JPH04316217A - Analog/digital converting circuit - Google Patents

Abstract

PURPOSE:To reduce the cost of an A/D conversion circuit by composing the A/D conversion circuit with a comparator and peripheral equipments only. CONSTITUTION:A velocity commanding voltage 7 is turned to an LPF output 71 removing a higher harmonic component by passing through an LPF(low pass filter) 1. A comparator 2 compares the LPF output 71 of the voltage 7 with a triangular wave 8 having a fixed frequency and a fixed amplitude. In the output 71, a level position to cross the triangular wave 8 is made different corresponding to the level. Therefore, the output of the comparator 2 is turned to a pulse width modulation signal 9 corresponding to the level of the output 71. A microprocessor 3 calculates deviation between a digitally converted velocity commanding value and the revolution speed of a motor 5 from an encoder 6 and controls an inverter 4 so that the deviation can be zero.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an analog-to-digital conversion circuit suitable for use in, for example, a motor control circuit.

0002

2. Description of the Related Art For example, some motor control circuits use a microprocessor and are controlled by software. FIG. 4 shows a conventional example of a motor control circuit using such software. The speed command voltage, which is an analog signal, is passed through a low-pass filter 1 to remove noise and other harmonic components, and then is processed by an analog-to-digital converter IC 15. The signal is converted into a digital signal, which is input into the microprocessor 16 to control the output frequency of the inverter 4 and the rotational speed of the motor 5. The rotational speed of the motor 5 is detected by an encoder 6. The microprocessor 16 calculates the deviation between the speed command signal and the actual rotational speed of the motor 5, and controls the inverter 4 so that this deviation becomes zero.

0003

SUMMARY OF THE INVENTION The conventional motor control circuit described above uses an analog-to-digital converter IC, which has the disadvantage of high cost. Also, since it is necessary to connect the analog/digital converter IC and the microprocessor with a large number of wires, such as 10 or 12 depending on the number of bits, the input/output port of the microprocessor is connected from the analog/digital converter IC. There is also the problem that the microprocessor cannot be used effectively because the microprocessor is occupied by the other lines.

[0004] The present invention has been made to solve these problems, and is an analog-to-digital converter I.
An analog processor that eliminates the need for C and reduces costs while also making effective use of microprocessor ports.
The purpose is to provide digital conversion circuits.

[0005]

[Means for Solving the Problems] The present invention provides a comparator that compares a command signal, which is an analog signal, with a triangular wave of a constant frequency and a constant amplitude to convert it into a pulse width modulation signal, and a positive or negative signal of the pulse width modulation signal. It is characterized by having a counter that counts clock pulses only during the interval and converts them into digital signals.

[0006]

[Operation] By comparing the command signal, which is an analog signal, with the triangular wave using a comparator, it is possible to convert it into a pulse width modulation signal according to the command signal level. A digital signal can be obtained by counting clock pulses with a counter only in the positive or negative section of this pulse width modulation signal. This digital signal corresponds to the command signal level.

[0007]

Embodiments Hereinafter, embodiments of the analog-to-digital conversion circuit according to the present invention will be described with reference to FIGS. 1 to 3. The illustrated embodiment is an example in which an analog-to-digital conversion circuit is applied to a motor speed control circuit, similar to the conventional example shown in FIG. Therefore, the same reference numerals are given to the same components as those of the conventional example shown in FIG.

In FIG. 1, a speed command voltage 7, which is an analog signal, is input to a low-pass filter 1, and the output of the low-pass filter 1 and a triangular wave 8 are input to a comparator 2. The output of the comparator 2 is input to a microprocessor 3 having a timer 31. The microprocessor 3 uses the internal clock pulse in the timer 31 to obtain a digital signal corresponding to the speed command voltage, and also controls the timer 31 so that the deviation between the rotational speed signal of the motor 5 from the encoder 6 and the digital signal becomes zero. The inverter 4 is controlled.

Next, the operation of the above embodiment will be explained in detail with reference to FIG. The speed command voltage 7 is shown in Fig. 2 (a
), it contains noise and other harmonic components. This speed command voltage 7 is passed through the low-pass filter 1 to become a low-pass filter output from which harmonic components are removed (see reference numeral 71 in FIG. 2(b)).

A low-pass filter output 71 of the command voltage 7 is compared by a comparator 2 with a triangular wave 8 having a constant frequency and a constant amplitude. As shown in FIG. 2(b), the level position at which the low-pass filter output 71 of the command voltage 7 crosses the triangular wave 8 differs depending on its level. Therefore, the output of the comparator 2 becomes a pulse width modulation (PWM) signal 9 as shown in FIG. 2(c) that corresponds to the level of the low-pass filter output 71 of the command voltage 7. In other words, the width of the "H" section of the PWM signal 9 represents the magnitude of the command voltage 7.

As is well known, the timer 31 of the microprocessor 3 has a counter for counting internal clock pulses of a constant frequency as shown in FIG. 2(d). The timer 31 receives the “H” level of the PWM signal 9 as shown in FIG. 2(e).
Count the above clock pulses in the interval. Therefore, this count value is a digital signal. As shown in FIG. 2(f), the counter of the timer 31 transfers the count value to the counter buffer at the falling edge of the PWM signal 9, and clears the counter value. The count value at the falling edge of the PWM signal 9 is stored in the counter buffer as shown in FIG. 2(g).

In this way, the speed command voltage 7, which is an analog signal shown in FIG. 2(a), is converted into a digital signal through a series of operations from FIG. 2(b) to (g). The value of the counter buffer, which is this digital signal, is used as a speed command value for speed control by software. That is, the microprocessor 3 calculates the deviation between the digitally converted speed command value and the rotational speed of the motor 5 from the encoder 6, and controls the inverter 4 so that the deviation becomes zero.

[0013] Here, the resolution of the above embodiment will be discussed using specific numbers. Assuming that the internal clock of the microprocessor 3 is 8 MHz and the frequency of the triangular wave is 800 Hz, the digital output data changes from 0 to 9999. That is, 13.3(=log210000)b
It has a resolution of 12 bits, exceeding that of a 12-bit analog-to-digital converter IC.

Next, the response frequency will be considered. As mentioned above, the frequency of the triangular wave is 800 Hz, and the digital output data is updated at 800 Hz. Therefore, according to the sampling theorem, analog input of 400 Hz or more cannot be reproduced as output data. However, since the cutoff frequency for motor speed control is around 100 Hz, there is no problem in practical use for motor speed control.

According to the embodiment described above, the analog
Since an analog-to-digital conversion circuit can be configured with only a comparator and its peripheral components without using a digital converter IC, the cost is low.Also, even if software control is performed using a microprocessor, the comparator Wiring to the microprocessor is 1
Since a book is sufficient, the microprocessor port can be used effectively. Furthermore, when used in a motor speed control circuit, the response frequency is at a level that poses no practical problem, and the resolution exceeds that of conventional analog-to-digital converter ICs.

Note that the triangular wave to be compared with the speed command voltage also includes a sawtooth wave. In the above embodiment, FIGS. 2(c)(d)(
As shown in e), the clock pulses are counted during the "H" section of the PWM signal, but the clock pulses may be counted during the "L" section of the PWM signal. In this case, when the command voltage is high, the count value becomes small. Further, the count value may be multiplied by a constant or divided by a constant.

FIG. 3 shows another embodiment. This example is
A gate array (logic circuit) 10 having a built-in timer 11 is used, and the timer 11 in the gate array 10 is used to count only the positive or negative period of the PWM signal from the comparator 2. Therefore, the timer within microprocessor 12 is not utilized. The gate array 10 and the microprocessor 12 are connected by a data bus 13 and an address bus 14 having an appropriate number of bits.

The operation of the embodiment shown in FIG. 3 is the same as that of the previously described embodiments, so a description thereof will be omitted. This embodiment also has the advantage that it is not necessary to use an analog-to-digital converter IC. However, the embodiment shown in FIG. 1 is preferable because it has the drawbacks of an increased number of components and a large number of connections between the gate array 10 and the microprocessor 12.

The present invention is applicable not only to motor speed control circuits but also to analog-to-digital conversion circuits for various circuits.

[0020]

[Effects of the Invention] According to the present invention, an analog-to-digital conversion circuit can be configured only with a comparator and its peripheral components without using an analog-to-digital converter IC, so the analog-to-digital conversion circuit can be constructed at low cost. can be provided.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of a motor control circuit including an embodiment of an analog-to-digital conversion circuit according to the present invention.

FIG. 2 is a timing chart showing the operation of the embodiment.

FIG. 3 is a block diagram showing an example of a motor control circuit including another embodiment of the analog-to-digital conversion circuit according to the present invention.

FIG. 4 is a block diagram showing an example of a motor control circuit including an example of a conventional analog-to-digital conversion circuit.

[Explanation of symbols]

2 Comparator 7 Command signal 8 Triangle wave 9 Pulse width modulation signal

Claims (1)

[Claims] Claim 1: A comparator that compares a command signal, which is an analog signal, with a triangular wave of a constant frequency and a constant amplitude and converts it into a pulse width modulation signal, and a comparator that counts clock pulses only in the positive or negative section of the pulse width modulation signal. An analog-to-digital conversion circuit comprising a counter that converts a signal into a digital signal.