CN101788578A - Oscilloscope with front end analog circuit - Google Patents

Abstract

A digital oscilloscope with an analog front-end circuit, comprising a signal input module, an input attenuation module, a programmable amplifier, a bandwidth limiting module, an ADC driver module, an A/D conversion module, a control processing module, and a D/A conversion module connected in series in sequence , the input attenuation module includes a resistance-capacitance network with multiple paths, a switch unit and an operational amplifier unit connected in series. The switch unit is controlled by the control processing module, so that one branch in the resistance-capacitance network is connected to the input end of the operational amplifier unit, and the other branches are grounded. The resistance-capacitance network and the operational amplifier unit work together to attenuate the input signal of the oscilloscope. The invention adopts a resistance-capacitance network with multiple paths, satisfies the input high resistance of the oscilloscope, and attenuates the input signal in different proportions, thereby enlarging the dynamic range of the input signal.

Description

An oscilloscope with an analog front-end circuit

technical field

The invention relates to the field of measuring devices for displaying electrical variables in a wave form, in particular to the field of digital oscilloscopes.

Background technique

Commonly used digital oscilloscopes generally include analog front-end circuits, ADC sampling circuits, trigger circuits, digital processing circuits and display circuits. Among them, the analog front-end circuit completes a series of functions such as input high impedance, buffering, attenuation and ADC driving of the input signal to be measured. How to achieve multi-proportional attenuation of the input signal while achieving high input impedance has always been a problem that plagues technicians.

In the prior art, referring to FIG. 1, a digital oscilloscope 1 includes a signal input module 10, an input resistor 11, an input attenuation module 12, a programmable amplifier 13, a bandwidth limiting module 14, an ADC driver module 15, and an A/D conversion module connected in series in sequence. module 16 and a control processing module 17, and a D/A conversion module 18 connected in series between the control processing module 17 and the input attenuation module 12.

The signal input module 10 includes a signal input terminal 101 and an AC/DC conversion unit 102 , and the input attenuation module 12 includes a junction field effect transistor 121 , an adding circuit 122 and a resistor 123 .

The signal is input by the signal input terminal 101, and connected to the gate of the junction field effect transistor 121 through the AC/DC conversion unit 102. The AC/DC conversion unit 102 is composed of a capacitor connected in parallel with a switch to realize AC/DC switching. The gate of the field effect transistor 121 is connected to the 1MΩ resistor 11 to ground, the drain of the junction field effect transistor 121 is connected to the power supply VCC, the source is grounded through a resistor 123, and the source is connected to an input terminal of the adding circuit 122 at the same time, and the adding circuit The other input end of 122 is connected to D/A conversion module 18, is used to control internal DC bias, the output of adding circuit 122 is connected to programmable amplifier 13, and programmable amplifier 13 output is connected to bandwidth limiting module 14, and bandwidth limiting module 14 The output is connected to the ADC driving module 15, and the output signal of the ADC driving module 15 is sent to the A/D conversion module 16 for analog-to-digital conversion, and the signal after the analog-to-digital conversion is sent to the control processing module 17, and the control processing module 17 outputs a gain control signal For the programmable amplifier 13, the amplification factor of the digital programmable amplifier 13 is controlled. The control processing module 17 also outputs a bandwidth limit signal to control the bandwidth of the bandwidth limit module 14 .

The signal input module 10 is mainly used for receiving input signals, performing AC/DC conversion on the input signals, and realizing functions such as attenuation and impedance matching. The input attenuation module 12 is mainly used to attenuate the signal to achieve matching of high frequency and low frequency. The programmable amplifier 13 is mainly used to amplify the signal, the bandwidth limiting module 14 is mainly used to complete the bandwidth control, the ADC driving module 15 is used to complete the driving operation of the signal before the digital-to-analog conversion, and the A/D conversion module 16 is used to complete the signal The digital-to-analog conversion function, the control processing module 17 is used to complete a series of functions such as triggering, storage and display, and with the continuous development of the oscilloscope technology, the control processing module will also be used to complete many new functions.

It can be seen that in the prior art, in order to achieve high input impedance and attenuation of the input signal, the input signal is connected to the input attenuation module 12 through the grounded 1MΩ resistor 11, and then through the junction field effect transistor 121 and the adding circuit 122 to attenuate the signal, the above method mainly has the following two problems:

1. Since the dynamic range of the input signal is completely determined by the gate of the junction field effect transistor, and because the input high impedance is realized through the grounding of the 1MΩ resistor 11, only one path is connected to the field effect transistor, and multi-ratio attenuation cannot be realized. The above-mentioned Both lead to a small dynamic range of signal input;

2. Since the frequency response flatness of the JFET is poor, and there is no other circuit structure for adjusting the frequency response, the frequency response flatness of the signal is poor.

Contents of the invention

In order to solve the first problem in the prior art, the present invention provides an oscilloscope with an analog front-end circuit.

The oscilloscope with an analog front-end circuit includes a signal input module, an input attenuation module, and a control processing module connected in series, and the input attenuation module includes a resistance-capacitance network, a switch unit and An operational amplifier unit, the resistance-capacitance network includes a plurality of resistance-capacity circuits, the input terminals of each resistance-capacity circuit are connected to the output terminals of the signal input module, and the switch unit is used to select the Any output terminal of the resistance-capacitance network is connected to the operational amplifier unit, and the other output terminals of the resistance-capacitance network are grounded.

In the oscilloscope of the present invention, among the plurality of resistance-capacitance circuits, at least one resistance-capacitance circuit may include a circuit composed of a resistor and a capacitor connected in parallel.

In the oscilloscope of the present invention, among the plurality of resistance-capacitance circuits, at least one resistance-capacitance circuit may include two output terminals, and include a first circuit, a second circuit and a third circuit, and the first A circuit and the second circuit are connected in series between the input terminal and an output terminal of the resistance-capacitance circuit, and the first circuit and the third circuit are connected in series at the input of the resistance-capacitance circuit Between the terminal and the other output terminal, the first circuit, the second circuit and the third circuit are circuits composed of a resistor and a capacitor connected in parallel.

In the oscilloscope of the present invention, the operational amplifier unit may include an operational amplifier, the operational amplifier has a positive input terminal, a negative input terminal and an output terminal, and the positive input terminal of the operational amplifier For grounding, the negative input terminal of the operational amplifier is used to connect the switch unit, and a feedback resistor is connected between the negative input terminal and the output terminal of the operational amplifier.

In the oscilloscope of the present invention, a compensation circuit may be connected in parallel at both ends of the feedback resistor.

In the oscilloscope of the present invention, the compensation circuit may be composed of a compensation resistor and a compensation capacitor connected in series.

In the oscilloscope of the present invention, the compensation circuit may include a varactor diode connected in parallel at both ends of the feedback resistor, and the control processing module communicates with the varactor through a D/A conversion module The control terminal of the diode is connected.

In the oscilloscope of the present invention, the compensation circuit may include a varactor diode connected in parallel at both ends of the feedback resistor, and the control processing module communicates with the D/A conversion module through the The control terminal connection of the varactor diode. The oscilloscope of the present invention can not only meet the high-impedance input requirement of the oscilloscope, but also can attenuate the input signal in multiple proportions and expand the dynamic range of the input signal.

In order to solve the second problem in the prior art, the present invention provides another oscilloscope with an analog front-end circuit.

The oscilloscope with an analog front-end circuit includes a signal input module, an input attenuation module, and a control processing module connected in series in sequence, and the input attenuation module includes a serial connection between its input terminal and output terminal. An operational amplifier, the operational amplifier has a positive input terminal for grounding and a negative input terminal for connecting the input terminal of the input attenuation module in series, at the output terminal of the operational amplifier and the negative input terminal A compensation network controlled by the control processing module is connected between the terminals, and the compensation network is used to adjust the frequency characteristics of the operational amplifier.

In the oscilloscope of the present invention, the compensation network may include a varactor diode, a first capacitor, a second capacitor, a first current limiting resistor and a second current limiting resistor, the first The capacitor is connected in series between the negative pole of the varactor diode and the input terminal of the compensation network, and the second capacitor is connected in series between the positive pole of the varactor diode and the output terminal of the compensation network , the first current-limiting resistor is connected in series between the cathode of the varactor diode and the control processing module, and the second current-limiting resistor is connected in series between the anode of the varactor diode and the ground between.

In the oscilloscope of the present invention, a compensation resistor can be connected in series between the input terminal and the output terminal of the compensation network.

In the oscilloscope of the present invention, the control processing module can control the compensation network through a D/A conversion module.

In the oscilloscope of the present invention, among the plurality of resistance-capacitance circuits, at least one resistance-capacitance circuit may include a circuit composed of a parallel connection of a resistor and a capacitor.

In the oscilloscope of the present invention, among the plurality of resistance-capacitance circuits, at least one resistance-capacitance circuit may include two output terminals, and include a first circuit, a second circuit and a third circuit, and the first A circuit and the second circuit are connected in series between the input terminal and an output terminal of the resistance-capacitance circuit, and the first circuit and the third circuit are connected in series at the input of the resistance-capacitance circuit Between the terminal and the other output terminal, the first circuit, the second circuit and the third circuit are circuits composed of a resistor and a capacitor connected in parallel.

In the oscilloscope of the present invention, among the plurality of resistance-capacitance circuits, at least one resistance-capacitance circuit may include a circuit composed of a parallel connection of a resistor and a capacitor.

In the oscilloscope of the present invention, among the plurality of resistance-capacitance circuits, at least one resistance-capacitance circuit may include two output terminals, and include a first circuit, a second circuit and a third circuit, and the first A circuit and the second circuit are connected in series between the input terminal and an output terminal of the resistance-capacitance circuit, and the first circuit and the third circuit are connected in series at the input of the resistance-capacitance circuit Between the terminal and the other output terminal, the first circuit, the second circuit and the third circuit are circuits composed of a resistor and a capacitor connected in parallel.

In the oscilloscope of the present invention, a feedback resistor can be connected between the negative input terminal and the output terminal of the operational amplifier.

The oscilloscope of the present invention adjusts the frequency response of the circuit through the compensation network, so that the flatness of the frequency response of the circuit is better.

Description of drawings

FIG. 1 is a schematic structural diagram of a digital oscilloscope in the prior art.

Fig. 2 is a schematic structural diagram of the digital oscilloscope 2 in the first embodiment.

Fig. 3 is a schematic structural diagram of the digital oscilloscope 3 in the second embodiment.

FIG. 4 is a schematic structural diagram of the compensation network 3120 in the second embodiment.

Detailed ways

The first embodiment of the present invention will be described below with reference to FIG. 2 .

As shown in FIG. 2 , the digital oscilloscope 2 includes a signal input module 20 , an input attenuation module 21 , a signal processing module 22 and a D/A conversion module 28 connected in series between the input attenuation module 21 and the signal processing module 22 .

The signal input module 20 includes a signal input terminal, a resistor 202 and an AC/DC conversion unit connected in series in sequence. The signal input terminal is formed by a connector 201, and the AC/DC conversion unit is formed by connecting a capacitor 203 and a switch 204 in parallel. The capacitor 203 is 47nF, and the switch 204 is a CMOS analog switch KAQY214S. The input signal is input by the connector 201 and sent to the AC/DC conversion unit through the resistor 202. When the switch 204 is closed, the capacitor 203 is short-circuited, and the signal passes through directly. It is a DC coupling mode. When the switch 204 is turned off, the signal directly flows through Capacitor 203, the DC is isolated, is AC coupling. The AC/DC converted signal is sent to the input attenuation module 21 .

The input attenuation module 21 includes a resistor-capacitor network 210 , a switch unit 211 and an operational amplifier unit 212 connected in series in sequence. The resistance-capacitance network 210 is made up of two resistance-capacity circuits, the first resistance-capacity circuit is connected in parallel between the input terminal In and the first output terminal Out1 of the resistance-capacity network 210 by a resistor 2101 and a capacitor 2102, and the second resistance-capacity circuit is composed of a resistor 2103 and capacitor 2104 are connected in parallel between the input terminal In and the second output terminal Out2 of the RC network 210 . The switch unit 211 is an analog switch 2111 with two input terminals and one output terminal, and each input terminal of the analog switch 2111 has a default resistance value, that is, when a certain switch is disconnected, the path is grounded through the default resistance value and closed The switch is directly connected to the computing unit 212. In this embodiment, the default resistance value is 0Ω, and the default resistance value can also be 50Ω. The first output terminal Out1 and the second output terminal Out2 of the RC network 210 are respectively connected to the input terminals In1 and In2 of the switch 2111 . The operational amplifier unit 212 includes an operational amplifier 2121, a feedback resistor 2124, a compensation network 2120, a resistor 2125, and a filter capacitor 2126. The positive input terminal In+ of the operational amplifier 2121 is grounded, and the negative input terminal In- is connected to the output terminal Out of the switch 2111, and the control The processing module 27 is connected to the negative input terminal In- of the operational amplifier 2121 through the resistor 2125 and the D/A conversion module 28, the filter capacitor 2126 is connected in series between the resistor 2125 and the ground, the output terminal of the operational amplifier 2121 is connected to the input of the signal processing module 22 The feedback resistor 2124 is connected between the negative input terminal and the output terminal of the operational amplifier 2121, the compensation network 2120 is connected in parallel to both ends of the feedback resistor 2124, and the compensation network 2120 is composed of a compensation resistor 2123 and a compensation capacitor 2122 in series.

In this embodiment, resistor 2101=1.05MΩ, capacitor 2102=15pF, resistor 2103=18.8MΩ, capacitor 2104=0.6pF, feedback resistor=464kΩ, compensation resistor 2123=34.65MΩ, compensation capacitor 2122=27pF, resistor 2125= 249kΩ, filter capacitor 2126 = 100nF.

In this embodiment, the control processing module 27 sends a control signal to the switch 2111, the output terminal Out of the control switch 2111 is connected to its input terminal In1, and the input terminal In2 is grounded through a default resistor, that is, the output terminal Out1 of the resistance-capacitance network 210 is connected to the input terminal In1. The negative input terminal In- of the operational amplifier 2121 is connected. Since the positive input terminal of the operational amplifier 2121 is grounded, according to the principle of virtual short and virtual disconnection of the operational amplifier, the output terminal Out1 of the resistance-capacitance network 210 is grounded, and the output terminal Out2 of the resistance-capacitance network 210 The input terminal In2 of the switch 2111 is grounded, so it can be seen that the two output terminals of the resistance-capacitance network 210 are at the ground level. Since the parallel connection value of the resistor 2101 and the resistor 2103 is approximately equal to 1MΩ, it can be seen from the above that no matter the switch 2111 selects For any input terminal, the input resistance of the RC network 210 is equal to 1MΩ, that is, the input resistance of the oscilloscope 2 is about 1MΩ.

In this embodiment, the attenuation circuit for the input signal is formed by the resistance-capacitance network 210, the switch unit 211 and the operational amplifier unit 212. The attenuation circuit can realize the attenuation ratio of two different gears, and the resistance in the resistance-capacitance network 210 The capacitor and the capacitor are the main paths of the low-frequency signal and the high-frequency signal respectively, and the ratio of the resistance value and the reciprocal ratio of the capacitor value are equal to realize the matching of the high frequency and the low frequency. When the switch 2111 connects the output terminal Out1 of the RC network 210 to the negative input terminal In- of the operational amplifier 2121, the resistor 2101 or capacitor 2102, the operational amplifier 2121, the feedback resistor 2124, the compensation resistor 2123 and the compensation capacitor 2122 form a proportional attenuation circuit , when a low-frequency signal is input, the attenuation ratio is approximately equal to the feedback resistor 2124/resistor 2101≈1/2, when a high-frequency signal is input, the attenuation ratio is approximately equal to the compensation capacitor 2122/capacitor 2102≈1/2, if the input signal amplitude V, then the signal amplitude output by the operational amplifier 2121 is V/2; when the switch 2111 connects the output terminal Out2 of the RC network 210 to the negative input terminal of the operational amplifier 2121, the resistor 2103 or the capacitor 2104, the operational amplifier 2121, the feedback Resistor 2124, compensating resistor 2123 and compensating capacitor 2122 form a proportional attenuation circuit. When a low-frequency signal is input, the attenuation ratio is approximately equal to the feedback resistor 2124/resistor 2103≈1/40. When a high-frequency signal is input, the attenuation ratio is approximately equal to the compensating capacitor 2122 /Capacitance 2104≈1/40, if the input signal amplitude is V at this time, then the output signal amplitude of the operational amplifier 2121 is V/40, thus expanding the dynamic range of the input signal.

In this embodiment, the compensation resistor 2123 and the compensation capacitor 2122 are used to adjust the frequency response of the input signal of the oscilloscope. Since the frequency range of the input signal of the oscilloscope is relatively large, the flatness of the frequency response of the input signal can be improved.

In this embodiment, the control processing module 27 outputs the offset signal OFFSET to the D/A conversion module 28, and the D/A conversion module 28 converts the signal OFFSET into an analog signal and sends it to the operational amplifier 2121 through the resistor 2125 for adjusting the operation The output terminal voltage of the amplifier 2121, when the input signal has a large bias, can adjust OFFSET so that the output of the operational amplifier 2121 is within the allowable operating voltage range. The signal attenuated by the operational amplifier 2121 is sent to the signal processing module 22 .

The signal processing module 22 includes a programmable amplifier 23 , a bandwidth limiting module 24 , an ADC driving module 25 , an A/D converting module 26 and a control processing module 27 connected in series in sequence. The programmable amplifier 23 receives the signal output by the input attenuation module 21, performs signal processing according to the gain control signal GainControl output by the control processing module 27, realizes signal amplification to the oscilloscope, and then sends the amplified signal to the bandwidth limiting module 24 for control processing Module 27 outputs bandwidth limiting signal BWLMT to bandwidth limiting module 24 to realize the selection of bandwidth limiting, and the signal output by bandwidth limiting module 24 is sent to ADC driver module 25, and the signal is adjusted into a signal that A/D conversion module 26 is suitable for collecting, then by The A/D conversion module 26 performs analog-to-digital conversion of the signal, and finally sends it to the control processing module 27 for signal processing, for processing such as signal storage and display.

As a further illustration, the resistance-capacitance network 210 in this embodiment can also be composed of more than two resistance-capacitance circuits. At the same time, it is necessary to select a switch 2111 with a corresponding input terminal, so that an input attenuation circuit with more attenuation ratios can be realized. The dynamic range of the input signal is expanded.

As a further illustration, the resistor 2101, capacitor 2102, resistor 2103, and capacitor 2104 in this embodiment can all be realized by multiple resistors and multiple capacitors connected in series or in parallel, as long as the resistance value meets the needs, and the capacitor can be selected and adjusted Capacitors, so that the values of resistors and capacitors can be fine-tuned, which is more convenient for circuit debugging.

As a further illustration, the compensation capacitor 2122 in this embodiment can be an adjustable capacitor

As a further illustration, the compensation network in this embodiment can replace the compensation resistor 2123 and the compensation capacitor 2122 with an adjustable capacitor, and the control processing module 27 sends a control signal according to the change of the attenuation ratio and is converted into an analog signal by the D/A conversion module 28. After receiving the signal, the adjustable capacitor is controlled to adjust the frequency response of the circuit. The specific implementation of this compensation network can be seen in the second embodiment.

The second embodiment of the present invention will be described below in conjunction with accompanying drawings 3 and 4 .

As shown in FIG. 3 , the digital oscilloscope 3 includes a signal input module 30 , an input attenuation module 31 , a signal processing module 22 and a D/A conversion module 28 connected in series between the input attenuation module 21 and the signal processing module 22 .

The signal input module 30 includes a signal input terminal, a resistor 202 and an AC/DC conversion unit connected in series in sequence, and a parallel circuit of a resistor 205 and a capacitor 206 is connected in series behind the AC/DC conversion unit, and the signal input terminal is formed by a connector 201. The AC/DC conversion unit is composed of a capacitor 203 and a switch 204 connected in parallel, the capacitor 203 is 47nF, and the switch 204 is a CMOS analog switch KAQY214S. The input signal is input by the connector 201 and sent to the AC/DC conversion unit through the resistor 202. When the switch 204 is closed, the capacitor 203 is short-circuited, and the signal passes through directly. It is a DC coupling mode. When the switch 204 is turned off, the signal directly flows through Capacitor 203, the DC is isolated, is AC coupling. The AC/DC converted signal is sent to the parallel circuit of the resistor 205 and the capacitor 206 , and the signal is divided and sent to the input attenuation module 31 .

The input attenuation module 31 includes a resistor-capacitor network 310 , a switch unit 311 and an operational amplifier unit 312 connected in series in sequence. The resistance-capacitance network 310 is made up of two resistance-capacity circuits, the first resistance-capacity circuit is connected in parallel between the input terminal In and the output terminal Out1 of the resistance-capacitance network 310 by a resistor 3101 and a capacitor 3102, and the second resistance-capacity circuit is formed by the first circuit , the second circuit and the third circuit, and the first circuit and the second circuit are connected in series between the input terminal In and the output terminal Out2 of the RC network 310, and the first circuit and the third circuit are connected in series at the input of the RC network 310 Between terminal In and output terminal Out3, the first circuit is a parallel circuit of resistor 3103 and capacitor 3104, the second circuit is a parallel circuit of resistor 3105 and capacitor 3104, and the third circuit is a parallel circuit of resistor 3107 and capacitor 3108. The switch unit 311 is an analog switch 3111 with three input terminals and one output terminal, and each input terminal of the analog switch 3111 has a default resistance value, that is, when a certain switch is turned off, the path is grounded through the default resistance value. In the example, the default resistance value is 0Ω, and the default resistance value can also be 50Ω. The output terminal Out1 , the output terminal Out2 and the output terminal Out3 of the RC network 310 are respectively connected to the input terminals In1 , In2 and In3 of the switch 3111 . The operational amplifier unit 312 includes an operational amplifier 2121, a feedback resistor 2124, a compensation network 3120, a resistor 2125, and a filter capacitor 2126. The positive input terminal In+ of the operational amplifier 2121 is grounded, and the negative input terminal In- is connected to the output terminal Out of the switch 3111, and the control The processing module 27 is connected to the negative input terminal In- through the resistor 2125 and the D/A conversion module 28, the filter capacitor 2126 is connected in series between the resistor 2125 and the ground, the output terminal of the operational amplifier 2121 is connected to the input terminal of the signal processing module 22, and the feedback The resistor 2124 is connected between the negative input terminal In- and the output terminal of the operational amplifier 2121, the compensation network 3120 is connected in parallel to both ends of the feedback resistor 2124, and the control processing module 27 is controlled by the D/A conversion module 28 and the compensation network 3120 terminal COMP connection.

As shown in Figure 3 and Figure 4, the compensation network 3120 is composed of a varactor diode 31201, a first capacitor 31204, a second capacitor 31205, a first current limiting resistor 31202 and a first current limiting resistor 31203, and the first capacitor 31204 is connected in series with the feedback Between the resistor 2124 and the negative pole of the varactor diode 31201, the second capacitor 31205 is connected in series between the feedback resistor 2124 and the positive pole of the varactor diode 31201, and the first current limiting resistor 31202 is connected in series between the negative pole of the varactor diode 31201 and the compensation network 3120 Between the control terminal COMP, the second current limiting resistor 31203 is connected in series between the anode of the varactor diode 31201 and the ground, and the control terminal COMP is connected to the D/A conversion module 28 .

In this embodiment, resistor 205=resistor 3103=resistor 3107=909kΩ, resistor 3101=resistor 3105=100kΩ, capacitor 206=500pF, capacitor 3102=capacitor 3106=100pF, capacitor 3104=capacitor 3108=12pF, feedback resistor=464kΩ , first capacitor 31204=second capacitor 31205=180pF, first current limiting resistor 31202=second current limiting resistor 31203=2kΩ, resistor 2125=249kΩ, filter capacitor 2126=100nF.

In this embodiment, the control processing module 27 sends a control signal to the switch 311, the output terminal Out of the control switch 3111 is connected to the input terminal In1, and the input terminals In2 and In3 are grounded through a default resistor, that is, the output terminal of the resistance-capacitance network 310 Out1 is connected to the negative input terminal In- of the operational amplifier 2121. Since the positive input terminal In+ of the operational amplifier 2121 is grounded, according to the principle of virtual short and virtual disconnection of the operational amplifier, the output terminal Out1 of the resistance-capacitance network 310 is grounded, and the output terminal Out1 of the resistance-capacitance network 310 is grounded. The output terminals Out2 and Out3 are grounded through the input terminals In2 and In3 of the switch 31111, so it can be seen that the output terminals Out1, Out2 and Out3 of the resistance-capacitance network 310 are all ground level, because the resistance 205+resistance 3101||(resistance 3103+(resistance 3105||resistance 3107))≈1MΩ, so it can be seen from the above that no matter which input terminal is selected by the switch 3111, the input resistance of the RC network 310 is approximately equal to 1MΩ, that is, the input resistance of the oscilloscope 3 is approximately 1MΩ.

In this first embodiment, the attenuation circuit for the input signal is formed by the resistance-capacitance network 310, the switch unit 311 and the operational amplifier unit 312. The capacitor and the capacitor are the main paths of the low-frequency signal and the high-frequency signal respectively, and the ratio of the resistance value and the reciprocal ratio of the capacitor value are equal to realize the matching of the high frequency and the low frequency. Since the resistor 205 in the signal input module 30 has already divided the input signal once, if the amplitude of the input signal is V, then the voltage at the input terminal of the resistance-capacitance network 310 becomes V/10, and when the switch 3111 makes the resistance-capacitance When the output terminal Out1 of the network 310 is connected to the negative input terminal In- of the operational amplifier 2121, the resistor 3101 or the capacitor 3102, the operational amplifier 2121 and the feedback resistor 2124 form an attenuation circuit. When a low-frequency signal is input, the attenuation ratio is approximately equal to the feedback resistor 2124/ Resistor 3101≈5. When a high-frequency signal is input, the attenuation ratio is approximately equal to the capacitance/capacitance 3102≈5 of the compensation network 3120. If the input signal amplitude is V/10, the output signal amplitude of the operational amplifier 2121 is V/2 ; When the switch 3111 made the output terminal Out2 of the RC network 310 and the negative input terminal In- of the operational amplifier 2121 connected, the resistor 3103, the resistor 3105 and the resistor 3107 have carried out a voltage division to the signal again, so the resistor 3105 input voltage V/100, resistor 3105 or capacitor 3106, operational amplifier 2121 and feedback resistor 2124 form an attenuation circuit. When a low-frequency signal is input, the attenuation ratio is approximately equal to the feedback resistor 2124/resistor 3105≈5. When a high-frequency signal is input, the attenuation The ratio is approximately equal to the capacitance/capacitance 3106≈5 of the compensation network 3120. If the input signal amplitude is V/100 at this time, the signal amplitude output by the operational amplifier 2121 is V/20; when the switch 3111 makes the output terminal Out3 of the resistance capacitance network 310 When connected to the negative input terminal In- of the operational amplifier 2121, the resistor 3103, resistor 3105 and resistor 3107 divide the signal again at this time, so the input voltage of the resistor 3105 becomes V/100, and the resistor 3107 or the capacitor 3108, the operation The amplifier 2121 and the feedback resistor 2124 form a proportional circuit. When a low-frequency signal is input, the attenuation ratio is approximately equal to the feedback resistor 2124/resistor 3107≈1/2. When a high-frequency signal is input, the attenuation ratio is approximately equal to the capacitance/capacitance 3108 of the compensation network 3120 ≈1/2, if the input signal amplitude is V/100 at this time, then the signal amplitude output by the operational amplifier 2121 is V/200, thus expanding the dynamic range of the input.

In this embodiment, when the switch 3111 selects the input terminal In1, In2 or In3, the control processing module 27 outputs different adjustment signals to the D/A conversion module 28, and after the D/A conversion module 28 converts it into an analog signal, Send it to the control terminal COMP to change the reverse bias voltage of the varactor diode 31201, thereby adjusting its capacitance. The first capacitor 31204 and the second capacitor 31205 AC-couple the varactor diode 31201 to the feedback resistor 2124, so that the compensation network 3120 The capacitance is equivalent to the series connection value of the first capacitor 31204, the second capacitor 31205 and the varactor diode 31201, and the values of the first capacitor 31204 and the second capacitor 31205 are much larger than the capacitance value of the varactor diode 31201, so the capacitance value of the compensation network 3120 Approximate to the reverse bias capacitance of the varactor diode 31201. The control processing module 27 adjusts the capacitance of the compensation network 3120 to make the low-frequency response of the circuit consistent with the high-frequency response, so that the frequency response of the circuit has a good flatness.

In this embodiment, the control processing module 27 outputs the offset signal OFFSET to the D/A conversion module 28, and the D/A conversion module 28 converts the signal into an analog signal and sends it to the operational amplifier 2121 through the resistor 2125 for adjusting the operation The output terminal voltage of the amplifier 2121, when the input signal has a large bias, can adjust OFFSET so that the output of the operational amplifier 2121 is within the allowable operating voltage range. The signal attenuated by the operational amplifier 2121 is sent to the signal processing module 22 .

The signal processing module 22 includes a programmable amplifier 23 , a bandwidth limiting module 24 , an ADC driving module 25 , an A/D converting module 26 and a control processing module 27 connected in series in sequence. The programmable amplifier 23 receives the signal output by the input attenuation module 31, performs signal processing according to the gain control signal GainControl output by the control processing module 27, realizes signal amplification to the oscilloscope, and then sends the amplified signal to the bandwidth limiting module 24 for control processing Module 27 outputs bandwidth limiting signal BWLMT to bandwidth limiting module 24 to realize the selection of bandwidth limiting, and the signal output by bandwidth limiting module 24 is sent to ADC driver module 25, and the signal is adjusted into a signal that A/D conversion module 26 is suitable for collecting, then by The A/D conversion module 26 performs analog-to-digital conversion of the signal, and finally sends it to the control processing module 27 for signal processing, for processing such as signal storage and display.

As a further illustration, the resistance-capacitance network 310 in this embodiment can also be composed of two or more than three resistance-capacitance circuits, and at the same time, it is necessary to select a switch 3111 with a corresponding input terminal to achieve input attenuation with more attenuation ratios. The circuit further expands the dynamic range of the input signal.

As a further illustration, the resistor 205, capacitor 206, resistor 3101, capacitor 3102, resistor 3103, capacitor 3104, resistor 3105, capacitor 3106, resistor 3107, and capacitor 3108 in this embodiment can be composed of multiple resistors and multiple capacitors in series Or realize in parallel, as long as the resistance value meets the needs, and the capacitor can be an adjustable capacitor, so that the values of the resistor and capacitor can be fine-tuned, which is more convenient for circuit debugging.

As a further illustration, the compensation network 3120 in this embodiment may be connected in series with a compensation resistor, or the method as in the first embodiment may be used to realize the frequency response of the adjustment circuit by connecting the compensation resistor and the compensation capacitor in series.

As a further illustration, in the two embodiments of the present invention, a damping resistor can be connected in parallel in the RC network to adjust the response of the circuit to the step signal.

As a further illustration, in the two embodiments of the present invention, the analog switch can be selected such as ADG904 and ADG919 of ADI Company.

As a further illustration, in the two embodiments of the present invention, the operational amplifier needs to be a field-effect type high-bandwidth amplifier, such as OPA6xx series of TI Company.

The digital oscilloscope of the present invention, by providing an input attenuation circuit with multiple attenuation ratios, simultaneously realizes high input impedance and greatly expands the dynamic range of the input signal, and by providing a compensation network, realizes adjusting the frequency response of the circuit, making the circuit Low frequency response is consistent with high frequency response.

The above specific embodiments are only used to illustrate the present invention, not to limit the present invention. Any non-creative creations made by those skilled in the art based on the above design ideas should be considered within the scope of protection of this patent.

Claims (7)

1. An oscilloscope with an analog front-end circuit, comprising a signal input module, an input attenuation module, and a control processing module connected in series in sequence, It is characterized in that, The input attenuation module includes a resistance-capacitance network, a switch unit and an operational amplifier unit connected in series in sequence, The resistance-capacitance network includes a plurality of resistance-capacity circuits, and the input end of each resistance-capacity circuit is connected with the output end of the signal input module, The switch unit is used to select any one output terminal of the RC network to be connected to the operational amplifier unit, and ground the other output terminals of the RC network. 2. The oscilloscope according to claim 1, characterized in that, among the plurality of resistance-capacitance circuits, at least one resistance-capacitance circuit comprises a circuit composed of a resistor and a capacitor connected in parallel. 3. The oscilloscope according to claim 2, wherein, among the plurality of resistance-capacitance circuits, at least one resistance-capacitance circuit includes two output terminals, and includes a first circuit, a second circuit and a third circuit , the first circuit and the second circuit are connected in series between the input terminal and an output terminal of the resistance-capacitance circuit, and the first circuit and the third circuit are connected in series in the Between the input terminal and the other output terminal of the resistance-capacitance circuit, the first circuit, the second circuit and the third circuit are circuits composed of a resistor and a capacitor connected in parallel. 4. The oscilloscope according to claim 1, 2 or 3, wherein the operational amplifier unit comprises an operational amplifier, and the operational amplifier has a positive input terminal, a negative input terminal and an output terminal, The positive input terminal of the operational amplifier is used for grounding, the negative input terminal of the operational amplifier is used for connecting the switch unit, and a feedback resistor. 5. The oscilloscope according to claim 4, characterized in that a compensation circuit is connected in parallel at both ends of the feedback resistor. 6. The oscilloscope according to claim 5, wherein the compensation circuit is composed of a compensation resistor and a compensation capacitor connected in series. 7. The oscilloscope according to claim 5, wherein the compensation circuit comprises a varactor diode connected in parallel at the two ends of the feedback resistor, and the control processing module communicates with a D/A conversion module through a D/A conversion module. The control terminal of the varactor diode is connected.

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