JPH0362605A - Frequency modulation circuit - Google Patents

Abstract

PURPOSE:To reduce the cost and to improve the noise characteristic by providing a reference oscillator, a phase comparator comparing the phase of an output of the reference oscillator, and an output of a voltage controlled oscillator, an integration circuit integrating a frequency modulation input signal and an adder. CONSTITUTION:The phase of an output signal of a reference oscillator 1 and that of an output signal of a voltage controlled oscillator 5 are compared by a phase comparator 2 and an error signal is fed to an adder 3. Moreover, a frequency modulation signal is supplied from an input terminal 7 to an integration circuit 6, converted into a phase modulation signal and fed to the adder 3. The adder 3 adds the error signal and the phase modulation signal and supplies an output to a loop amplifier 4, the signal is amplified by the amplifier 4 to control the phase of the output signal of the voltage controlled oscillator 5. That is, the output signal of the oscillator 5 is controlled by the output signal of the oscillator 1 and frequency modulation is applied by a frequency modulation signal and a frequency modulation output is obtained from an output terminal 8. Since the circuit is constituted without using a voltage controlled reference oscillator, the design is facilitated, the cost is reduced and the noise characteristic is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a frequency modulation circuit, and more particularly to a frequency modulation circuit that is optimal for reducing output signal noise and cost.

[Conventional technology] A conventional frequency modulation circuit of this type is shown in FIG.

In FIG. 2, a frequency modulated signal is applied to input terminal 25. In FIG. This frequency modulation circuit constitutes a phase-locked loop from a voltage-controlled reference oscillator 19 whose frequency can be modulated by a modulation signal, a phase comparator 12, a loop amplifier 14, and a voltage-controlled oscillator 5.

Due to this phase-locked loop, the phase of the output signal of the voltage controlled oscillator 15 follows the phase of the output signal of the voltage controlled reference oscillator 19. Therefore, when the output signal of the voltage controlled reference oscillator 19 is frequency modulated, the output signal of the voltage controlled oscillator 15 is also frequency modulated, and as a result, a frequency modulated output is obtained from the output terminal 18.

[Problems to be Solved by the Invention] The conventional frequency modulation circuit described above applies frequency modulation to the output of the voltage controlled reference oscillator 19, so when considering a crystal oscillator that is generally used as the voltage controlled reference oscillator 19. , a voltage-controlled crystal oscillator that can be modulated is required. Voltage-controlled crystal oscillators have more complex and expensive circuits than regular crystal oscillators, and the Q of the circuit is higher due to modulation.
There is a problem that the noise characteristics deteriorate due to a decrease in the sharpening liquid.

[Means for Solving the Problems] The present invention has been made in view of the above problems, and aims to obtain a frequency modulation circuit with good noise characteristics at a low cost. A reference oscillator, a phase comparator that compares the phases of the output of the reference oscillator and the output of the voltage controlled oscillator, an integrating circuit that integrates the frequency modulated input signal, and an adder that adds the output of the integrating circuit and the output of the phase comparator. and a voltage controlled oscillator whose frequency is controlled by the output voltage of the adder.

[Example] Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a block diagram showing one embodiment of a frequency modulation circuit according to the present invention.

In FIG. 1, the output signal of a reference oscillator 1 and the output signal of a voltage controlled oscillator 5 are phase-compared by a phase comparator 2, and an error signal is supplied to an adder 3.

The frequency modulation signal is applied from the input terminal 7 to the integrating circuit 6, converted into a phase modulation signal, and supplied to the adder 3.

Therefore, in the adder 3, the error signal that is the output of the phase comparator 2 and the phase modulation signal that is the output of the integrating circuit 6 are added. The output signal of adder 3 is amplified by loop amplifier 4,
The phase of the output signal of voltage controlled oscillator 5 is controlled.

With this configuration, since the voltage controlled oscillator 5 is phase synchronized, the output phase of the voltage controlled oscillator 5 is the output phase of the reference oscillator and the signal converted from the frequency modulation signal to the phase modulation signal by the integrating circuit 6. It follows the phase obtained by adding the phase of .

That is, the output signal of the voltage controlled oscillator 5 is controlled by the output signal on the reference oscillator and frequency modulated by the frequency modulation signal, resulting in a frequency modulated output from the output terminal 8.

This eliminates the need for the voltage-controlled reference oscillator 19 (FIG. 2), which is difficult to design, expensive, and has poor noise characteristics.
A frequency modulation circuit can be constructed, the design is easy, and a frequency modulation circuit with good noise characteristics can be obtained at a low cost.

[Effects of the Invention] As explained above, the present invention includes a reference oscillator, a phase comparator that compares the phases of the output of the reference oscillator and the output of the voltage controlled oscillator, and an integrating circuit that integrates a frequency modulated input signal. The design is easy and inexpensive because it is configured to include an adder that adds the output of the integrating circuit and the output of the phase comparator, and a voltage-controlled oscillator whose frequency is controlled by the output voltage of the adder. It becomes possible to obtain a frequency modulation circuit with good noise characteristics.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a frequency modulation circuit according to the present invention, and FIG. 2 is a block diagram showing a conventional frequency modulation circuit. l... Reference oscillator 2... Phase comparator 3... Adder loop amplifier voltage controlled oscillator integration circuit input terminal output terminal

Claims (1)

[Claims] a reference oscillator, a phase comparator that compares the phases of the output of the reference oscillator and the output of the voltage controlled oscillator, an integration circuit that integrates the frequency modulated input signal, and adds the output of the integration circuit and the output of the phase comparator. and a voltage controlled oscillator whose frequency is controlled by the output voltage of the adder.