CN212111556U - Analog channel circuit of digital oscilloscope and digital oscilloscope - Google Patents
Analog channel circuit of digital oscilloscope and digital oscilloscope Download PDFInfo
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- CN212111556U CN212111556U CN202020565320.2U CN202020565320U CN212111556U CN 212111556 U CN212111556 U CN 212111556U CN 202020565320 U CN202020565320 U CN 202020565320U CN 212111556 U CN212111556 U CN 212111556U
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Abstract
The utility model provides a digital oscilloscope's analog channel circuit and digital oscilloscope, first attenuation module including parallel connection, second attenuation module and third attenuation module, through first change over switch to first attenuation module, the tertiary decay of measured signal is realized to second attenuation module and third attenuation module selectivity output, the quantity of relay switch has been reduced, digital oscilloscope's inner space has been saved, and first attenuation module, second attenuation module and third attenuation module have all increased the protection impedance module, the voltage signal of measurable quantity hundred volt range, and can ensure operating personnel, the machine does not take place to electrocute, high temperature, danger such as catch fire, accord with digital oscilloscope's ann rule requirement.
Description
Technical Field
The utility model relates to a digital oscilloscope technical field, concretely relates to digital oscilloscope's analog channel circuit and digital oscilloscope.
Background
The digital oscilloscope is an indispensable tool for designing, manufacturing and maintaining electronic equipment, and can be applied to various strong and weak current measurement environments. For example, in a strong current measurement environment of hundreds of volts including CATII or above, besides the requirement that the analog channel of the digital oscilloscope is safely isolated from the ground, the requirement that the interior of the channel meets the requirement of basic insulation on a measured signal is also required, so that the dangers of electric shock, high temperature, fire and the like of operating personnel and machines are ensured not to occur, namely the safety regulations of the digital oscilloscope are met; in addition, the digital oscilloscope can also work in a weak current measurement environment to measure weak signals to be measured in millivolt level.
For the tested signals with different voltage amplitudes, an analog channel circuit of the existing digital oscilloscope attenuates the tested signals with different voltage amplitudes in a multi-stage series attenuation mode. Fig. 6 is a block diagram of an analog channel circuit of a conventional digital oscilloscope, in which a measured signal passes through two serially connected relay switches to select different attenuation resistor modules, for example, when the amplitude of the measured signal is small, both the relay switch 1 and the relay switch 2 are switched to a straight-through branch without attenuation resistors, and at this time, the amplitude of the measured signal is directly output to a voltage clamping module without attenuation; when the amplitude of the measured signal is large, the relay switch 1 is switched to the straight-through branch, the relay switch 2 is switched to the attenuation resistance module 2, and the amplitude of the measured signal is attenuated through the attenuation resistance module 2; when the amplitude of the measured signal is large, the relay switch 1 and the relay switch 2 are switched to the attenuation resistance module, and the amplitude of the measured signal is greatly attenuated through the attenuation resistance module 1 and the attenuation resistance module 2 which are connected in series, so that the amplitude of the measured signal after being attenuated can be within a safety range.
However, since the voltage withstanding capability of the relay switch is generally proportional to the volume, the higher the voltage withstanding capability is, the larger the volume is, and two relay switches exist in the existing analog channel circuit, which occupies the space of the analog channel in the larger digital oscilloscope, and the through branch does not have any protective impedance. Therefore, the existing analog channel circuit can not measure large voltage signals with the amplitude of hundreds of volts and does not meet the safety regulation requirement of a digital oscilloscope.
Disclosure of Invention
The utility model discloses the technical problem who mainly solves how to provide a digital oscilloscope simulation channel circuit who not only saves space but also accords with the ann rule requirement.
According to a first aspect, an embodiment provides an analog channel circuit of a digital oscilloscope, including a coupling module, a first attenuation module, a second attenuation module, a third attenuation module, a first switch, an impedance transformation module, and an amplitude adjustment module;
the coupling module is used for carrying out alternating current coupling or direct current coupling on a detected signal;
the input end of the first attenuation module, the input end of the second attenuation module and the input end of the third attenuation module are respectively connected with the output end of the coupling module;
the first attenuation module is used for carrying out primary attenuation on the amplitude of the output signal of the coupling module;
the second attenuation module is used for carrying out secondary attenuation on the amplitude of the output signal of the coupling module;
the third attenuation module is used for carrying out three-level attenuation on the amplitude of the output signal of the coupling module;
the first end of the first switch is switched among the output end of the first attenuation module, the output end of the second attenuation module and the output end of the third attenuation module, the second end of the first switch is connected with the input end of the impedance conversion module, and the first switch is used for selecting one of the signals output by the first attenuation module, the second attenuation module and the third attenuation module and outputting the selected signal to the impedance conversion module;
the impedance transformation module is used for carrying out impedance transformation on the attenuation signal;
the input end of the amplitude adjusting module is connected with the output end of the impedance conversion module and is used for adjusting the amplitude of the signal output by the impedance conversion module to be within a preset range.
Furthermore, the attenuation multiple of the amplitude of the output signal of the coupling module by the first attenuation module is smaller than the attenuation multiple of the amplitude of the output signal of the coupling module by the second attenuation module, and the attenuation multiple of the amplitude of the output signal of the coupling module by the second attenuation module is smaller than the attenuation multiple of the amplitude of the output signal of the coupling module by the third attenuation module.
The first end of the second change-over switch is connected with the output end of the coupling module, the second end of the second change-over switch is switched between the first output end and the second output end, and the second change-over switch is used for connecting the output end of the coupling module with one of the first output end and the second output end;
the first output end is connected with the input end of the first attenuation module and the input end of the second attenuation module;
the second output end is connected with the input end of the third attenuation module.
Further, when the amplitude of the detected signal is smaller than a first preset threshold, the first end of the first switch is connected with the output end of the first attenuation module, when the amplitude of the detected signal is greater than or equal to the first preset threshold and smaller than a second preset threshold, the first end of the first switch is connected with the output end of the second attenuation module, when the amplitude of the detected signal is greater than or equal to the second preset threshold, the first end of the first switch is connected with the output end of the third attenuation module, wherein the first preset threshold is smaller than the second preset threshold;
when the amplitude of the detected signal is smaller than a second preset threshold value, a second end of the second change-over switch is connected with the first output end; when the measured amplitude is larger than or equal to a second preset threshold value, a second end of the second change-over switch is connected with a second output end;
the first change-over switch is an analog input switch, and the second change-over switch is a relay switch.
Furthermore, the first attenuation module, the second attenuation module and the third attenuation module respectively comprise a protection impedance module and a first frequency compensation module, the input end of the protection impedance module is connected with the output end of the coupling module and is used for limiting the current of the signal output by the coupling module, and the output end of the protection impedance module is connected with the input end of the impedance transformation module; the first frequency compensation module is connected in parallel at two ends of the protection impedance module and is used for performing primary compensation on the bandwidth of the loss of the output signal of the coupling module.
Furthermore, the second attenuation module and the third attenuation module further comprise a divider resistor and a second frequency compensation module, wherein the input end of the divider resistor is connected with the output end of the protection impedance module, and the output end of the divider resistor is connected with the ground; the second frequency compensation module is connected in parallel at two ends of the divider resistor;
the voltage dividing resistor is used for dividing the voltage of the output signal of the coupling module; and the second frequency compensation module is used for carrying out secondary compensation on the bandwidth of the loss of the output signal of the coupling module.
Further, the protection impedance module comprises one or more protection resistors connected in series, and the first frequency compensation module comprises at least one compensation capacitor connected in parallel at two ends of the protection resistor.
Furthermore, the protection impedance module comprises a first protection resistor, a second protection resistor and a third protection resistor, wherein one end of the first protection resistor is connected with the first output end, the other end of the first protection resistor is connected with one end of the second protection resistor, the other end of the second protection resistor is connected with one end of the third protection resistor, and the other end of the third protection resistor is connected with the output end of the protection impedance module;
the first frequency compensation module comprises a first compensation capacitor, a second compensation capacitor and a third compensation capacitor, wherein the first compensation capacitor is connected in parallel at two ends of a first protection resistor, the second compensation capacitor is connected in parallel at two ends of a second protection resistor, and the third compensation capacitor is connected in parallel at two ends of a third protection resistor;
the second frequency compensation module comprises a fourth compensation capacitor, a fifth compensation capacitor and a sixth compensation capacitor, one end of the fourth compensation capacitor is connected with the output end of the protection impedance module, the other end of the fourth compensation capacitor is connected with one end of the fifth compensation capacitor, the other end of the fifth compensation capacitor is connected with the ground, and the sixth compensation capacitor is connected at two ends of the fifth compensation capacitor in parallel.
The voltage clamping device further comprises a first voltage clamping module, a second voltage clamping module and a third voltage clamping module;
the input end of the first voltage clamping module is connected with the output end of the first attenuation module and is used for clamping the voltage of the first-level attenuation signal within a first preset voltage range;
the input end of the second voltage clamping module is connected with the output end of the second attenuation module and is used for clamping the voltage of the secondary attenuation signal within a second preset voltage range;
and the input end of the third voltage clamping module is connected with the output end of the third attenuation module and is used for clamping the voltage of the three-level attenuation signal within a third preset voltage range.
According to a second aspect, an embodiment provides a digital oscilloscope, including an analog channel circuit, an analog-to-digital sampling circuit, a processor and a display screen, where the analog channel circuit is the analog channel circuit described in the above embodiment;
the input end of the analog-digital sampling circuit is connected with the output end of the analog channel circuit and is used for sampling an output signal of the analog channel circuit;
the input end of the processor is connected with the output end of the analog-digital sampling circuit and used for carrying out data processing on the sampling signal;
the display screen is connected with the output end of the processor and used for displaying the processed signals.
According to the analog channel circuit of the digital oscilloscope and the digital oscilloscope, the first attenuation module, the second attenuation module and the third attenuation module are connected in parallel, the first switch is used for selectively outputting the first attenuation module, the second attenuation module and the third attenuation module to realize three-level attenuation of a measured signal, the number of relay switches is reduced, the space of an analog channel in the digital oscilloscope is saved, the protection impedance module is additionally arranged on the first attenuation module, the second attenuation module and the third attenuation module, voltage signals with hundreds of volts of amplitude can be measured, the dangers of electric shock, high temperature, fire and the like of an operator and a machine can be avoided, and the safety regulation requirement of the digital oscilloscope is met.
Drawings
FIG. 1 is a schematic diagram of a digital oscilloscope according to an embodiment;
FIG. 2 is a schematic diagram of an embodiment of an analog channel circuit;
FIG. 3 is a schematic diagram of an analog channel circuit according to another embodiment;
FIG. 4 is a circuit diagram of a first attenuation module of an embodiment;
FIG. 5 is a circuit diagram of a second attenuation block or a third attenuation block of an embodiment;
fig. 6 is a block diagram of an analog channel circuit of a conventional digital oscilloscope.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings. Wherein like elements in different embodiments are numbered with like associated elements. In the following description, numerous details are set forth in order to provide a better understanding of the present application. However, those skilled in the art will readily recognize that some of the features may be omitted or replaced with other elements, materials, methods in different instances. In some instances, certain operations related to the present application have not been shown or described in detail in order to avoid obscuring the core of the present application from excessive description, and it is not necessary for those skilled in the art to describe these operations in detail, so that they may be fully understood from the description in the specification and the general knowledge in the art.
Furthermore, the features, operations, or characteristics described in the specification may be combined in any suitable manner to form various embodiments. Also, the various steps or actions in the method descriptions may be transposed or transposed in order, as will be apparent to one of ordinary skill in the art. Thus, the various sequences in the specification and drawings are for the purpose of describing certain embodiments only and are not intended to imply a required sequence unless otherwise indicated where such sequence must be followed.
The numbering of the components as such, e.g., "first", "second", etc., is used herein only to distinguish the objects as described, and does not have any sequential or technical meaning. The term "connected" and "coupled" when used in this application, unless otherwise indicated, includes both direct and indirect connections (couplings).
Referring to fig. 1, fig. 1 is a schematic structural diagram of a digital oscilloscope according to an embodiment, where the digital oscilloscope includes a signal input terminal 10, an analog channel circuit 20, an analog-to-digital sampling circuit 30, a processor 40, and a display screen 50, where the signal input terminal 10 is connected to a circuit to be tested and used for inputting a signal to be tested, the signal input terminal 10 is connected to an input terminal of the analog channel circuit 20, the analog channel circuit 20 is used for performing impedance conversion, amplitude adjustment, and other processing on the signal to be tested, an input terminal of the analog-to-digital sampling circuit 30 is connected to an output terminal of the analog channel circuit 20 and used for sampling an output signal of the analog channel circuit 20, an input terminal of the processor 40 is connected to an output terminal of the analog-to-digital sampling circuit 30 and used for performing data processing on the sampled signal, and the display screen 50 is connected to an. Since the analog-to-digital sampling circuit 30 can only sample the signal to be tested within a preset range, the amplitude of the signal to be tested input by the signal input terminal 10 needs to be adjusted.
In this embodiment, please refer to fig. 2, fig. 2 is a schematic structural diagram of an analog channel circuit of an embodiment, and the analog channel circuit 20 includes a coupling module 201, a first attenuation module 203, a second attenuation module 204, a third attenuation module 205, a first switch 209, an impedance transformation module 210, and an amplitude adjustment module 211.
The coupling module 201 is configured to perform ac coupling or dc coupling on a signal to be measured input by the signal input terminal 10, where the coupling module 201 in this embodiment is one of an ac coupling module and a dc coupling module, when the signal to be measured is an ac signal, the coupling module 201 is an ac coupling module, such as a coupling capacitor, and when the signal to be measured is a dc signal, the coupling module 201 is a dc coupling module, such as a coupling inductor.
The input end of the first attenuation module 203, the input end of the second attenuation module 204 and the input end of the third attenuation module 205 are respectively connected with the output end of the coupling module 201, the first attenuation module 203 is used for performing first-level attenuation on the amplitude of the output signal of the coupling module, the second attenuation module 204 is used for performing second-level attenuation on the amplitude of the output signal of the coupling module, and the third attenuation module 205 is used for performing third-level attenuation on the amplitude of the output signal of the coupling module, wherein the attenuation multiple of the amplitude of the output signal of the coupling module by the first attenuation module 203 is smaller than that of the amplitude of the output signal of the coupling module by the second attenuation module 204, the attenuation multiple of the amplitude of the output signal of the coupling module by the second attenuation module 204 is smaller than that of the amplitude of the output signal of the coupling module by the third attenuation module 205, in other words, the degrees of the amplitude attenuation of the first-level attenuation, the second-level attenuation, the degree of attenuation of the first-level attenuation to the signal amplitude is smaller than that of the second-level attenuation, and the degree of attenuation of the second-level attenuation to the signal amplitude is smaller than that of the third-level attenuation. In this embodiment, the amplitude of the signal is the voltage amplitude of the signal, and after attenuation, the voltage amplitude of the signal is correspondingly reduced.
A first end of the first switch 209 is switched among the output end of the first attenuation module 203, the output end of the second attenuation module 204, and the output end of the third attenuation module 205, a second end of the first switch 209 is connected to the input end of the impedance transformation module 210, and the first switch 209 is configured to select one of the signals output by the first attenuation module 203, the second attenuation module 204, and the third attenuation module 205 and output the selected signal to the impedance transformation module 210. According to the amplitude of the output signal of the measured signal after being coupled by the coupling module 201, selecting a corresponding attenuation module to attenuate the amplitude of the signal, for example, when the amplitude of the output signal of the coupling module 201 is small, the amplitude of the signal does not need to be attenuated or only needs to be attenuated in a micro range, and connecting the output end of the first attenuation module 203 with the impedance conversion module 210 through the first switch 209; when the amplitude of the signal output by the coupling module 201 is large, the amplitude of the signal needs to be attenuated to a large extent, and a large attenuation multiple is needed, and the output end of the second attenuation module 204 is connected with the impedance transformation module 210 through the first switch 209; when the amplitude of the signal output by the coupling module 201 is very large, the amplitude of the signal needs to be attenuated to a great extent at this time, and a great attenuation multiple is needed, the output end of the third attenuation module 205 is connected with the impedance transformation module 210 through the first switch 209, and the first attenuation module 203, the second attenuation module 204 and the third attenuation module 205 can be connected in parallel through the switching of the first switch 209, and different attenuation modules are selectively connected according to the amplitude of the signal to be measured, so that the measurement from a tiny amplitude signal to a hundreds of volt amplitude signal is realized.
The impedance transformation module 210 is configured to perform impedance transformation on the attenuated signal, and since the attenuated signal input to the impedance transformation module has a large impedance after the amplitude of the signal is attenuated by the attenuation module, in order to make the digital oscilloscope have good frequency characteristics, the attenuated signal of the large impedance needs to be transformed into an attenuated signal of a small impedance by the impedance transformation module 210. The impedance transformation module 210 in this embodiment may use an existing impedance transformation circuit of a digital oscilloscope, such as JEFET amplification or high frequency operational amplifier.
The input end of the amplitude adjusting module 211 is connected to the output end of the impedance transforming module 210, and is configured to adjust the amplitude of the signal output by the impedance transforming module 210 to a preset range. After the signal amplitude is attenuated by the first attenuation module 203, the second attenuation module 204, and the third attenuation module 205, the signal amplitude is already adjusted within a smaller amplitude range, and the amplitude adjustment module 211 precisely adjusts the amplitude of the signal output by the impedance transformation module 210 according to the requirement of the analog-to-digital sampling circuit 30 on the signal amplitude, adjusts the signal amplitude to a preset range, and outputs the signal amplitude to the analog-to-digital sampling circuit 30 for sampling.
The amplitude adjustment module 211 in this embodiment may be a variable gain amplifier circuit.
In this embodiment, an operator controls the first switch according to the amplitude of the measured signal displayed on the display screen of the oscilloscope, and when the amplitude of the measured signal is smaller than a first preset threshold value, that is, when the amplitude of the signal is smaller, attenuation is not required or only needs to be performed slightly at this time, the operator controls the first end of the first switch 209 to be connected to the output end of the first attenuation module 203; when the amplitude of the detected signal is greater than or equal to the first preset threshold and smaller than the second preset threshold, that is, when the amplitude of the signal is large, the amplitude of the signal needs to be attenuated to a large extent, and an operator controls the first end of the first switch 209 to be connected with the output end of the second attenuation module 204; when the amplitude of the detected signal is greater than or equal to the second preset threshold value, namely the signal amplitude is very large, the signal amplitude needs to be attenuated to a very large degree at the moment, an operator controls the first end of the first switch to be connected with the output end of the third attenuation module, and the first preset threshold value is smaller than the second preset threshold value. The first switch 209 in this embodiment may be an analog input switch of one out of three, such as a TMUX6104 analog input switch of TI, which has a maximum power supply of ± 16.5V and a bandwidth of 400 MHz.
The control module in this embodiment may be a voltage-controlled transistor switch circuit, and the coupling module outputs different voltage amplitudes to turn on or off the transistor switch circuit, so as to control the switching of the first switch 209 and the second switch 202.
In order to further adjust the voltage amplitude of the signal input to the impedance transformation module 210, the present embodiment further includes a first voltage clamping module 206, a second voltage clamping module 207, and a third voltage clamping module 208. The input end of the first voltage clamp module 206 is connected to the output end of the first attenuation module 203, and is configured to clamp the voltage of the first-level attenuation signal within a first preset voltage range; the input end of the second voltage clamp module 207 is connected to the output end of the second attenuation module 204, and is configured to clamp the voltage of the second-level attenuation signal within a second preset voltage range; the input of the third voltage clamp block 208 is coupled to the output of the third attenuation block 205 for clamping the voltage of the three level attenuated signal within a third predetermined voltage range, such that the voltage of the attenuated signal is clamped within a specific voltage range. As shown in fig. 5, when the voltage at the input end of the voltage clamping module is greater than 10.7V, the diode D1 is turned on, the diode D2 is turned off, the voltage at the output end of the voltage clamping module is fixed at 10.7V (10+0.7V), and 0.7V is the forward conduction voltage drop of the silicon diode; when the voltage at the input end of the voltage clamping module is less than-10.7V, the diode D1 is cut off, because the voltage at the input end of the diode D2 is 0.7V higher than the voltage at the output end, the diode D2 is turned on, and the voltage at the output end of the voltage clamping module is fixed at-10.7V, so that the voltage at the output end of the first voltage clamping module, the second voltage clamping module and the third voltage clamping module can be limited to be between-10.7V and 10.7V.
Referring to fig. 3, in order to prevent the current of the signal output by the coupling module 201 from being too large, the first attenuation module 203, the second attenuation module 204, and the third attenuation module 205 in this embodiment each include a protection impedance module, an input terminal of the protection impedance module is connected to an output terminal of the coupling module 201 for limiting the current of the signal output by the coupling module 201, an output terminal of the protection impedance module is connected to an input terminal of the impedance transformation module 210, wherein the protection impedance module includes one or more protection resistors connected in series, and parasitic inductance and capacitance exist due to the protection resistor not being an ideal resistor, and the parasitic inductance and capacitance decrease the bandwidth of the whole path, that is, when the ac signal passes through the protection resistor, the bandwidth of the ac signal is attenuated due to the influence of the parasitic inductance and capacitance, and the attenuation becomes more and more significant as the frequency of the ac signal increases, therefore, another path needs to be provided to enable the alternating current signal to pass through, that is, the bandwidth of the output signal of the coupling module is compensated, the first attenuation module 203, the second attenuation module 204, and the third attenuation module 205 further include a first frequency compensation module, the first frequency compensation module is connected in parallel to two ends of the protection impedance module and is used for performing primary compensation on the bandwidth lost by the output signal of the coupling module 201, in this embodiment, the first frequency compensation module includes at least one compensation capacitor, and the compensation capacitor is connected in parallel to two ends of the protection resistor. The protection impedance module in this embodiment may be formed by connecting a plurality of hundreds of K-ohm non-pin resistors (MELFs) in series, and may well absorb voltage pulses in a signal to be measured, and may also use a mega-ohm resistor to ensure that a circuit module in an analog channel circuit does not cause a large current even if a fault occurs. In this embodiment, the input end of each protection impedance module is the input end of each corresponding attenuation module, and the output end of each protection impedance module is the output end of each corresponding attenuation module.
After the signal output by the coupling module 201 is limited by the protection resistor and the bandwidth compensation is performed by the compensation capacitor, the first attenuation module 203 can directly output the signal to the impedance transformation module 210, the second attenuation module 204 and the third attenuation module 205 also need to attenuate the signal amplitude, the second attenuation module 204 and the third attenuation module 205 also include a voltage dividing resistor, the input end of the voltage dividing resistor is connected with the output end of the protection impedance module, the output end of the voltage dividing resistor is connected with the ground, the voltage dividing resistor is used for dividing the voltage of the signal output by the coupling module 201, the voltage dividing resistor divides the voltage of the signal, the voltage amplitude of the signal output by the second attenuation module 204 and the third attenuation module 205 is the voltage amplitude on the voltage dividing resistor, the attenuation multiple of the second attenuation module 204 and the third attenuation module 205 to the amplitude of the coupling module output signal is a ratio of the voltage amplitude of the coupling module output signal to the voltage amplitude of the voltage dividing resistor at both ends.
Similarly, for the ac signal, the voltage dividing resistor also has parasitic inductance and capacitance, and bandwidth compensation needs to be performed on the signal, so the second attenuation module 204 and the third attenuation module 205 further include a second frequency compensation module, the second frequency compensation module is connected in parallel to two ends of the voltage dividing resistor, and the second frequency compensation module is used for performing secondary compensation on the bandwidth lost by the signal output by the coupling module 201. The attenuation times of the output signals of the coupling module 201 by the second attenuation module 204 and the third attenuation module 205 are different depending on the number of the protection resistors, the resistance values of the resistors, and the resistance values of the voltage dividing resistors. In this embodiment, the input terminal of the protection resistor is the input terminal of the protection impedance module, and the output terminal of the protection resistor is the output terminal of the protection impedance module.
When the detected signal is a signal with a large voltage amplitude, the voltage amplitude of the voltage signal output by the output end of the first attenuation module is large, and the voltage across the voltage dividing resistor in the second attenuation module may also be large, so that the diode D1 or D2 in the first voltage clamping module and the second voltage clamping module is turned on in the forward direction, resulting in the equivalent resistor R of the diode D1 or D2D1、RD2Becomes very small, and the input impedance of the branch circuit connected with the first attenuation module is the resistance value and R of the protection resistorD1||RD2Sum due to the equivalent resistance R of the diode D1 or D2D1、RD2The input impedance of a branch circuit connected with the first attenuation module is not approximate to infinity any more and does not meet the requirement of 1M omega +/-5 percent of input impedance, so that the measurement result of the oscilloscope on the measured signal is influenced; the input impedance of the branch circuit connected with the second attenuation module is the resistance value of the protection resistor and the divider resistor RD1||RD2Sum, equivalent resistance R at diode D1 or D2D1、RD2In the very small case, the requirement of 1M Ω ± 5% of the input impedance is not satisfied. Therefore, the present embodiment further includes a second switch 202, a first end of the second switch 202 is connected to the output end of the coupling module 201, a second end of the second switch 202 switches between a first output end and a second output end, the second switch 202 is configured to connect the output end of the coupling module 201 to one of the first output end and the second output end, where the first output end is connected to the input end of the first attenuation module 203 and the input end of the second attenuation module 204; a second output is connected to an input of a third attenuation block 205. In this way, when the detected signal is a large signal, the second switch connects the signal output by the coupling module to the third attenuation module 205 through the second output terminal, and since the voltage across the voltage dividing resistor in the third attenuation module 205 is not too large after voltage division, the third voltage clamping moduleThe middle diode D1 or D2 can not be conducted in the forward direction, and the requirement that the input impedance of the oscilloscope exceeds 1M omega +/-5% is avoided. The method specifically comprises the following steps: assuming that the ground resistance from the coupling module to the first attenuation module is denoted as R ' 1, and R ' 1 is equal to the sum of the impedances of all the protection resistors in the first attenuation module and the input impedance of the impedance transformation module, at this time, it can be considered that R ' 1 is infinite; the ground resistance from the coupling module to the second attenuation module is recorded as R '2, and the R' 2 is equal to the sum of all protection resistors and voltage dividing resistors in the second attenuation module; thus when the first output terminal is selected by the second changeover switch, the input impedance looking into this moment is equal to the parallel impedance of R ' 1 and R ' 2, approximately equal to R ' 2; when the second output end is selected through the second change-over switch, the input impedance seen at the moment is the sum R' 3 of all the protection resistors and the divider resistor in the third attenuation module, so that the input impedance can be ensured to be less than 1M omega +/-5% by selecting the resistance values of the divider resistor and the protection resistor in each attenuation module.
In this embodiment, the switching control of the second switching is the same as that of the first switching switch, and is controlled by an operator, and when the amplitude of the detected signal is smaller than a second preset threshold, the operator controls the second end of the second switching switch 202 to be connected with the first output end; when the amplitude of the detected signal is greater than or equal to the second preset threshold, the operator controls the second end of the second switch 202 to be connected with the second output end. The second switch 202 in this embodiment may be a relay switch, wherein a first end of the second switch 202 is a stationary end of the relay switch, and a second end of the second switch is a moving end of the relay switch, and when the amplitude of the detected signal is greater than a second preset threshold, the moving end of the relay switch switches between the first output end and the second output end. In an embodiment, the moving end of the relay switch includes a normally closed contact and a normally open contact, and the second output end is used as the normally closed contact in this embodiment, and when the control module detects that the signal amplitude is smaller than the second preset threshold, the moving end of the relay switch is switched from the normally closed contact to the normally open contact, that is, the second end of the second switch 202 is connected to the first output end.
Referring to fig. 4, fig. 4 is a circuit diagram of a first attenuation module according to an embodiment, where the protection impedance module includes a first protection resistor R1, a second protection resistor R2, and a third protection resistor R3, one end of the first protection resistor R1 is connected to the first output end, that is, the input end of the protection impedance module is connected to the first output end, the other end of the first protection resistor R1 is connected to one end of the second protection resistor R2, the other end of the second protection resistor R2 is connected to one end of the third protection resistor R3, and the other end of the third protection resistor R3 is connected to the input end of the protection impedance module.
The first frequency compensation module comprises a first compensation capacitor C1, a second compensation capacitor C2 and a third compensation capacitor C3, wherein the first compensation capacitor C1 is connected in parallel at two ends of a first protection resistor R1, the second compensation capacitor C2 is connected in parallel at two ends of a second protection resistor R2, and the third compensation capacitor C3 is connected in parallel at two ends of a third protection resistor R3.
Referring to fig. 5, fig. 5 is a circuit diagram of a second attenuation module or a third attenuation module according to an embodiment, in which the second frequency compensation module includes a fourth compensation capacitor C4, a fifth compensation capacitor C5, and a sixth compensation capacitor C6, one end of the fourth compensation capacitor C4 is connected to the output end of the protection impedance module, the other end of the fourth compensation capacitor C4 is connected to one end of a fifth compensation capacitor C5, the other end of the fifth compensation capacitor C5 is connected to ground, and the sixth compensation capacitor C6 is connected in parallel to two ends of the fifth compensation capacitor C5. As shown in fig. 5, the voltage dividing resistor is R4, so the voltage output by the second attenuation module or the third attenuation module to the impedance transformation module is: VOUT is R4/(R1+ R2+ R3+ R4) × VIN, where VIN is the voltage of the output signal of the coupling module, and the resistances of R1, R2, R3, and R4 in the circuit shown in fig. 5 are all 249K Ω, so the attenuation multiple of the second attenuation module or the third attenuation module shown in fig. 5 is 3, and the equivalent impedance at the input end of the second attenuation module or the third attenuation module is R1+ R2+ R3+ R4 is 996K Ω, which meets the requirement of 1M Ω ± 5% of input impedance. The fifth compensation capacitor (C5) in the circuit of fig. 5 is a variable capacitor. It should be noted here that the protection resistors and the voltage dividing resistors of different attenuation modules have different resistance values.
In the second attenuation module or the third attenuation module, the first compensation capacitor (C1), the second compensation capacitor (C2), the third compensation capacitor (C3), the fourth compensation capacitor (C4), the fifth compensation capacitor (C5) and the sixth compensation capacitor (C6) need to satisfy the following relations to realize complete compensation:
(R1+R2+R3)*(C1*C2*C3/(C1+C2+C3))＝R4*(C4*(C5+C6)/C4+C5+C6)
wherein, R1 is the first protection resistor, R2 is the second protection resistor, R3 is the third protection resistor, R4 is divider resistor.
In the first attenuation module, the first compensation capacitor (C1), the second compensation capacitor (C2) and the third compensation capacitor (C3) need to satisfy the following relations to realize complete compensation:
(R1+R2+R3)*(C1*C2*C3/(C1+C2+C3))＝Rin*Cin
wherein, R1 is a first protection resistor, R2 is a second protection resistor, R3 is a third protection resistor, Rin is an input terminal equivalent resistor of the impedance transformation module, and Cin is an equivalent capacitor of the input terminal of the impedance transformation.
It is right to have used specific individual example above the utility model discloses expound, only be used for helping to understand the utility model discloses, not be used for the restriction the utility model discloses. To the technical field of the utility model technical personnel, the foundation the utility model discloses an idea can also be made a plurality of simple deductions, warp or replacement.
Claims (10)
1. An analog channel circuit of a digital oscilloscope is characterized by comprising a coupling module, a first attenuation module, a second attenuation module, a third attenuation module, a first selector switch, an impedance conversion module and an amplitude adjustment module;
the coupling module is used for carrying out alternating current coupling or direct current coupling on a detected signal;
the input end of the first attenuation module, the input end of the second attenuation module and the input end of the third attenuation module are respectively connected with the output end of the coupling module;
the first attenuation module is used for carrying out primary attenuation on the amplitude of the output signal of the coupling module;
the second attenuation module is used for carrying out secondary attenuation on the amplitude of the output signal of the coupling module;
the third attenuation module is used for carrying out three-level attenuation on the amplitude of the output signal of the coupling module;
the first end of the first switch is switched among the output end of the first attenuation module, the output end of the second attenuation module and the output end of the third attenuation module, the second end of the first switch is connected with the input end of the impedance conversion module, and the first switch is used for selecting one of the signals output by the first attenuation module, the second attenuation module and the third attenuation module and outputting the selected signal to the impedance conversion module;
the impedance transformation module is used for carrying out impedance transformation on the attenuation signal;
the input end of the amplitude adjusting module is connected with the output end of the impedance conversion module and is used for adjusting the amplitude of the signal output by the impedance conversion module to be within a preset range.
2. The circuit of claim 1, wherein the first attenuation module attenuates the amplitude of the coupling module output signal by a factor less than a factor by which the second attenuation module attenuates the amplitude of the coupling module output signal, the factor by which the second attenuation module attenuates the amplitude of the coupling module output signal being less than a factor by which the third attenuation module attenuates the amplitude of the coupling module output signal.
3. The circuit of claim 1, further comprising a second switch, a first end of the second switch being coupled to the output of the coupling module, a second end of the second switch switching between the first output and the second output, the second switch being adapted to couple the output of the coupling module to one of the first output and the second output;
the first output end is connected with the input end of the first attenuation module and the input end of the second attenuation module;
the second output end is connected with the input end of the third attenuation module.
4. The circuit of claim 3, wherein the first terminal of the first switch is connected to the output terminal of the first attenuation module when the amplitude of the measured signal is less than a first predetermined threshold, the first terminal of the first switch is connected to the output terminal of the second attenuation module when the amplitude of the measured signal is greater than or equal to the first predetermined threshold and less than a second predetermined threshold, and the first terminal of the first switch is connected to the output terminal of the third attenuation module when the amplitude of the measured signal is greater than or equal to the second predetermined threshold, wherein the first predetermined threshold is less than the second predetermined threshold;
when the amplitude of the detected signal is smaller than a second preset threshold value, a second end of the second change-over switch is connected with the first output end; when the measured amplitude is larger than or equal to a second preset threshold value, a second end of the second change-over switch is connected with a second output end;
the first change-over switch is an analog input switch, and the second change-over switch is a relay switch.
5. The circuit of claim 1, wherein the first attenuation module, the second attenuation module and the third attenuation module each comprise a protection impedance module and a first frequency compensation module, an input terminal of the protection impedance module is connected to an output terminal of the coupling module for limiting a current of a signal output by the coupling module, and an output terminal of the protection impedance module is connected to an input terminal of the impedance transformation module; the first frequency compensation module is connected in parallel at two ends of the protection impedance module and is used for performing primary compensation on the bandwidth of the loss of the output signal of the coupling module.
6. The circuit of claim 5, wherein the second attenuation module and the third attenuation module further comprise a voltage divider resistor and a second frequency compensation module, wherein an input terminal of the voltage divider resistor is connected to an output terminal of the protection impedance module, and an output terminal of the voltage divider resistor is connected to ground; the second frequency compensation module is connected in parallel at two ends of the divider resistor;
the voltage dividing resistor is used for dividing the voltage of the output signal of the coupling module; and the second frequency compensation module is used for carrying out secondary compensation on the bandwidth of the loss of the output signal of the coupling module.
7. The circuit of claim 6, wherein the protection impedance module comprises one or more protection resistors connected in series, and wherein the first frequency compensation module comprises at least one compensation capacitor connected in parallel across the protection resistors.
8. The circuit of claim 7, wherein the protection impedance module comprises a first protection resistor (R1), a second protection resistor (R2), and a third protection resistor (R3), one end of the first protection resistor (R1) is connected to the first output terminal, the other end of the first protection resistor (R1) is connected to one end of the second protection resistor (R2), the other end of the second protection resistor (R2) is connected to one end of the third protection resistor (R3), and the other end of the third protection resistor (R3) is connected to the output terminal of the protection impedance module;
the first frequency compensation module comprises a first compensation capacitor (C1), a second compensation capacitor (C2) and a third compensation capacitor (C3), wherein the first compensation capacitor (C1) is connected in parallel to two ends of a first protection resistor (R1), the second compensation capacitor (C2) is connected in parallel to two ends of a second protection resistor (R2), and the third compensation capacitor (C3) is connected in parallel to two ends of a third protection resistor (R3);
the second frequency compensation module comprises a fourth compensation capacitor (C4), a fifth compensation capacitor (C5) and a sixth compensation capacitor (C6), one end of the fourth compensation capacitor (C4) is connected with the output end of the protection impedance module, the other end of the fourth compensation capacitor (C4) is connected with one end of the fifth compensation capacitor (C5), the other end of the fifth compensation capacitor (C5) is connected with the ground, and the sixth compensation capacitor (C6) is connected in parallel at two ends of the fifth compensation capacitor (C5).
9. The circuit of claim 1, further comprising a first voltage clamping module, a second voltage clamping module, and a third voltage clamping module;
the input end of the first voltage clamping module is connected with the output end of the first attenuation module and is used for clamping the voltage of the first-level attenuation signal within a first preset voltage range;
the input end of the second voltage clamping module is connected with the output end of the second attenuation module and is used for clamping the voltage of the secondary attenuation signal within a second preset voltage range;
and the input end of the third voltage clamping module is connected with the output end of the third attenuation module and is used for clamping the voltage of the three-level attenuation signal within a third preset voltage range.
10. A digital oscilloscope comprising an analog channel circuit, an analog-to-digital sampling circuit, a processor and a display screen, wherein the analog channel circuit is the analog channel circuit of any one of claims 1 to 9;
the input end of the analog-digital sampling circuit is connected with the output end of the analog channel circuit and is used for sampling an output signal of the analog channel circuit;
the input end of the processor is connected with the output end of the analog-digital sampling circuit and used for carrying out data processing on the sampling signal;
the display screen is connected with the output end of the processor and used for displaying the processed signals.
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| CN202020565320.2U CN212111556U (en) | 2020-04-16 | 2020-04-16 | Analog channel circuit of digital oscilloscope and digital oscilloscope |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113075439A (en) * | 2021-06-04 | 2021-07-06 | 深圳市鼎阳科技股份有限公司 | Input impedance protection circuit and method of digital oscilloscope and digital oscilloscope |
| WO2022206733A1 (en) * | 2021-03-29 | 2022-10-06 | 普源精电科技股份有限公司 | Signal transmission network, chip, and signal processing device |
| WO2023111123A1 (en) * | 2021-12-16 | 2023-06-22 | B&R Industrial Automation GmbH | Signal transfer assembly with capacitive coupling |
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2020
- 2020-04-16 CN CN202020565320.2U patent/CN212111556U/en active Active
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2022206733A1 (en) * | 2021-03-29 | 2022-10-06 | 普源精电科技股份有限公司 | Signal transmission network, chip, and signal processing device |
| CN113075439A (en) * | 2021-06-04 | 2021-07-06 | 深圳市鼎阳科技股份有限公司 | Input impedance protection circuit and method of digital oscilloscope and digital oscilloscope |
| WO2023111123A1 (en) * | 2021-12-16 | 2023-06-22 | B&R Industrial Automation GmbH | Signal transfer assembly with capacitive coupling |
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