JPS6240819A - Threshold voltage detecting circuit - Google Patents

Abstract

PURPOSE:To detect automatically a threshold voltage of a logical gate by inputting an analog signal to be inputted to a digital circuit from an analog circuit, to the logical gate for inverting the polarity of its input, and feeding back its output to the input. CONSTITUTION:An input signal from an analog circuit is inputted to a point A. In case the point A has become a level being near a low level, its output becomes a level being near a high level by an inverter (logical gate circuit) 30. It is fed back by resistances 41, 42 and the point A becomes a high level side. By repeating this feedback, the point A is varied so that input/output power of the inverter 30 becomes equal. Accordingly, the potential of the point A becomes a threshold voltage, and even if a power supply voltage, etc. are varied, the point A is varied by following a drift of the input signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a circuit for detecting the threshold voltage of a digital circuit into which the output of an analog circuit is input.

[Conventional technology]

Conventionally, as an example of an analog circuit and a digital circuit into which the output thereof is input, there is a delay circuit that inverts the logic at an arbitrary timing within one period of a reference pulse, and this circuit is connected to a resistor 2 and a resistor 2 as shown in FIG. An integrating circuit 20 consisting of a capacitor 3 is combined with logic games 1-1a and 1-1b.

Figure (a) is its circuit diagram, with resistor 2 and capacitor 3.
is attached outside the IC. The delay timing of this delay circuit can be changed by making either the resistor 2 or the capacitor N3 variable.

Next, the operation will be explained. The same figure (bl; As shown in this figure, when a certain pulse is added to the input of the i! expansion circuit, the first logic game) ・A pulse which is the inversion of the pulse is obtained at the output of 1a.This inversion pulse is Resistor 2 and capacitor 3
If it is integrated using , the voltage waveform at point P will have a sawtooth shape. When this is inputted to the second logic gate 1b, this logic gate 1b is inputted to the second logic gate 1b.
If the voltage is below the threshold voltage, it is determined to be a low level and a high level is output, and when the level is below the threshold voltage, a low level is output. In this way, a pulse waveform is obtained in which the output voltage is inverted. The degree of delay of this output pulse waveform with respect to the input pulse waveform is determined by changing the time constant determined by changing the resistance value of the resistor 2 or the capacitance value of the capacitor 3 attached externally to the IC and the logic game 1) a, lb is determined by the variation in threshold voltage.

[Problem that the invention seeks to solve]

As described above, conventional delay circuits have the drawback that the degree of delay is unstable because the threshold voltage fluctuates due to changes in the power supply voltage of the logic gate.
The disadvantage is that an externally installed resistor or capacitor value must be adjusted to determine the degree of

This invention was made in order to solve the problems of the conventional ones as described above, and the threshold value set 1F of the logic gate of the digital circuit is can be detected automatically, making digital circuits stable! It is an object of the present invention to provide a threshold voltage detection circuit that can perform IJ production.

[Means to resolve the problem]

The threshold voltage detection circuit according to the present invention includes a logic gate 1- which receives the output of an analog circuit which is input into a digital circuit and inverts its polarity, and a resistor connected between the output terminal of the logic gate and the output terminal of the logic gate. It has been established that

Further, the threshold voltage of the digital circuit output from the connection point of the resistors is added to the output of the analog circuit in place of the DC component in the output of the analog circuit.

[Effect]

In this invention, the logic data 1 whose input polarity is inverted is
- Since the output is fed back to its input by a resistor, the footbank loop follows the input signal from the analog circuit and outputs a threshold voltage.

Furthermore, since the threshold voltage is applied to the analog circuit in place of the DC component being output, the operation of the digital circuit is stabilized.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a threshold voltage detection circuit according to an embodiment of the present invention, and in the figure, 30 is an input circuit constructed using the same gate 1- as the first stage logic circuit of the 1H5Z digital circuit shown in the figure. <-Yu (logic gate times f#G), 41.4
2 is a resistor for feeding back the output voltage of the inverter 30 to be equal to its input voltage, and 40 is a power supply VDD and a resistor 41. '42 connection point human G-connected resistance, 4
3 is a capacitor connected between the connection point A and the ground.

Next, the operation will be explained. An input signal from an analog circuit (not shown) is input to point A and G in FIG. Near 1
This force (feedback by the resistors 41 and 42 makes point A more)\I level side. After that, by repeating the above-mentioned steps, inverter 3
0, the output voltage changes to be equal, and the feedback group oscillates around the stable point. Therefore, the potential at point A becomes a threshold voltage, and even if there are fluctuations in the power supply voltage, etc., point A changes to follow the drift of the input signal.

FIG. 2 shows a delay circuit constructed using the circuit of the embodiment described above, and the circuit can be roughly divided into three blocks. In the figure, 10 is an input terminal, 1) is a sawtooth wave generation circuit (analog circuit), 22 is a capacitor, 12
1 is a threshold voltage detection circuit, and 13 is a logic gate (digital circuit).

In this delay circuit, a sawtooth wave generating circuit 1) integrates a reference pulse at an input terminal 10 using its resistor and capacitor to create a harmonic waveform. This output waveform is transferred to the capacitor 22
The DC voltage from the two-threshold voltage detection circuit 12 devised this time is applied. By inputting this waveform to the logic gate 13,
The same waveform as before can be obtained more stably and without adjustment.

Here, FIG. 4 shows its specific configuration. In comparison with FIG. 2, in the figure, 1) is a sawtooth generating circuit, 12
1 is a threshold voltage detection circuit, and 13 is a logic gate.

Note that in the same figure, °ζ and 44 are resistances.

In addition, FIG. 5 shows N as another example of the installation shown in FIG.

A 1/2 period delay circuit using R data 1- is shown, and the sixth
The timing chart is shown in the figure. In the figure, I.C.
l-IC4 is a NOR circuit, and 45.46 is a resistor.

In this circuit, the reference pulse is inverted by the ICI, and the resistor 2. By integrating this pulse by capacitor 3, a sawtooth wave is obtained. This DC voltage is capacitated by a capacitor 22, and the threshold voltage detected by the IC 2 is added thereto to provide an input to the input circuit 103. By inputting this output pulse and reference pulse to IC31C4,
The output pulse of IC4 can generate a pulse that rises exactly 1/2 cycle later than the reference pulse.

Although the circuit shown in FIG. 5 is a pulse circuit that obtains a timing delay of 1/2 cycle, any delay can be obtained by adding the output of a clamp circuit to the threshold voltage.

Furthermore, although frequency dividing circuits are often used in digital circuits, they can also be applied to circuits that double the frequency.

In this way, in the conventional delay circuit, the delayed output of the reference pulse was obtained by external adjustment, but by providing the threshold voltage detection circuit according to this embodiment, the adjustment can be automatically performed internally. In addition, even if the power supply voltage changes, the threshold voltage can follow the change, so there is no need to adjust it again, and there is no need to think about the variation in logic gates because it is made into a 1,000-sub IC. Furthermore, if resistors and capacitors can be integrated into one chip, there will be less variation in elements, and a delay circuit can be constructed with relatively high accuracy.

In addition, in the above embodiment, the threshold voltage detection circuit was applied to the delay circuit, but if the ink face part in the analog-digital mixed circuit, especially the part where the output of the analog circuit is input to the digital circuit, It can be applied to any type of circuit and has the effect of stably operating digital circuits.

〔Effect of the invention〕

As described above, according to the threshold voltage detection circuit according to the present invention, an analog signal to be input from an analog circuit to a digital circuit is input to a logic gate that inverts the polarity of the input, and the output of the logic gate is input. Therefore, even if the output of the analog circuit drifts, the threshold value of the logic gate of the digital circuit that follows it can be automatically detected, which has the effect of stably operating the digital circuit.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a threshold voltage detection circuit according to an embodiment of the present invention, FIG. 2 is a diagram showing a delay circuit using the circuit in FIG. 1, and FIG. 3 is a diagram showing the configuration of a normal delay circuit. 4 and 5 are diagrams showing the specific configuration of the circuit of FIG. 2, and FIG. 6 is a timing chart of the circuit of FIG. 5. In the figure, 30 is an inverter (logic gate circuit), 4
0 to 42 are resistors, 43 is a capacitor, 12 is a threshold voltage detection circuit, 1) is a sawtooth wave generation circuit (analog circuit)
, 13 are logic gates (digital circuits).

Claims (2)

[Claims] (1) A logic gate circuit that receives the output of an analog circuit that should be input to a digital circuit, inverts the polarity of the input, and outputs it; and a resistor that connects the input terminal and output terminal of the logic gate circuit. , a threshold voltage detection circuit outputting a threshold voltage of a logic gate of the digital circuit from the connection point. (2) The threshold voltage detection circuit according to claim 1, wherein the threshold voltage is applied to the output of the analog circuit instead of a DC component of the output.