JP2005061921A - Signal voltage-time conversion circuit and sensor device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a signal voltage-time conversion circuit which converts a signal voltage, which can be a positive or negative value by zero signal level, into time, and in which the calibration of the zero signal level is not basically necessary, the calibration of conversion sensitivity can be performed without affecting the zero signal level, and conversion resolution can be doubled. <P>SOLUTION: The circuit comprises a positive-negative sign judgment means and an absolute value width pulse generation means. The circuit outputs a time width pulse which is proportional to an absolute value of an input signal voltage which can be a positive or negative value by zero signal level. The pulse starts by a starting instruction and discharge a capacitor which is charged to the input signal voltage by a direct-current electricity source whose direction is determined based on the sign judgment result. The pulse ends when the voltage reduces to the zero signal level. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention uses as input a signal voltage that can be positive or negative with reference to a no-signal level, and generates and outputs a pulse having a time width proportional to the absolute value of the input signal voltage and a positive / negative sign of the input signal voltage. The present invention relates to a signal voltage-time conversion circuit.

There are various needs for detecting a physical quantity whose change is relatively slow, further converting it into a digital value and taking it into a computer to monitor and control the target physical state. One example is described in Patent Document 1. In this document, in order to monitor the battery voltage, a pulse having a time width proportional to the voltage is generated by a voltage-time conversion circuit, and the pulse width is measured by the number of reference clocks and converted into a digital value. The voltage-time conversion uses a time during which the voltage when the capacitor charged to the measured battery voltage is discharged with a constant current decays to the threshold voltage. This method is excellent in that high-accuracy digital conversion can be performed with a relatively simple circuit if it can be accepted that a single data conversion takes a time longer than the pulse width. For example, when the voltage-time converted pulse width full scale is 1 millisecond and the reference clock frequency is 1 MHz, resolution as an A / D converter equivalent to about 10 bits can be obtained.
The data conversion cycle at this time is 1 kHz.

JP 2001-204141 A

Many physical quantities can take either positive or negative values centered on zero. For example, acceleration and angular velocity are examples, and an output signal of a sensor for detecting this is usually output after being amplified and offset adjusted so that the zero level of each physical quantity becomes a predetermined reference potential. Therefore, the output signal changes in a positive or negative manner in proportion to the physical quantity with reference to the reference potential.

When such a signal voltage is converted into a pulse by the voltage-time conversion circuit, for example, when a positive input voltage is given as V +, a signal zero voltage as V0, and a negative input voltage as V-,
Corresponding to each, a pulse having a time width of T +, T0, T− is obtained in a magnitude relationship of T +>T0> T−. Actually, since the pulse width for each input voltage varies depending on various factors, it is necessary to calibrate the pulse width T0 corresponding to no signal and to calibrate the pulse width corresponding to a known voltage, that is, sensitivity. At this time, it is a necessary condition for completing the calibration without repeating that the calibrations of the two do not influence each other.

However, in the above prior art, if the current value of the discharge current source is changed in order to calibrate the sensitivity, the pulse width corresponding to the no-signal voltage changes, so that the above condition cannot be satisfied.
In addition, the pulse width change range must cover from the pulse width corresponding to the negative full scale to the pulse width corresponding to the positive full scale, and the data conversion cycle becomes longer due to the longer longest pulse width. Is a drawback. On the contrary, when the data conversion cycle is predetermined, there is a problem that the conversion resolution determined from the reference clock for time measurement is lowered.

Therefore, an object of the present invention is a signal voltage-time conversion circuit that converts a signal voltage that can be taken positive or negative with respect to the signal zero level as an input and converts the signal voltage into time. It is an object of the present invention to provide a signal voltage-time conversion circuit that can calibrate conversion sensitivity without affecting the signal zero level and that can double the conversion resolution. Still another object is to provide a sensor device that can easily and accurately interface with a microcomputer using the signal voltage-time conversion circuit.

The signal voltage-time conversion circuit according to the present invention comprises a positive / negative sign determination means and an absolute value width pulse generation means, and the positive / negative sign determination means for a signal voltage input that can be positive or negative with reference to the signal zero level. The sign of the input signal voltage is determined to output a positive / negative sign, and the absolute value width pulse generating means outputs a pulse having a time width proportional to the absolute value of the input signal voltage.

More specifically, the absolute value width pulse generating means includes a capacitor, a DC current source connected to the capacitor, and a DC current source that can be switched between a sink type and a source type (source), and a capacitor voltage positive / negative determination circuit. A pulse is generated by the process described in (1). First, after the capacitor is charged to the input signal voltage, it is disconnected from the input signal voltage source by a start command, and thereafter, the capacitor is discharged by the current of the DC current source, and the voltage goes to the signal zero level in proportion to the transition of time. Attenuates. The positive / negative judgment circuit of the capacitor voltage is used to judge whether the voltage of the capacitor is positive or negative with reference to a reference potential corresponding to a signal zero level. The type of the DC current source is determined based on the judgment result at the start command time. At the time of determination, it becomes a suction type (sink), and at the time of negative determination, it becomes a spring type (source). Then, at the moment when the attenuation of the capacitor voltage advances and reaches the reference potential and exceeds the reference potential, the determination of the positive / negative determination circuit of the capacitor voltage is inverted, so that the pulse is terminated at the inversion time of this determination.

The function of the positive / negative sign determination means is equivalent to the determination function performed by the capacitor voltage positive / negative determination circuit at the start command time, and can be realized by a method similar to this. It is also possible to use both. The pulse width of the resulting pulse is (absolute voltage of input signal x
Capacitor capacity / DC current source current magnitude), and the pulse width is zero when there is no signal, that is, when the signal voltage is zero. Therefore, calibration of the signal zero level is basically unnecessary, and there is an advantage that the influence on the signal zero level does not occur even if the conversion sensitivity is calibrated by changing the magnitude of the current of the DC current source. . Furthermore, since the change range of the pulse width is half that of the prior art, there is an advantage that the data conversion cycle can be shortened. Conversely, when the data conversion cycle is predetermined, the conversion resolution determined from the time measurement reference clock can be doubled. This can be interpreted as the fact that the positive / negative sign output carries 1 bit.

As described above, according to the present invention, in a signal voltage-time conversion circuit that converts a signal voltage that can be positive or negative with respect to the signal zero level as an input and converts it into time, the calibration of the signal zero level is performed. A signal voltage-time conversion circuit that can calibrate the conversion sensitivity without affecting the signal zero level basically without any influence and that can double the conversion resolution can be obtained. Furthermore, it is possible to provide a sensor device that can easily and accurately interface with a microcomputer using this signal voltage-time conversion circuit.

Further detailed embodiments according to the present invention will be described below. Prior to the explanation
The expression method of the input signal etc. is defined as follows. A voltage that changes according to a change in physical quantity is defined as a signal voltage (Vin), and a DC potential corresponding to zero of the physical quantity is defined as a signal zero level (Vre
f). Therefore, Vin takes a positive or negative value corresponding to a positive or negative change in physical quantity. In addition, when the signal is expressed by ground potential, it is Vref + Vin.

FIG. 1 shows a first embodiment of the present invention. In FIG. 1, the switch 2 is controlled to be opened and closed by a start command pulse, and is turned on before time To and turned off when the start command pulse falls at time To. Therefore, the capacitor 1 has an input signal voltage (Vref + Vin
) And then disconnected from the input signal voltage source by the start command. The comparator 4 compares the voltage of the capacitor 1 with a reference potential (Vref) corresponding to the signal zero level, and outputs 1 when positive and 0 when negative. The latch circuit 4 latches the comparator output data applied to the D terminal at the falling edge of the start command pulse and outputs it to the Q terminal. The DC current source 3 has the same current magnitude and has a function of switching between a suction type (sink) and a source type (source). When the Q output of the latch circuit 5 is 1, it becomes a suction type (sink). The mold is controlled so that it becomes a springing mold (source). The exclusive OR gate 6 receives the Q output of the latch circuit 5 and the output of the comparator 4 as two inputs, and outputs a logical value 1 when the two input logical values are different. The NOR gate 7 outputs a target pulse based on the output of the exclusive OR gate 6 and the NOR logic of the start command pulse.

The operation according to the above configuration will be described with reference to FIG. 2 when Vin is positive and negative. When Vin is positive, a logical value 1 is generated at the output of the comparator 4 at time To, and the latch circuit 5 latches this with a start command and continuously outputs the logical value 1 to the Q terminal. As a result, the DC current source 3 is determined to be a suction type, and thereafter, the voltage of the capacitor 1 decreases in proportion to the transition of time. Until the capacitor voltage reaches the signal zero level, the output of the comparator maintains the same logic value, and the exclusive OR gate 6 outputs the logic value zero because the two input logic values are the same value. Comparator 4 at the moment when the capacitor voltage drops below the signal zero level
Is inverted, only one input of the exclusive OR gate 6 inverts the logical value and outputs the logical value 1. Therefore, the target pulse is obtained by taking the NOR logic of the output of the exclusive OR gate 6 and the start command pulse. The pulse width of the obtained pulse is determined by the absolute value of the input signal voltage Vin × capacitor capacity / the magnitude of the current of the DC current source. Further, a positive / negative sign corresponding to the positive / negative of the input signal voltage can be obtained from the Q terminal of the latch circuit 5.

Next, when Vin is negative, a logical value 0 is generated at the output of the comparator 4 at time To, and the latch circuit 5 latches this with a start command and continuously outputs a logical value 0 to the Q terminal. To do. As a result, the direct current source 3 is determined as a spring-out type, and thereafter, the voltage of the capacitor 1 rises in proportion to the transition of time. Until the capacitor voltage reaches the signal zero level, the output of the comparator maintains the same logic value, and the exclusive OR gate 6 outputs the logic value zero because the two input logic values are the same value. When the output of the comparator 4 is inverted at the moment when the capacitor voltage exceeds the signal zero level, only one input of the exclusive OR gate 6 inverts the logic value and outputs the logic value 1. The rest is the same as when Vin is positive.

FIG. 3 shows input signal-to-pulse width conversion characteristics obtained in this embodiment. The pulse width is proportional to the absolute value of the input signal voltage, and has a characteristic of turning back and forth at the origin O.

The pulse polarity and the logic gate combination shown in this embodiment are merely examples, and the present invention is not limited to this as long as an equivalent function can be obtained. For example, a target pulse can be obtained by using a T-type flip-flop and clearing the state with a start command pulse and then toggle-inverting the state using the output transition of the exclusive OR gate 6 as a clock input.

A second embodiment of the present invention is shown in FIG. In the drawing, the above-described variations of the first embodiment are written in a comprehensive manner. The positive / negative determining means 8 determines whether the capacitor voltage is positive or negative with respect to the signal zero level, and has the same function as the comparator 4. The positive / negative inversion detecting means 9 is for making an output transition when the determination result of the positive / negative determining means 8 is inverted. The pulse generation means 10 starts a pulse in response to a start command and ends the pulse by a transition of the output of the positive / negative inversion detection means 9. The rest is the same as in the first embodiment. With the above configuration, a pulse having a time width proportional to the absolute value of the input signal voltage and a positive / negative sign indicating the positive / negative of the input signal voltage can be obtained as in the first embodiment.

FIG. 5 shows a third embodiment of the present invention. This embodiment differs from the second embodiment in that the minimum width pulse adding circuit 11 is provided and the current value control means 33 is provided in the direct current source 3. First, the minimum width pulse adding circuit 11 will be described. When the input signal voltage is a minute value close to zero, the pulse width obtained in the first embodiment is a minute value. When the pulse width is measured by the number of reference clocks and converted to a digital value, the measurement may become unstable if the pulse width is as small as the reference clock period. The minimum width pulse adding circuit 11 adds a minimum width pulse having a time width of 1.5 times the reference clock period or more from the start command as a starting point, so that the input signal voltage is a minute value close to zero. Since a predetermined pulse width is secured, the pulse width can be measured stably.

FIG. 6 shows the input signal-to-pulse width conversion characteristics obtained in the third embodiment. In the region where the absolute value of the input signal voltage is small, the characteristics do not fall below the minimum pulse width. Taking the case where the reference clock frequency for time measurement is 1 MHz as an example, the minimum pulse width may be designed to be 2 microseconds. When the signal voltage is converted so that the full scale is 1 millisecond in this design, the full pulse will be full. The ratio of the minimum width to the scale is 0.2%. That is, the maximum conversion error for a signal voltage near zero is 0.2%, which is a sufficiently acceptable range for general applications. Note that the insertion location, pulse polarity, and the like of the minimum width pulse adding circuit 8 are not limited to those shown in the figure, and can be appropriately changed to equivalent logic gates.

Next, the current value control means 33 will be described. The current value control means 33 changes and controls both the current values of the current sources of the suction type (sink) or the spring type (source). As described above, the pulse width of the pulse is determined by the absolute value of the input signal voltage Vin × capacitor capacity / current current of the DC current source. Therefore, the conversion sensitivity of the input signal voltage to the pulse width is adjusted by controlling the current value. It is possible. FIG. 7 shows sensitivity adjustment characteristics. This sensitivity adjustment function can be used to correct manufacturing variations of the conversion circuit itself, and can also be used to correct manufacturing variations of other devices and circuits as in the fourth embodiment described below. Is possible. Or it can utilize also when changing a sensitivity according to the utilization purpose of an apparatus.

FIG. 8 shows a fourth embodiment of the present invention. This is an application example to a sensor device. The sensor is not particularly limited, but here, description will be made assuming an acceleration sensor using a piezoresistive bridge.
A signal obtained by amplifying the detection voltage of the acceleration sensor bridge 12 by the amplifier 13 is used as an input signal of the circuit shown in the third embodiment. The detection signal of the sensor is weak and usually has a zero level deviation, that is, a large deviation between the offset and the detection sensitivity. Accordingly, the amplifier 13 first adjusts the signal zero level to a predetermined voltage by offset adjustment,
Then adjust the gain. In general, the use of a semi-fixed resistor for adjustment is inferior in productivity, so that digital adjustment using adjustment value data stored in a semiconductor memory is often required. The offset adjustment can be realized relatively easily by applying a DC voltage obtained by D / A converting the adjustment value data to the amplifier. The gain adjustment adopts a method such as switching a resistor that determines the gain with an electronic switch. In many cases, fine adjustment is difficult.

Therefore, in this embodiment, the gain adjustment in the amplifier 13 is coarse adjustment, and fine adjustment is performed by the current value control means in the subsequent stage. The sensitivity fine adjustment means 16 causes the DC value obtained by D / A conversion of the fine adjustment digital data stored in the memory to act on the current value control means 33 to thereby apply the direct current source 3.
The current value is finely adjusted. Thereby, the total sensitivity including the sensor and the circuit is finely adjusted. Further, the present invention has a feature that the signal zero level is not affected even if the sensitivity is adjusted by changing the current value, and the present embodiment is realized by utilizing this feature. The sensitivity adjustment function of this embodiment can also be used to correct a sensitivity drift due to temperature in combination with a temperature detection means provided separately. Further, the pulse and the positive / negative sign obtained in this embodiment are suitable for an interface with a microcomputer, and simple and highly accurate signal transfer is possible.

It is a figure which shows the 1st Example of this invention. It is a figure explaining operation | movement of a 1st Example. It is a figure which shows the characteristic of the input signal voltage versus pulse width of 1st Example. It is a figure which shows the 2nd Example of this invention. It is a figure which shows the 3rd Example of this invention. It is a figure which shows the characteristic of the input signal voltage versus pulse width of a 3rd Example. It is a figure which shows the sensitivity adjustment characteristic of a 3rd Example. It is a figure which shows the 4th Example of this invention.

Explanation of symbols

1 capacitor, 2 switch, 3 direct current source, 31 sink current source,
32 current source, 33 current value control means, 4 comparator, 5 latch circuit,
6 exclusive OR gate, 7 NOR gate, 8 positive / negative judgment means,
9 Positive / negative inversion detecting means, 10 pulse generating means, 11 minimum width pulse adding circuit.

Claims (7)

Input a signal voltage that can be positive or negative with reference to the signal zero level, and generate and output a pulse with a time width proportional to the absolute value of the input signal voltage and the sign of the input signal voltage. A characteristic signal voltage-time conversion circuit. Absolute value width pulse generating means for outputting a pulse having a time width proportional to the absolute value of the input signal voltage with respect to an input of a signal voltage that can be positive or negative with respect to the signal zero level, and positive / negative of the input signal voltage The absolute value width pulse generating means includes a capacitor and a direct current source, starts a pulse in response to a start command, and the current direction of the capacitor charged to the input signal voltage is determined based on the positive / negative determination result. The pulse is terminated at the time when the voltage is attenuated to the signal zero level by being discharged by the determined DC current source, and the input signal voltage is input to the pulse having a time width proportional to the absolute value of the input signal voltage. A signal voltage-time conversion circuit, wherein the signal voltage is converted into a positive / negative sign and output. The signal voltage-time conversion circuit according to claim 1, wherein the capacitor, a positive / negative determination means,
A DC current source, a positive / negative inversion detecting means, and a pulse generating means; after the capacitor is charged to the input signal voltage, it is disconnected from the input signal voltage source by a start command, and thereafter the current of the DC current source The discharged voltage is attenuated toward the signal zero level in proportion to the transition of time, the positive / negative determination means determines the positive / negative of the capacitor voltage with respect to the signal zero level, and the DC current source determines the positive / negative of the positive / negative determination means The direction of the current is determined based on the result, and the positive / negative inversion detection means transitions the output when the determination result of the positive / negative determination means inverts, and the pulse generation means starts a pulse in response to a start command and A signal that ends a pulse by an output transition, and generates and outputs a pulse having a time width proportional to the absolute value of the input signal voltage and a positive / negative sign indicating the positive / negative of the input signal voltage Pressure - time conversion circuit. 4. The signal voltage-time conversion circuit according to claim 1, further comprising a circuit for limiting and outputting a minimum pulse width value for a pulse having a time width proportional to an absolute value of an input signal voltage. A signal voltage-time conversion circuit. 5. The signal voltage-time conversion circuit according to claim 2, wherein the direct current source includes means for changing the magnitude of the current value, and the conversion sensitivity of the signal voltage-time conversion can be adjusted. A signal voltage-time conversion circuit. A sensor, an amplifier that inputs a detection signal of the sensor, adjusts and outputs the signal zero level of the amplified signal voltage to a predetermined reference potential, a capacitor, a positive / negative determining means, a DC current source, and a positive / negative inversion A detection means and a pulse generation means; the capacitor is charged to the output voltage of the amplifier and then disconnected from the amplifier by a start command; thereafter, the capacitor is discharged by the current of the DC current source and proportional to the transition of time Then, the voltage is attenuated toward the reference potential, the positive / negative determining means determines whether the capacitor voltage is positive or negative with respect to the reference potential, and the direct current source determines the direction of the current based on the positive / negative determining result of the positive / negative determining means. The positive / negative inversion detecting means shifts the output when the determination result of the positive / negative determining means inverts, and the pulse generating means starts a pulse in response to a start command, and changes the output of the positive / negative inversion detecting means. Te terminates the pulse sensor device, characterized in that the absolute value to generate a sign indicating positive or negative pulse and the detection signal proportional to the time width output of the detection signal of the sensor. 8. The sensor device according to claim 7, wherein the direct current source includes means for changing a magnitude of a current value, and sensitivity adjustment of the sensor device is enabled.

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