JPH04207627A - Oscillation circuit - Google Patents

Abstract

PURPOSE:To select an oscillating frequency with a selection signal at an oscillation circuit by varying an input threshold level of the oscillation circuit so as to vary the Schmitt width thereby varying the oscillating frequency. CONSTITUTION:P-channel transistors(TRs) 1, 3, 5, 7, 9, 11 and N-channel TRs 2, 4, 6, 8, 10, 12 forming a feedback inverter of the oscillation circuit are connected in parallel by plural TRs and a switch 13 is provided to the oscillation circuit so as to use a selection signal thereby acting an optional number of TRs like the feedback inverter. That is, the oscillation circuit varies the drive capability of the feedback inverter by changing number of TRs 1-12 acting like the feedback inverter with a selection signal. Thus, the oscillating frequency is varied by changing the Schmitt width. Thus, the oscillating frequency is changed freely by changing the Schmitt width.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an oscillation circuit using a Schmitt inverter.

[Conventional technology]

A conventional oscillation circuit using a Schmitt inverter is shown in FIG.

In the figure, IN is the input terminal of the oscillation circuit, OUT is the output terminal of the oscillation circuit, (1) and (2) are the P-channel transistor and N-channel transistor that constitute the inverter at the first stage input to the oscillation circuit, (3) and (4) ) are the P-channel transistor and N-channel transistor of the next stage inverter, (
5) and (6) (P-channel transistor and N-channel transistor of the third stage inverter, (7) and (8) are the P-channel transistor and N-channel transistor of the feedback inverter, and C is the capacitor of the external circuit of the oscillation circuit. ,R
is the resistance of the external circuit.

Next, the operation will be explained.

The oscillation circuit is in the form of a Schmitt inverter, and the output of the first stage inverter consisting of transistors (1) and (2) is inverted by the second stage inverter consisting of transistors (3) and (4). By connecting the output of a feedback inverter composed of transistors (7) and (8) which receives the amplified signal as input, the input/output characteristics of this circuit exhibit hysteresis characteristics.

This hysteresis characteristic is shown in FIG. Input IN is “L”
” to “H”, the output OUT is connected to the input IN or V
When it is 1H, it changes from “H” to “L”, and whether the input is “
When transitioning from “H” to “L”, the output OUT is connected to the input I
Changes from "L" to "H" when N or V'lL. This V
(The values of H, V 1 L are transistors (1), (2
+.

+71. It is determined by the driving ability of the transistor (8), and the larger the driving ability of the transistor (7), the higher the V IH becomes.
IL becomes low.

When a resistor R is connected between the input IN and the output OUT of this oscillation circuit, and a capacitor C is connected to the input IN, this oscillation circuit starts oscillating. The process of this oscillation will be explained in accordance with time with reference to FIG. First of all, input IN or “L”
If so, the output OUT becomes "H", the capacitor C connected to the input is charged to the "H" level from the transistor (5) via the resistor R, and the voltage at the input IN gradually increases. When the voltage of the input IN reaches V4, the output 0LIT is inverted and becomes an "L" level output. Output 0LI
Since T becomes "L", the capacitor C is now discharged to the "L" level from the transistor (6) via the resistor R, and the voltage of the input IN gradually decreases from VIM. Then, when the voltage of the input IN drops below VIL, the output OUT is inverted and becomes the "H" level, and charging of the capacitor C starts. Since the oscillation circuit repeats this operation, the output O
The UT will periodically repeat "H" and "L". The waveform of the input IN at this time is shown in FIG.

The frequency of this oscillation is determined by the charging/discharging characteristics of capacitor C and the input threshold voltage ■Width of IH and Vl'L (Schmitt width)
Determined by Furthermore, the charging and discharging characteristics are determined by the values of the external capacitor C and the resistor R.

[Invention or problem to be solved]

Since the conventional oscillation circuit was configured as above,
Once the external capacitor C and resistor R were determined, the Schmitt width was fixed in the circuit, so there was a problem that the oscillation frequency could not be changed.

This invention was made to solve the above-mentioned problems, and aims to provide an oscillation circuit in which the Schmitt width can be freely changed to freely change the oscillation station and wave number.

[Means to solve the problem]

In the oscillation circuit according to the present invention, the P-channel transistor and the N-channel transistor that constitute the feedback inverter of the conventional oscillation circuit are each configured by connecting a plurality of transistors in parallel, and an arbitrary number of transistors can be used as the feedback inverter using a selection signal. It is equipped with a switch so that it can be activated.

[Effect]

In the oscillation circuit according to the present invention, the driving ability of the feedback inverter can be changed by changing the number of transistors acting as the feedback inverter using a selection signal, and thereby the oscillation frequency can be changed by changing the Schmitt width.

〔Example〕

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

In Figure 1, IN is the input terminal of the oscillation circuit, 0LIT
are the output terminals of the oscillation circuit, (1) and (2) are the P-channel transistors and N-channel transistors that make up the inverter in the first stage input to the oscillation circuit, and (3) and (4) are the P-channel transistors and N-channel transistors in the next stage inverter. Transistors (5) and (6) (or P-channel transistor and N-channel transistor of the third stage inverter, (7) and (9)
) is the P-channel transistor of the feedback inverter, (8)
and 00) are N-channel transistors of the feedback inverter,
αυ is a P-channel transistor that acts as a switch that causes the P-channel transistor (9) to operate as a feedback inverter, 0z is an N-channel transistor that acts as a switch that causes the N-channel transistor α0) to operate as a feedback inverter, and 03 is a P-channel transistor αD or N-channel The polarity of the selection signal that enters the P-channel transistor 0υ is set to N so that it turns on at the same time as transistor α2.
An inverter is used to reverse the polarity of the selection signal input to the channel transistor α2, C is a capacitor of an external circuit of the oscillation circuit, and R is a resistor of the external circuit.

Next, the operation will be explained.

First, when the selection signal is “L”, transistors 0υ and 02
is in the OFF state, so transistor (9) and αO)
does not operate as a feedback inverter, and the transistor (7)
Only (8) operates as a feedback inverter.

At this time, the circuit is in the same Schmitt inverter state as the conventional oscillation circuit, so it exhibits the same hysteresis characteristics as the conventional oscillation circuit. This hysteresis characteristic is as shown by the solid line in Figure 2, and when the input IN transitions from "L" to "H", the output OUT goes "H" when the input IN or V181.
When the input IN changes from "H" to "L", the output OUT changes from "L" to "H" when the input IN or Vl is 1.

Next, when the selection signal is “H”, the transistors 0υ and Oz
Since transistors (9) and 00) also operate as feedback inverters, the driving capability of the feedback inverter increases. If you want to, input IN or “L”
The threshold value V I H2 when transitioning from to “H” is V
When the input IN transitions from "H" to "L", the threshold value VIL2 becomes lower than VIL. The hysteresis characteristic at this time is shown by the dotted line in FIG.

If a resistor R is connected between the input IN and the output 0LITO of the second oscillation circuit, and a capacitor C is connected to the input IN, oscillation is performed using the same oscillation principle as that of a conventional oscillation circuit. The waveform of the input IN at this time is shown in FIG. When the selection signal is "L", the threshold values of the oscillation circuit are V I Hl and Vl, 1, and the input waveform oscillates between VIHI and VILI as shown by the solid line in FIG. The period at this time is T (roaring. On the other hand,
When the selection signal is “H”, the threshold of the oscillation circuit is V IH
Since □ and V and L2, the input waveforms are VI82 and V IL
2 as shown by the dashed line in FIG. The cycle at this time is T2. The rising and falling characteristics of these two waveforms are the charging and discharging characteristics of the capacitor C, and are determined by the values of the capacitor C and the resistor R, so they have the same characteristics.

Therefore, V is smaller than the width of V I Hl and VILI.
Since the widths of 1112 and VIL2 are wider, the period of T2 is longer than that of TI.

Therefore, by switching the selection signal between "L" and "H", the Schmitt width changes and the oscillation frequency changes.

Note that in the above embodiment, 1 operates as a feedback inverter.
In addition, it is possible to select any number of transistors from among multiple transistors as transistors that operate as a feedback inverter using multiple selection signals. You can also do it.

Further, in the above embodiment, the P-channel transistor and the N-channel transistor are selected as a pair, but they may be selected separately or in different numbers. Further, the switch may be assembled in the following manner.

〔Effect of the invention〕

As described above, according to the present invention, the oscillation frequency can be changed by changing the input threshold of the oscillation circuit and changing the input width, so when a microcomputer requires both high-speed and low-speed operation, This can be achieved by switching the oscillation frequency using a selection signal using a single oscillation circuit.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an oscillation circuit which is an embodiment of the present invention.
Figure 2 is a curve diagram showing the input/output characteristics of the oscillation circuit in Figure 1;
Figure 3 is an input waveform diagram of the oscillation circuit in Figure 1, Figure 4 is a circuit diagram of a conventional oscillation circuit, Figure 5 is a curve diagram showing the input/output characteristics of the oscillation circuit in Figure 4, and Figure 6 is a diagram of the input/output characteristics of the oscillation circuit in Figure 4. 5 is an input waveform diagram of the oscillation circuit of FIG. 4. FIG. In the figure, (1), (3), (5), (7),
(91, Ql) is a P-channel transistor, (2),
(4), (6), (8), αO), (IZ) N-channel transistor, α3 indicates an inverter. In the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] In a CR oscillation circuit using a Schmitt inverter that creates a Schmitt characteristic using a feedback inverter, the feedback inverter is configured with a plurality of transistors connected in parallel, and an arbitrary number of transistors are operated as the feedback inverter by a selection signal. An oscillation circuit characterized in that the driving capacity of a feedback inverter can be changed, thereby changing the Schmitt width and changing the oscillation frequency.