JPH01160104A - Digital control type oscillation circuit - Google Patents

Abstract

PURPOSE:To obtain an optional oscillating frequency with high stability and to facilitate the change in the setting frequency by constituting a capacitor deciding the oscillation frequency of the oscillation circuit by a variable capacitor circuit capable of subjecting to digital control so as to eliminate the need for any crystal vibrator. CONSTITUTION:A switch 5 switches a capacitor 6 and a switch control terminal 8 controls a switch comprising a variable capacitance circuit comprising plural switches 5 and the capacitor 6. Then let the capacitance of the variable capacitance circuit comprising plural switches 5 and the capacitor 6 be C, each capacitor is individually switched by a switch drive circuit based on a digital code fed externally to set and vary the capacitance C. Thus, the oscillating frequency is set and varied easily and the oscillating frequency with high stability is obtained easily by controlling the capacitance C of the variable capacitor circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a digitally controlled oscillation circuit that digitally controls an oscillation frequency.

[Conventional technology]

FIG. 3 is a diagram showing, for example, a conventional oscillation circuit, [WK
Well, (9) is an inverter, (2) is a resistor, (7) is an oscillation frequency output terminal, (6) is a capacitor, 1 (I is a variable capacitor, and I is a crystal resonator.

Next, the operation will be explained. The oscillation frequency of an oscillation circuit using a crystal resonator is determined by the electrical equivalent constant of the crystal resonator αD and the load capacitance when looking at the oscillation circuit side from both ends of the crystal resonator α°C. The variable capacitor αG performs fine adjustment of the oscillation frequency.

[Problem that the invention seeks to solve]

Conventional oscillation circuits are configured as described above, so in order to accurately match the oscillation frequency, it is necessary to select a crystal resonator according to the load capacitance on the oscillation circuit side. There were problems such as a limited setting range.

This invention was made to solve the above-mentioned problems, and it is possible to obtain a highly stable oscillation frequency without using a crystal resonator, and to obtain an oscillation circuit with a wide setting range of oscillation frequency. The purpose is to

[Means for solving the problem] The oscillation circuit according to the present invention is constructed without using a crystal resonator, and the capacitance for determining the oscillation frequency is formed by a capacitive element array composed of a plurality of capacitive elements. The device is constructed of a variable capacitance circuit such as a switch that connects and disconnects the capacitive element array, and controls the connection and disconnection of the switch by applying an external signal.

[Effect]

The variable capacitance circuit according to the present invention controls the oscillation frequency by switching the switch on and off using a digital code applied from the outside and varying the capacitance value.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, (1) is an operational amplifier circuit, (2) (3) (
4) are resistors whose values are R1, R2e and R5, respectively.

(5) is a switch that connects and disconnects the capacitor (6). (7) is an output terminal, and (8) is a switch control terminal, which controls the switch of a variable capacitance circuit consisting of a plurality of switches (5) and a capacitor (6).

In the digitally controlled oscillator circuit configured as described above, the operational amplifier circuit (1) operates as a comparator, and the resistors R1 (2) and R2 (3) are used to generate hysteresis. Assuming that the capacitance value of a variable capacitance circuit consisting of a plurality of switches (5) and capacitors (6) is O, the oscillation frequency Rfo of this circuit is approximately expressed by the following equation.

to -17 (2-0-13) The variable capacitance circuit connects and disconnects each capacitor individually by a switch drive circuit based on an externally applied digital code to set and vary the capacitance value 0.

Therefore, from the above equation, by setting and varying the capacitance value 0, the oscillation frequency can be easily set and varied.

Furthermore, by controlling the capacitance value of the variable capacitance circuit, a highly stable oscillation frequency can be easily obtained.

Furthermore, in the above embodiment, one end of the capacitor (6) in the variable capacitor circuit is grounded, but in an oscillation circuit as shown in FIG. 2, a variable capacitor circuit is connected between the input and output of the inverter (9). May be inserted. In this circuit, the oscillation frequency f
o is approximately expressed by the following equation.

to −Ra/ (4·o, R2, R3) In the above equation as well, by controlling the value of the capacitance value 0 using the variable capacitance circuit, the same effect as in the above embodiment can be achieved.

In this way, the oscillation frequency can be easily controlled by replacing the capacitor that determines the oscillation frequency with a variable capacitance circuit and controlling the capacitance value from the outside.

〔Effect of the invention〕

As described above, according to the present invention, the capacitance that determines the oscillation frequency of the oscillation circuit is configured with a digitally controllable variable capacitance circuit, eliminating the need for a crystal oscillator, so that any highly stable oscillation frequency can be achieved. Since it does not use a crystal oscillator, it is easy to change the set layer wave number, and it has the advantage of being compact.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a digitally controlled oscillator according to one embodiment of the invention, FIG. 2 is a circuit diagram showing another embodiment of the invention, and FIG. 3 is a circuit diagram showing a conventional oscillation circuit. . In the figure, (1) is an operational amplifier circuit, (2), (3
), (4) is a resistor, (5) is a switch, (6) is a capacitor, (7) is an output terminal, and (8) is a switch control terminal. In addition, in the figures, the same symbols indicate the same or equivalent parts〇

Claims (1)

[Claims] In an oscillation circuit in which a feedback path is formed by a resistor or a capacitor in a circuit having an amplification factor of 1 or more, the capacitor that determines the oscillation frequency is constituted by a capacitor array consisting of a plurality of capacitors, and the capacitor A digital device characterized in that the oscillation frequency is controlled by providing switches for connecting and disconnecting the columns and a switch drive circuit for sending digital switching signals to each switch, and controlling the capacitive element columns on or off. Controlled oscillation circuit.