JP2003161747A - Method and circuit for measurement of high-frequency electric power - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-frequency electric power measuring circuit whose measurement accuracy is high by constituting a bridge circuit by using an indirectly heated thermistor. <P>SOLUTION: The high-frequency electric power measuring circuit is constituted of an indirectly heated thermistor TH1 in which signal electric power to be measured from the outside is input to a heater resistance R1, an indirectly heated thermistor TH2 in which a substitutional voltage corresponding to the signal electric power to be measured is input to a heater resistance R4, a fixed resistance R5 and a fixed resistance R6 which constitute the bridge circuit 1 by including a heat detecting element R2 in the thermistor TH1 and a heat detecting element R3 in the thermistor TH2, a differential amplifier 2 which amplifies a differential voltage based on a change in resistance values of the elements R2, R3 in the thermistor TH1 and the thermistor TH2 and which outputs the substitutional voltage, and a voltmeter 3 which measures the substitutional voltage to be output from the differential amplifier 2. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency power measuring circuit, and more particularly to a high precision high frequency power measuring circuit using an indirectly heated thermistor.

[0002]

2. Description of the Related Art Conventionally, this type of high frequency power measuring circuit has been
A circuit that measures effective power using a thermistor is widely used.

There are two types of thermistors, a negative thermistor (NTC) whose electric resistance decreases as the temperature rises, and a positive thermistor (PTC) whose electric resistance increases, and a thermistor called a direct heating type. There is a thermistor called a heat type.

The direct-heat type thermistor is a thermistor which utilizes the fact that the temperature rises due to self-heating due to direct energization and the electrical resistance changes secondarily. The indirectly heated thermistor is heated by an external heater. It is a thermistor that utilizes the change in its electrical resistance.

In the conventional high frequency power measuring circuit using the direct heating type thermistor, the resistance value of the thermistor is changed by inputting the signal power to be measured, and further, in the low frequency range by using a coupling capacitor for cutting off direct current. Since the input impedance is deviated, there is a problem that the power cannot be accurately measured in a wide frequency band.

Further, in a high frequency power measuring circuit using a direct heat type thermistor, there is also an automatic balancing type power measuring circuit which measures the power by balancing the input of the signal power to be measured and the replacement AC signal with a thermistor bridge circuit. However, there is a problem that the replacement AC signal generating circuit is complicated.

[0007]

The conventional high-frequency power measuring circuit described above is accurate because the resistance value of the thermistor changes when a direct heating type thermistor is used and the input impedance due to the coupling capacitor is deviated. The disadvantage is that it cannot measure the power.

Further, the automatic balance type power measuring circuit using the direct heating type thermistor has a drawback that the replacement AC signal generating circuit is complicated.

The object of the present invention is to eliminate such drawbacks of the prior art by constructing a bridge circuit using an indirectly heated thermistor, whereby a high frequency power measuring circuit capable of highly accurate power measurement in a wide frequency band. To provide.

[0010]

The high frequency power measuring method of the present invention comprises a bridge circuit composed of first and second indirectly heated thermistors and first and second fixed resistors. An external signal power to be measured is input to the thermal thermistor, and a differential voltage based on a resistance value change of the first indirectly heated thermistor and the second indirectly heated thermistor is input to the second indirectly heated thermistor. It is characterized in that an amplified replacement voltage is inputted and the signal power under measurement is calculated and obtained from the amplified replacement voltage.

The first and second indirectly heated thermistors each include a heat sensing element and a heater resistance for heating the heat sensing element, and each heat sensing element has the same resistance temperature characteristic.
A bridge circuit is formed with the first and second fixed resistors having the same resistance temperature characteristic, and the bridge circuit is provided close to each other.

Further, the heater resistance of the first indirectly heated thermistor is set to a characteristic impedance and the signal power to be measured is input, and the second indirectly heated thermistor is amplified by the heater resistance. Further, the replacement voltage is applied.

The high frequency power measuring circuit of the present invention is a high frequency power measuring circuit comprising a bridge circuit composed of first and second indirectly heated thermistors and first and second fixed resistors. Externally measured signal power is input to the first indirectly heated thermistor, and the second indirectly heated thermistor changes resistance values of the first indirectly heated thermistor and the second indirectly heated thermistor. It is characterized in that a replacement voltage obtained by amplifying a difference voltage based on is applied.

The first and second indirectly heated thermistors each have a heat sensing element and a heater resistance for heating the heat sensing element, and each heat sensing element has the same resistance temperature characteristic.
A bridge circuit is formed with the first and second fixed resistors having the same resistance temperature characteristic, and the bridge circuit is provided close to each other.

Further, the heater resistance of the first indirectly heated thermistor is set to a characteristic impedance and the signal power to be measured is inputted, and the second indirectly heated thermistor is amplified by the heater resistance. Further, the replacement voltage is applied.

In the high frequency power measuring circuit of the present invention, the first indirectly heated thermistor for inputting the signal power to be measured from the outside to the heater resistance, and the replacement voltage corresponding to the signal power to be measured are supplied to the heater resistance. Inputting a second indirectly heated thermistor, and first and second fixed resistors that form a bridge circuit including the heat sensing elements of the first indirectly heated thermistor and the second indirectly heated thermistor. And the first
Of the indirectly heated thermistor and the second indirectly heated thermistor, a differential amplifier that amplifies a difference voltage based on a change in resistance value of the heat sensing element and outputs the replacement voltage, and the replacement voltage is measured. It is characterized by comprising a voltage measuring means.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of the high frequency power measuring circuit of the present invention.

In this embodiment shown in FIG. 1, an indirectly heated thermistor TH1 for inputting a signal power to be measured from the outside to a heater resistance R1 and a replacement voltage corresponding to the signal power to be measured are input to a heater resistance R4. Fixed resistors R5 and R6 that form the bridge circuit 1 including the indirectly heated thermistor TH2, the heat sensing elements R2 and R3 of the indirectly heated thermistor TH1 and the indirectly heated thermistor TH2, and the indirectly heated thermistor TH1 and the indirectly heated type. The differential amplifier 2 that amplifies the difference voltage based on the resistance change of the thermal sensing elements R2 and R3 of the thermistor TH2 and outputs the replacement voltage, and the voltmeter 3 that measures the replacement voltage output from the differential amplifier 2 It is configured.

Next, the operation of the high frequency power measuring circuit of this embodiment will be described in detail with reference to FIG.

The indirectly heated thermistors TH1 and TH2 are composed of heat sensing elements R2 and R3 and heater resistors R1 and R4 for heating the heat sensing elements R2 and R3, respectively.

If the resistance value of the heater resistor R1 is set to a characteristic impedance (for example, 50Ω) and does not change with temperature, the heater resistor R1 becomes a terminating resistor for an input high frequency signal without reflection and has a wide band. Can be used.

The resistance value of the heat sensing element R2 changes according to the heat generation of the heater resistance R1, and according to the change of the resistance value,
The potential of the terminal P2 is changed.

The heat sensing element R3 is selected to have the same electrical characteristics with respect to the resistance value and temperature as the heat sensing element R2, and is arranged so that the indirectly heated thermistors TH1 and TH2 have equal thermal environmental conditions. As a result, even if the ambient temperature changes or the signal power to be measured changes, fluctuations in the potential difference due to changes in the resistance values of the heat sensing elements R2 and R3 can be minimized and temperature compensation can be performed.

The heater resistor R4 is a heat sensing element R2, R3.
The voltage amplified by the differential amplifier 2 is input according to the difference in the voltage drop due to the change in the resistance value, and heats the heat sensing element R3. Therefore, the heater resistance R4 does not have to have the same resistance value as the heater resistance R1 as long as the characteristics do not change with temperature change.

The fixed resistors R5 and R6 are selected to have the same resistance value and electrical characteristics with respect to temperature, and constitute the bridge circuit 1 together with the heat sensing elements R2 and R3.

The resistor 7 appropriately divides the voltage applied to the bridge circuit, and can be inserted on the ground potential side.

The differential amplifier 2 amplifies the potential difference based on the resistance change of the heat sensing elements R2 and R3, and supplies the amplified voltage to the heater resistor R4 of the indirectly heated thermistor TH2.

A resistor R provided on the output side of the differential amplifier 2
The capacitor 10 and the capacitor C1 are for smoothing the output of the differential amplifier 2, and the diode D1 is for limiting the negative voltage so that the reverse voltage is not applied to the voltmeter 3.

Next, the operation when the signal power to be measured is input will be described.

First, when the signal power to be measured is not input, the heater resistance R1 of the indirectly heated thermistor TH1 does not generate heat, so the temperature of the heat sensing element R2 is almost the same as the ambient temperature in a steady state. Therefore, the terminal P2
The voltage value of is a steady-state value divided by the resistors R7, R5, and R2 from the positive power supply voltage. Also, the resistor R5,
Since the value of R6 is the same and the resistance values of the heat sensing elements R2 and R3 are also the same, the terminals P2 and P3 have the same potential under the condition that the potential of the terminal P4 is 0V. The differential amplifier 2 is
There is no output because the terminals P2 and P3 have the same potential. Therefore, the voltage value of the terminal P4 is 0V, and the heater resistance R
No fever at 4.

When the signal power to be measured is input from the high frequency signal input terminal P1, the signal power to be measured is consumed by the heater resistor R1 of the indirectly heated thermistor TH1 and becomes a heat source to heat the heat sensing element R2. The heat sensing element R2 is heated and its temperature rises, and its electric resistance value increases. Therefore, as the potential of the terminal P2 rises, the differential amplifier 2 generates a positive voltage at its output. The positive voltage generated at the output of the differential amplifier 2 is the resistance R10 and the capacitor C1.
And is applied to the heater resistance R4 of the indirectly heated thermistor TH2. At this time, the diode D1 is in the off state because the reverse voltage is applied.

Heat sensing element R3 of indirectly heated thermistor TH2
When the heater resistance R4 generates heat, the electric resistance value increases,
The potential of the terminal P3 rises. The output voltage of the differential amplifier 2 decreases as the potential difference between the terminals P2 and P3 decreases, and the differential amplifier 2 enters a balanced state when the electric resistance values of the heat sensing elements R2 and R3 become equal. In this equilibrium state, the power consumed by the heater resistance R4 (R) of the indirectly heated thermistor TH2 is equal to the power consumed by the heater resistance R1 of the indirectly heated thermistor TH1 (Win), and therefore,
The voltage (V) of the terminal P4 corresponding to the electric power consumed by the heater resistance R1 of the indirectly heated thermistor TH1, that is, the replacement voltage is V ² = Win × R (1), and the voltage (V) of the terminal P4 is measured. Then, the value of the signal power under measurement input from the input terminal P1 can be obtained from the formula Win = V ² / R (2).

Next, when the signal power to be measured input from the input terminal P1 is reduced, the amount of heat generated by the heater resistance R1 of the indirectly heated thermistor TH1 is reduced, and the temperature of the heated heat sensing element R2 is reduced. The electric resistance value decreases as well. As a result, the differential amplifier 2 receives a negative potential difference and outputs a negative voltage, and this negative voltage is applied to the diode D.
Since 1 is turned on, it acts to release the charge accumulated in the capacitor C1 via the resistor R10, and no voltage is applied to the heater resistor R4 of the indirectly heated thermistor TH2. Therefore, the temperature of the heat sensing element R3 of the indirectly heated thermistor TH2 decreases and the electric resistance value also decreases. As a result, the potential of the terminal P3 follows the terminal P2 and decreases,
As the electric resistance values of the heat sensing element R2 of the indirectly heated thermistor TH1 and the heat sensing element R3 of the indirectly heated thermistor TH2 become equal, the potential difference from the terminal P3 becomes smaller and the equilibrium state is reached. Even in this state, the electric power consumed by the heater resistance R4 of TH2 is equal to the electric power (Win) consumed by the heater resistance R1 of the indirectly heated thermistor TH1. The value of the measured signal power can be obtained from the equation (2) based on the equation (1). Therefore, the value of the signal power to be measured (Win) can be obtained from the voltage (V) of the terminal P4 indicated by the voltmeter 3.

Next, another embodiment of the present invention will be described. FIG. 2 is a block diagram showing another embodiment of the high frequency power measuring circuit of the present invention.

Referring to FIG. 2, fixed resistors R5 and R6 and heat sensing elements R2 and R that constitute the bridge circuit 1 are provided.
A variable resistor RV1 is added to compensate for the slight difference in the electrical resistance value of No. 3. Also, the heat sensing elements R2 and R3
Is a thermistor (PTC) with a positive resistance temperature characteristic in Fig. 1.
However, in FIG. 2, a thermistor (NTC) having a negative resistance temperature characteristic is used. In this case, the input terminal of the differential amplifier 2 is connected to the opposite polarity to that of FIG.

[0036]

As described above, the high frequency power measuring method and the high frequency power measuring circuit of the present invention have the following effects.

The first effect is that by forming a bridge circuit with two indirectly heated thermistors having the same resistance temperature characteristic and two fixed resistors and using them in close proximity, fluctuations in the signal power under measurement and the surroundings. The effect of temperature can be removed.

The second effect is that since the input signal is terminated by the characteristic impedance (for example, 50Ω), there is no reflection and accurate power measurement in a wide frequency band is possible.

The third effect is that by using the indirectly heated thermistor, since the high frequency signal input side and the measurement circuit side are electrically insulated, it is possible to eliminate the wraparound phenomenon such as the influence of the ground potential. Is.

The fourth effect is that since the measuring circuit side is DC, the circuit structure can be simplified and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing one embodiment of a high frequency power measuring circuit of the present invention.

FIG. 2 is a block diagram showing another embodiment of the high-frequency power measuring circuit of the present invention.

[Explanation of symbols]

1 bridge circuit 2 differential amplifier 3 voltmeter

Claims (7)

[Claims] 1. A bridge circuit is composed of first and second indirectly heated thermistors and first and second fixed resistors, and a signal power to be measured from the outside is input to the first indirectly heated thermistor. Then, a replacement voltage obtained by amplifying a differential voltage based on a resistance value change of the first indirectly heated thermistor and the second indirectly heated thermistor is input to the second indirectly heated thermistor, and the amplified replaced A method for measuring high frequency power, characterized in that the measured signal power is calculated from voltage. 2. The first and second indirectly heated thermistors each include a heat sensing element and a heater resistor for heating the heat sensing element.
Each of the heat sensing elements has the same resistance temperature characteristic, forms a bridge circuit with the first and second fixed resistors having the same resistance temperature characteristic, and is provided in proximity to each other. 1. The method for measuring high frequency power according to 1. 3. A heater resistance of the first indirectly heated thermistor is set to a characteristic impedance, and the signal power to be measured is input to the first indirectly heated thermistor.
The high frequency power measuring method according to claim 1 or 2, wherein the amplified replacement voltage is applied to the heater resistance. 4. A high-frequency power measuring circuit comprising a bridge circuit composed of first and second indirectly heated thermistors and first and second fixed resistors, wherein the first indirectly heated thermistor. A replacement voltage obtained by inputting a signal power to be measured from the outside, and amplifying a differential voltage based on a change in resistance value of the first indirectly heated thermistor and the second indirectly heated thermistor by the second indirectly heated thermistor. A high-frequency power measurement circuit, characterized in that a voltage is applied. 5. The first and second indirectly heated thermistors each include a heat sensing element and a heater resistor that heats the heat sensing element.
Each of the heat sensing elements has the same resistance temperature characteristic, forms a bridge circuit with the first and second fixed resistors having the same resistance temperature characteristic, and is provided in proximity to each other. 4. The high frequency power measuring circuit according to 4. 6. The first indirectly heated thermistor has its heater resistance set to a characteristic impedance and receives the signal power to be measured, and the second indirectly heated thermistor is
The high frequency power measuring circuit according to claim 4 or 5, wherein the amplified replacement voltage is applied to the heater resistance. 7. A first indirectly heated thermistor for inputting a measured signal power from the outside to a heater resistance, and a second indirectly heated thermistor for inputting a replacement voltage corresponding to the measured signal power to a heater resistance. And first and second fixed resistors that form a bridge circuit including the heat sensing elements of the first indirectly heated thermistor and the second indirectly heated thermistor, and the first indirectly heated type. A differential amplifier that amplifies a difference voltage based on a change in resistance value of the heat sensing elements of the thermistor and the second indirectly heated thermistor and outputs the replacement voltage; and a voltage measuring unit that measures the replacement voltage. And a high-frequency power measuring circuit comprising: