JPH03250815A - A/d converter - Google Patents

Abstract

PURPOSE:To ensure a stable output even when a level change in an analog signal due to external disturbance exists by applying positive feedback to each signal conversion circuit converting an analog signal into a digital signal so as to provide a hysteresis characteristic. CONSTITUTION:Resistor R2 of signal conversion circuits 21-25 are connected in series and the series connection of the resistors connects to ground via a resistor R, then a low potential side of each resistor R2 reaches a voltage corresponding to the circuit, and the voltage is fed to a base of a transistor(TR) Q2 as a reference voltage via a resistor R3. On the other hand, an output signal of a TR Q3 is fed to the base of the TR Q2 via resistors R3, R4 and a diode D1. Then the loop acts like a positive feedback loop and the feedback quantity is set so that each conversion circuit shows the hysteresis characteristic. Since the positive feedback characteristic is provided in the level conversion circuit in this way, even when an analog signal is fluctuated in the vicinity of the border of an identification level due to external disturbance, the fluctuation is absorbed by the circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an A/D converter having hysteresis characteristics.

[Prior Art] As is well known, there is an A/D converter that converts the level of an analog signal into a multi-bit digital signal. In this method, a signal conversion circuit is provided for each analog signal level of a plurality of values, and analog signals are supplied to the signal conversion circuit in parallel.

In this way, as shown in FIG. 5, an output signal is obtained from the signal conversion circuit whose level is lower than that of the supplied analog signal, so that the analog signal is converted into a multi-bit digital signal. For example, in Figure 5, the level of an analog signal is expressed as a 5-bit digital signal, and the symbol A
For an analog signal with a level represented by , bits bo, b
l, b2 are at "0" level, bit b3. b4 becomes the "1" level. In this case, the greater the number of bits in the digital signal, the more accurately the analog signal can be converted into a digital signal, and in order to make the boundaries of the level range clearer, the discrimination characteristics at the boundaries are made more convenient. In other words, if it exceeds a certain boundary level, it will immediately output a "0" level digital signal, and if it falls below a certain boundary level, it will output a "0" level digital signal.
'' level, the digital signal was set to ``1'' level.

[Problems to be Solved by the Invention] However, since such conventional devices require accuracy as described above, the level of the digital signal may be "1" or "0" after a certain level of the analog signal. However, this method causes the output level to fluctuate due to disturbances such as noise or analog signal level drift, so it is not suitable for use as an A/D converter for fuzzy controllers. There wasn't.

[Means for Solving the Problems] In order to solve these problems, the present invention applies positive feedback to the level conversion circuit of the A/D converter to give it hysteresis characteristics.

[Since the active level conversion circuit has a positive feedback characteristic, even if the analog signal fluctuates due to disturbance near the boundary of the discrimination level, the fluctuation is absorbed.

[Embodiment] FIG. 1 is a circuit diagram showing an embodiment of the present invention. In FIG. Each circuit is comprised of transistors Q1 to Q5, resistors R1 to R4, a diode Dl, and a digital signal output terminal T. The resistors R2 of each circuit are connected in series across all the circuits, one end of the series circuit is supplied with power supply voltage from the power supply voltage supply terminal 3, and the other end is grounded via the resistor R.

The device configured in this way has a resistor R2 of each signal conversion circuit.
are connected in series and grounded through the resistor R, so the low potential side of the resistor R2 becomes a voltage corresponding to the circuit, and this voltage is applied to the transistor Q2 through the resistor R3.
is supplied as a reference voltage to the base of For this reason,
When an analog signal is supplied to the analog signal input terminal 1, the level of the analog signal is compared in each signal conversion circuit with a reference voltage supplied to that circuit. The reference voltages supplied to each signal conversion circuit correspond to the plurality of predetermined analog signal levels described above.

First, when no analog input signal is supplied, the transistor Q1 is turned on, the transistors Q2 and Q3 are turned off, and a signal at rH level is output from the digital signal output terminal T. Then, for circuits to which an analog signal is supplied and whose level is higher than the reference voltage, transistor Qt is turned off, so transistors Q2,
Qs turns on and the output signal changes from r)(J level to “L”
” level. Therefore, a digital signal corresponding to the level of the analog signal is output. In addition,
If this output is viewed as negative logic, the rH output corresponds to logic "0" and the "L" output corresponds to logic "1".

On the other hand, the output signal of the transistor Qs is the resistance R3゜R,,
D, and is supplied to the base of transistor Q2. This loop is a positive feedback loop, and the amount of feedback is set so that each conversion circuit exhibits hysteresis characteristics. Figure 2 shows the characteristics of this circuit. When the analog input level exceeds a certain level, the digital signal will change in level, but even if the analog input level becomes slightly lower than that level due to disturbance etc., there is a hysteresis characteristic. Therefore, no change in the level of the digital signal occurs, and the digital output level changes when the analog input level becomes lower than the value determined by the hysteresis characteristic. Therefore, even if the input level fluctuates somewhat, the output level remains stable.

Note that in each signal conversion circuit, the portion surrounded by a dotted line is a positive feedback loop. Also, instead of providing a positive feedback loop in the circuit as shown in Fig. 1, an external D/A loop is provided as shown in Fig. 3.
A positive feedback loop composed of the converter 10 and the analog computing unit 11 may be provided.

In this circuit, a comparison voltage input as shown by the dotted line in FIG. 4 is supplied, and an output shown by the solid line is obtained, and a hysteresis characteristic can be generated without positive feedback.

In this way, there is no need to change the circuit of the A/D converter itself, so the module or IC can be used as is.

[Effects of the Invention] As explained above, the present invention provides positive feedback to the signal conversion circuit that converts analog signals into digital signals to provide hysteresis characteristics, so that it is stable even when the level of the analog signal changes due to disturbance. This has the effect of ensuring a high output.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, Fig. 2 is a graph showing its characteristics, Fig. 3 is a block diagram showing another embodiment, and Fig. 4 is a graph showing the characteristics of Fig. 3. , FIG. 5 is a graph showing the characteristics of the conventional device. 1...Analog signal input terminal, 21-25...
Signal conversion circuit, 3... Power supply voltage supply terminal, R, R1
-R4...Resistor, Q1-Q3...Transistor, Dl...-Diode, T...Digital signal output terminal.

Claims (1)

[Claims] In an A/D converter having signal conversion circuits provided corresponding to each of a plurality of predetermined analog signal levels, each signal conversion circuit performs positive feedback to a state exhibiting hysteresis characteristics. An A/D converter characterized by being subjected to.