JPH0346332Y2 - - Google Patents

Description

[Detailed description of the invention] <Industrial application field> The invention generates a main signal pulse whose on-off duty ratio is related to the capacitance value of a variable capacitance element that changes according to an input physical quantity, and The present invention relates to a physical quantity conversion device that transmits a device output based on pulses, and more particularly to a physical quantity conversion device that generates a temperature correction signal based on a pulse signal from a detection circuit and performs temperature compensation using this signal.

<Conventional Example> A physical quantity conversion device that detects the above-mentioned change in capacitance value as a pulse signal of an on-off duty ratio related thereto is known from, for example, Japanese Patent Laid-Open No. 14714/1983. In addition, regarding a method of electrically correcting temperature fluctuation errors caused by mechanical mismatching of the detector in such a device, the applicant has proposed a physical quantity conversion system equipped with a temperature correction circuit as shown in Figure 1. An application for the device has been filed.

In this figure, the part surrounded by the one-dot chain line is the detector part, the part is the detection circuit part, the part is the conversion circuit part that transmits the on-off duty pulse signal from this detection circuit as a current output, and the part is the part from the above-mentioned detection circuit. This is a temperature correction signal generation circuit portion that generates a temperature correction signal based on the pulse signal.

The detector portion is, for example, a differential capacitance type sensor in which the capacitances C _H and _CL differentially change depending on the input physical quantity.

The detection circuit part is, for example, disclosed in the previous publication, JP-A-57
A circuit as shown in No. 14714, which has a simple circuit configuration and is not easily affected by stray capacitance, is used. In this circuit, G ₁ and G ₂ have variable capacitance on the output side.
A NAND gate connected to one pole of C _H and _CL , _G3 is a NAND gate whose inputs are connected to the outputs of NAND gates _G1 and _G2 , and the output side is connected to one end of the constant value current limiting circuit _CC1 . The other end of this constant value current limiting circuit is the other pole of the variable capacitors C _H and _CL and is connected to the movable electrode as a common connection point.
COM is a comparator with one input connected to the connection point A between the movable electrode and constant value current limiting circuit CC ₁ , and the other input connected to the reference power supply, and the output pulse from this is connected to the counter CT in the subsequent stage. ₁ and at the same time NAND gate G ₁ through inverter G ₄ ,
G is given to one input of ₂ . Furthermore, the pulse signal from the counter CT ₁ is applied to the other input of the NAND gate G ₂ , and the pulse signal obtained by inverting the output of the counter CT ₁ by the inverter G ₅ is applied to the other input of the NAND gate G ₁ . ing.

The operation of the detection circuit having such a configuration will be explained. The gate circuits G ₁ to _{G 5} act as switching means for selectively applying the outputs of the gates G ₁ and G ₂ to one pole of the variable capacitances C _H and _CL . When a gate output is given to one of the variable capacitors, charging and discharging to this capacitor is performed via the constant value current limiting circuit _CC1 ,
A pulse signal having a width corresponding to this variable capacitance is output from the comparator COM. This pulse width signal is applied to a counter CT ₁ and once a certain number of pulses have been counted, the output of the count is inverted and the other variable capacitance is then measured. As a result, the on- _off duty ratio C _L /(C _H +
A main signal pulse associated with the variable capacitance is obtained, C _L ).

In the conversion circuit section, FL ₁ is a smoothing circuit that smoothes the main signal pulse from the detection circuit, and A ₁ is a non-inverting input terminal that adds the bias voltage from variable resistor VR ₁ to the voltage obtained in smoothing circuit FL ₁ . This amplifier has a feedback voltage from a feedback resistor R _f applied to its inverting input terminal, and its output is given to a transistor T _r1 for output current control.
T ₁ and T ₂ are positive and negative terminals, which are connected to the load R _l and the power source E _S by a pair of electric wires L ₁ and L ₂ . CC ₂ is a constant current circuit, and ZD is a Zener diode that supplies a constant voltage V _Z as a circuit power supply.

Such a conversion circuit is extremely common and detailed explanation will be omitted, but the main pulse signal given from the previous stage detection circuit is smoothed in the smoothing circuit FL ₁ and given to the operational amplifier A ₁ , and this output voltage is The transistor T _r1 is controlled by
Output voltage I _p related to the variable capacitance above is applied to L ₁ and L ₂
flows.

In the temperature correction signal generation circuit, MM ₁ is a monostable multivibrator to which the main signal pulse from the detection circuit is applied, and SW ₁ is a switch driven by a pulse signal with a constant time width from this monostable multivibrator. , switching the main signal pulse. SW ₂ and SW ₃ are switches driven in opposite phases by the inverted main signal pulse given by the inverter G ₅ , and the switch SW ₂ is turned on when the above-mentioned inverted main signal pulse is “H”. FL ₃ is a smoothing circuit that smoothes the pulse signal applied via switch SW ₂ , SW ₄ and SW ₅ are switches driven in opposite phase by the above main signal pulse, and switch SW ₂ is a smoothing circuit that smooths the pulse signal given through switch SW 2. is turned on when is "H". FL ₄ is a smoothing circuit that smoothes the pulse signal applied via switch SW ₄ , A ₂ is a smoothing circuit to which a voltage proportional to the voltage obtained by FL ₃ is applied to the inverting input terminal, and a smoothing circuit to the non-inverting input terminal. The obtained voltage is applied to FL ₄ , and it is an operational amplifier that performs these subtractions. In addition, monostable multivibrator
The output pulses of NAND gates G ₁ and G ₂ whose periods are related to the variable capacitors C _H and _CL can also be used as input pulses _of MM 1.

The operation of this temperature correction signal generation circuit will be explained with reference to the waveform diagram of FIG. Figure 2a shows the _on -off duty ratio T ₁ /(T ₁
+T ₂ ) main signal pulse. However, T ₁ and T ₂ have the following relationship, respectively: T ₁ ∝C _L = C ₀・ε1/1−K ₁ ΔP …(1) T2∝C _H =C ₀・ε1/1+K ₁ ΔP …(2) (However, C ₀ : initial capacitance value,
ε: Dielectric constant of pressure medium, ΔP: Pressure change, K ₁ :
constant).

T ₁ /(T ₁ +T ₂ ) can be further rewritten as follows from equations (1) and (2) above.

T ₁ /T ₁ +T ₂ = C _L /C _H +C _L = 1 + K ₁ ΔP/2...(3) Figure 2 b shows the output of the monostable multivibrator MM ₁ , and at the rising edge of the pulse shown in Figure 2 a. Triggered capacity of this monostable multivibrator
It is a pulse with a constant time width T ₀ determined by C ₀ and resistance R ₀ . The switch SW ₁ is driven by this constant time width pulse, and passes the pulse with pulse width T ₁ for a period of T ₀ . As a result, the switch SW ₁ performs the calculation T ₁ /T ₀ ∝ε/1−K ₁ ΔP・Vz (4), and the related DC voltage is obtained at point B of the smoothing circuit FL ₂ . .

This DC voltage is multiplied by the above-mentioned inverted main signal pulse with an on-off duty ratio of T ₂ /(T ₁ +T ₂ ) in the switch SW ₂ , and is sent to the smoothing circuit FL ₃ as shown below.
Obtain the signal voltage V _FL3 related to the dielectric constant ε.

V _FL3 =T ₁ /T ₀・T ₂ /T ₁ +T ₂ ∝εVz/1−K ₁ ΔP・1−K ₁ ΔP/2=ε/2・Vz …(5) On the other hand, the dielectric constant ε is ε = ε ₀ (1+αΔt) ...(6) Since the voltage V _FL3 is a signal related to temperature, ε ₀ is the dielectric constant of the pressure medium at a reference temperature such as room temperature 20℃, α is the pressure media-specific constants).

Voltage V _FL3 , e.g. conversion circuit operational amplifier
By adding it to the signal voltage and applying it to the non-inverting input terminal of _A1 , it is possible to correct zero-point temperature fluctuations caused by mismatching of the detector mechanism.

On the other hand, for the temperature correction signal for span fluctuation correction, the above correction signal is added to a switch circuit consisting of switches SW ₄ and SW ₅ in the subsequent stage, multiplied by the main signal pulse, and the above multiplication result is combined with the signal voltage in amplifier A _2.
V can be obtained by subtracting with _FL3 . In other words, switch SW ₄ has a signal voltage of ε・Vz/2.
Turn V _FL3 on and off with the main signal pulse, smoothing circuit FL ₄
Generate a voltage V _FL4 as shown below.

V _FL4 = ε/2・1+K ₁ ΔP/2・Vz …(7) Add this voltage to the non-inverting input terminal of amplifier A ₂ ,
By subtracting the voltage ε·Vz/2 obtained from the filter circuit FL ₃ , the voltage V _A2 proportional to the dielectric constant ε and the input physical quantity ΔP as shown below can be obtained.

V _A2 ∝・K ₁ ΔP = ε ₀ (1+αΔt)K ₁ ΔP …(8) As in the case of the previous zero point correction, this correction signal is
When applied to the non-inverting input of the operational amplifier A ₁ , the coefficient of ΔP changes with temperature, which compensates for span temperature fluctuations caused by mismatching of the detector mechanics.

By the way, ₁ and T ₀ in the above equation (4) have the following relationship: T ₁ =C _L・Vz/i ₁ ...(9) T ₀ ∝C ₀・R ₀ ...(10), and equation (5) is It can be rewritten as follows.

T ₁ /T ₀・T ₂ /T ₁ +T ₂ ∝Vz/i ₁・R ₀・C _L /C ₀・Vz・C _H /C _L +C _H =Vz/i ₁・R ₀・ε/2・Vz …(11) However, i ₁ : Charging and discharging current of variable capacitances C _H and _CL .

A precondition for obtaining a correct result from this calculation is that the charging/discharging current i ₁ to the variable capacitances C _H and _CL performed via the constant value current limiting circuit CC ₁ does not vary depending on the temperature. However, since the circuit configuration is simple, the constant value current limiting circuit CC ₁ may be implemented using a field effect transistor (FET) as shown in Figure 3, for example.
A pair of constant current circuits using FET ₁ and FET ₂ are connected with opposite polarity to each other, and a diode D ₁ , which has a direction opposite to the other constant current, is connected to these constant current circuits.
A bipolar constant current limiting circuit with D ₂ connected is used.

In such a circuit, the current i ₁ changes with temperature depending on the temperature characteristics of the FET used. That is, the current i ₁
is expressed as follows.

i ₁ = I _DSS [1-i ₁・Rs/Vp] …(12) However, Vp: pinch-off voltage, I _DSS : drain current, Rs: source-gate resistance.

As is clear from this equation, the current i ₁ changes when Vp and I _DSS change with temperature. Of course, resistance
Although it is possible to compensate for temperature fluctuations in the current _i1 by using a temperature sensing element or a resistor with a large temperature coefficient for Rs, it is difficult to select and adjust components and increases costs.

<Purpose of the invention> The technical background to be solved by the invention is to obtain a circuit in the above-mentioned physical quantity conversion device in which the influence of temperature fluctuations in the current i ₁ does not appear on the temperature correction signal.

<Summary of the invention> In the invention, in the temperature correction signal generation circuit,
A constant value current limiting circuit having the same configuration as the constant value current limiting circuit of the detection circuit is provided to remove the influence of the constant current i ₁ in the process of calculating the temperature correction signal.

<Embodiment> FIG. 4 shows a specific example of the temperature correction signal generation circuit according to the present invention. In this figure, elements that are substantially the same as those in FIG. _FF1 is a flip-flop to which a main signal pulse or a pulse signal related to the variable capacitances C _H and _CL is applied as a trigger pulse from the detection circuit, and is reset by the output of the counter _CT2 . Switch _SW1 is driven by the output of this flip-flop. _G6 is a NAND gate whose one input terminal is supplied with the output of the flip-flop _FF1 , and whose other input is supplied with the voltage at the connection point between one end of the constant current limiting circuit _CC3 and one pole of the capacitor _C1 . Note that the constant value current limiting circuit CC ₃ uses a circuit having the same configuration as the constant value current limiting circuit CC ₁ used in the detection circuit. _G7 is an inverter whose input terminal is supplied with the output of the NAND gate _G6 , and whose output terminal is connected to the other pole of the capacitor _C1 and the input terminal of the inverter _G8 . The output of inverter G ₈ is given to counter CT ₂ , while constant value current limiter circuit CC ₃
connected to the other end.

The circuit configured in this way constitutes a one-shot circuit, in which the output pulse of the oscillator circuit consisting of the NAND gate G ₆ , inverters G ₇ , G ₈ , capacitor C ₁ , and constant value current limiting circuit CC ₃ is kept constant by the counter CT ₂ . A pulse with a constant time width _T0 is outputted through a flip-flop _FF1 which is reset by the output of a counter _CT2 which is set by an input pulse from a detection circuit.

The operation of the temperature correction signal generation circuit shown in FIG. 4 will be explained with reference to the waveform diagram in FIG. 5. When a main signal pulse with an on-off duty ratio T ₁ /(T ₁ +T ₂ ) shown in FIG. 5a is given to flip-flop FF ₁ , the Q output becomes "H" as shown in FIG. 5c,
The oscillation circuit starts oscillating (FIG. 5b). At this time, the time width t ₁ of the oscillation pulse obtained at the output side of the inverter G ₈ is related to the current i ₂ flowing through the constant value current limiting circuit CC ₃ and the capacitance C ₁ as follows.

t ₁ = Vz/i ₂・C ₁ …(13) When this pulse is counted a certain number n by the counter CT ₂ , a certain time width T ₀ is applied to the flip-flop FF ₁ .
A pulse output (FIG. 5c) having the following values is obtained. This time width T ₀ is also related to the current i ₂ as follows.

T ₀ ∝n・t ₁ =n・Vz/i ₂・C ₁ (14) If the switch SW ₁ is driven using such a pulse, the following calculation will be performed by this switch.

T ₁ /T ₀ = Vz・i ₂ /i ₁・C _L /C ₁・Vz (15) Here, constant value current limiting circuits CC ₁ and CC ₃ have the same configuration and are used under the same temperature conditions. Therefore, i ₁ ∝
The relationship i ₂ holds, and the above equation (15) can be expressed as follows.

T ₁ /T ₀ =K ₂ C _L /C ₁ …(16) However, K ₂ : Constant.

In this way, the smoothing circuit FL ₂ obtains a signal voltage that is unrelated to the temperature fluctuations of the charge/discharge current i ₁ , and by using this voltage and multiplying it by the main signal pulse in the switch SW ₂ , it is unrelated to the temperature fluctuations of the above current. If a zero point correction signal is obtained, furthermore, switch SW ₄ multiplies this signal by the main signal pulse, and amplifier A ₂ subtracts this calculation result from the above zero point correction signal. A span temperature fluctuation correction signal that is independent of temperature fluctuations is obtained.

<Effects of the invention> In the invention, in the temperature correction signal generation circuit,
A constant value current limiting circuit with the same configuration as the constant value current limiting circuit in the above detection circuit is used, and in the process of calculating the temperature correction signal, the influence of the charging/discharging current of the above detection circuit is removed. The effect of fluctuations does not appear on the temperature correction signal.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a conventional physical quantity conversion device equipped with a temperature correction signal generation circuit, Fig. 2 is a waveform diagram for explaining the operation of the device shown in Fig. 1, and Fig. 3 is shown in Fig. 1. FIG. 4 is a specific example of the constant value current limiting circuit used in the device, FIG. 4 is a specific example of the temperature correction signal generating circuit in the present invention, and FIG. 5 is a waveform diagram for explaining the operation of the circuit shown in FIG. 4. 1...Detector, C _H , C _L ...Variable capacitance,
...Detection circuit, CC ₁ ...Constant current limit circuit, ...
...Conversion circuit, ...Temperature correction signal generation circuit, CC ₃
... Constant value current limit circuit, FF ₁ ... Flip-flop.

Claims (1)

[Scope of utility model registration request] first and second variable capacitance elements whose capacitance value at least one of them changes in accordance with an input physical quantity, and charging and discharging of these capacitance elements via a constant value current limiting circuit to relate to the capacitance value of these capacitance elements. a detection circuit that generates a main signal pulse whose on-off duty ratio is related to the capacitance value based on the pulse signal, and a conversion circuit that transmits a device output based on the main signal pulse; A constant time width pulse generation circuit including a constant value current limiting circuit having the same configuration as the constant value current limiting circuit of the detection circuit is used to generate a constant time width pulse signal based on the main signal pulse or a pulse signal related to the capacitance value of the capacitive element. 1. A physical quantity conversion device comprising: a temperature correction signal generation circuit which generates a temperature signal for correction by calculating the signal and the main signal pulse.