JPH02302108A - Frequency modulation circuit - Google Patents

Abstract

PURPOSE:To realize no adjustment, frequency stability and stability of frequency shift width by providing an FF circuit frequency-dividing an output carrier from an oscillation circuit oscillating a carrier of a double frequency into 1/2 and outputting two kinds of carriers whose phase difference is 90 deg. so as to add directly a phase modulation wave to the oscillating circuit. CONSTITUTION:A crystal 12 is used as an oscillation element of a carrier oscillation circuit 11 to oscillate a carrier 2fc whose frequency is twice the required carrier fc. A carrier 2fc inputted in an ECL type T-FF circuit 13 is subject to 1/2 frequency division resulting in obtaining a carrier fc component and carrier fc-90 with a delay of 90 deg.. A signal wave fs and the carrier fc-90 are multiplied at a balanced modulation circuit 14, from which a phase modulation signal fPM (which is same as conventional one and is A.fs.fc-90) is obtained. The signal fPM is added to the carrier fc at an adder circuit 15 to obtain the frequency modulation signal fPM.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a frequency modulation (FM) circuit used in communication equipment, television receivers, radio receivers, etc.
In particular, the present invention relates to a frequency modulation circuit that can achieve a high degree of stability without adjustment.

[Conventional technology]

Frequency modulation is a modulation method in which the frequency of a carrier wave is shifted from the center frequency according to the amplitude of a signal wave.The frequency modulation circuit of the vector synthesis method, which is an indirect frequency modulation method, is shown in Figure 3. It is composed of

1 is a carrier wave oscillation circuit, and the oscillation frequency of the carrier wave fc is determined by a tank circuit 2 consisting of a coil L and a capacitor C. 3 is a phase shift circuit that shifts the phase of this carrier wave fc by 90 degrees, and is composed of a resistor and a capacitor. 4 is this 9
a balanced modulation circuit that creates a phase modulated (PM) wave by multiplying a carrier wave fc-9° phase-shifted by 0 degrees and a signal wave fs; 5
is an adding circuit that adds this phase modulated wave to the carrier wave fc to obtain a frequency modulated wave fF)1.

In this circuit, when the carrier wave fc oscillated by the oscillation circuit 1 is phased by 90 degrees in the phase shift circuit 3 and multiplied by the signal wave fs in the balanced modulation circuit 4, fp+=A−f 5−rc−
'T.

is added to the carrier wave fc in the adder circuit 5, and
This becomes a frequency modulated wave fFM. A is the amplitude.

[Problem to be solved by the invention]

However, in this circuit, when adding the output of the balanced modulation circuit 4 to the output of the oscillation circuit 1, there is no other way than to add the current directly to the oscillation circuit 1. Therefore, when widening the frequency deviation width, it is difficult to add the current to the oscillation circuit 1 without adjustment. Since the oscillation element has a high Q, an LC tank circuit 2 with a low Q must be used.

Therefore, a problem of variation occurs, and since a capacitor is also used in the phase shift circuit 3, the carrier wave f obtained here is
. -,. Further, there is a problem in that the variation in the amplitude is further added, and when integrated circuits are implemented, the variation in the frequency deviation width is directly affected.

The present invention has been made in view of these points, and its purpose is to provide a frequency modulation circuit that eliminates adjustment, stabilizes the frequency, and stabilizes the frequency deviation width.

[Means for Solving the Problems] For this purpose, the present invention obtains a phase modulated signal by shifting the phase of a carrier wave by 90 degrees and multiplying this phase shifted wave by a signal wave, and then combining the phase modulated signal and the carrier wave. In the frequency modulation circuit that obtains a frequency modulated wave by adding , an oscillation circuit that oscillates a carrier wave with a frequency twice that of the above-mentioned carrier wave, and an oscillation circuit that oscillates a carrier wave with a frequency twice that of the above-mentioned carrier wave, and divides the output carrier wave from the oscillation circuit into two and divides the frequency of the output carrier wave by 9.
An FF circuit that outputs two types of carrier waves with a 0 degree phase difference,
a balanced modulation circuit that multiplies one output general transmission wave of the FF circuit by a signal wave; and an addition circuit that adds the phase modulation signal obtained from the balanced modulation circuit and the other output carrier wave obtained from the FF circuit. It was configured to have the following.

〔Example〕

Examples of the present invention will be described below. FIG. 1 is a diagram showing a frequency modulation circuit of one embodiment. In this embodiment, a crystal 1 is used as the oscillation element of the carrier wave oscillation circuit 11.
2 is used, thereby oscillating a carrier wave 2fc having twice the frequency of the required carrier wave fc. 13 is ECL
This is a type of T-FF circuit, in which the frequency of the input carrier wave 2fc is divided by two to obtain a carrier wave rC-9° component delayed by 90 degrees from the carrier wave fc acid component. 14 is a balanced modulation circuit, and 15 is an adder circuit.

In this embodiment, the signal wave fs and the carrier wave f c-9° are multiplied in the balanced modulation circuit 14, and from there, the phase modulation signal f of f pH=A-f S-f c-90 is obtained as in the conventional case. can be obtained. This signal fP1. I is the adder circuit 15
A frequency modulated signal f2.4 is obtained by adding it to the carrier wave fc.

With this configuration, there is no need to vary the frequency in the oscillation circuit itself as in the configuration shown in Figure 3, and therefore a wide frequency shift can be achieved even if an oscillation element with a high Q is used. Moreover, since a phase shift circuit using RC is not required, a stable frequency modulated wave can be obtained without adjustment.

FIG. 2 is a diagram showing a more specific frequency modulation circuit. Here, the output carrier wave 2fc from the oscillation circuit 11 is taken into the T-type FF circuit 13 via the buffer 16, where the carrier wave 2fc is converted into a carrier wave fc, a carrier wave f, and so on. 9
゜, carrier wave f9゜1110% carrier wave f e, 2'70
The frequency is divided as follows, and carrier waves with different phases of 90 degrees are obtained, among which carrier wave fc and carrier wave f C41110
is sent to the adder circuit 15 via buffers 17 and 18. Also, the carrier wave f c-'l. , carrier wave f c +27° are sent to the balanced modulation circuit 14 via the buffer 19, and a signal multiplied by the signal wave fs in the balanced modulation circuit 14 is sent to the addition circuit 15 via the buffer 20. Therefore, since the adder circuit 15 adds the carrier wave and the phase modulated wave from the buffer 18, the frequency modulated signal fF
M is obtained. Note that buffers 16 to 20 here
is for timing adjustment.

〔Effect of the invention〕

As explained above, according to the present invention, the frequency is stabilized because the phase modulated wave is not directly added to the oscillation circuit, and there is no need for a phase shift circuit using resistors or capacitors, so there is no need for adjustment man-hours. Furthermore, there are advantages such as less variation in frequency deviation width when integrated circuits are formed.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a frequency modulation circuit according to an embodiment of the present invention,
FIG. 2 is a circuit diagram embodying the circuit, and FIG. 3 is a conventional circuit diagram of the same circuit. Agent Patent Attorney Tsuneaki Nagao Figure 1 Signal Wave

Claims (1)

[Claims] (1) A frequency modulation circuit that obtains a phase modulation signal by shifting the phase of a carrier wave by 90 degrees and multiplying this phase shift wave by a signal wave, and obtains a frequency modulation wave by adding the phase modulation signal and the carrier wave. an oscillation circuit that oscillates a carrier wave with twice the frequency of the carrier wave; an FF circuit that divides the output carrier wave from the oscillation circuit into 1/2 and outputs two types of carrier waves having a 90 degree phase difference; A balanced modulation circuit that multiplies one output carrier wave of the FF circuit by a signal wave, and an addition circuit that adds the phase modulation signal obtained from the balanced modulation circuit and the other output carrier wave obtained from the FF circuit. A frequency modulation circuit characterized by: