JPS613520A - Oscillating circuit - Google Patents

Abstract

PURPOSE:To attain accurately a duty factor of 50% by providing a voltage controlled oscillation circuit oscillating a signal having a frequency being an integral number of multiple of a desired value and a frequency divider frequency- dividing the frequency of the signal outputted from the said voltage controlled oscillating circuit. CONSTITUTION:A signal outputted from the voltage controlled oscillating circuit 2 is formed to a signal having a frequency twice a desired value and this signal is frequency-divided into 1/2 by the frequency divider 5, then even when the duty ratio of an output pulse 7 of the said voltage controlled oscillator 2 is not 50% but, e.g., T1>T2, a waveform 8 of the signal outputted from the frequency divider 5 frequency-dividing the signal into 1/2 is obtained as T3=T4=T1+T2 and the duty ratio of 50% is obtained accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an oscillation circuit that minimizes waveform distortion of an output signal.

[Prior art]

FIG. 1 shows a conventional oscillation circuit. In FIG. 1, 1 is an input terminal for applying a voltage to control the oscillation frequency;
Reference numeral 2 designates a voltage controlled oscillation circuit which inputs a voltage for controlling the oscillation frequency and outputs an oscillation signal, and 3 designates an output terminal for outputting a signal output from the voltage controlled oscillation circuit to the outside.

In an oscillation circuit configured in this way, even if the circuit type of the voltage controlled oscillation circuit 2 is selected very carefully, especially when the frequency is high, the signal output from the oscillation circuit as shown in Fig. The duty factor of waveform 4 is 5.
It won't be 0%. This means that the signal has even-order harmonic distortion, and when this signal is used in a video modulation circuit of a VTR, there are problems such as loss of image quality.

[Summary of the invention]

The present invention has been made in view of these points, and its purpose is to provide an oscillation circuit that can accurately set the signal duty factor to 50% even at high frequencies. be.

In order to achieve such an object, the present invention includes an oscillation circuit that includes a voltage controlled oscillation circuit that oscillates a signal with a frequency that is an integral multiple of a desired value, and a frequency divider that divides the frequency of the signal into an integer fraction. It has been established that

[Embodiments of the invention]

The present invention will be explained in detail based on examples.

FIG. 3 shows an embodiment of the oscillation circuit according to the present invention, and FIG. 4 shows waveforms for explaining its operation. In FIG. 3, 5 is a frequency divider that divides the frequency of the input signal, and 6 is a transmission line that transmits the signal output from the voltage controlled oscillation circuit 2 to the frequency divider 5. In FIG. 3, the same or equivalent parts as in FIG. 1 are given the same reference numerals.

The oscillation circuit of this embodiment has a configuration in which the signal output from the voltage controlled oscillation circuit 2 is a signal having a frequency twice the desired value, and the frequency of this signal is divided into 1/2 by the frequency divider 5. It has become. The signal waveforms at this time are shown in Figure 4 (a) and (b).
). In FIG. 4 ta+, 7 is the waveform of the signal output from the voltage controlled oscillation circuit 2, and T1 and T2 are the high level time width and the low level time width. Further, in FIG. 4(b), 8 is the waveform of the signal output from the frequency divider 5, and T3 and T4 are the time width of the high level and the time width of the low level.

3 and 4, the waveform 7 of the signal output from the voltage controlled oscillation circuit 2 is shown in FIG.
, >T, the frequency divider 5 divides the frequency by 1/2.
The waveform 8 of the signal output from the oscillation circuit, that is, the waveform of the signal output from this oscillation circuit is shown in FIG.
Since 3=Tt=T+ +T2, the duty factor is exactly 50%, and even-order distortion does not occur. In this embodiment, the case where the oscillation frequency of the voltage controlled oscillation circuit 2 is twice the desired frequency has been described, but the effect is exactly the same even when the oscillation frequency is an arbitrary integer multiple.

〔Effect of the invention〕

The present invention provides a voltage controlled oscillation circuit that oscillates a signal with a frequency that is an integer multiple of a desired value, and a frequency divider that divides the frequency of the signal output from the voltage controlled oscillation circuit into an integer divided. Since the duty factor of the signal output from the oscillation circuit can be set to exactly 50%, the output signal can be used in the video modulation circuit of a VTR without deteriorating the image quality.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a conventional oscillation circuit, FIG. 2 is a waveform diagram of a signal output from the conventional oscillation circuit, FIG. 3 is a system diagram of an oscillation circuit according to the present invention, and FIG. FIG. 4(b) is a waveform diagram of a signal output from a voltage-controlled oscillation circuit constituting an oscillation circuit, and FIG. 4(b) is a waveform diagram of a signal output from a frequency divider constituting the oscillation circuit.1... Input terminal, 2... Voltage controlled oscillation circuit, 3
... Output terminal, 5... Frequency divider, 6... Transmission line, 7, 8... Waveform, TI+ T2, T3.
Ta...Time width.

Claims (1)

[Claims] A voltage controlled oscillation circuit that oscillates a signal having a frequency that is an integer multiple of a desired value, and a frequency divider that divides the frequency of the signal output from the voltage controlled oscillation circuit into an integer fraction. oscillation circuit.