JPS5857818A - Switching circuit - Google Patents

Abstract

PURPOSE:To obtain a stable output even with a minute AC component included in an input signal, by changing the 1st and 2nd reference voltage with the output of the 2nd comparator and picking up an output signal from the output of the 1st comparator. CONSTITUTION:When a signal applied to an input terminal 1 is changed from high to low potential, the signal is compared with the 1st reference voltage 5 at the 1st comparator 2, an output 4 changes from high to low potential, the output 4 and the 2nd reference voltage 7 are compared at the 2nd comparator 6 and the potential at the point C changes from high to low potential. Through the change of the potential at the point C, the 2nd reference voltage 7 is changed to a high voltage to lower the potential at the point C acceleratingly. Through the rapid change in the potential of the point C, the 1st reference voltage 5 is changed to a high value to bring the potential of the output 4 to a sufficiently stable low potential practically even if a minute AC signal such as noise is included in the input 1. When the input 1 changes from low to high potential, the 1st and 2nd reference voltages 5, 7 are changed to a low value, and the provision of excellent hysteresis characteristics as stated above can offer stable outputs.

Description

[Detailed Description of the Invention] The present invention relates to a switching circuit that generates an output signal when the input signal level exceeds a certain value, and the present invention relates to a switching circuit that generates an output signal when the input signal level exceeds a certain value. It is configured so that output can be obtained.

A block diagram of an example of a conventional switching circuit is shown in FIGS. 1 and 2.

In the switching circuit shown in FIG. 1, when the comparator
When an input signal containing an alternating current component as shown in FIG. 3 is applied to the input end 1, an unstable output as shown in FIG. 4 appears at the output end 4.

Next, in the switching circuit shown in FIG. 2, the input signal containing the AC component shown in FIG. 3 is applied to the input terminal 1, the gain of the comparator 2 is made infinite, and the output of the reference voltage generator 6 is applied to the output terminal 4 moves from high potential to low potential, from Vl to v
5, when moving from low potential to high potential, from v3 to vl
5, a stable output as shown in FIG. 5 can be obtained at the output terminal 4. The input/output characteristics in this case exhibit so-called hysteresis characteristics as shown in FIG. ΔV is a hysteresis width, which is determined based on conditions controlled by an external circuit connected to the output terminal 4 of the switching circuit.

In reality, the gain of the switching circuit is finite, so the input/output characteristics shown in FIG. 6 become as shown in FIG. 7. here,
The gain of the comparator 2 is set to be finite and constant regardless of the input level, and when the input of the reference voltage generator 6 reaches Va, its output is switched and positive feedback is created in the closed loop formed with the p comparator 2. It is assumed that the potential at the output terminal 4 changes irreversibly.

In FIG. 7, in the region of Δv1 or Δ■3, the comparator 2 operates as a linear amplifier, and the minute AC component included in the input is amplified and appears in the output, so the output terminal 4
There is no problem if the detection level of the external circuit connected to is exactly equal to Va, but it is common that the detection level is different from Va or the detection level is I[, △■
In a part of the region of 1 or Δ■3, the external circuit operates unstablely.

Therefore, making Δv1 and Δ■5 as small as possible is a condition for a switching circuit that can obtain a stable output, and to that end, it is naturally required to make the gain of comparator 2 as large as possible. However, there are limits due to various negative factors. The present invention aims to provide a circuit that increases the gain of the comparator 2 to the maximum extent, further reduces Δv1 and ΔV3i, and stabilizes the output.

The contents will be explained below using the attached drawings.

A block diagram of an embodiment of the present invention is shown in FIG. The output drives the reference voltage generator 5 and the second reference voltage generator 7. Here, the gain of the second comparator 6 is finite and constant regardless of the input level, and its output is assumed to be in opposite phase to the input in order to correspond to the specific example described later, but even if it is in phase, There is no problem. The output of the second reference voltage generation booklet changes from l'ivb to Va when the potential at the 0 point, which is the output of the second comparator 6, moves from a low potential to a high potential.
When the potential changes from high to low, it switches from vO to vb. Here, assuming that the relationship Vb ) Va ) Vo holds true, and that the detection level of the external circuit connected to the output terminal 4 has a central value approximately equal to Va and that its width is sufficiently smaller than Vb - Va, The input/output characteristics of the switching circuit shown in FIG. 8 are as shown in FIG. 9. In FIG. 9, D indicates the potential at point C in FIG. 8, and the region of linear operation is ΔY'l and Δ≠, and Δv1 and Δ
It is significantly smaller than V3. If the difference between vb and VaO, which is the output of the reference voltage generator 7, is made as large as possible, Δv1 and Δ≠ will become even smaller. Also, the hysteresis width △V' (= V'5 - V'1) is smaller than that of the conventional circuit, but as mentioned above, it is controlled by external factors, so it may be the same width as the conventional circuit or the desired width. All you have to do is set the constants so that

In FIG. 9, the gains of comparators 2 and 6 are exaggerated and shown small for the sake of clarity, so in reality △v1
The present invention makes it possible to provide a switching circuit that can provide a sufficiently stable output for practical use even when the input contains an alternating current component.

FIG. 10 shows a specific circuit example of the present invention. This circuit is an example designed to be suitable for IC implementation. In FIG. 10, 9 to 16 constitute a first comparator 2'lr;
16 to 18 constitute the first reference voltage generator 6, and 21 to 18 constitute the first reference voltage generator 6.
24 constitutes the second comparator 6, 26 and 26 constitute the second reference voltage generator 8, and 27 to 36 constitute the external circuit 6 connected to the output terminal 4.

36 is a positive power supply VC10. To explain the details, 1 is an input terminal to which an input signal is applied, and is connected to the grounded transistor 10 via a bias resistor 9. Transistors 10 and 11 constitute a differential amplifier, their common emitters are grounded via a constant current source 12, the collector of the transistor 10 is connected to the positive power supply Vaa, and the collector of the transistor 11 is connected via a load resistor 13. Connected to the positive power supply VOO and to the base of the emitter follower transistor 140. The pace of the transistor 11 is connected to the positive power supply Vaa via a bias resistor 16, grounded via a constant current source 18, and connected to a potential shift resistor 17.
It is connected to the emitter of the switching transistor 2o via. The emitter of the transistor 14 is connected via a level shift resistor 19 to the output terminal 4 of the switching circuit and to the grounded terminal of the transistor 22 via a constant current source 15. Transistors 22 and 23 constitute a differential amplifier, and their common emitters are connected to the positive power supply VOO via a current source 21, and the collector of transistor 22 is grounded via a load resistor 24 and connected to the base of transistor 2o. The collector of the transistor 23 is grounded, and the base is connected to a constant voltage source 26 via a potential adjustment resistor 25 and to the collector of the transistor 2o.

Transistors 31' and 32 constitute the entire differential amplifier,
Their common emitters (l-j: grounded via the current source 33, their respective collectors connected to the positive power supply VOO via the load resistors 29 and 30i, and connected to the output terminals 34 and 35. The base of the transistor 31 is bias resistor 27
The transistor 32 is connected to a constant voltage source 26 through a bias resistor 28 and grounded through a bias resistor 28, and the base of the transistor 32 is connected to the output terminal 4.

Next, the operation will be explained with reference to FIGS. 10 and 11. When the potential at point D' in FIG. 10 is low, the switching transistor 2oFi is off, so the resistors 17 and 2
The voltage drop at 5 is almost zero. E at this time
The potentials at point and F point are respectively vl and v in FIG.
Set to b. When the potential at point D' increases, transistor 20 is turned on, and current flows from constant voltage source 26 to constant current source 18 via resistors 26 and 17, and the current flowing through resistor 16 decreases. Therefore, the potential at point E becomes higher than vl, and the potential at point F becomes lower than vb.

The potentials at point E and point F at this time are set to 3 and Va in FIG. 11, respectively. Further, the potential at point G is set to a value close to Vo in FIG. Note that in order to change the potential at point E, the resistor 17 may be coupled to the current source 18, and the current of the current source 18 may be changed. Under the above conditions, when input terminal 1 is higher than vb, transistor 10.23°32 is turned on, and transistors 11 and 22 are turned on.
．． 31 is turned off and the potential at point D' is low, so points E and F
The potentials at the points are vl and vb, respectively. Therefore, even if the potential at input terminal 1 drops to Vb, the potential at output terminal 4 does not change at all, and when the potential at input terminal 1 drops to a value close to V'1, first differential amplifier 10°11 stops operating. For the first time, the potential at the output terminal 4 decreases along H in FIG.
Subsequently, the differential amplifiers 22 and 23 start operating, and the potential at point D' rises as shown in FIG. 11I. The potential of input terminal 1 is v
When the voltage reaches l, the switching transistor 2o turns on and raises the potential at point E. As a result, the potential at the output end 4 instantaneously and irreversibly reaches the lowest potential VL. During this period, the differential amplifiers 31 and 32 are in the 11th linear operation region.
Since the settings are as shown in the figure, a complete switching operation is performed and the potential at the output terminal 34 changes as shown in FIG. 11.

When transistor 2o turns on, the potential at point F also changes from vb to V.
Wait until the potential at the input terminal 1 rises again. A similar explanation holds true even when the potential at the input terminal 1 rises from a potential lower than vl, so the explanation will be omitted here. In order for the switching circuit shown in FIG. 10 to more reliably operate as described above, it is effective to connect a capacitor in parallel with the resistor 26 so that the change in potential at point F is delayed from the change in potential at point E.

As explained above, according to the present invention, it is possible to obtain a switching circuit that can obtain a sufficiently stable output for practical use even when the input contains minute alternating current components. It is possible to realize an ideal switching circuit by combining it with an external circuit.

[Brief explanation of the drawing]

Figures 1 and 2 are block diagrams of conventional switching circuits, Figures 3, 4, 5, 6, and 7 are explanations of the operation of the conventional switching circuit, and Figure 8 is a block diagram of a conventional switching circuit. FIG. 9 is a block diagram of an embodiment of the invention, FIG. 9 is a detailed explanatory diagram of the invention, FIG. 10 is a circuit diagram based on the embodiment of the invention, and FIG. 11 is an explanatory diagram of the operation of the same circuit. 1...--Input end, 2, 6...--Comparator, 3
...Reference voltage source, 4...Output end, 5,
7...Reference voltage generator. Name of agent: Patent attorney Toshio Nakao and 1 other person @
1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 3-person car Figure 8 Figure 9

Claims (1)

[Claims] a first voltage source that compares the input signal with a first reference voltage to obtain an output;
and a second comparator that obtains an output by comparing the output of the first comparator and a second reference voltage, and the output of the second comparator is the first reference voltage. and a switching circuit that changes a second reference voltage and extracts an output signal from the output of the first comparator.