, wherein,

The two independent DC power supply voltages are respectively connected to the pre-amplification unit and the frequency-selective amplifying unit, and are used to independently supply power to the pre-amplification unit and the frequency-selective amplifying unit;

The pre-amplification unit: used to provide a pre-set range of pre-amplification multiples to amplify the signal and noise buried in the noise together;

The frequency-selective amplifying unit: connected to the pre-amplifying unit, including an amplifying unit composed of an LC frequency-selecting network designed to have a resonance center frequency of 1 MHz and a triode, for further amplifying the filtered 1 MHz useful signal.

Preferably, the inductance L ₀ and the capacitor C ₀ in the frequency selection amplifying unit are combined to form a frequency selection network, the resonant frequency of which is 1 MHz, and the equivalent impedance after resonance is used as the load of the triode T ₀ to further amplify the frequency of 1 MHz. Signal.

Preferably, the frequency selection amplifying unit further includes R ₄ and R ₅ , R ₄ and R ₅ are voltage dividing resistors, and the DC supply voltage provides a DC bias voltage for the transistor T ₀ through R ₄ and R ₅ .

Preferably, the pre-amplification unit includes a negative feedback operational amplification unit, R ₀ and R ₁ , R ₀ and R ₁ and the negative feedback operational amplification unit have a combined structure through negative feedback, so that within a wider frequency range, With stable magnification.

Moreover, the negative feedback operational amplifier unit is a low-noise high-bandwidth operational amplifier or a triode amplifier circuit.

Preferably, the pre-amplification unit further includes R ₂ and R ₃ as voltage dividing resistors, which respectively provide DC bias voltages for the positive and negative input terminals of the negative feedback operational amplification unit.

The amplifier also includes an input coupling unit and an output coupling unit, the input coupling unit is set at the input front end of the pre-amplification unit, and the output coupling unit is set at the output rear end of the frequency selection amplifying unit. Moreover, it also includes a third coupling unit, which is arranged between the preamplifier unit and the frequency selective amplifying unit.

The invention provides another method for measuring the common-mode rejection ratio of a high-resistance high-voltage differential probe at a frequency of 1 MHz.

For the part with a low attenuation coefficient of 1/100, first make the high-impedance standard source FLUKE 5700A output a 1MHz sine wave signal to the positive and negative input terminals of the high-impedance differential probe. _Then short the positive and negative input ends of the high impedance differential probe to keep the output of the high impedance standard source FLUKE 5700A unchanged, and input it between the short input end of the high impedance differential probe and the common ground , directly read the common-mode voltage peak-to-peak measurement result V _c1 on the digital oscilloscope, and calculate the common-mode rejection ratio CMRR ₁ =20×lg(V _d1 /V _c1 ) of the part with a low attenuation coefficient of 1/100;

For the part with a high attenuation coefficient of 1/1000, first measure the 1MHz differential mode voltage peak-to-peak measurement voltage result V _d2 ;

Set in the part with low attenuation coefficient 1/100, connect the rear end of the high-impedance high-voltage differential probe to the amplifier, and obtain the amplified common-mode voltage peak-to-peak measurement result V _cg1 , according to the previously obtained unamplified common-mode voltage peak-to-peak measurement result V _c1 , it can be calculated that the amplifier corresponds to the actual magnification of the high-impedance high-voltage differential probe A=V _cg1 /V _c1 ;

Set at the part with a high attenuation coefficient of 1/1000, connect the rear end of the high-impedance high-voltage differential probe to the amplifier, and obtain the amplified common-mode voltage peak-to-peak measurement result V _cg2 ; thus calculate the actual common-mode voltage peak-to-peak measurement result V at 1MHz frequency _c2 = V _cg2 /A;

Calculate the actual common mode rejection ratio CMRR ₂ =20×1g(V _d2 /V _c2 ) of the probe at 1 MHz in the high attenuation factor 1/1000 part.

Compared with the prior art, the present invention has the advantage that it can amplify the amplifier of the 1MHz common-mode output signal buried in the noise in a targeted manner. The first part is a high-bandwidth low-noise amplification unit, which will be buried in the Weak signals and noise in the noise are amplified together. The second part is the narrow-band frequency selective amplification part, which will filter the 1MHz useful signal and further amplify it. At the same time, ensure a good isolation design between the front-stage amplification and the rear-stage frequency selection. The front and rear stages use their own power supplies to eliminate the mutual influence between the two-stage units, thereby smoothly realizing the 1MHz frequency point sharing of the high-impedance high-voltage differential probe. Measurement of Mode Suppression Ratio.

Description of drawings

Fig. 1 is a kind of structural representation of the amplifier that is used for measuring high-impedance high-voltage differential probe 1MHz common-mode rejection ratio of the present invention;

Fig. 2 is a kind of circuit diagram that is used for measuring the amplifier of 1MHz common-mode rejection ratio of high resistance high voltage differential probe of the present invention;

FIG. 3 is a circuit diagram of another amplifier used for measuring the 1MHz common-mode rejection ratio of a high-impedance high-voltage differential probe according to the present invention.

FIG. 4 is a schematic diagram of differential mode measurement connection in a method for measuring the common mode rejection ratio of a high-impedance high-voltage differential probe at a frequency of 1 MHz according to the present invention.

Fig. 5 is a schematic diagram of the common mode measurement connection of a method for measuring the common mode rejection ratio of a high-impedance high-voltage differential probe at a frequency of 1 MHz according to the present invention.

6 is a schematic diagram of common-mode measurement connection of an amplifier connected in a method for measuring the common-mode rejection ratio of a high-impedance high-voltage differential probe at a frequency of 1 MHz according to the present invention.

Detailed ways

The present invention is described in detail below in conjunction with embodiment, present embodiment implements under the premise of technical solution of the present invention, has provided detailed implementation mode, does not limit the present invention, therefore, protection scope of the present invention is not limited to following Example.

Referring to Fig. 1 to Fig. 6, the present invention will be described in detail.

Please refer to Fig. 1, an amplifier for measuring the 1 MHz common-mode rejection ratio of a high-impedance high-voltage differential probe, including a preamplifier unit 12, a frequency-selective amplifying unit 13 and two independent DC power supply voltages, wherein,

The two independent DC power supply voltages are respectively connected to the preamplifier unit 12 and the frequency-selective amplifying unit 13, and are used to independently supply power to the preamplifier unit and the frequency-selective amplifying unit;

The pre-amplification unit 12: used to provide a pre-amplification factor in a preset range, and amplify the signal and noise buried in the noise together;

The frequency-selective amplifying unit 13: connected to the pre-amplifying unit 12, includes an amplifying unit composed of an LC frequency-selecting network designed to have a resonant center frequency of 1 MHz and a triode, and is used to further amplify the filtered useful signal of 1 MHz.

Referring to FIG. 2 , it is a schematic diagram of an example of an amplifier for measuring the 1 MHz common-mode rejection ratio of a high-impedance high-voltage differential probe. It includes a pre-amplifier unit, a frequency-selective amplifier unit and two independent DC power supply voltages V ₁ and V ₂ .

The pre-amplification unit includes several voltage-dividing resistors and a low-noise, high-bandwidth operational amplifier circuit. In this example, the voltage-dividing resistors include two R ₂ and R ₃ .

The low-noise high-bandwidth operational amplifier circuit comprises an amplifier input resistance R ₀ , an amplifier output resistance R ₁ and a low-noise high-bandwidth operational amplifier A, and the amplifier input resistance R ₀ and the amplifier output resistance R ₁ are related to the low-noise high-bandwidth operation Amplifier A negative feedback structure connection. V ₁ is the DC power supply voltage of the preamplifier unit. R ₀ and R ₁ and the low-noise, high-bandwidth operational amplifier A are combined with a negative feedback structure, so that they have a stable amplification factor in a wide frequency range. At the same time, it has a large input dynamic range. R ₂ and R ₃ are voltage divider resistors, which provide DC bias voltage for the positive and negative input terminals of the operational amplifier respectively.

Frequency-selective amplifying unit: connected to the pre-amplifying unit, including an amplifying unit composed of an LC frequency-selecting network designed to have a resonant center frequency of 1MHz and a triode, which is used to further amplify the filtered 1MHz useful signal. The inductance L ₀ and the capacitor C ₀ in the frequency selection amplifying unit are combined to form a frequency selection network, its resonant frequency is 1MHz, and its equivalent impedance after resonance is used as the load of the triode T ₀ to further amplify the 1MHz signal. The frequency selection amplifying unit further includes R ₄ and R ₅ , R ₄ and R ₅ are voltage dividing resistors, and the DC power supply voltage provides a DC bias voltage for the triode T ₀ through R ₄ and R ₅ .

On the one hand, the inductor L ₀ and the capacitor C ₀ are combined to form a frequency-selective network with a resonance frequency of 1 MHz. On the other hand, the equivalent impedance after resonance is used as the load of the triode T ₀ to further amplify the 1 MHz signal. V ₂ is the DC power supply voltage of the frequency selection amplifying unit.

The frequency selection network composed of inductance L ₀ and capacitor C ₀ , the resonant center frequency f ₀ can be obtained by the following formula:

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\sqrt{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}}$

Where f ₀ =1MHz is required, the inductance of the inductor L ₀ is calculated according to the capacitance of the selected capacitor C ₀ . The inductance is hand-wound with enameled wire, which can be wound to the desired inductance (inductance of about L ₀ value), and then in the debugging process, by changing the tightness of the winding inductance, the frequency selection network The center frequency of the resonant frequency is 1MHz.

The amplifier for measuring the 1MHz common-mode rejection ratio of the high-impedance high-voltage differential probe also includes an input coupling unit 11 and an output coupling unit 14, the input coupling unit 11 is provided with the input front end of the preamplification unit 12, and the output coupling unit 14 is arranged at the selected The output rear end of the frequency amplifying unit 13.

In this example, the input coupling unit 11 adopts the input coupling capacitor C ₁ , and the output coupling unit 14 adopts the output coupling capacitor C ₃ .

The amplifier also includes a third coupling unit, which is arranged between the preamplifying unit 12 and the frequency selective amplifying unit 13 . In this example, the third coupling unit may use two stages of cascaded coupling capacitors C ₂ .

The input terminal coupling capacitor C ₁ is electrically connected to the input terminal of the preamplifier unit, and the two-stage cascaded coupling capacitor C ₂ is electrically connected between the output terminal of the preamplifier unit and the input terminal of the frequency selection amplifier unit, and the output terminal The coupling capacitor _C3 is electrically connected to the output terminal of the frequency-selective amplifying unit.

Referring to FIG. 3 , the present invention provides another amplifier for measuring the 1 MHz common-mode rejection ratio of a high-impedance high-voltage differential probe. The negative feedback operational amplifier unit in Figure 2 is a low-noise high-bandwidth operational amplifier, and the negative feedback operational amplifier unit in Figure 3 is amplified by a triode circuit. Likewise, the amplifying unit passes through the combination of the transistor _T1 and the resistor _R1 .

The invention provides another method for measuring the common-mode rejection ratio of a high-resistance high-voltage differential probe at a frequency of 1 MHz.

Referring to Figure 4, for the part with a low attenuation coefficient of 1/100, first make the high-impedance standard source FLUKE 5700A output a 1MHz sine wave signal to the positive and negative input terminals of the high-impedance differential probe, and its output level can reach up to 20V. On the digital oscilloscope Directly read the differential mode voltage peak-to-peak measurement result V _d1 ;

Referring to Figure 5, then short the positive and negative input ends of the high-impedance differential probe, so that the output of the high-impedance standard source FLUKE 5700A remains unchanged, input between the short-circuit input end of the high-impedance differential probe and the common ground, and display on the digital oscilloscope Directly read the common-mode voltage peak-to-peak measurement result V _c1 , and calculate the common-mode rejection ratio CMRR ₁ =20×lg(V _d1 /V _c1 ) of the part with a low attenuation coefficient of 1/100;

For the part with a high attenuation coefficient of 1/1000, first measure the 1MHz differential mode voltage peak-to-peak measurement voltage result V _d2 ;

Referring to Figure 6, set it at the low attenuation coefficient of 1/100, connect the amplifier to the rear end of the high-impedance high-voltage differential probe, and obtain the amplified common-mode voltage peak-to-peak measurement result V _cg1 , according to the previously obtained unamplified common-mode voltage peak The peak measurement result V _c1 can be calculated to obtain the actual magnification of the amplifier corresponding to the high-impedance high-voltage differential probe A=V _cg1 /V _c1 ;

Set at the part with a high attenuation coefficient of 1/1000, connect the rear end of the high-impedance high-voltage differential probe to the amplifier, and obtain the amplified common-mode voltage peak-to-peak measurement result V _cg2 ; thus calculate the actual common-mode voltage peak-to-peak measurement result V at 1MHz frequency _c2 = V _cg2 /A;

Calculate the actual common mode rejection ratio CMRR ₂ =20×lg(V _d2 /V _c2 ) of the probe at 1 MHz in the high attenuation factor 1/1000 part.

Compared with the prior art, the present invention has the advantage that it can specifically amplify the amplifier of the 1MHz common-mode output signal buried in the noise, thereby smoothly realizing the measurement of the common-mode rejection ratio at the 1MHz frequency point of the high-impedance high-voltage differential probe.

What is disclosed above is only a specific embodiment of the present invention, but the present invention is not limited thereto, and any changes conceivable by those skilled in the art should fall within the protection scope of the present invention.

Claims (7)

1. An amplifier for measuring the 1MHz common-mode rejection ratio of a high-impedance high-voltage differential probe, is characterized in that it includes a preamplifier unit, a frequency-selective amplifier unit and two independent DC supply voltages, wherein, The two independent DC power supply voltages are respectively connected to the pre-amplification unit and the frequency-selective amplifying unit, and are used to independently supply power to the pre-amplification unit and the frequency-selective amplifying unit; The pre-amplification unit: used to provide a pre-amplification factor in a preset range, and amplify the signal and noise buried in the noise together; The frequency-selective amplifying unit: connected to the pre-amplifying unit, including an amplifying unit composed of an LC frequency-selecting network designed to have a resonant center frequency of 1 MHz and a triode, for further amplifying the filtered 1 MHz useful signal; It also includes a third coupling unit, which is arranged between the pre-amplification unit and the frequency-selective amplifying unit. 2. the amplifier that is used to measure high resistance high voltage differential probe 1MHz common-mode rejection ratio as claimed in claim 1, is characterized in that, The inductance L ₀ and the capacitor C ₀ in the frequency selection amplifying unit are combined to form a frequency selection network, the resonant frequency of which is 1 MHz, and its resonant equivalent impedance serves as the load of the triode T ₀ to further amplify the 1 MHz signal. 3. the amplifier that is used to measure high resistance high voltage differential probe 1MHz common-mode rejection ratio as claimed in claim 2, is characterized in that, described frequency selection amplifying unit also comprises R ₄ and R ₅ , R ₄ and R ₅ are divider piezoresistor, the DC power supply voltage provides DC bias voltage for the triode _T0 through _R4 and _R5 . 4. the amplifier that is used to measure high resistance high voltage differential probe 1MHz common-mode rejection ratio as claimed in claim 1, is characterized in that, The pre-amplification unit includes a negative feedback operational amplification unit, R ₀ and R ₁ , R ₀ and R ₁ and the negative feedback operational amplification unit have a combined structure through negative feedback, so that it has a stable amplification within a wide frequency range multiple. 5. the amplifier that is used for measuring high-impedance high-voltage differential probe 1MHz common-mode rejection ratio as claimed in claim 4, is characterized in that, negative feedback operational amplifier unit is a low-noise high-bandwidth operational amplifier or a triode amplifier circuit. 6. the amplifier that is used to measure high-impedance high-voltage differential probe 1MHz common-mode rejection ratio as claimed in claim 4, is characterized in that, described preamplifier unit also comprises R ₂ and R ₃ are divider resistors, are negative respectively The positive and negative input terminals of the feedback operational amplifier unit provide a DC bias voltage. 7. the amplifier that is used to measure high resistance high voltage differential probe 1MHz common-mode rejection ratio as claimed in claim 1, is characterized in that, also comprises input coupling unit, output coupling unit, and described input coupling unit is arranged on preamplifier unit The input front-end, the output coupling unit is set at the output rear-end of the frequency-selective amplifying unit.