JPS601991B2 - demodulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a demodulator, and more particularly to a multi-frequency FCK (frequency shift) demodulator used in a remote monitoring and control system.

Figure 1 is a block diagram showing an example of a conventional FSK demodulator, where 1 is a bandpass filter, 2 is an amplifier, 3 is a discriminator, 4 is a mixer, and 5 is a VC0 (voltage controlled oscillator) (generally 6 is a VCO control circuit (generally a local oscillator control circuit), 10 is an FSK signal input terminal, 11 is a demodulated signal output terminal, and 12 is a control terminal.

In FIG. 1, a bandpass filter 1, an amplifier 2, and a discriminator 3 are fixed frequency devices, and a terminal 1
When the carrier frequency of the FSK signal input from 0 changes, the control terminal 12 is used to control the VCO control circuit 6 (for example, by manually changing the settings of the VCO control circuit 6), and the VCO control circuit 6 By changing the DC voltage applied to VC05 and changing the output frequency of VC05, mixer 4
An intermediate frequency signal having a constant frequency determined by the pass frequency band of the bandpass filter 1 is outputted from the terminal 1, demodulated by the discriminator 3, and outputted from the terminal 11.

FIG. 3 is an explanatory diagram for explaining the operation of the circuit shown in FIG. 1. FIG. 3 a is a frequency spectrum, FIG. 3 b is an input frequency versus output voltage characteristic of the discriminator 3, and FIG. 3 c is FIG. 3d shows the demodulated signal outputted from the terminal 11 corresponding to the frequency change of the signal inputted from the terminal 10 and FIG. 3c. In Fig. 3a, the carrier wave frequency is f, and an FSK signal of frequency f when the key is off, frequency f when the key is on, and 1△f arrives at the terminal 10', and the VC
Let the output frequency of 05 be f, . Then, the output frequency of the amplifier 2 becomes f, (f,=f,, -f,) and fi+Δf. If the discriminator 3 is set to output a negative voltage in response to the input of the frequency fi and to output a positive voltage in response to the frequency fi + △f, the The demodulated output shown in Figure 3d is obtained. Also, frequency shift △f
If the value of does not change and the carrier wave frequency simply changes from f, to L', the output frequency of VC05 is changed to f, . From f,
2 to fFf, 2-f2. Conventional FS
Since the K demodulator is configured as described above, when a plurality of types of transmission signals, which are composed of carrier waves having different frequencies modulated with respective signals, are inputted from the terminal 10 while being switched in time, , the oscillation frequency of VC05 is changed in response to the frequency change of the carrier wave, and the bandpass filter 1
At the input point, an intermediate frequency signal input with a constant frequency is obtained, or when two or more of the above-mentioned types of transmission signals are simultaneously input from the terminal 10, only the desired type of transmission signal is input as an intermediate frequency signal. It is difficult to input to the amplifier 2 in the form of The disadvantage is that it takes a long time to respond to change the oscillation frequency. The purpose of the present invention is to eliminate the above-mentioned drawbacks in the conventional FSK demodulator, and for this reason, in this invention, a tone detection circuit is added to detect the type of carrier wave inputted to the terminal 10', and by this detection, the VCO is controlled. VC05 is controlled via circuit 6, and VC05 is controlled with respect to the frequency of the input carrier wave.
The present invention provides an FSK demodulator that can match the oscillation frequency of 0.05 and thereby respond in a short time to changes in the type of input carrier wave.Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram showing one embodiment of the present invention.
The same reference numerals as in the figure indicate the same or corresponding parts, and block 7 surrounded by a dotted line is a tone detection circuit, 71, 72, . . .
It includes a plurality of tone detectors designated 7n.

If there are n types of carrier wave frequencies f, f2, . …
For example, when a carrier wave of frequency f2 arrives at the terminal 10, the tone detector 72 outputs a signal and controls the VC05 via the VCO control circuit 6. When the frequency of the carrier wave is changed to f, the output signal of the tone detector 72 disappears, the tone detector 71 outputs a signal, and the VCO control circuit 6, the VC05 is controlled to oscillate at a frequency of a value indicated by f, 10, i.e., when the carrier frequency of the transmitted signal arriving at the terminal 1 is changed from f2 to f, the oscillation frequency of the VC05 immediately changes to f2. The frequency changes from ten fi to f, ten f, and the intermediate frequency is always kept at fi.

If a transmission signal with carrier frequency f, and a transmission signal with carrier frequency f2 arrive at terminal 1 at the same time, output signals are simultaneously output from tone detectors 71 and 72 and input to VCO control circuit 6, but VCO By providing a logic circuit within the control circuit 6, it is possible to prioritize the selected transmission signals.

In the above explanation, a demodulator for FSK signals has been described as an example, but it is clear that the present invention has similar effects as a demodulator for FM and AM signals. As described above, according to the present invention, it is possible to construct a demodulator that has a quick response time for receiving an FSK signal whose carrier frequency is changed at random times.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a conventional FSK demodulator,
FIG. 2 is a block diagram showing an embodiment of the present invention, and FIG. 3 is an explanatory diagram for explaining the operation of the circuit shown in FIG. 1. In the figure, 1 is a bandpass filter, 2 is an amplifier, 3 is a discriminator, 4 is a mixer, 5 is VC○, 6 is V
CO control circuit 7 is a tone detector. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. A plurality of types of transmission signals constituted by modulating a plurality of types of carrier waves having mutually different frequencies with respective signals are transmitted while being switched in time, or two or more types of the above transmission signals are transmitted. When transmitted simultaneously, in a demodulator that receives and demodulates multiple types of transmitted signals, a tone detection circuit inputs the transmitted signals, detects the type of carrier wave contained therein, and outputs a signal to display this. Then, the output signal of this tone detection circuit is inputted, and a frequency control signal for controlling the oscillation frequency is outputted from this signal, and a local control signal is generated so as to always oscillate a frequency having a predetermined frequency difference with respect to the frequency of the carrier wave included in the above-mentioned transmission signal. A demodulator comprising: a local oscillator control circuit that controls an oscillator. 2. When the output signal of the tone detection circuit indicates the simultaneous presence of two or more types of carrier waves, the local oscillator control circuit responds to a signal that indicates the type of carrier wave with the highest priority according to a predetermined priority order. The demodulator according to claim 1, wherein the demodulator outputs a frequency control signal.