JPH11225081A - Frequency modulation transmitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a degree of frequency modulation constant independently of the frequency of a carrier signal. SOLUTION: In the transmitter, a signal from an input terminal 1 is fed to a frequency modulator 2, where frequency modulation(FM) is conducted at a fixed frequency f2, and a modulated signal is fed to a mixer 3. Furthermore, a voltage controlled variable frequency oscillator 4 is provided, and an output of the oscillator 4 and a signal from a reference vibrator 6 through a programmable frequency divider 7 are fed to a phase comparator 5, and a detected phase difference signal is fed to a control terminal of the oscillator 4 via a low pass filter 8. Thus, a signal with a frequency f1 in response to a frequency division ratio of the programmable frequency divider 7 is extracted from the oscillator 4 and fed to a mixer 3. Thus, the mixer 3 generates an FM signal modulated around a center of a frequency f1±f2. Then the signal is fed to a band pass filter 9, from which an FM signal with a frequency of f1-f2 is selected and the FM signal is fed to an antenna 11 through an amplifier 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency modulation transmitter suitable for use in, for example, a wireless microphone.

[0002]

2. Description of the Related Art In a wireless microphone, for example, a specified carrier frequency band (87.5 to 1) is used.
07.9 MHz) is divided into a plurality of channels, and transmission of an audio signal or the like is performed using a frequency modulation transmitter set to a carrier frequency for each channel. Therefore, as a frequency modulation transmitter used for such an application, for example, a circuit configuration as shown in FIG. 2 is known.

That is, in FIG. 2, for example, a variable frequency oscillator 21 of a voltage control type is provided. The signal from the variable frequency oscillator 21 is supplied to the phase comparator 22 and, for example, the signal from the reference oscillator 23 is supplied to the phase comparator 22 through the programmable frequency divider 24. Then, the detected signal of the phase difference is applied to the low-pass filter 25.
To the control terminal of the variable frequency oscillator 21.

As a result, a so-called phase locked loop is formed. Therefore, from the variable frequency oscillator 21, for example, a designated carrier frequency band (87.5 to 107.9M)
Hz), an extremely stable frequency is oscillated,
By switching the frequency division ratio of the programmable frequency divider 24, a signal of the carrier frequency f _T of each arbitrary channel is extracted.

Further, for example, an audio signal supplied to an input terminal 20 is supplied to a variable frequency oscillator 21. As a result, the carrier frequency f _T of the extracted signal is modulated by the audio signal to perform frequency modulation (hereinafter referred to as FM). The modulated signal is power-amplified by the amplifier 26 and supplied to the antenna 27, so that the above-described FM transmission of the audio signal from the input terminal 20 is performed.

[0006]

In [0005] However such a device, for example, to the carrier frequency f _T of the signals taken by the variable frequency oscillator 21 is slightly modulated,
For example, a varicap diode is used.

In this case, in a normal varicap diode, the characteristics fluctuate depending on the carrier frequency f _T which is originally taken out.
The modulation degree of M) is changed. That is, due to a change in the characteristics of the varicap diode, for example, when the carrier frequency f _T is small, the degree of modulation increases, and the carrier frequency f _{T
As T} increases, the degree of modulation decreases.

For this reason, in the conventional device, the level of the audio signal supplied to the input terminal 20 is adjusted in accordance with, for example, a change in the modulation factor for each carrier frequency f _T , or the signal is demodulated on the receiving side (not shown). Means such as adjusting the level of the audio signal to be used are taken, but in any case, an operation for adjustment is required or an extra circuit configuration is required.

This application has been made in view of such a point, and the problem to be solved is that the modulation degree of frequency modulation is changed by the frequency of the carrier signal in the conventional apparatus. It is.

[0010]

For this reason, in the present invention, an input signal is frequency-modulated at an arbitrary fixed frequency, and then this modulated signal is frequency-converted to a predetermined carrier frequency band. Therefore, according to this, the modulation degree of frequency modulation can be made constant regardless of the frequency of the carrier signal.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a modulator for frequency-modulating an input signal based on an arbitrary fixed frequency, and a frequency converter for frequency-converting a signal modulated by the modulator to a predetermined carrier frequency band. And a container.

The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an example of a frequency modulation transmitter to which the present invention is applied.

In FIG. 1, for example, an audio signal supplied to an input terminal 1 is supplied to a frequency modulator 2. Thus, any fixed frequency f2 (eg, 10.7 MHz)
Is modulated by the above-mentioned audio signal and frequency-modulated (hereinafter F
M). This modulated FM signal is supplied to a mixer 3 described later.

Further, for example, a voltage-controlled variable frequency oscillator 4 is provided. The signal from the variable frequency oscillator 4 is supplied to the phase comparator 5, and the signal from the reference oscillator 6 is supplied to the phase comparator 5 through the programmable frequency divider 7. Then, the signal of the detected phase difference is supplied to the control terminal of the variable frequency oscillator 4 through the low-pass filter 8.

Thus, a so-called phase locked loop is formed. In this case, the variable frequency oscillator 4
From a predetermined frequency band (98.2-118.
At 6 MHz, an extremely stable frequency is oscillated, and by switching the frequency division ratio of the programmable frequency divider 7, a signal having a carrier frequency f1 of an arbitrary channel is extracted.

The signal of the carrier frequency f1 is supplied to the mixer 3. As a result, the mixer 3 mixes (multiplies) the FM signal modulated around the frequency f2 and the signal of the carrier frequency f1, and performs frequency conversion. That is, by the frequency conversion in the mixer 3, the FM modulated around the frequency f1 ± f2
A signal is formed.

Therefore, the frequency f1 is further calculated from these signals.
A bandpass filter 9 is provided for selecting an FM signal modulated around -f2. That is, a signal from the low-pass filter 8 for controlling the above-described variable frequency oscillator 4 is supplied to the band-pass filter 9, and a pass band of the band-pass filter 9 is extracted so as to extract an FM signal modulated around the frequency f1 -f2. Control is performed.

The FM signal modulated around the frequencies f 1 -f 2 selected by the band-pass filter 9 is
The power of the audio signal is amplified by the amplifier 10 and supplied to the antenna 11.
Transmission is performed.

That is, in this apparatus, for example, (98.2-118.6 MHz + 10.7 MH)
z) and (98.2-118.6 MHz-10.
7 MHz). Therefore, by controlling the pass band of the above-described band-pass filter 9 and selecting the latter signal, it is possible to extract a signal of the above-described specified carrier frequency band (87.5 to 107.9 MHz), for example.

In this case, the audio signal supplied to the input terminal 1 is supplied to the frequency modulator 2 and frequency-modulated at a fixed frequency f2 (for example, 10.7 MHz). 87.5-107.
9 MHz), the modulation degree of frequency modulation does not change, and stable frequency modulation can always be performed.

Therefore, in this device, after the input signal is frequency-modulated at an arbitrary fixed frequency, this modulated signal is frequency-converted to a predetermined carrier frequency band, so that the frequency modulation of the carrier signal is independent of the frequency of the carrier signal. The degree of modulation can be constant.

Thus, in the conventional apparatus, for example, the level of the audio signal supplied to the input terminal is adjusted according to the change in the modulation factor for each carrier frequency, or the level of the audio signal demodulated on the receiving side is adjusted. It is not necessary to take any measures such as the above, and no extra work for adjustment and no extra circuit configuration for the adjustment are required.

Thus, according to the above-described frequency modulation transmitter, a modulator for frequency-modulating an input signal based on an arbitrary fixed frequency, and a frequency for frequency-converting a signal modulated by the modulator into a predetermined carrier frequency band. By having the converter, the modulation degree of frequency modulation can be made constant regardless of the frequency of the carrier signal.

In the above description, the FM signal modulated around the frequency f1 -f2 is extracted using the band-pass filter 9. However, the FM signal modulated around the frequency f1 + f2 is extracted. You may do so. Of course, in that case, the frequency band of the signal oscillated by the variable frequency oscillator 4 is changed.

The frequency band of the signal oscillated by the variable frequency oscillator 4 is also changed by an arbitrary fixed frequency f2 at which the frequency of the audio signal is modulated by the frequency modulator 2.

Further, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0027]

Therefore, according to the first aspect of the present invention, the frequency of an input signal is modulated at an arbitrary fixed frequency, and then the modulated signal is frequency-converted into a predetermined carrier frequency band. The modulation degree of frequency modulation can be made constant regardless of the frequency.

Thus, in the conventional device, for example, the level of the audio signal supplied to the input terminal is adjusted according to the change in the modulation factor for each carrier frequency, or the level of the audio signal demodulated on the receiving side is adjusted. It is not necessary to take any measures such as the above, and no extra work for adjustment and no extra circuit configuration for the adjustment are required.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an example of a frequency modulation transmitter to which the present invention is applied.

FIG. 2 is a configuration diagram of a conventional frequency modulation transmitter.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 input terminal, 2 frequency modulator, 3 mixer, 4 variable frequency oscillator, 5 phase comparator, 6 reference oscillator, 7
... Programmable frequency divider, 8 ... Low-pass filter, 9 ...
Bandpass filter, 10 ... Amplifier, 11 ... Antenna

Claims (3)

[Claims] 1. A modulator for frequency-modulating an input signal based on an arbitrary fixed frequency, and a frequency converter for frequency-converting a signal modulated by the modulator to a predetermined carrier frequency band. And a frequency modulation transmitter. 2. The frequency modulation transmitter according to claim 1, wherein a predetermined frequency signal is supplied to each of said frequency converters to convert the frequency into a signal of an arbitrary carrier frequency band. . 3. The frequency modulation transmitter according to claim 2, wherein a frequency signal supplied to the frequency converter is formed using a phase locked loop, and the frequency conversion is performed using a control signal of the phase locked loop. A frequency modulation transmitter for controlling a pass band of a filter circuit for selecting a signal taken out of a transmitter.