JPH0487414A - Cr oscillating circuit - Google Patents

Abstract

PURPOSE:To enlarge the utilization range of a power supply voltage by combining a first comparator having a PNP input stage and a second comparator having an NPN input stage, and connecting an NPN type active element and a PNP type active element to an output of the former and an output of the latter, respectively. CONSTITUTION:When a power source VCC is applied, an output of a second comparator 12 becomes a low level, a first transistor Q1 is turned on, and an output terminal TOUT becomes high. However,an output of 11 is a low level and a second transistor Q2 remains turned off. Therefore, a capacitor C1 is charged through a fourth resistor R4, and when its charging voltage exceeds a prescribed value, outputs of 11 and 12 become a high level and Q2 is tuned on, and Q1 is tuned off. As a result, C1 starts to discharge through R4, and when a voltage of C1 drops to a value determined in advance, the outputs of 11 and 12 are varied to a low level, respectively. In such a way, in an output terminal TOUT an oscillation output of a frequency determined by the capacity of C1 and a resistance value of R4 is obtained.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a low voltage operation type CR oscillation circuit.

(Prior Art) An example of this type of CR oscillation circuit will be described with reference to FIG.

In FIG. 7, this CR oscillation circuit includes a comparator 7
1 and 1st. It includes a voltage dividing circuit including second resistors R, R2 and a capacitor C2, and the positive input terminal, that is, the non-inverting input terminal, of the comparator 71 is connected to the voltage dividing point of the voltage dividing circuit, and the capacitor C1 is A negative input terminal, that is, an inverting input terminal, of the comparator 71 is connected. A third resistor R1 for positive feedback is connected between the output of the comparator 71 and the voltage dividing circuit, and a fourth resistor R4 for negative feedback is connected between the output of the comparator 71 and the capacitor C1.
is 11! ! has been done.

In this circuit, when the power supply VCC is applied, the comparator 7
1 becomes high level, and the capacitor C is charged through the fourth resistor R4. And capacitor C
When the charging voltage of C1 increases to the voltage at the non-inverting input terminal, the output of comparator 71 is inverted and capacitor C1 starts discharging. As a result, when the voltage at the 1 inverting input terminal decreases to a predetermined value, the output of the comparator 71 becomes high level again. Thereafter, by repeating the above-described operation, an oscillation output with a frequency determined by the capacitance of the capacitor C1 and the resistance value of the fourth resistor R4 is obtained at the output terminals T,.

(Problem to be solved by the invention) By the way, in this type of CR oscillation circuit, the comparator 7
The applicable range of the power supply vcc is determined depending on whether the input stage 1 is of the NPN type or the PNP type.

Normally, in the case of an NPN type input stage, the operating voltage power supply VCC is in the range of -0.1 to 1 (V), and in the case of a PNP type input stage, the operating voltage VCC is in the range of -1 to 0.2 (V). )
There is a range of degrees. Therefore, in the above-mentioned oscillation circuit, there is a restriction that it is necessary to use either the PNP type or the NPN type depending on the usage range of the power supply VCC.

Therefore, one object of the present invention is to provide a CR oscillation circuit that can expand the range of use of power supply voltage.

(Means for Solving the Problems) A CR oscillation circuit according to the present invention includes a first comparator having a PNP input stage and a second comparator having an NPN input stage, the first . The negative side input terminal of the second comparator has the first. A voltage dividing circuit including a second resistor is connected, a charging/discharging capacitor is connected to the positive input terminal, an NPN active element is connected to the output of the first comparator, and an NPN active element is connected to the output of the first comparator. A PNP type active element is connected to each output, the output terminals of the NPN type active element and the PNP type active element are connected to each other, and a positive feedback circuit is connected between the connection point and the voltage dividing circuit. In addition, a charging/discharging circuit is connected between the connection point and the capacitor.

Note that instead of the charging/discharging circuit, a circuit may be used that switches charging/discharging of the capacitor according to the output of the second comparator using a combination of a constant current source and a current mirror circuit.

(Example) A first example of the present invention will be described with reference to FIGS. 11 to 3.

FIG. 11 is a configuration diagram of the CR oscillation circuit, which is characterized in that it includes a first comparator 11 having a PNP input stage and a second comparator 12 having an NPN input stage.

Between the power supply VCC line and the earth GND line,
1st. A voltage dividing circuit including second resistors R1 and R2 is connected, and its voltage dividing point is the first. Second comparator 11, 12
are connected to each inverting input terminal of the On the other hand, the first. Second
One end of a capacitor C1 is connected to each non-inverting input terminal of the comparators 11 and 12, and the other end of the capacitor C1 is connected to the ground GND line. Further, the output of the first comparator 11 is connected to the base terminal of the second transistor Q2 via the sixth resistor R8, and the output of the second comparator 12 is connected to the base terminal of the second transistor Q2 via the fifth resistor R5. It is connected to the base terminal of transistor Q1 of No. 1.

1st. Second transistor Q1. Q2 has its collector terminals connected to each other, and furthermore, the first transistor Q has its emitter terminal connected to the power supply VCC line, and the second
The emitter terminals of the transistors Q2 are respectively connected to the ground GND line. The output terminal T a w + is drawn out from the connection point of each collector terminal, and the fourth
through the resistor R4 of the first. second comparator 11,
12 non-inverting input terminals.

The third resistor R1 acts as a positive feedback circuit.

The fourth resistor R4 acts as a negative feedback circuit (charging/discharging current).

When the power supply Vcc is applied to this CR oscillation circuit, the NPN
The output of the second comparator 12 having an input stage becomes a low level, and the first transistor Q1 is turned on.
Output terminal T0. ．． becomes high.

However, the first comparator 11 with a PNP input stage
The output of Q2 is at a low level and the second transistor Q2 remains off. This causes capacitor C3 to charge through fourth resistor R4.

When the charging voltage exceeds a predetermined value, the first comparator 1
1's output becomes high level and the second transistor Q2
is turned on, the output of the second comparator 12 becomes high level, and the first transistor Q is turned off. As a result, capacitor C1 begins to discharge through fourth resistor R4.

When the voltage of the capacitor C1 decreases to a predetermined value, the output of the first comparator 11 becomes low level.
The outputs of the second comparators 12 each change to low level.

In this way, an oscillation output with a frequency determined by the capacitance of the capacitor C3 and the resistance value of the fourth resistor R4 is obtained at the output terminal T OM + . Note that the level of the oscillation output can be set with the third resistor R2.

FIG. 2 shows a well-known circuit example of the first comparator 11, which has an input stage of PNP type transistors Q21 and Q2. To briefly explain the operation, when the base potential VBI of the transistor Q21 rises to a predetermined value,
The collector side potential VC2 of the transistor Q22 is
rises. Due to this.

Transistor Q25 becomes conductive and its collector side potential V
C5 falls and transistor 026 becomes conductive, causing its collector side potential VC6 to rise and output terminal V o w
+ provides high level output. Of course, when the base potential of the transistor Q22 rises, the operation is opposite to that described above, and an inverted output is obtained at the output terminals v,,1.

FIG. 3 shows a well-known circuit example of the second comparator 12, which has an input stage formed by an NPN type transistor Q3t+032. The operation is similar to that of the circuit shown in FIG.

FIG. 4 shows a specific example of a circuit in which the circuits shown in FIGS. 1 to 3 are combined.

FIG. 5 shows the circuit configuration of the second embodiment of the present invention, and
A circuit for switching between charging and discharging the capacitor C1 is connected to the circuit shown in the figure.

The charge/discharge switching circuit 41 includes a constant current source CC of the current ICC and a third . 4th. Fifth transistor Q ) * Q4 +Q
, and the sixth current mirror circuit. A seventh transistor Q, whose base terminal is connected to the output of the first transistor Q1 via a current mirror circuit formed by the seventh transistor Q, Q, and a resistor R, and whose collector terminal is connected to the base terminal of the seventh transistor Q7, 8 transistors Q8.

The CR oscillation circuit will be explained with reference to FIG. 6 showing the signal waveforms of each part. When the power is turned on, the P point voltage (the voltage of the capacitor C1) becomes O(V), so the first comparator 11 ．． The output of the second comparator 12 becomes low level, and the first transistor Q1 is turned on and the second transistor Q2 is turned off. For this reason, the output terminal T,...
l becomes high level, and the condition is set to turn on the eighth transistor Q8.

The ratio between the collector current IC4 of the fourth transistor Q4 and the collector current IC5 of the fifth transistor Q is 2:1.
, and the collector current IC6 of the sixth transistor Q6 and the collector current I of the seventh transistor Q
The ratio with C7 is 1:1. Capacitor C is the fifth transistor Q.

is charged with the collector current IC5, and the resistor R1゜R2,
When the voltage rises to the voltage set by R, the first comparator 11. The output of the second comparator 12 becomes high level, the first transistor Q is turned off, the second transistor Q2 is turned on, and the output terminal T01 becomes low level.

This turns off the eighth transistor Q8 and capacitor C1.

I CC() -1C7-I C5-I C5 is discharged, and the voltage V decreases. And resistors R+, R2,
When the voltage decreases to the voltage set by R3, the first comparator 11. The output of the second comparator 12 becomes low level, the first transistor Q1 is turned on, the second transistor Q2 is turned off, and the output terminal T01. is at the No. 1 level.

This turns on the eighth transistor Q8, and the capacitor C1.

It is charged in ICCΦ-1cs-0-1 (s).This operation is repeated thereafter to generate oscillation.

By the above operation, the output terminal T. 1. The voltage V2 of
The result is a pulse-like waveform as shown in the figure. A feature of the two-OCR oscillation circuit is that, by using a constant current source, the voltage v1 at point P varies linearly as the capacitor C1 is charged and discharged. That is, compared to the first embodiment in which the voltage change becomes non-linear as the end of charging or discharging approaches, the slope of the change in charge/discharge voltage is constant, so the timing of charge/discharge switching becomes constant and stable. becomes.

(Effects of the Invention) As explained above, the CR oscillation circuit according to the present invention has the following features:
By combining a comparator with a PNP type input stage and a comparator with an NPN type input stage,
The range of use for the power supply VCC can be expanded.

In particular, the CR oscillation circuit according to the present invention is effective for low frequency oscillation, and has the advantage of being able to provide a large amplitude without deteriorating accuracy due to mismatching of transistors.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of the first embodiment of the present invention, FIG.
The figures show circuit examples of the first and second comparators shown in Fig. 1, and Fig. 4 shows the circuits of Fig. 1, Fig. 2, and
A specific circuit diagram of the first embodiment of the present invention combining the circuits shown in the figure, FIG. 5 is a circuit diagram of the second embodiment of the present invention, and FIG.
The figure shows signal waveforms at various parts in FIG. 5, and FIG. 7 shows an example of a conventional CR oscillation circuit. In the figure, 11 is a first comparator with a PNP input stage, 12 is a second comparator with an NPN input stage, 4
1 is a charge/discharge switching circuit, and 71 is a comparator. Figure 2 Figure 3

Claims (2)

[Claims] (1) First comparator with PNP input stage and NP
and a second comparator having N input stages, and negative input terminals of the first and second comparators have first and second input stages.
A voltage dividing circuit consisting of a resistor is connected, a charging/discharging capacitor is connected to the positive input terminal, an NPN type active element is connected to the output of the first comparator, and an NPN type active element is connected to the output of the second comparator. connects PNP type active elements respectively, connects the output terminals of the NPN type active element and the PNP type active element to each other, connects a positive feedback circuit between the connection point and the voltage dividing circuit, and , A CR oscillation circuit characterized in that a charging/discharging circuit is connected between the connection point and the capacitor. (2) In the CR oscillation circuit according to claim (1), instead of the charging and discharging circuit, a combination of a constant current source and a current mirror circuit is used to charge and discharge the capacitor according to the output of the second comparator. A CR oscillation circuit characterized by comprising a switching circuit.