JPH04281605A - Oscillation control circuit - Google Patents

Abstract

PURPOSE:To realize the oscillation control circuit in which a post-stage circuit is not operated for a small amplitude at the start of oscillation and the post stage circuit starts its operation after the amplitude reaches a prescribed amplitude or over. CONSTITUTION:A CMOS Schmitt trigger inverter ST1 whose one inverting potential (2.0V) is lower than an inverting potential (2.5V) of a CMOS inverter and whose the other inverting potential (3.0V) is higher than the inverting potential (2.5V) of the CMOS inverter is connected to an output of the CMOS inverter IV1 forming the oscillation circuit. Thus, till the oscillation output of the CMOS inverter IV1 exceeds any one inverting potential of the CMOS Schmitt trigger inverter ST1, the post-stage circuit connected to the output of the CMOS Schmitt trigger inverter ST1 is inoperative. Thus, noise is generated by the operation of the post-stage but since the amplitude of the oscillation output is sufficiently increased, the prevention of the oscillation due to the effect of noise is not caused.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oscillation control circuit.

0002

[Prior Art] When transmitting the oscillation output of a crystal oscillation circuit using CMOS transistors to a subsequent stage, a second CMOS inverter is connected to the output of a first CMOS inverter constituting the oscillation circuit, and the output of the second CMOS inverter is connected to the subsequent stage. Connecting the circuit. In this type of circuit, conventionally, the inversion potential of the first CMOS inverter and the inversion potential of the second CMOS inverter were the same.

0003

[Problem to be solved by the invention] In the above conventional circuit,
The oscillation output with minute amplitude at the start of oscillation is the second CMOS.
The signal is inverted by an inverter, and the inverted output puts the subsequent circuit into operation. Therefore, there is a problem in that the oscillation operation becomes unstable due to the influence of noise generated in the subsequent stage circuit, and the transition from a minute amplitude oscillation operation to a normal amplitude oscillation operation is hindered.

An object of the present invention is to provide an oscillation control circuit in which the subsequent stage circuit does not operate when the amplitude is small at the start of oscillation, but starts operating after the amplitude reaches a certain level. .

[0005]

[Means for Solving the Problems] In the present invention, an inversion potential of one of the outputs of an oscillation circuit having a CMOS inverter and a crystal resonator connected in parallel to the CMOS inverter is lower than the inversion potential of the CMOS inverter. CM whose other inversion potential is higher than that of the CMOS inverter
I connected an OS Schmitt trigger inverter.

[0006]

Embodiment FIGS. 1A to 1C show an embodiment of an oscillation control circuit according to the present invention.

Each circuit element shown in FIG. 1(A) is as follows. IV1 is a CMOS inverter, as shown in Figure 1 (
It has input/output characteristics (transfer characteristics) as shown in B), and its inversion potential (logical threshold voltage) is 2.5 volts. The inversion potential here is the input voltage at the midpoint between the falling start input voltage and the falling end input voltage in the input/output characteristics, and normally the output voltage is half (2.5 volts) of the power supply voltage (5 volts). volts). QZ1 is a crystal oscillator, R1 is a feedback resistor, C1 and C2
is a capacitor. The above circuit elements constitute an oscillation circuit. ST1 is a CMOS Schmitt trigger inverter and has input/output characteristics as shown in FIG. Reversal potential (3
．． 0 volt) is higher than the inversion potential of CMOS inverter IV1. This CMOS Schmitt trigger inverter S
A subsequent stage circuit (not shown) having a CMOS configuration is connected to the output of T1. Note that the circuits described above are housed within the same IC chip.

Next, the operation of this embodiment will be explained with reference to FIG. As shown in Figure 2(A), when the power is turned on, C
An oscillation output with minute amplitude is generated from MOS inverter IV1. The amplitude of this oscillation output gradually increases, but as shown in Fig.
As shown in (B), the CM
The output of the OS Schmitt trigger inverter ST1 is not inverted. The oscillation output of CMOS inverter IV1 is CMOS
When the inversion potential of either Schmitt trigger inverter ST1 is exceeded, the CMOS Schmitt trigger inverter S
An inverted output is generated from T1, and the subsequent circuit becomes operational. After that, the oscillation output of CMOS inverter IV1 becomes CMOS
The first inversion potential (2
．． 0 volts) and the second reversal potential (3.0 volts), the CMOS Schmitt trigger inverter ST1
The output of is inverted. Noise is generated by the operation of the subsequent stage circuit, but at this time the amplitude of the oscillation output is sufficiently large, so the oscillation operation is not hindered.

[0009]

[Effects of the Invention] In the present invention, a CMOS Schmitt trigger inverter is provided at the output of the CMOS inverter, in which one inversion potential is lower than the inversion potential of the CMOS inverter, and the other inversion potential is higher than the inversion potential of the CMOS inverter. , after the amplitude of the oscillation output of the CMOS inverter reaches a certain level or more, the subsequent circuit starts operating. Therefore, the oscillation operation is not hindered by the influence of noise generated in the subsequent circuit.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of an oscillation control circuit according to the present invention.

FIG. 2 explains the operation of FIG. 1;

[Explanation of symbols]

IV1...CMOS inverter ST1...CMOS Schmitt trigger inverter QZ1
……Crystal oscillator

Claims (1)

[Claims] 1. An oscillation circuit comprising a CMOS inverter and a crystal resonator connected in parallel to the CMOS inverter, and an oscillation output from the CMOS inverter is input to generate a signal having the same frequency as the oscillation frequency of the oscillation circuit. an oscillation control circuit comprising a CMOS Schmitt trigger inverter, one of which has an inverted potential lower than the inverted potential of the CMOS inverter and the other of which has an inverted potential higher than the inverted potential of the CMOS inverter.