JPH02266610A - Oscillation circuit - Google Patents

Abstract

PURPOSE:To make the duty cycle of a rectangular wave stable and to improve the reliability of the circuit operation by applying constant current charging in a charge/discharge circuit. CONSTITUTION:A transistor(TR) whose base connect to the output of a frequency-voltage(FV) converter 1 and a DC constant voltage source 20 connecting to the emitter of the TR 18 via a resistor 19 are provided, and a charge/discharge circuit 4 and a capacitor 17 connect to a collector of the TR 18. Since the output voltage of the FV converter 1 is a base bias voltage of a TR 4, a constant charge current is supplied to the charge/discharge circuit 4 connecting the collector of the TR 4 from the constant voltage source 20 at the emitter of the TR 4 to be turned on by a horizontal synchronizing signal with an input frequency. Thus, even when the input frequency is changed, the rectangular wave signal with an always stable duty is outputted to improve the reliability of the circuit operation.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an oscillation circuit for a display device that is effective as a terminal such as a computer and that realizes image display by automatically following horizontal synchronizing signals of a wide range of frequencies.

2. Description of the Related Art A conventional technique for forming a sawtooth wave from a horizontal synchronization signal input will be described below with reference to FIGS. 2 and 3.

Here, in Fig. 2, the arbitrary repetition period is T, and what is the Parnu width of the ON period? , ,T,/τ is the duty,
Nureshi hold level Hv □ Toss. In Figure 3,
1 is a frequency-voltage (yv) Humberta, 2#i comparator,
3 #i switch, 4 is a discharge circuit, 6 is a waveform shaping circuit, 6
is the output circuit, 7, 8°9 is the reference DC voltage source, 10, 11
．． 12 is an operational amplifier, 13 14, 15.16 is a resistor,
17 is a capacitor.

Generally, a rectangular wave is obtained by slicing the sawtooth υ wave shown in FIG. 2 at a threshold level V□ and shaping it into a rectangular wave having a constant pulse width.

However, in the oscillation circuit of a horizontal synchronization signal automatic tracking type display, it is necessary to keep the duty τ1/T constant and operate the common output circuit efficiently. For this purpose, conventionally, as shown in FIG. 3, multiple stages of operational amplifiers 10, 11, and 12 are provided to detect the voltage output from the Fv converter 1, and comparators 2, 1, and 12 are provided. The Nwitch 3 switches the operational amplifiers 10, 11.12, and applies the output voltage as the power supply voltage to the OR charge/discharge circuit 4.17 to generate a sawtooth wave, and then set the threshold level V.
The waveform shaping circuit 6 shapes the rectangular wave having a duty T, /T determined by □, and supplies it to the output circuit 6.

Problems to be Solved by the Invention In the conventional circuit as described above, the power supply voltage is directly compared with the output voltage reference voltage of the FW converter, and is supplied from multiple stages of operational amplifiers to a charging/discharging circuit consisting of a capacitor resistor. Since the sawtooth wave is generated by the input frequency, the linearity of the sawtooth wave is poor, and the duty changes due to the input frequency being varied. Therefore, the wider the input frequency range, the more it is necessary to subdivide, and after subdivision, nonlinearity remains in the sawtooth wave, and the duty changes, and the amount of nonlinearity changes around the switching of the operating amplifier. It was large at the input frequency.

The present invention solves the conventional problems, and aims to provide an oscillation circuit with highly reliable circuit operation that can always output a square wave signal with a stable duty even when the input frequency changes. It is something.

Means for Solving the Problems In order to solve the above problems, the present invention uses a switching element to use a DC voltage corresponding to the input frequency as a bias voltage for turning on and off the switching element, and turns the on state through the switching element.

The charging/discharging circuit is configured to be charged with a constant current from a constant current voltage source provided at the output of the switching element.

Effect: With the above configuration, the charging/discharging circuit performs a constant current charging operation, so that it is possible to obtain good linearity in the sawtooth waveform, which is a single oscillation waveform. Therefore, even after the ζ-tooth wave is generated and shaped into a rectangular wave with a duty determined by the threshold level, the duty can be kept constant over a wide range of input frequencies.

EXAMPLE Hereinafter, an oscillation circuit according to an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the oscillation circuit of the present invention. In Figure 1, 1 is a YV converter, 5 is a waveform shaping circuit, 6 is an output circuit, and 4 is a capacitor 4a and a resistor 4.
The discharge circuit consisting of b, 17 is a capacitor, and 6 or more are the same as the configuration of the conventional example shown in FIG. The feature of this application is that FW
and a transistor 18 whose pace is connected to the output of the converter 1.

A DC constant voltage source 2oK6 is connected to the emitter of the transistor 18 via a resistor 19.

A charge/discharge circuit 4 is connected to the collector of the transistor 18. It is located where capacitor 17 is connected.

In FIG. 1, the output voltage of the Fv converter 1 becomes the pace bias voltage of the transistor 4.

As a result, the constant voltage source 2 of the emitter of the transistor 4 which is turned on in response to a horizontal synchronization signal of a certain input frequency
A constant charging current is supplied from o to the charging/discharging circuit 4 of the collector. As a result, a sawtooth wave with good linearity in the charging period can always be generated for horizontal synchronizing signals with a wide range of input frequencies. Therefore, the duty of the rectangular wave obtained by shaping this sawtooth wave is always kept constant.

Effects of the Invention According to the present invention, it is possible to improve the reliability of a single circuit operation for stabilizing rectangular wave duty with an extremely simple circuit configuration, which is extremely useful in practice.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of an oscillation circuit in an embodiment of the present invention, Fig. 2 is a waveform diagram of a sawtooth wave generated in a conventional oscillation circuit, and Fig. 3 shows the configuration of a conventional oscillation circuit. It is a block diagram. 4... Charge/discharge circuit, 18... Transistor, 20... DC constant voltage source. Name of agent: Patent attorney Shigetaka Awano and one other person Figure 18
Naoguchi voltage source diagram

Claims (1)

[Claims] An oscillation circuit for a display device that automatically follows horizontal synchronization signal input over a wide range of frequencies, comprising a converter that receives the horizontal synchronization signal as input and performs frequency-to-voltage conversion, and a switching element to which an input bias is applied by the output of the converter. , a constant voltage source coupled to the output side of the switching element, and a charging/discharging circuit in which a charging current is supplied from the constant voltage source by the switching element turned on by applying an input bias. oscillation circuit.