CN103884888B - Oscillograph with function of multimeter - Google Patents

Abstract

The invention discloses an oscilloscope with the function of a multimeter, which includes a signal input terminal, an input stage buffer and an addition circuit module, a programmable amplifier module, a D/A conversion module, and a control processing module; it also includes a branch line circuit module, the The shunt linear circuit module includes a high-frequency subtraction amplification circuit module, a coupling unit module, a high-speed ADC conversion module, a low-frequency amplification circuit module and a high-precision low-speed ADC conversion module. The improvement of the hardware circuit on the channel of the oscilloscope realizes a high-precision multimeter, and the circuit is simple and does not occupy the volume of the oscilloscope. The invention can also realize the high-precision voltage measurement function, the resistance measurement function and the on-off circuit measurement function of the multimeter on the oscilloscope, and can also enable the oscilloscope to have an isolation function.

Description

Oscilloscope with Multimeter Function

technical field

The invention relates to the field of electric variable testing, in particular to an oscilloscope with a multimeter function.

Background technique

Among the basic electronic measurement instruments, the multimeter is one of the most widely used measuring instruments, and the voltage measurement, resistance measurement, and open-circuit test on the multimeter are the most used functions. If it is possible to add a real high-precision multimeter function to the oscilloscope, which can accurately measure the voltage value, resistance value, and test whether there is a short circuit, it will be convenient for users to use the common functions of the multimeter while using the oscilloscope, and it will have a great market prospect. .

There are currently two types of oscilloscopes with multimeter functionality on the market. One type is a handheld oscilloscope, which generally adds two independent multimeter interfaces and test leads for multimeter measurement. An integrated multimeter chip is used internally to realize the multimeter function, generally a 4.5-digit or lower-precision oscilloscope.

The other is based on the digital oscilloscope, through the software to realize the voltage test function of the multimeter. With reference to Fig. 1, because the digital oscilloscope of prior art generally adopts high-speed ADC, most of them are 8-bit ADC, because ADC has only 8-bit precision, so the highest measurement precision that can realize is also only 2 ⁸ =256, promptly can realize maximum 3 Half-digit voltmeter measurement. At present, there are mainly two software implementation methods: one is to use the oscilloscope screen display data for voltage calculation (this is a common implementation method for voltage measurement on the oscilloscope), because the screen display data is generally compressed and extracted data from ADC sampling data , can not really reflect the original data, resulting in a decrease in measurement accuracy, so the measurement accuracy that can be achieved is low; the other is to use the original data sampled by the ADC for voltage measurement and calculation, which can retain the original data information to the greatest extent and can improve as much as possible. The measurement accuracy can only achieve a maximum accuracy of 3 and a half digits.

In the prior art, an independent multimeter circuit module needs to be added to the hand-held oscilloscope, the circuit is relatively complicated, the instrument is bulky, and the accuracy is not high. However, the use of software is limited by the number of digits of the high-speed sampling ADC of the oscilloscope (generally, the high-speed ADC is 8 digits), so it can only realize the voltmeter function with a maximum accuracy of 3.5 digits. There is no real oscilloscope that implements a high-precision multimeter on the oscilloscope test channel at present.

Contents of the invention

The technical problem to be solved by the present invention is the problem that the high-precision multimeter cannot be realized in the oscilloscope of the prior art, and the problem that an independent multimeter circuit module needs to be added when the multimeter is realized by hardware in the prior art, the circuit is complicated, and the volume of the instrument is large.

In order to solve the above technical problems, the present invention provides an oscilloscope with a multimeter function, comprising a signal input terminal, an input stage buffer and addition circuit module, a programmable amplifier module, a D/A conversion module, and a control processing module;

The signal input terminal is used to receive an external input signal;

The control processing module is used to control the D/A conversion module to output a bias DC signal to the input stage buffer and addition circuit module;

The input stage buffering and adding circuit module is used to output a buffering signal after adding the input signal and the bias DC signal;

The control processing module is also used to control the programmable amplifier module to amplify the buffer signal and output a gain amplified signal;

It is characterized in that it also includes a branching linear circuit module, the branching linear circuit module includes a high-frequency subtraction amplification circuit module, a coupling unit module, a high-speed ADC conversion module, a low-frequency amplification circuit module and a high-precision low-speed ADC conversion module;

The low-frequency amplifying circuit module is used to filter the gain-amplified signal and output a low-frequency gain-amplified signal;

The high-frequency subtraction amplification circuit module is used to subtract the low-frequency gain amplification signal from the gain amplification signal to output a high-frequency gain amplification signal;

The coupling unit module is used to perform high-pass filtering on the high-frequency gain amplification signal, and output a high-pass gain amplification signal;

The high-speed ADC conversion module is used to sample the high-pass gain amplification signal, and input the sampled high-speed sampling data into the control processing module;

The low-speed ADC conversion module is used to sample the low-frequency gain amplification signal, and input the sampled low-speed sampling data into the control processing module;

The control processing module is also used to add the high-speed sampling data and the low-speed sampling data into n-bit data, where n is greater than 8 and less than or equal to 24, and perform average value calculation or effective value calculation on the n-bit data, and Display the calculation results.

As an example, the control processing module includes a delay adjustment module, an interpolation module, a point-by-point addition module, a sampling control module, and a voltmeter function module. Delay the high-speed sampling data, and output the delayed high-speed sampling data; the interpolation module is used to interpolate the low-speed sampling data to obtain interpolated low-speed sampling data, and the point-by-point addition module, It is used to add the delayed high-speed sampling data and the interpolated low-speed sampling data to generate 24-bit data, and the sampling control module is used to control the sampling of the oscilloscope, store and display the sampled data, The voltmeter function module is used to calculate the average value or effective value of the 24-bit data, and display the calculation results.

As an example, the coupling unit module is formed by an RC high-pass filter circuit.

As an example, a controllable switch and a programmable current source module are sequentially connected between the signal input terminal and the control processing module, and the control processing module is also used to respectively control the Current gear selection for on-off and programmable current source modules.

As an example, the coupling unit module is composed of a transformer, and when the coupling unit module is a transformer, a first digital isolator is connected between the low-speed ADC module and the control processing module, and the A second digital isolator is connected between the programmable amplifier module and the control processing module, and a third digital isolator is connected between the D/A conversion module and the control processing module.

As an example, a controllable switch, a programmable current source module and a fourth digital isolator are sequentially connected between the signal input terminal and the control processing module, and the control processing module is also used to pass The fourth digital isolator respectively controls the on-off of the controllable switch and the current gear selection of the programmable current source module.

As an example, the branching linear circuit module further includes a buffer circuit module, the buffer circuit module is connected between the coupling unit module and the high-speed ADC conversion module, and is used to enhance the high-pass gain amplified signal , to drive the high-speed ADC conversion module.

The invention has the beneficial effects that: the improvement of the hardware circuit on the oscilloscope channel realizes a high-precision multimeter, and the circuit is simple and does not occupy the volume of the oscilloscope.

Description of drawings

Fig. 1 is the structural representation of prior art oscilloscope

Fig. 2 is the structural representation of a kind of oscilloscope preferred embodiment 1 with multimeter function of the present invention

Fig. 3 is a schematic diagram of the internal structure of the shunt linear circuit module 204 in the preferred embodiment 1 of the present invention

Fig. 4 is a schematic diagram of another modified structure of the control processing module 205 in the preferred embodiment 1 of the present invention

Fig. 5 is a schematic diagram of the internal circuit of the shunt linear circuit module 204 in the preferred embodiment 1 of the present invention

Fig. 6 is the structural representation of a kind of oscilloscope preferred embodiment 2 with multimeter function of the present invention

Fig. 7 is a schematic diagram of the second modified structure of the shunt linear circuit module 204 in the preferred embodiment 1 of the present invention

Fig. 8 (A) low frequency amplifying circuit module 2044 form 1 structural diagrams;

Fig. 8 (B) low-frequency amplifying circuit module 2044 form 2 structural diagrams;

Fig. 8 (C) low-frequency amplifying circuit module 2044 form 3 structural diagrams;

Fig. 8 (D) low-frequency amplifying circuit module 2044 form 4 structural diagrams;

Fig. 9 is a schematic diagram of the third modified structure of the shunt linear circuit module 204 in the preferred embodiment 1 of the present invention

Fig. 10 is a schematic diagram of the fourth variant structure of the shunt linear circuit module 204 in the preferred embodiment 1 of the present invention

Fig. 11 is another modified structure diagram of the low-frequency amplifying circuit module 2044 in the fourth modified structure of the shunt linear circuit module 204

Fig. 12 is a schematic structural view of Fig. 6, a preferred embodiment 3 of an oscilloscope with a multimeter function in the present invention

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and preferred embodiments.

Embodiment 1, with reference to Fig. 2 and Fig. 3, oscilloscope 200 comprises signal input end 201, input stage buffering and addition circuit module 202, programmable amplifier module 203, D/A conversion module 206, control processing module 205; Signal input end 201 receives an external input signal; the control processing module 205 controls the D/A conversion module 206 to output a bias DC signal to the input stage buffering and adding circuit module 202; the input stage buffering and adding circuit module 202 combines the input signal with After the bias DC signal is added, a buffer signal is output; the control processing module 205 also controls the programmable amplifier module 203 to amplify the buffer signal and output a gain amplified signal; the oscilloscope 200 also includes a branch line Linear circuit module 204, branching linear circuit module 204 includes high-frequency subtraction amplification circuit module 2041, coupling unit module 2042, high-speed ADC conversion module 2043, low-frequency amplification circuit module 2044 and high-precision low-speed ADC conversion module 2045; low-frequency amplification circuit module 2044 , filtering the gain amplification signal to output a low frequency gain amplification signal; the high frequency subtraction amplification circuit module 2041 subtracts the low frequency gain amplification signal from the gain amplification signal to output a high frequency gain amplification signal; the coupling unit module 2042. Perform high-pass filtering on the high-frequency gain amplification signal, and output a high-pass gain amplification signal; the high-pass filtering refers to AC coupling to the input end of the high-speed ADC conversion module 2043 by using an AC coupling method; the high-speed ADC conversion module 2043 , sampling the high-pass gain amplification signal, and inputting the sampled high-speed sampling data into the control processing module 205; the low-speed ADC conversion module 2045, sampling the low-frequency gain amplification signal, and inputting the sampled low-speed sampling data The control processing module 205; the control processing module 205 adds the high-speed sampling data and the low-speed sampling data into 24-bit data, and carries out average value calculation or effective value calculation on the 24-bit data, and completes the AC and DC voltage measurement of the multimeter function. Calculate the average value of the 24-bit data, which is the DC voltage function of the multimeter; calculate the effective value of the 24-bit data, and this is the AC voltage function of the multimeter. When using the multimeter function specifically, a multimeter measurement menu will be added to the oscilloscope display interface to call the multimeter function, and the multimeter measurement results will be displayed on the display interface. When performing multimeter measurements, you can connect the oscilloscope probe to the oscilloscope input BNC, and then connect the circuit under test for measurement. At this time, the accuracy of the 1:1 probe will be higher. A better way is to use an adapter to connect to the input BNC of the oscilloscope, then connect the multimeter probes to the adapter, and then measure.

The preferred embodiment 1 of the present invention adopts the branching linear circuit module 204, and the path through which the gain amplification signal passes is divided into a low-frequency path and a high-frequency path, and the low-frequency path adopts a high-precision low-speed ADC conversion module for sampling, so that the low-frequency path The data has the accuracy requirements of a high-precision voltmeter. And if there is no branching linear circuit module 204, only a high-speed ADC as shown in prior art Fig. 1 is used for sampling, since the number of sampling bits and the sampling rate are contradictory, in order to realize the main indicators of oscilloscope bandwidth and sampling rate, just An ADC with a high sampling number (such as 24 bits) cannot be selected, so that high-precision sampling of the signal cannot be realized. The addition of the shunt linear circuit module 204 effectively solves the contradiction between the bandwidth, sampling rate and precision of the high-speed ADC in the prior art, and can realize sampling with high bandwidth, sampling rate and high precision (only for DC and low-frequency signals) at the same time . According to the different requirements of oscilloscope and multimeter (oscilloscope is an observation instrument, the main requirements are high sampling rate and high bandwidth; multimeter is a measuring instrument, which requires high precision), divide the input signal into two parts, and realize the requirements of oscilloscope and multimeter respectively.

The high-precision multimeter realized in the preferred embodiment 1 of the present invention uses an oscilloscope to simulate the input terminal, and does not need to add an additional multimeter pen input terminal, which is further convenient to use. The high-precision voltmeter realized in the preferred embodiment 1 of the present invention does not affect the sampling rate of the oscilloscope, and the sampling rate of the oscilloscope is determined by the high-speed ADC conversion module.

In order to better realize the function of a high-precision multimeter in an oscilloscope, referring to FIG. 4, a modification of the preferred embodiment 1 of the present invention is that the control processing module 205 includes a delay adjustment module 2051, an interpolation module 2052, a step-by-step A point addition module 2053, a sampling control module 2055, a voltmeter function module 2054, and a delay adjustment module 2051 are used to delay the high-speed sampling data, compensate the delay of the low-frequency and low-speed path, and output the delayed High-speed sampling data; interpolation module 2052, carries out interpolation operation to described low-speed sampling data, makes low-speed data points equal to high-speed data points, obtains low-speed sampling data after interpolation, point-by-point addition module 2053, after described delay The high-speed sampling data and the interpolated low-speed sampling data are added point by point to generate 24-bit data, and the added 24-bit data is sent to the sampling control module 2055 to complete functions such as sampling, storage, and display of the oscilloscope, and the voltmeter function Module 2054, calculate the average value or effective value of the 24-bit data. Calculate the average value of the 24-bit data, which is the DC voltage function of the multimeter; calculate the effective value of the 24-bit data, and this is the AC voltage function of the multimeter. Since the control processing module 205 further adopts the delay adjustment module 2051, the interpolation module 2052, and the point-by-point addition module 2053, it can ensure that the data output by the point-by-point addition module 2053 is 24-bit data, thus ensuring higher multimeter accuracy .

As an example, when there is no delay between the low-speed sampling data and the high-speed sampling data, the control processing module 205 may not have the delay adjustment module 2051, and the output can also guarantee 24-bit data.

Referring to Fig. 5, it is a schematic diagram of the internal circuit of the branching linear circuit module 204 in the preferred embodiment 1 of the present invention, the branching linear circuit module 204 also includes a buffer circuit module 2046, and the buffer circuit module 2046 is connected between the coupling unit module 2042 and the high-speed ADC Between the conversion modules 2043 , it is used to enhance the high-pass gain amplified signal to drive the high-speed ADC conversion module 2043 . The coupling unit module 2042 is composed of an RC high-pass filter circuit to perform high-frequency coupling and isolate low-frequency. The cut-off frequency of the high-pass is determined by C2 and R6. The amplification circuit module 2041 subtracts the low-frequency gain amplification signal from the gain amplification signal to output a high-frequency gain amplification signal, and the frequency response curve of the high-frequency gain amplification signal is a band-pass frequency response curve, and the band-pass frequency response curve is There is a cutoff frequency in the low frequency band, and this cutoff frequency is defined as a low cutoff frequency; all frequency components of the output signal of the high frequency subtraction amplification circuit module 2041 can be coupled to the buffer circuit module 2046 . Other circuit modules of the branching linear circuit module 204 will be described in detail in the following embodiments.

As an example, if the output of the coupling unit module 2042 can drive the high-speed ADC conversion module 2043 , there may be no buffer circuit module 2046 .

Referring to FIG. 6 , the oscilloscope 300 also includes a controllable switch 301 and a programmable current source module 302 , and the control processing module 205 controls the on-off of the controllable switch 301 and the current gear selection of the programmable current source module 302 . In turn, multi-level resistance measurement and on-off test are realized. When the user selects the resistance measurement function, the control processing module 205 controls the controllable switch 301 to close, connects the programmable current source module 302 to the signal input terminal 201 of the oscilloscope, and sets the programmable current source according to different resistance measurement gear settings . When the resistance under test is connected to the signal input terminal 201 of the oscilloscope, a current I flows through the resistance under test to form a voltage. Through the high-precision voltage measurement of the oscilloscope, and then divided by the current I, the resistance value is obtained.

Since the input resistance of the oscilloscope is 1MΩ, the measurement is the parallel connection of the measured resistance and 1MΩ. Therefore, when the measured resistance <= 10kΩ, its error is very small, less than 1%. When the measured resistance is larger, the measurement error is larger. On-off measurement is actually a kind of resistance measurement. When the resistance value is close to 0Ω, it indicates a short circuit. Diode polarity measurement is also a kind of resistance measurement. When the diode is reversed, the resistance is very large. When the diode is forward-conducting, the resistance is very small, such as a silicon tube, the forward voltage drop is close to 0.7V, and the polarity of the diode can be judged by measuring the resistance and voltage.

As an example, an attenuation switching module is also connected between the oscilloscope signal input terminal 201 and the input stage buffering and adding circuit module 202. The attenuation switching module is controlled by the control processing module to select the attenuation, and can choose straight-through or attenuation output, which is mainly used for When the oscilloscope is in the high vertical sensitivity gear, the signal is attenuated first, and then input into the following circuit, otherwise the input signal amplitude is too large, which will saturate the subsequent circuit and cannot work effectively; while in the small vertical sensitivity gear of the oscilloscope, due to The signal amplitude is not large, and the attenuation network chooses straight-through to directly connect the signal to the subsequent circuit. The attenuation network is generally composed of resistors and capacitors, and has a relatively flat amplitude-frequency response within the entire bandwidth of the oscilloscope.

Referring to FIG. 7 , it is a schematic diagram of the second variant structure of the shunt linear circuit module 204 in the preferred embodiment 1 of the present invention, wherein the coupling unit module 2042 is composed of a transformer, and the transformer plays a role of high-frequency isolation here, and when the coupling unit module 2042 When a transformer is used, a first digital isolator 2047 is connected between the low-speed ADC module 2045 and the control processing module 205, where the first digital isolator plays the role of low-frequency isolation. The coupling unit module 2042 in the branch linear circuit module 204 is composed of a transformer, and a first digital isolator 2047 is added at the same time, which can realize an isolated oscilloscope with a voltmeter function.

In this variant structure embodiment, the circuit forms of the low-frequency amplifier circuit module 2044 can have the following four forms:

As shown in Figure 8(A), form 1 follows the circuit, and the circuit bandwidth is determined by the amplifier itself.

As shown in Figure 8(B), Form 2 is a low-pass follower circuit, and the circuit bandwidth is determined by R1, C1 and the amplifier bandwidth.

As shown in Figure 8(C), form 3, RC low-pass first, and then the amplifier follows, the circuit bandwidth is determined by R, C and the amplifier bandwidth.

As shown in Figure 8(D), Form 4 is an active second-order low-pass amplifier. The circuit bandwidth is determined by R1, C1, R2, C2 and the amplifier bandwidth.

Of course, the low-frequency amplifying circuit module 2044 may also adopt a multi-stage amplifier or cascaded low-pass filter, or other known active low-pass filter circuit forms, which does not affect the inventiveness of the present invention.

The amplifier U1 in the low-frequency amplifier circuit module 2044 is preferably a low-bandwidth high-precision amplifier. The amplifier U1 can use any high-precision amplifier to meet the requirements for low-frequency sampling accuracy. Of course, precision, low noise, low distortion, and low bias current can also be selected. , Low temperature drift, these better amplifiers can help realize the technical effect of low frequency and high precision. For example, choose AD823 and AD8639 of ADI Company.

The circuit form of the high-frequency subtraction and amplification circuit module 2041 is a proportional operation circuit, because the gain of the low-frequency path is 1, so R2=R3=R4=R5, and the gain of the high-frequency path is also 1. Assuming that the signal input is Vin and the output of the low-frequency amplifying circuit module is Vlf, then U2 outputs Uhf=Vin-Vlf.

The amplifier U2 in the high-frequency subtractive amplification circuit module 2041 can be any high-speed amplifier, as long as it can meet the maximum bandwidth and maximum voltage amplitude required by the design. Of course, choosing a larger bandwidth, low noise, and low distortion amplifier can help realize the design bandwidth requirements. For example, AD8038 and AD8012 of ADI Company.

The low-speed ADC module 2045 in this modified structure embodiment adopts a Σ-ΔADC (also known as a Delta-Sigma modulation analog-to-digital converter), and the optimal solution is to use a 24bit ADC, which can achieve higher measurement accuracy, such as ADI's AD7763 is a Σ-Δ ADC with 24bit, 625kHz sampling rate and 109dB dynamic range. The AD7763 output is an SPI interface, which requires 3-way digital isolation to isolate the sampled digital signal.

As an example, when the coupling unit module 2042 uses an RC high-pass filter circuit, the output of the AD77763 does not need a digital isolator for isolation.

The suboptimal solution of the low-speed ADC module 2045 and the digital isolator in this embodiment of the modified structure is to use the analog-to-digital converter AD7401A with isolation of ADI Company. It is an isolated 16-bit sigma-delta modulator capable of 5000Vrms isolation for 1 minute. It converts the input into a high-speed 1-bit data stream, and then through the internal transformer isolation, input a 20MHz frequency clock MCLKIN, as the sampling clock of the modulator, and output 1-bit data MDAT. In this way, only one device is needed to realize the functions of the Σ-Δ ADC and the digital isolator, and the circuit structure is simple.

Of course, to use the AD7401A, you need to connect the low-frequency path signal to its input, VIN+, and the ground of the measurement channel to VIN-.

The coupling unit module 2042 in this modified structure embodiment adopts a transformer. In order to realize the bandwidth required by the design, the maximum operating frequency of the transformer needs to be greater than the bandwidth required by the design, and the minimum operating frequency of the transformer needs to be extended to less than 10kHz, extending the minimum operating frequency To less than 10kHz, in order to have a certain overlap with the operating frequency of the low-frequency path, so that the sum of the output of the low-frequency and high-frequency paths can reflect the input signal. Moreover, the withstand voltage between the primary and secondary stages must meet design expectations. In this embodiment, the transformer winding method adopts the transmission line transformer method, which can achieve better frequency response. Other forms of transformers are also available, but the frequency response is slightly worse.

The best choice for the transformer core is a soft ferrite ring with high magnetic permeability, such as the R10K series of Beijing Qixing Flying Electronics Co., Ltd., such as R10K-H13x7x5. For example, the A10 series of Yuefeng Electronic Materials Co., Ltd., such as A10-T12x6x4.

The wire adopts three-layer insulated wire, which can achieve very high withstand voltage, such as the TEX-E three-layer insulated wire of Furukawa Electronics Co., Ltd., with a wire diameter of Ф0.20mm. For example, the TIW-B direct soldering type three-layer insulated wire of Shunzheng Electronics Co., Ltd. has a wire diameter of Ф0.20mm.

The transmission line transformer in the embodiment of the modified structure can realize a working frequency of 1 kHz at the lowest and 200 MHz at the highest, and the fluctuation of the amplitude-frequency response within the frequency band is very small.

R6 in the buffer circuit module 2046 in this variant structure embodiment is a load resistor on the secondary side of the transformer, and is used to adjust the amplitude-frequency response of the transformer. The selected value is 1.2kΩ. The amplifier U3 is a fully differential operational amplifier to meet the differential input requirements of the second analog-to-digital converter. The LMH6554 of TI is selected, and the input and feedback resistors R7=R8=R9=R10=300Ω.

As an example, the buffer circuit module 2046 may not be used in this variant structure embodiment.

The ADC conversion module 2043 in this variant structure embodiment can select any ADC that meets the design sampling rate requirement. For example, choose TI's 8-bit 1Gsa/s ADC, model ADC08D1000. For example, choose the 8-bit 1Gsa/s ADC of E2V Company, model AT84AD001B.

Referring to FIG. 9 , it is a schematic diagram of the third modified structure of the shunt linear circuit module 204 in the preferred embodiment 1 of the present invention. The difference between the third modified structure shown in FIG. 9 and the second modified structure shown in FIG. 7 is that the transformer The driving and receiving of T1 adopt differential mode. The amplifier of the high-frequency subtraction amplifier circuit module 2041 is a fully differential amplifier, and the output of the amplifier is a differential signal, which is connected to both ends of the primary side of the transformer T1 for driving the transformer. The gain amplification signal and the low frequency gain amplification signal are connected to two input ends of the differential amplification circuit to form a subtraction circuit. Resistance value R2=R3=R4=R5=300Ω.

Referring to FIG. 10 , it is a schematic diagram of a fourth variant structure of the shunt linear circuit module 204 in the preferred embodiment 1 of the present invention. This variant structure embodiment provides a shunt linear circuit for differential signal input. The signal input is a differential signal, and the low-frequency amplifying circuit module 2044 also adopts a fully differential amplifying circuit, and its bandwidth can be selected according to the requirements of the low-frequency path, or an additional low-pass filter circuit can be added to ensure that the bandwidth of the low-frequency path meets the requirements of the low-speed ADC conversion module 2045 signal input requirements. Such as ADI's fully differential amplifier AD8476. Referring to FIG. 11 , the low frequency amplifying circuit module 2044 can also use two single-ended amplifiers to respectively amplify the P and N terminals of the differential input signal at low frequency, and the selection of the amplifiers is the same as above. The difference between the high-frequency subtraction amplifier circuit module 2041 and the third deformation structure shown in Figure 9 is that the fully differential amplifier constitutes a proportional operation circuit, and the resistors R1, R2, R3, R4, R5, and R6 are selected to be equal, all of which are 300Ω . In this way, the output of U1 is the subtraction of the input signal and the output of the low-frequency amplifier circuit.

Referring to Fig. 12, in the oscilloscope 400, since a transformer and a digital isolator are used in the shunt linear circuit module 204 (the specific circuit can be combined with reference to Fig. 7, Fig. 9 and Fig. 10), the programmable amplifier module 203 and the control processing module A second digital isolator is connected between 205 , and a third digital isolator 402 is connected between the D/A conversion module 206 and the control processing module 205 . A controllable switch 301, a programmable current source module 302 and a fourth digital isolator 403 are sequentially connected between the signal input terminal 201 and the control processing module 205, and the control processing module 205 is respectively controlled by the fourth digital isolator 403 The on-off of the controllable switch 301 and the current gear selection of the programmable current source module 302 . In turn, multi-level resistance measurement and on-off test are realized. When the user selects the resistance measurement function, the control processing module 205 controls the controllable switch 301 to close, connects the programmable current source module 302 to the signal input terminal 201 of the oscilloscope, and sets the programmable current source according to different resistance measurement gear settings . When the resistance under test is connected to the signal input terminal 201 of the oscilloscope, the circuit I flows through the resistance under test to form a voltage. Through the high-precision voltage measurement of the oscilloscope, and then divided by the current I, the resistance value is obtained. Since the input resistance of the oscilloscope is 1MΩ, the measurement is the parallel connection of the measured resistance and 1MΩ. Therefore, when the measured resistance <= 10kΩ, its error is very small, less than 1%. When the measured resistance is larger, the measurement error is larger.

On-off measurement is actually a kind of resistance measurement. When the resistance value is close to 0Ω, it indicates a short circuit. Diode polarity measurement is also a kind of resistance measurement. When the diode is reversed, the resistance is very large. When the diode is forward-conducting, the resistance is very small, such as a silicon tube, the forward voltage drop is close to 0.7V, and the polarity of the diode can be judged by measuring the resistance and voltage.

An attenuation switching module is also connected between the oscilloscope signal input terminal 201 and the input stage buffering and adding circuit module 202. The attenuation switching module is controlled by the control processing module. The attenuation selection can be selected through or attenuation output. It is mainly used for the oscilloscope at high vertical sensitivity. In the gear position, the signal is attenuated first, and then input into the following circuit, otherwise the input signal amplitude is too large, which will saturate the subsequent circuit and cannot work effectively; while in the small vertical sensitivity gear of the oscilloscope, because the signal amplitude is not large, The attenuation network selects thru, connecting the signal directly to subsequent circuitry. The attenuation network is generally composed of resistors and capacitors, and has a relatively flat amplitude-frequency response within the entire bandwidth of the oscilloscope.

As an example, in this embodiment, the attenuation switching module 404 may not be connected, and the multimeter's high-precision voltage measurement function, resistance measurement function, and open-circuit measurement function can still be realized on the oscilloscope, and the oscilloscope also has an isolation function. The isolation function is to transfer the electrical signal from the input side of the oscilloscope to the output side, but the input side and the output side are electrically isolated, which increases the safety of the oscilloscope.

As an example, in this embodiment, the controllable switch 301, the programmable current source module 302 and the fourth digital isolator 403 may not be connected, and the high-precision voltage measurement function of the multimeter can still be realized on the oscilloscope, and the oscilloscope also has the isolation Function.

As an example, the control processing module in this embodiment is realized by FPGA.

The above are only preferred embodiments of the present invention, and it should be understood that the descriptions of the above preferred embodiments are only used to help understand the method and core idea of the present invention, and are not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, etc. made within the idea and principle of the present invention shall be included in the protection scope of the present invention.

Claims (9)

1. a kind of oscillograph with function of multimeter, including a signal input part, an input stage buffering and add circuit Module, a programmable amplifier module, a D/A modular converter, a control process module；The signal input part is used for Receive an external input signal；

The control process module, for controlling the D/A modular converters to export a bias direct current signal to the input stage Buffering and add circuit module；

The input stage buffering and add circuit module, for the input signal and the bias direct current signal to be carried out into addition After computing, a buffering signals are exported；

The control process module, it is additionally operable to control the programmable amplifier module to put buffering signals progress gain Greatly, a gain amplified signal is exported；

Characterized in that, also including a split-path linear circuit module, the split-path linear circuit module subtracts including a high frequency Method amplification circuit module, a coupling unit module, a high-speed ADC modular converter, a low-frequency amplifier circuit module and height Precision low speed ADC modular converters；

The low-frequency amplifier circuit module, for being filtered to the gain amplified signal, export a low-frequency gain amplification Signal；

The high frequency subtraction amplification circuit module, it is defeated for the gain amplified signal to be subtracted into the low-frequency gain amplified signal Go out a high-frequency gain amplified signal；

The coupling unit module, for carrying out high-pass filtering to the high-frequency gain amplified signal, export a high pass gain Amplified signal；

The high-speed ADC modular converter, for being sampled to the high pass gain amplified signal, and the high speed after sampling is adopted Sample data input control process module；

The low speed ADC modular converters, for being sampled to the low-frequency gain amplified signal, and the low speed after sampling is adopted Sample data input control process module；

The control process module, it is additionally operable to the high-speed sample data and the low speed sampled data being summed into n-bit data, N is more than 8 and is less than or equal to 24, and n-bit data is carried out into mean value calculation or virtual value calculating, and result of calculation is shown.

2. oscillograph according to claim 1, it is characterised in that the control process module includes a delay adjustment mould Block, an interpolating module, point-by-point summation module, a sampling control module, a function of voltmeter module, the delay Adjustment module, for entering line delay, the high-speed sample data after output delay to the high-speed sample data；The interpolation mould Block, for carrying out interpolation arithmetic to the low speed sampled data, obtain the low speed sampled data after interpolation, the point-by-point addition mould Block, for the high-speed sample data after the delay to be added with the low speed sampled data after the interpolation, 24 data are generated, The sampling control module is used to control the sampling of oscillograph, data after sampling is stored, shown, the function of voltmeter Module, for 24 data to be carried out into mean value calculation or virtual value calculating, and result of calculation is shown.

3. oscillograph according to claim 1, it is characterised in that the coupling unit module uses RC high-pass filtering circuits Form.

4. according to the oscillograph described in claim 1,2 or 3, it is characterised in that at the signal input part and the control Also be linked in sequence a gate-controlled switch and a programmable current source module between reason module, and the control process module is additionally operable to The break-make of the gate-controlled switch and the electric current gear selection of programmable current source module are controlled respectively.

5. oscillograph according to claim 1 or 2, it is characterised in that the coupling unit module is formed using transformer, And when the coupling unit module uses transformer, between the low speed ADC modular converters and the control process module First digital isolator is connected, one the is connected between the programmable amplifier module and the control process module Two digital isolators, the 3rd digital isolator is connected between the D/A modular converters and the control process module.

6. oscillograph according to claim 5, it is characterised in that in the signal input part and the control process module Between be also linked in sequence a gate-controlled switch and a programmable current source module and the 4th digital isolator, the control Processing module is additionally operable to control the break-make and programmable current source of the gate-controlled switch respectively by the 4th digital isolator The electric current gear selection of module.

7. oscillograph according to claim 1 or 2, it is characterised in that the split-path linear circuit module also includes one Buffer circuit module, the buffer circuit module are connected between the coupling unit module and the high-speed ADC modular converter, For strengthening the high pass gain amplified signal, to drive the high-speed ADC modular converter.

8. oscillograph according to claim 4, it is characterised in that the split-path linear circuit module also includes a buffering Circuit module, the buffer circuit module are connected between the coupling unit module and the high-speed ADC modular converter, are used for Strengthen the high pass gain amplified signal, to drive the high-speed ADC modular converter.

9. oscillograph according to claim 6, it is characterised in that the split-path linear circuit module also includes a buffering Circuit module, the buffer circuit module are connected between the coupling unit module and the high-speed ADC modular converter, are used for Strengthen the high pass gain amplified signal, to drive the high-speed ADC modular converter.