JPH03218123A - A/D conversion circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an A/D conversion circuit that converts an analog signal voltage into a digital signal voltage.

[Conventional technology]

In order for a microcomputer to process an analog signal voltage from a temperature detection means that uses changes in the resistance value of a thermistor due to temperature changes, an A/D conversion circuit is required to convert the analog signal voltage into a digital signal voltage. However, when determining the magnitude of the analog signal voltage, for example, as shown in FIG. 3, an A/D conversion circuit consisting of a plurality of comparators 6a to 6d and resistors R2 to R9 was set up. [Problems to be Solved by the Invention] However, in the case of the above-mentioned A/D conversion circuit, if the number of times to classify and judge the size of captured data increases, the number of A/D conversion circuits will also increase, resulting in expensive and expensive Become something.

In addition, when using the A/D conversion circuit built into the microcontroller, the quantization step is fixed, so for signals with a minute change width, this is amplified and the quantization step is increased to a value larger than the quantization unit value. In addition, if the range of change is sufficiently large, a larger quantization step is advantageous in terms of noise, but this also has problems such as being unable to be adjusted. Therefore, an object of the present invention is to solve these problems and provide an A/D conversion circuit that can be easily implemented at low cost.

[Means to solve the problem]

The present invention has been made to solve the above problems, and includes an A/D conversion circuit that converts an analog signal voltage from a temperature detection means into a digital signal voltage.
The conversion circuit is configured by a charging/discharging means that repeats charging and discharging based on a control signal that is periodically input, and a comparator that compares the output voltage from the charging/discharging means with the analog signal voltage from the temperature detecting means. Configured.

[Effect]

With the above configuration, the time from when the output voltage from the charging/discharging means starts charging or from when the charging/discharging means starts to become equal to the analog signal voltage from the temperature detecting means can be digitally output. I can do it.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on FIGS. 1 and 2.

In the figure, ■ is a temperature detection means, 2 is an A/D conversion circuit that converts the analog signal voltage from the temperature detection means 1 into a digital signal voltage, and 3 is a control circuit for controlling the A/D conversion circuit 2; This is a microcomputer that processes input signals from the /D conversion circuit.

The temperature detection means 1 consists of a thermistor 4 and a resistor R1 connected in series between a power supply Vdd and ground, and point a is the output terminal of an analog signal voltage. The A/D conversion circuit 2 consists of a charging/discharging means 5 controlled by the microcomputer 3 and a comparator 6, and the charging/discharging means 5 includes a transistor 7 which becomes conductive when the control signal from the microcomputer 3 is L; The capacitor C1 is charged when the transistor 7 is turned on, and the resistor R2 is configured to discharge the charge stored in the capacitor C1 when the transistor 7 is turned off. The inverting input terminal (1) of the comparator 6 is connected to the output terminal a of the temperature detecting means 1, and the output side C of the comparator 6 is connected to the input terminal T2 of the microcomputer 3. It is connected to the. On the microcomputer 3 side, there is an oscillation circuit section 8, a frequency division circuit section 9, and a NAN
There is a D circuit 10, an AND circuit 11, a counter 12, etc.
The output signal from the oscillation circuit section 8 is output to the AND circuit 11 and the frequency dividing circuit section 9, and the two frequency-divided signals are output to the NAN.
D circuit 10, and the output terminal of the NAND circuit 10 is connected to the AND circuit 11, the clear signal input terminal of the counter 12, and the output terminal T1 that outputs the control signal to the A/D conversion circuit 2. , the input terminal of the AND circuit l1 is connected to the A
The output terminal of the AND circuit l1 is connected to the input terminal T2 which takes in the output signal of the /D conversion circuit, and the output terminal of the AND circuit l1 is connected to the counter 1.
It is connected to the input terminal of 2.

The main parts of the temperature detection means I A/D conversion circuit 2 and microcomputer 3 have been explained above.
This will be explained using the diagram and FIG.

The oscillation circuit section 8 outputs l, 0 signals as shown in FIG.

The frequency dividing circuit section 9 divides and outputs the frequency into two signals as shown in B and C in FIG. 2, and the NAND circuit 10 outputs the frequency as shown in
The signal is converted into a signal as shown in FIG.

If the output level at point D shown in FIG. 1 is H, the AND circuit 11 and the counter 12 are maintained in an operable state, but the transistor 7 on the A/D conversion circuit 2 side is of PNP type, so it is not operable. Therefore, the levels at point b and point C in FIG. 1 are in the L state as shown at the left end of FIG. When the output level at the point D is reversed from H to L, the AND circuit 11 stops operating, the counter 12 is cleared, and the transistor 7 is turned on.

Due to the conduction of the transistor 7, the capacitor C1 is charged, and the potential at point b rises to the level b shown in FIG.
When the analog signal voltage shown by the broken line is outputted, the output of the comparator 6 continues to be at level H as shown in FIG. 2C.

Next, when the input level to transistor 7 is reversed from L to H as shown in FIG. The charge is discharged by the resistor R2, and the potential at point b decreases from the level shown in FIG. 2b to approximately 0 with the passage of time. Furthermore, as mentioned above, when the level at point D is inverted from L to H, AND circuit l1 also becomes operational, so A
The output level of the ND circuit 11 becomes H, and the counter l2 starts counting as shown in FIG. is reversed from H to L as shown in Figure 2C, and A
The output level of the ND circuit l1 becomes L, and the counter 12 stops counting. If the voltage level output from the output terminal a of the temperature detection means 1 is higher than the level a shown in FIG. Since the time becomes shorter, the counter value also decreases, and if the voltage level at the output terminal a is lower than the position shown in the figure, the above-mentioned H
The time at the end of the reversal from L to L increases, and the counter value also increases. Therefore, the level of the temperature detected by the temperature detection means 1 can be known from this counter value, and can be extracted as a digital signal necessary for driving and controlling the microcomputer.

In addition, in the A/D conversion circuit of the present invention, the charging/discharging means 5
The quantization step can be changed by adjusting the CR constant of , and the operation on the microcomputer 3 side can also be handled by software. [Effects of the Invention] As described above, the A/D conversion circuit as described above can be constructed with a smaller number of parts than the conventional one, so it is easy and inexpensive to manufacture, and the CR constant can be adjusted. This allows the quantization step to be easily adjusted, which is also effective as a noise countermeasure.

[Brief explanation of drawings]

Fig. 1 is an A/D conversion circuit diagram showing an embodiment of the present invention, Fig. 2 is an operation waveform diagram of the same embodiment, and Fig. 3 is an A/D conversion circuit diagram showing a conventional example.
/D conversion circuit diagram. In the figure, 1-.1 degree detection means, 2- A/D conversion circuit,
3-microcomputer, 4--thermistor, 5-1111 charging/discharging means, 6-1 comparator, 7--1 transistor,
81 oscillation circuit 9.1 frequency division circuit section, 10-N A N
D circuit, 11-A N D circuit, 12-counter, R1 to R3-resistance, c i------- capacitor,
Vdd----1 power supply, T I-output end, T2----
- Only one person can do it.

Claims (1)

[Claims] In an A/D conversion circuit that converts an analog signal voltage from a temperature detection means into a digital signal voltage, a charging/discharging means repeats charging and discharging the A/D conversion circuit based on a control signal that is periodically input; A characterized in that it is constituted by a comparator that compares the output voltage from the charging/discharging means and the analog signal voltage from the temperature detecting means.
/D conversion circuit.