JPH03214908A - Fm modulator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an FM module used in the field of AV equipment. Conventional technology In recent years, FM modulators have become more and more popular as AV equipment becomes more diverse.
Since the development of the so-called Hi-Fi system, which converts various audio signals into FM and listens to high-quality sounds using an FM receiver system, it has become widely used. Also, in the l{A field, FM is used for various purposes such as door horns.
For modulation, the carrier oscillator must have a reactance element configuration, and an L/C oscillation configuration is used. Problems to be Solved by the Invention However, this conventional L/C oscillation configuration has the problem of poor carrier frequency setting accuracy and stability. Therefore, the purpose of the present invention is to improve the accuracy and stability of carrier frequency setting. Means for Solving the Problems and to achieve this object, the present invention provides a modulation signal input terminal, an FM modulator whose input terminal is connected to the modulation signal input terminal, and an FM modulator having an output terminal connected to the modulation signal input terminal. a mixer having a first input terminal connected thereto; a local oscillator having an output terminal connected to a second input terminal of the mixer; and an FM wave output terminal connected to an output terminal of the mixer. , the FM modulator is provided with a frequency variable means, and
The carrier frequency of this FM modulator is lower than the carrier frequency of the local oscillator.

If the above configuration is used, the carrier frequency output from the FM wave output terminal is determined by mixing the carrier frequency of the local oscillator and the adjustable carrier frequency of the FM modulator in a mixer, so the setting accuracy and This results in high stability. Embodiment As shown in FIG. 1, the FM modulator of this embodiment includes a modulation signal input terminal l, an FM modulator 2 whose input terminal is connected to the modulation signal input terminal l, and this FM modulator 2.
a mixer 3 whose first input terminal is connected to the output terminal of the mixer 3; a local oscillator 4 whose output terminal is connected to the second input terminal of the mixer 3; and a filter 5 connected to the output terminal of the mixer 4. and an FM wave output terminal 6 connected via the
The FM modulator 2 is provided with a frequency variable means 2a, and the frequency f. 4~6M
Hz and the carrier frequency r0 of the local oscillator 4 is 70
It is lower than ~90MHz. And F.M.
The carrier frequency fc is the low frequency signal f. and high frequency signal f
In the FM modulator 2, the carrier frequency f is set to approximately 4 to 6 MHz. If this frequency is set, it is possible to set the frequency setting accuracy within ±5 KHz and the frequency stability within ±15 KHz. In the local oscillator 4, if the carrier frequency f0 is set to 70 to 90 MHz and a crystal resonator or a crystal-based SAW resonator is used as the oscillation element, the stability will be within ±10 kHz. Therefore,
carrier frequency f. When both the signals with the carrier frequency f0 and the carrier frequency f0 are mixed in the mixer 3, a difference or sum signal is generated, and this signal is mixed with the carrier frequency f. If you set it to , it will be as follows. rc=r. ±f, Frequency setting accuracy: ±5KHz Frequency stability: ±5K + ±IOK} Specification = ±25K7 As mentioned above, it is possible to set an FM modulated carrier frequency with very high setting accuracy and stability. ．． Regarding the difference or sum signal frequency, it is sufficient to extract only the desired signal using the filter 5 as shown in Fig. 2. The mixer 3 is a simple balanced mixer (SBM).
) by using carrier frequency r. is suppressed F
Signal leakage from M wave output terminal 6 is eliminated. Effects of the Invention As described above, the present invention provides a modulation signal input terminal, an FM modulator whose input terminal is connected to the modulation signal input terminal, and a first input terminal of which is connected to the output terminal of the FMSiit device. a local oscillator whose output terminal is connected to a second input terminal of the mixer; and an FM wave output terminal connected to the output terminal of the mixer;
f:! In addition to providing a frequency variable means in the
The carrier frequency of the M modulator is lower than the carrier frequency of the local oscillator. Therefore, the carrier frequency output from the FM wave output terminal is determined by mixing the carrier frequency of the local oscillator and the carrier frequency of the adjustable FM modulator in a mixer, so the setting accuracy and stability can be improved. The result will be a high value.

[Brief explanation of drawings]

Claims (2)

[Claims] (1) a modulation signal input terminal, an FM modulator whose input terminal is connected to the modulation signal input terminal, and a mixer whose first input terminal is connected to the output terminal of the FM modulator;
a local oscillator whose output terminal is connected to a second input terminal of the mixer; and an FM connected to the output terminal of the mixer.
a wave output terminal, the FM modulator is provided with a frequency variable means, and the carrier frequency of the FM modulator is lower than the carrier frequency of the local oscillator.
modulator. (2) The FM modulator according to claim 1, wherein a filter is interposed between the output terminal of the mixer and the FM wave output terminal.