JP2009145172A - Passive probe device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a passive probe device capable of acquiring stable voltage division accuracy, even when a probe head receives a great temperature change. <P>SOLUTION: In this passive probe device wherein a signal Vin to be measured is inputted into a probe head 10, and a signal having a voltage divided with a prescribed impedance ratio is outputted to an oscilloscope through a cable 21 and an interface part 30, a variable resistance means VR and a variable capacitor means VC in the interface part 30 are controlled by a correction control means 32, in correspondence with a detection signal of a temperature sensor 13 in the probe head 10, so as to compensate a change of the impedance ratio caused by a temperature change of a resistance Rhead and a capacitor Chead of the probe head 10. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a passive probe device used for an oscilloscope or the like, and more particularly to a passive probe device that can be used in a wide temperature range.

Conventionally, a passive probe has been used in many oscilloscopes because it has advantages such as being easy to cope with a wide temperature range and a wide input voltage range and being robust compared to an active probe.

  FIG. 4 is a circuit configuration diagram showing a conventional general oscilloscope passive probe device. The oscilloscope passive probe device 100 includes a probe head 1 to which a signal to be measured Vin is input, a cable 2 that propagates a signal output from the probe head 1, and an interface unit that adjusts the impedance ratio of the signal that passes through the cable 2. 3 and outputs a signal obtained by dividing the signal to be measured Vin by a predetermined impedance ratio to the input unit 4 of the oscilloscope.

  In the probe head 1, one end of the parallel circuit composed of the resistor Rhead and the capacitor Chead is connected to the input terminal 11.

  The cable 2 is a coaxial cable, and at one end thereof, the inner conductor is connected to the other end of the parallel circuit composed of the resistor Rhead and the capacitor Chead, and the outer conductor is connected to the GND terminal. The cable 2 has a stray capacitance Ccable with the GND terminal.

  In the interface unit 3, the inner conductor at the other end of the cable 2 is connected to the output terminal 31 for the coaxial cable, and the outer conductor is connected to the GND terminal. The adjustment variable capacitor Cadj has one end connected to the internal conductor of the cable 2 and the other end connected to the GND terminal so as to be in parallel with the input impedance of the oscilloscope.

  In the input unit 4 of the oscilloscope, the input terminal 41 is a terminal for a coaxial cable connected to the output terminal 31 of the passive probe device 100. The input resistance Rin and the input capacitance Cin are equivalent input impedances of the oscilloscope, each having one end connected to the input terminal 41 and the other end connected to the GND terminal. The amplifier 42 amplifies a signal input via the input terminal 41.

  The operation of the apparatus of FIG. 4 will now be described. The signal to be measured Vin is input to the probe head 1, and a signal divided by a predetermined impedance ratio is output to the input unit 4 of the oscilloscope via the cable 2 and the interface unit 3.

A parallel circuit including a resistor Rhead and a capacitor Chead in the probe head 1, an input resistance Rin and an input capacitance Cin in the oscilloscope input unit 4, an adjustment variable capacitor Cadj in the interface unit 3, and a floating capacitance Ccable in the cable 2. The parallel circuit constitutes a voltage divider for the signal to be measured Vin.

A typical example of a passive probe device with a voltage division ratio of 10: 1 (voltage gain 1/10) is shown below. From DC to the frequency f1 corresponding to the time constant of Rhead and Chead, the resistance Rhead (9 MΩ) of the probe head 1 and the input resistance Rin (1 MΩ) of the oscilloscope form an impedance ratio of 9: 1. Get the partial pressure ratio. At a frequency f1 or higher, the capacitor Chead of about 10 pF of the probe head 1, the input capacitance Cin of the oscilloscope, and all the capacitances Cin + Cadj + Ccable (about 90 pF) in parallel form an impedance ratio of 9: 1. A partial pressure ratio of 10: 1 is obtained. In this case, a resistor having a relatively small tolerance is available for the resistor, and thus a fixed resistor is usually used. However, since the capacitor and the stray capacitance have a large tolerance and a temperature coefficient, the variable capacitor Cadj is used. The impedance ratio due to the capacitance is adjusted to 9: 1 accurately.

  Prior art documents related to passive probe devices include the following.

JP-A-6-331657

  In the conventional passive probe device, the measurement with the specified partial pressure accuracy can be performed by adjusting the variable capacitor Cadj at the environmental temperature at which the measurement is performed.

However, when continuously measuring over a wide temperature range using a thermostatic chamber test or the like, the probe head 1 directly connected to the measurement target in the thermostatic chamber is placed in the same temperature environment as the measurement target. Therefore, the voltage division ratio changes due to the temperature drift of the internal resistor Rhead and the capacitor Chead. In addition, since the temperature coefficient of the resistor Rhead and the capacitor Chead are different, even if the passive probe device is adjusted in the reference temperature state, the impedance ratio due to the resistance and the impedance ratio due to the capacitance do not coincide with each other. Correct measurement cannot be performed.

FIG. 5 is a characteristic curve diagram showing frequency characteristics of voltage gain of a conventional passive probe device. There is a step in the frequency characteristic 52 (dotted line) when there is a temperature change after the adjustment, compared to the flat frequency characteristic 51 (solid line) measured directly with the passive probe device adjusted at the reference temperature.

  An object of the present invention is to provide a passive probe device that can obtain a stable partial pressure accuracy even when the probe head is subjected to a large temperature change.

In order to achieve such a problem, the invention according to claim 1 of the present invention is:
In a passive probe device in which a signal to be measured is input to a probe head and a signal divided by a predetermined impedance ratio is output to an oscilloscope via a cable and an interface unit.
Variable resistance means and variable capacitor means provided in the interface unit so as to be in parallel with the input impedance of the oscilloscope;
A temperature sensor provided in the probe head;
Correction control means for controlling the variable resistance means and the variable capacitor means in response to a detection signal of the temperature sensor so as to cancel out the change in the impedance ratio due to temperature changes in the resistance of the probe head and the capacitor. It is characterized by that.

The invention according to claim 2
The passive probe device according to claim 1,
The correction control means includes
A memory in which the probe head resistance and the temperature coefficient of the capacitor are stored in advance;
A correction value of the variable resistance means and the variable capacitor means is calculated based on a signal output from the memory in response to a detection signal output from the temperature sensor, and the variable resistance means and the variable resistance means based on the correction value And a control circuit for controlling the variable capacitor means.

The invention described in claim 3
The passive probe device according to claim 1,
The correction control means includes
A memory in which correction values of the variable resistance means and the variable capacitor means with respect to temperature changes of the probe head and the capacitor are stored in advance;
And a control circuit for controlling the variable resistor means and the variable capacitor means corresponding to the memory output corresponding to the detection signal of the temperature sensor.

The invention according to claim 4
In the passive probe device according to any one of claims 1 to 3,
The variable resistance means includes
A plurality of resistance elements;
And a switch for switching the plurality of resistance elements.

The invention according to claim 5
In the passive probe device according to any one of claims 1 to 3,
The variable capacitor means includes
A plurality of capacitor elements;
And a switch for switching the plurality of capacitors.

The invention described in claim 6
In the passive probe device according to any one of claims 1 to 3,
An electronic load is used as the variable resistance means.

The invention described in claim 7
In the passive probe device according to any one of claims 1 to 3,
A variable capacitance diode is used as the variable capacitor means.

  As is apparent from the above description, according to the present invention, a signal to be measured is input to the probe head, and a passive signal is output to the oscilloscope through the cable and the interface unit and the signal divided by a predetermined impedance ratio. In the probe apparatus, variable resistance means and variable capacitor means provided in the interface unit so as to be in parallel with the input impedance of the oscilloscope, a temperature sensor provided in the probe head, and resistance and capacitance of the probe head By providing correction control means for controlling the variable resistance means and the variable capacitor means in response to the detection signal of the temperature sensor so as to cancel out the change in the impedance ratio due to temperature change, the probe head is greatly improved. In case of a temperature change It is possible to provide a passive probe device capable of obtaining stable min 圧確 degree.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a configuration block diagram showing an example of a passive probe apparatus according to an embodiment of the present invention. The same parts as those in FIG. 4 are denoted by the same symbols, and redundant description is omitted.

In the passive probe device 101, the temperature sensor 13 monitors the temperature of the probe head 10 and outputs a temperature detection signal to the transmission line 21. The control circuit 321 of the interface unit 30 controls the values of the variable resistance means VR and the variable capacitor means VC based on a signal output from the memory 322 corresponding to the temperature detection signal input via the transmission line 21. The memory 322 is a calibration data memory in which the temperature coefficients of the resistance Rhead and the capacitor Chead of the probe head 10 are stored in advance.

Here, the control circuit 321 and the memory 322 correspond to the detection signal of the temperature sensor 13 in accordance with the detection signal of the temperature sensor 13 so that the change of the impedance ratio due to the temperature change of the resistance Rhead of the probe head 10 and the capacitor Chead is canceled out. And the correction control means 32 which controls the variable capacitor means VC is comprised.

FIG. 2 is a circuit diagram showing an example of the variable resistance means VR. In series with the main resistance element Rmain, a step switching circuit is connected in which a plurality of resistors R1 to Rn weighted by binary steps or the like are switched by switches S11 to S1n.

FIG. 3 is a circuit diagram showing an example of the variable capacitor means VC. In parallel with the variable main capacitor element Cmain, a step switching circuit is connected in which a plurality of capacitors C1 to Cn weighted by binary steps or the like are switched by switches S21 to S2n.
The operation of the apparatus of FIG. 1 will now be described.

  A temperature detection signal output from the temperature sensor 13 in the probe head 10 is sent to the control circuit 321 via the transmission line 21. The control circuit 321 reads the temperature coefficients of the resistance Rhead and the capacitor Chead of the probe head 10 corresponding to the temperature detection signal from the memory 322, and cancels the impedance ratio change due to the temperature change of the resistance Rhead and the capacitor Chead based on this signal. Thus, the correction values of the variable resistor means VR and the variable capacitor means VC are calculated. Based on this correction value, the control circuit 321 controls the values of the variable resistance means VR and the variable capacitor means VC.

The initial setting of the passive probe device 101 is performed as follows.
The temperature coefficients of the resistance Rhead and the capacitor Chead of the probe head 10 are measured in advance and stored in the memory 322.
Further, in a state where the passive probe device 101 is connected to an oscilloscope at normal temperature, the variable resistance means VR is set to the set center value, and the variable capacitor means VC is set to the center of the variable range by the weighting capacitors C1 to Cn, the frequency characteristics are The variable main capacitor Cmain of the probe is adjusted so as to be flat. By initially setting the variable resistance means VR and the variable capacitor means VC in this way, the values can be controlled in both plus and minus directions.

During operation of the passive probe device 101, the temperature sensor 13 of the probe head 10 always monitors the temperature of the probe head 10. When a temperature change is detected during the measurement, the control circuit 321 reads the temperature coefficients of the resistance Rhead and the capacitor Chead of the probe head 10 from the memory 322, and maintains an impedance ratio of 9: 1 based on the temperature coefficient data. The values of the variable resistance means VR and the variable capacitor means VC are calculated and set as the values of the variable resistance means VR and the variable capacitor means VC.

  As described above, the variable resistor means VR and the variable capacitor means VC have a plurality of resistors R1 to Rn and capacitors C1 to Cn weighted by binary steps and the like, and the main capacitor Cmain is variable. The adjustment range and setting resolution required for the correction can be obtained.

According to the passive probe device configured as described above, a robust passive probe device that can easily handle a wide temperature range and a wide input voltage range as compared with the active probe has a built-in compensation circuit for temperature change, Since the influence of the temperature coefficient of the resistor and capacitor can be corrected, constant voltage division accuracy and frequency flatness can be automatically realized over a wide temperature range without having a special mechanism on the oscilloscope side. Can do.

  The correction control means 32 corresponds to a memory in which correction values of the variable resistance means VR and the variable capacitor means VC with respect to temperature changes of the resistance Rhead and the capacitor Chead of the probe head 10 are stored in advance, and a detection signal of the temperature sensor 13. You may comprise with the control circuit which controls the variable resistance means VR and the variable capacitor means VC corresponding to a memory output.

Further, the variable resistance means VR of the probe interface unit 30 may use an electronic load or the like that can be continuously changed, instead of step switching by a switch.

  The variable capacitor means VC of the probe interface unit 30 may be a variable capacitance diode or the like that can be continuously varied, instead of step switching by a switch.

Further, the impedance ratio is not limited to 9: 1 and can take any value.

Further, the passive probe device according to the present invention is not limited to an oscilloscope but can be used in various measuring instruments.

1 is a configuration block diagram showing an example of a passive probe device according to an embodiment of the present invention. It is a circuit diagram which shows an example of the variable resistance means VR. It is a circuit diagram which shows an example of the variable capacitor means VC. It is a circuit block diagram which shows the conventional general passive probe apparatus for oscilloscopes. It is a characteristic curve figure which shows the frequency characteristic of the voltage gain of the conventional passive probe apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Probe head 21 Cable 13 Temperature sensor 30 Interface part 32 Correction control means 101 Passive probe apparatus 321 Control circuit 322 Memory C1-Cn Multiple capacitor element Chead Probe head capacitor R1-Rn Multiple resistance element Rhead Probe head resistance S11- S1n Switches S21 to S2n for switching a plurality of resistance elements Switches VC for switching a plurality of capacitors Variable capacitor means VR Variable resistance means Vin Signal to be measured

Claims (7)

In a passive probe device in which a signal to be measured is input to a probe head and a signal divided by a predetermined impedance ratio is output to an oscilloscope via a cable and an interface unit.
Variable resistance means and variable capacitor means provided in the interface unit so as to be in parallel with the input impedance of the oscilloscope;
A temperature sensor provided in the probe head;
Correction control means for controlling the variable resistance means and the variable capacitor means in response to a detection signal of the temperature sensor so as to cancel out the change in the impedance ratio due to temperature changes in the resistance of the probe head and the capacitor. A passive probe device characterized by that. The correction control means includes
A memory in which the probe head resistance and the temperature coefficient of the capacitor are stored in advance;
A correction value of the variable resistance means and the variable capacitor means is calculated based on a signal output from the memory in response to a detection signal output from the temperature sensor, and the variable resistance means and the variable resistance means based on the correction value The passive probe apparatus according to claim 1, further comprising a control circuit that controls the variable capacitor means. The correction control means includes
A memory in which correction values of the variable resistance means and the variable capacitor means with respect to temperature changes of the probe head and the capacitor are stored in advance;
2. The passive probe device according to claim 1, further comprising a control circuit for controlling the variable resistance means and the variable capacitor means in response to the memory output corresponding to the detection signal of the temperature sensor. The variable resistance means includes
A plurality of resistance elements;
The passive probe device according to any one of claims 1 to 3, further comprising a switch for switching the plurality of resistance elements. The variable capacitor means includes
A plurality of capacitor elements;
The passive probe device according to any one of claims 1 to 3, further comprising a switch for switching the plurality of capacitors. 4. The passive probe device according to claim 1, wherein an electronic load is used as the variable resistance means. 4. The passive probe device according to claim 1, wherein a variable capacitance diode is used as the variable capacitor means.

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