CN201449401U - Oscilloscope Vertical Input Channel Protector - Google Patents

Abstract

The utility model relates to a protector for a vertical input channel of an oscilloscope, comprising a DC power supply module and an amplifying circuit capable of providing DC power to the protector for a vertical input channel of an oscilloscope; a fixed attenuator, a protection tube, an impedance matching network and a bias adjustment circuit; The purpose of the utility model is to provide an oscilloscope vertical input channel protector that can set the protection threshold according to actual needs, does not change the characteristic impedance of the original circuit, and does not generate distortion to the input signal, which solves the problem of the existing oscilloscope vertical input channel protection circuit. There are technical problems such as high protection threshold, changing the characteristic impedance of the original circuit and distorting the input signal. The vertical input channel protector of the oscilloscope does not affect the amplitude and front and rear edges of the measured signal, and also solves the problems of impedance matching and signal attenuation when the input signal is small and the protector does not protect.

Description

Oscilloscope Vertical Input Channel Protector

technical field

The utility model relates to a circuit protector, in particular to an oscilloscope vertical input channel protector for measuring fast and large-amplitude signals.

Background technique

In the physical measurement of fast pulsed rays, the amplitude of a signal often ranges from mV to several kV. In many cases, in addition to measuring the full waveform of this large-amplitude signal, it is also necessary to measure the initial segment of the mV level. However, the attenuator cannot be used for the measurement of the initial section of the signal. In this case, the vertical sensitivity of the oscilloscope needs to be set higher, so the vertical input channel of the oscilloscope is particularly vulnerable to damage.

At present, two types of protection circuits are often used in electrical measurement: one is the insurance tube plus resistance attenuation network shown in Figure 1. In this circuit, the fuse is a hot-melt device, which can withstand a large impact current, but the response speed is slow, so it often damages the resistance attenuation network. The other type is a transient voltage suppressor diode TVS (Transient Voltage Suppressor) protection circuit as shown in FIG. 2 . In this circuit, when the two ends of the TVS tube are impacted by an instantaneous large current, the impedance can be suddenly reduced at a speed of ^10-12 seconds, absorbing the large current flowing through it, and clamping the voltage between its two ends at a A lower value, so that the components of the subsequent circuit will not be damaged by the impact of transient high current, is widely used in the rapid overvoltage protection of circuit components. However, through actual circuit experiments, it can be known that TVS is suitable for preventing instantaneous interference of large surge currents such as lightning strikes and power equipment start-stops, but it is not suitable for protecting the vertical input channel of the oscilloscope when measuring fast pulse and large-amplitude signals.

"Journal of Instrumentation" 2008, Volume 29, Issue 4 discloses a protection circuit for the vertical input channel of an oscilloscope using the switching characteristics of a diode. At both ends of the diode, when the signal is greater than the forward conduction voltage of the diode, the diode acts as a switch and discharges the current, thereby protecting the following components. When the switching diode is forward-conducting, there is a microvariable resistance of several ohms to tens of ohms. The variable resistance value is inconsistent with the characteristic impedance of the original circuit, and the signal generates negative reflection here, which distorts the input signal and affects the measurement results. Therefore, the protection circuit is equipped with an impedance matching network. However, when the signal at both ends of the diode is small and the protection circuit does not work, the matching network increases the impedance of the original circuit and changes the characteristic impedance of the original circuit. The signal is reflected here, which also distorts the input signal and affects the measurement. result. It has been proved by experiments that when the input signal is small and no protective effect occurs, the entire protection circuit has about 8% positive reflection on the measured signal. At the same time, since it is connected in series in the circuit, the impedance matching network increases the protection threshold of the entire protection circuit regardless of whether the protection function occurs.

Contents of the invention

The purpose of the utility model is to provide an oscilloscope vertical input channel protector that can set the protection threshold according to actual needs, does not change the characteristic impedance of the original circuit, and does not produce distortion to the input signal, which solves the problem of the existing oscilloscope vertical input channel protection. The circuit has technical problems such as high protection threshold, changing the characteristic impedance of the original circuit, and distorting the input signal.

The technical solution of the utility model is:

An oscilloscope vertical input channel protector, including a DC power supply module U5 and an amplifying circuit U4 that can provide DC power to the oscilloscope vertical input channel protector; its special feature is that it also includes a fixed attenuator U1, a protection tube D, an impedance Matching network U2 and bias adjustment circuit U3;

One end of the fixed attenuator U1 is used as the positive input end of the vertical input channel protector of the oscilloscope, and the other end is connected to the positive input end of the amplifier circuit U4, which is used for attenuating the Negative reflection produced by variable resistance;

The two ends of the impedance matching network U2 are connected in parallel with the two input ends of the amplifier circuit U4, which is used to eliminate the impedance increase caused by the amplifier circuit U4 and the protection tube D when the input signal is small and the protection tube D does not work. positive reflection;

One end of the bias adjustment circuit U3 is connected to the DC power supply circuit U5, and the other end is connected to the positive input end of the amplifier circuit U4, so that the output of the vertical input channel protector of the oscilloscope is zero when there is no signal input;

The protection tube D is a high-frequency switching diode, and its two ends are connected in parallel with the two input terminals of the amplifier circuit U4, and are used to clamp the input of the amplifier at the high frequency when the input signal of the vertical input channel protector of the oscilloscope is large. The forward conduction voltage of the switching diode;

The reverse input terminal of the amplifying circuit U4 is grounded, and its output terminal is used as the output terminal of the vertical input channel protector of the oscilloscope to amplify the input signal attenuated by the fixed attenuator U1, and its amplification factor is the same as the attenuation factor.

The above-mentioned DC power supply module U5 includes a bipolar switching DC power supply (+VCC/-VCC) and a power supply polarity selection switch.

The above-mentioned impedance matching network U2 is a matching resistor R3; the bias adjustment circuit U3 includes a series adjustment resistor R4 and a trimming resistor Rw; the amplifying circuit U4 includes an integrated operational amplifier A, an amplifying resistor R1 and a feedback resistor R2, the amplifying The resistor R1 is connected to the positive input terminal of the integrated operational amplifier A, and the feedback resistor R2 is connected between the output terminal of the integrated operational amplifier A and the positive input terminal.

The above-mentioned fixed attenuator U1 is a patch attenuator.

The protection tube D is a high-frequency switching diode MIMA141KT1-D, and the integrated operational amplifier A is an integrated operational amplifier THS3201.

The technical effect of the utility model is:

1. The utility model uses a fixed attenuator at the input end of the protector. When the protection tube is turned on, the negative reflection signal generated by the microvariable resistance is attenuated by the fixed attenuator, so that the protector will not affect the amplitude and front and rear of the measured signal. influence along.

2. The signal does not produce regular reflection. The utility model adds an impedance matching network and uses an amplifying circuit composed of an integrated operational amplifier, which effectively solves the problems of impedance matching and signal attenuation when the input signal is small and the protector does not protect.

3. Due to the high bandwidth of the selected device, the protector of the utility model can work reliably in the frequency band of DC-200MHz.

4. As long as the input signal is greater than the set protection threshold, the protector of the utility model can work normally, so it can effectively protect the vertical input channel of the oscilloscope.

5. Reduce costs. Since the maintenance cost of the existing high-end oscilloscope due to the damage of the vertical input channel is tens of thousands of yuan, the utility model can save a lot of money and reduce the use cost.

Description of drawings

Fig. 1 is the functional block diagram of existing insurance tube plus resistance attenuation network;

Fig. 2 is a schematic block diagram of an existing TVS tube protection circuit;

Fig. 3 is the functional block diagram of the vertical input channel protector of the oscilloscope of the present invention;

Fig. 4 is the circuit diagram of the embodiment of the vertical input channel protector of the oscilloscope of the present invention;

Reference signs: R1-amplifying resistance, R2-feedback resistance, R3-matching resistance, R4-adjusting resistance, Rw-trimming resistance, U1-fixed attenuator, U2-impedance matching network, U3-bias adjustment circuit, U4- Amplifying circuit, U5-DC power supply module, D-protection tube, A-integrated operational amplifier, +VCC/-VCC-bipolar switching DC power supply.

Detailed ways

The utility model oscilloscope vertical input channel protector, referring to Fig. 3, includes a fixed attenuator U1, an impedance matching network U2, a bias adjustment circuit U3, a protection tube D, an amplifying circuit U4 and a DC power supply module U5 for providing DC power to the protector .

Referring to Figure 4, the fixed attenuator U1 is used as the positive input terminal of the protector of the vertical input channel of the oscilloscope, and is used to attenuate the negative reflection generated by the microvaristor when the protection tube D is turned on due to a large input signal. Considering the size of the protector, the fixed attenuator U1 can use a patch device. Because the protection tube uses a switching diode, the microvariable resistance of several ohms to tens of ohms in the forward conduction is inconsistent with the characteristic impedance of the original circuit, and the measured signal produces negative reflection here, which distorts the input signal, so the attenuator is used for The negative reflection is attenuated to eliminate the influence of the negative reflection on the input signal to be measured. The attenuation multiple of the attenuator can be set according to the actual protection threshold. The protection threshold is the product of the attenuation factor and the diode conduction voltage.

The impedance matching network U2 is a pure resistance, that is, the matching resistor R3, which is set after the fixed attenuator U1, and connected in parallel with the input end of the protection tube D and the amplifier circuit U4, to eliminate the ineffectiveness of the protection tube D when the input signal is small The regular reflection generated by the increase of the impedance introduced by the amplifier circuit U4 and the protection tube D makes the input impedance of the entire protector match the impedance of the measurement circuit. The characteristic impedance of the coaxial cable measurement line is divided into 50Ω and 75Ω, usually 50Ω, and the matching resistor R3 is usually 50Ω.

The bias adjustment circuit U3 includes a series fixed resistor R4 and a fine-tuning resistor Rw; it is arranged between the DC power supply circuit U5 and the impedance matching network U2, and is used to make the output of the protector be zero when there is no signal input, that is, the baseline is kept balanced; The adjustment resistor R4 is used for coarse adjustment, and its value is about 100kΩ; the fine-tuning resistor Rw is used for fine adjustment, and its value is about 10kΩ.

The protection tube D is a high-frequency switching diode MIMA141KT1-D, and its two ends are connected in parallel with the two input terminals of the amplifier circuit U4, which is used to make the protector clamp the input of the amplifier to the forward conduction of the diode when the input signal is large. voltage, thereby protecting the vertical input channel of the oscilloscope at the rear end.

The amplifying circuit U4 is used to amplify the input signal attenuated by the fixed attenuator U1. In order to prevent the input signal from being attenuated, the amplification factor of the amplifier circuit is the same as the attenuation factor of the attenuator. The amplifying circuit U4 includes an integrated operational amplifier THS3201, an amplifying resistor R1 and a feedback resistor R2, the amplifying resistor R1 is connected to the positive input terminal of the integrated operational amplifier A, and the feedback resistor R2 is connected between the output terminal of the integrated operational amplifier A and the positive input terminal .

The DC power module U5 is powered by ±5V, 100mA high-precision bipolar switching DC power supply, and a power polarity selection switch is designed; when debugging, if the output signal of the protector is forward biased, the bias power supply is connected to the bipolar The negative power supply -VCC of the bipolar switching DC power supply; if the output signal of the protector is negatively biased, the bias power supply is connected to the positive power supply VCC of the bipolar switching DC power supply.

When the attenuation multiple is 5, R1 is 100Ω, R2 is 399Ω, R3 is 50Ω, R4 is 100kΩ, and Rw is 10kΩ to form an oscilloscope vertical input channel protector with a protection threshold of 3.5V.

Claims (5)

1. a vertical input channel protector of oscilloscope comprises DC power supplier (U5), amplifying circuit (U4) that direct supply can be provided to vertical input channel protector of oscilloscope; It is characterized in that: it also comprises fixed attenuator (U1), protection tube (D), impedance matching network (U2) and bias set circuti (U3);

One end of described fixed attenuator (U1) is as the positive input of vertical input channel protector of oscilloscope, the positive input of another termination amplifying circuit (U4), the negative reflection that little power transformation resistance produced when it was used for decay because of big protection tube (D) conducting of input signal;

The two ends of described impedance matching network (U2) are in parallel with two input ends of amplifying circuit (U4), are used for eliminating when the less and protection tube (D) of input signal is inoperative the normal reflection that impedance increase because of amplifying circuit (U4) and protection tube (D) introducing produces;

One termination DC power supply circuit (U5) of described bias set circuti (U3), the positive input of another termination amplifying circuit (U4) is used to make vertical input channel protector of oscilloscope to be output as zero when no signal is imported;

Described protection tube (D) is the HF switch diode, its two ends are in parallel with two input ends of amplifying circuit (U4), are used for making the input of amplifier be clamped at the forward conduction voltage of this HF switch diode when input signal is big at vertical input channel protector of oscilloscope;

The reverse input end ground connection of described amplifying circuit (U4), its output terminal is as the output terminal of vertical input channel protector of oscilloscope, is used to amplify the input signal that is fixed after the attenuator U1 decay, and its enlargement factor is identical with attenuation multiple.

2. vertical input channel protector of oscilloscope according to claim 1 is characterized in that: described DC power supplier (U5) comprise bipolarity switch DC power supply (+VCC/-VCC) and the electric power polarity selector switch.

3. according to claim 1 or 2 described vertical input channel protector of oscilloscope, it is characterized in that: described impedance matching network (U2) is build-out resistor (R3); Described bias set circuti (U3) comprises the adjusting resistance (R4) and the semifixed resistor (Rw) of series connection; Described amplifying circuit (U4) comprises integrated operational amplifier (A), amplifies resistance (R1) and feedback resistance (R2), described amplification resistance (R1) is connected the positive input of integrated operational amplifier (A), and described feedback resistance (R2) is connected between the output terminal and positive input of integrated operational amplifier (A).

4. vertical input channel protector of oscilloscope according to claim 3 is characterized in that: described fixed attenuator (U1) is SMD attenuator.

5. vertical input channel protector of oscilloscope according to claim 3 is characterized in that: described protection tube (D) is HF switch diode MIMA141KT1-D, and described integrated operational amplifier (A) is integrated operational amplifier THS3201.

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