JPH076805B2 - Sensor signal processing circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a sensor signal processing circuit, in particular, a sensor signal which is integrated with a sensor element and can achieve a stable signal processing operation even under adverse environmental conditions. Regarding improvement of a processing circuit.

[Prior Art] A sensor that outputs an electrical detection signal according to various physical conditions is widely used. For example, a desired electrical output can be obtained by bringing a permanent magnet or the like close to a magnetoresistive element. You can

Normally, these sensor signals are digitally processed by the signal processing circuit, and a pulsed digital output is obtained when the sensor output voltage exceeds a predetermined value.

Such a sensor element is used, for example, as a rotation detection sensor of a rotating body, and is suitable for detecting a control signal for factory automation or car electronics.

Conventionally, various signal processing circuits have been proposed in order to take out an analog signal obtained from such a sensor element as a pulse-shaped digital output, but in the normal case, these processing circuits are equivalent to the output value of the sensor element. It is composed of a circuit for comparing with a reference value and converting it into a digital signal.

Conventionally, such a signal processing circuit is built in the control unit separately from the sensor element, and is connected to the sensor element by a cable or the like.

However, in recent years, in order to downsize the device and prevent voltage drop or noise mixing in a transmission line such as a cable, a signal processing circuit has been integrated with a sensor element. According to such a signal processing circuit integrated with a sensor element, it is possible to output a digital signal from the detection point, and it is possible to obtain a highly accurate detection signal while reducing the size of the device as a whole.

[Problems to be Solved by the Invention] However, since the signal processing circuit is installed at the detection point on the one hand, it is necessary to guarantee a correct detection signal even in a bad environment, for example, under conditions where the temperature changes drastically. There is a problem in that it is not possible to obtain a circuit with high reliability and stable detection action.

The present invention has been made in view of the above conventional problems,
It is an object of the present invention to provide an improved sensor signal processing circuit that enables a stable detection action even with a change in environmental temperature.

[Means for Solving the Problems] To achieve the above object, the present invention includes a switching transistor pair for comparing a sensor output with a reference value, and the sensor output is supplied to the base of one of the switching transistors. The comparison reference voltage is supplied to the base of the other switching transistor, and the processed output is taken out from the collector thereof.

A constant voltage source that supplies a constant voltage via a resistor is connected to the common emitter of the switching transistor pair, and a temperature compensating transistor is further connected to the constant voltage source.

A bias current is supplied to each transistor by the biasing transistor whose base is supplied with the constant voltage from the constant voltage source.

[Effect] Therefore, according to the present invention, even when the environmental temperature condition changes significantly, the base-emitter voltage of each transistor acts so as to cancel out the change due to temperature, and as a result, during the switching operation. It becomes possible to stabilize the temperature characteristics of the above with respect to a wide range of temperature changes.

[Embodiment] A preferred embodiment of the present invention will be described below with reference to the drawings.

1 and 2 show preferred embodiments of the sensor processing signal processing circuit according to the present invention as outputs "L" state and "H" state, respectively.

The analog output of a sensor element not shown in detail, for example, a magnetoresistive element is compared with a predetermined reference value and output as a pulsed digital signal of "L" or "H".

To perform the analog-to-digital conversion circuit of this embodiment includes a pair of switching transistor pair Q _3, Q _4,
The emitter of the two switching transistors Q _3, Q ₄ are commonly connected.

Then, the output of the sensor element is applied to the base of one switching transistor Q ₃ from the input terminal IN via the capacitor C ₁ .

In the embodiment, the collector of the switching transistor Q ₃ is grounded via the temperature compensating transistor Q ₁ which will be described in detail later.

The other switching transistor Q ₄ is supplied with a reference voltage at its base, and this reference voltage is the bias resistance.
It is formed by R ₄ and R ₅ . The collector of the switching transistor Q ₄ is grounded via the resistor R ₇ . Both switching transistors Q _3, each base potential of Q ₄ A, B and the collector potential C of the other switching transistor Q ₄ is shown in Figure 3, after the detailed description of the change in the potential at the working description of.

A characteristic of the present invention is that a constant voltage is supplied to the switching transistor pair Q ₃ and Q _4, and the base-emitter voltage of each transistor has a relatively large temperature dependence. This is because the transistors are arranged so as to cancel out the dependences from each other. For this reason, in this embodiment, a constant voltage source including a constant current source I _S and a Zener diode D ₁ is provided.

The constant current source I _S is supplied with the power supply V _CC, the constant current source I _S and a Zener diode D ₁ and the constant voltage V ₀ is obtained, the the constant voltage V ₀ via the resistor R ₃ It is supplied to the common emitter of the switching transistor pair Q _3, Q _4.

The anode of the Zener diode D ₁ of the constant voltage source is connected to the emitter of the temperature compensation transistors Q _1, the collector and base of the temperature compensation transistors Q ₁ is grounded are commonly connected.

In order to extract the signal processing output from the collector potential of the switching transistor Q ₄ , that is, the C potential, transistors Q ₅ and Q ₆ are provided in the embodiment. That is, the transistor Q ₅ has its base connected to the point C, its emitter grounded, and its collector connected to the base of the output transistor Q ₆ .

The output transistor Q ₆ has its emitter grounded and its collector connected to the output terminal OUT.

A bias transistor Q ₂ is provided to supply a temperature-compensated bias current to each of the transistors, a power supply V _CC is connected to the collector of the bias transistor Q ₂ , and the constant voltage is applied to the base thereof. V ₀ is being supplied.

And from the emitter of the biasing transistor Q ₂ ,
Both switching transistors Q ₃ and Q ₄ have resistors R ₁ and
The bias current, which has been made constant, is supplied from R ₂ and resistors R ₄ and R ₅ . That is, the resistance R ₁ connected in series,
The intermediate connection point of R ₂ is connected to the base of the switching transistor Q ₃ , and the intermediate connection point of resistors R ₄ and R _{5 which} are also connected in series is connected to the base of the switching transistor Q ₄ .

Similarly, the emitter of the biasing transistor Q ₂ is a resistor R ₈
Through the base of the output transistor Q ₆ and the emitter of the output transistor Q ₅ .

Further, in the embodiment, the switching transistor Q ₄
Resistor R ₆ between the base and the base of the output transistor Q ₆
Are connected.

The embodiment of the present invention is constructed as described above, and its operation will be described below.

FIG. 3 shows the potential changes at the points A, B and C when a sine wave signal as shown in FIG. 3 (a) is supplied from a sensor element such as a magnetoresistive element.

In the embodiment, a configuration is shown in which a digital signal is output from the sine wave signal of the sensor element at the zero cross point.

IN input voltage is supplied as A potential to the base of the switching transistor Q ₃ via the capacitor C _1, A potential from the time constant of the capacitor C ₁ and a resistor R ₂ at this time indicates a delayed from the input voltage slightly signal Has been done.

FIG. 1 shows a state in which the input voltage is lower than the B potential, which is the base potential of the switching transistor Q ₄ , and in the embodiment, this B potential is set to the zero-cross reference potential.

In the present invention, the B potential, which is the reference voltage, does not depend on the base-emitter potential of each transistor,
As a result, the temperature characteristic can be significantly reduced even when the signal processing circuit is placed in an environment where the temperature changes drastically.

The potential of each part of the switching transistors Q ₃ and Q ₄ will be described in detail below.

In the embodiment, the constant voltage V ₀ is supplied by the constant voltage source I _S and the zener diode D ₁ by the constant voltage source V
_{Even if CC} fluctuates, it is maintained at a nearly constant value,
In the present invention, since the temperature compensating transistor Q ₁ is connected to the constant voltage source, the constant voltage V ₀ itself varies depending on the base-emitter voltage of the temperature compensating transistor. That is, the constant voltage V ₀ is the Zener voltage
If V _D1 and the base-emitter voltage of the temperature compensating transistor Q ₁ are V _BE (Q ₁ ), then V ₀ = V _D1 + V _BE (Q ₁ ) ... (1)

Next, the bias transistor Q ₂ that supplies the bias current
The emitter potential V (Q ₂ E) is the value obtained by subtracting the base-emitter voltage of the transistor Q ₂ from the constant voltage V _{0, i.e., V (Q 2 E) =} V 0 -V BE (Q 2) = V _D1 + V _BE (Q ₁ ) -V _BE (Q ₂ ) ... (2) The base-emitter voltage of the bias transistor Q ₂ and the temperature compensating transistor Q ₁ can be selected to be almost the same value, and since they are exposed to almost the same temperature environment, the V _{BE of the} formula (2) is (Q ₁ ) and V
_BE (Q ₂ ) will be approximately equal, resulting in
Q ₂ of the emitter potential V (Q ₂ E) is _{V (Q 2 E) ≒ V} D1 ... (3) , and becomes substantially equal to the Zener voltage of the Zener diode D _1.

Therefore, the base potential of the switching transistor Q ₄ , that is, the B potential becomes a value obtained by dividing the emitter potential of the transistor Q ₂ by the bias resistors R ₄ and R ₅ , that is, the B potential.
V _B becomes V _B = V _D1 (R ₅ / R ₄ + R ₅ ) ... (4).

As a result, it is understood that the B potential V _B has a constant value determined only by the Zener voltage and the bias resistance value, and it is clear that the B potential V _B is independent of the base-emitter voltage of the transistor that depends on the temperature change.

Also, the emitter potential V of the switching transistor Q ₄
(Q ₄ E) is a value obtained by adding the base-emitter voltage of the transistor Q _{4 to} the B potential, and V (Q ₄ E) = V _D1 (R ₅ / R ₄ + R ₅ ) + V _BE (Q ₄ ) ... (5)

Therefore, the potential V _R3 across the common resistor R ₃ is equal to the constant voltage V ₀ ,
This is the difference from the emitter potential of this transistor Q ₄ , and V _R3 = V ₀ −V (Q ₄ E) = V _D1 + V _BE (Q ₁ ) −V _D1 (R ₅ / R ₄ + R ₅ ) −V _BE … ( 6) is shown.

Since the base-emitter voltages of the transistors Q ₁ and Q ₄ have substantially the same characteristics and are exposed to the same temperature environment, they cancel each other in the equation (6),
As a result, the voltage V _R3 across the resistor R ₃ is expressed as V _R3 = V _D1 −V _D1 (R ₅ / R ₄ + R ₅ ) = V _D1 (1-R ₅ / R ₄ + R ₅ ) ... (7) Therefore, the emitter current supplied to both switching transistors Q ₃ and Q ₄ is determined only by the Zener voltage V _D1 of the Zener diode and the resistors R ₄ and R ₅ , and the temperature dependence other than that caused by the Zener voltage. It is understood that it does not have.

As described above, according to the present invention, by connecting the constant voltage source and the temperature compensating transistor in series, the constant voltage supplied to the signal processing circuit is superposed with the potential component for compensating the temperature characteristic of the switching transistor. As a result, it becomes possible to cancel out the fluctuations in the voltage between the base and emitter of the transistor which fluctuate due to temperature changes, and obtain an extremely stabilized output signal.

The operation of this embodiment will be described in detail below.

In FIG. 1, the IN input voltage is supplied as the potential at the point A via the capacitor C ₁ , which is lower than the reference voltage in the figure, that is, the base voltage of the transistor Q ₄ , FIG. 3 (b).
Shows a current path in a hatched state.

The power supply voltage V _CC forms a current path as shown by the solid line through the constant voltage source and the temperature compensating transistor Q ₁ .

Further, a bias current indicated by a broken line flows from the bias transistor Q ₂ to determine the base potentials of both switching transistors.

As described above, since the A potential based on the IN input voltage is below the zero cross potential, in the state of FIG. 1, almost all the current from the common resistor R ₃ flows through the switching transistor Q ₃ , and therefore the transistor Q ₃ turns on. And the transistor
Q ₄ is kept off.

Therefore, in this state, the base potential of the output transistor Q ₅ becomes almost zero, so that the transistor Q ₅ is turned off, and as a result, a sufficient base current is supplied from the bias transistor Q ₂ to the base of the output transistor Q _6. As a result, the transistor Q ₆ is turned on and the “L” signal is output to the output OUT.

In the embodiment, the collector of the transistor Q ₃ flows to the temperature compensating transistor Q ₁ , so that the base-emitter voltage of the temperature compensating transistor Q ₁ rises due to the increase of its current value. As the constant voltage V ₀ also rises, the ON state of the transistor Q ₃ is further strengthened, which makes it possible to remarkably enhance the noise resistance characteristic.

On the other hand, if the A potential exceeds the zero-cross reference value,
Since the base current of the switching transistor Q ₃ is ON state is narrowed, the common resistor a constant current through the R ₃ little switches to the other transistor Q ₄ side, as shown in Figure 2, the resistance from the transistor Q ₄ Switch to the current flowing through R ₇ .

Therefore, the transistor Q ₅ is turned on, and as a result, the base potential of the output transistor Q ₆ is lowered, so that the transistor Q ₆ is turned off and the “H” signal is output from the OUT terminal.

Therefore, it is understood that the above switching operation provides a pulse output when the zero-cross reference value is exceeded.

Further, the resistor R ₆ has a function of giving hysteresis to the reference voltage supplied to the base of the transistor Q ₄ according to ON / OFF of the output transistor Q ₅ . This makes it possible to obtain an output without chattering even when noise is mixed in the sensor output voltage.

In FIG. 2, due to the ON action of the switching transistor Q ₄ and the output transistor Q ₅ , the base potential of the transistor Q ₄ , that is, the B potential, has its reference value lowered as shown in FIG. 3 (c), resulting in hysteresis. A potential can be applied, and the “H” output state of FIG. 2 can be maintained stably.

As described above, according to the present invention, a pulsed digital signal for switching between "L" and "H" is obtained according to the IN input voltage, and such a switching state is extremely stabilized in the embodiment. It is kept in the state.

Further, according to the present invention, as described above, the current flowing through the pair of switching transistors can be determined irrespective of the base-emitter potential of each transistor, so that a stable signal processing operation can be performed without being affected by the fluctuation of the environmental temperature. It becomes possible to do.

Although this embodiment uses a coupling capacitor C ₁ for the purpose of removing the DC bias potential of the base voltage of the sensor element output and the transistor Q _3, determines the base potential of the transistor Q ₄ paired with the transistor Q ₃ The coupling capacitor C ₁ can be omitted by changing the resistance R ₄ or R ₅ that operates.

[Effects of the Invention] As described above, according to the present invention, it is possible to obtain a miniaturized processing circuit that is integrated with a sensor element, and to prevent fluctuations in environmental temperature at the installation location of the sensor element. Also performs a stable processing action, and provides a constant current even when the power supply voltage fluctuates. Therefore, it is possible to perform a highly reliable detection action without depending on such a fluctuation.

[Brief description of drawings]

1 and 2 are circuit diagrams each showing a preferred embodiment of the sensor signal processing circuit according to the present invention, respectively showing the "L" and "H" output states. FIG. 3 is a waveform chart of each part in the above embodiment. Q ₃ , Q ₄ … Switching transistor I _S … Constant current source D ₁ … Zener diode Q ₁ … Temperature compensation transistor Q ₂ … Bias transistor Q ₅ , Q ₆ … Output transistor R ₃ … Common resistance R ₆ … For hysteresis setting resistance

Claims (1)

[Claims] 1. A sensor signal processing circuit integrated with a sensor element, comprising a pair of switching transistors whose emitters are commonly connected to each other, wherein the output of the sensor element is supplied to the base of one of the switching transistors. , A reference voltage is supplied to the base of the other switching transistor, and a constant voltage source for supplying a constant voltage via a resistor to a switching transistor pair whose processing output is taken out from its collector, and a common emitter of the switching transistor pair. A temperature compensation transistor connected to the constant voltage source, an output transistor that is supplied with the processing output of the switching transistor and outputs an on / off signal according to a sensor output, and a constant voltage from the constant voltage source is a base. Supplied and biased to each transistor Including the bias transistor that supplies current, the base-emitter voltages of the switching transistor, temperature compensation transistor, and bias transistor cancel each other out, stabilizing the temperature characteristics during switching operation against a wide range of temperature changes. A sensor signal processing circuit characterized by the above.