Fm demodulator

The present invention relates to an FM demodulator that demodulates an FM signal.

As a conventional FM demodulator, a limiter circuit that converts an input FM signal into a pulse, a delay circuit that delays one of the signals output by this limiter circuit, and the other signal output by the limiter circuit and its delay are used. It is known that it is composed of an AND circuit that outputs a signal obtained by a logical product calculation with a signal and a low frequency pass filter that obtains a demodulated signal by the output of this AND circuit (see, for example, Patent Document 1). ..<patcit num="1"><text>Japanese Unexamined Patent Publication No. 2002-368542</text></patcit>

<p> However, the FM demodulator described in Patent Document 1 has an AND circuit composed of transistors and the like, and performs logical operation of pulses. In this case, the width of the pulse is greatly affected by the capacitance component of the transistor, and when the frequency of the FM signal becomes high, the function as the FM demodulator is significantly deteriorated. In order to solve such a problem, a field effect transistor made of gallium arsenide (GaAs) may be used, but the frequency of the input FM signal is limited to about 5 [GHz].</p><p> Further, the delay circuit is generally a delay circuit in which several differential circuits are arranged in series. In such a configuration, there is a problem that the area and power consumption of the FM demodulator become large. Therefore, in view of the above points, an object of the present invention is to provide an FM demodulator that can extend the upper limit of the frequency of the input FM signal, and can realize low power consumption and low price. To do.</p>

<p> In order to solve the above problems and achieve the object of the present invention, the present invention has the following configuration. That is, the present invention includes a first amplitude detecting means for inputting an FM signal and detecting the amplitude of the FM signal, and an attenuating means for inputting the FM signal and reducing the amplitude of the FM signal in proportion to the frequency. , The second amplitude detecting means for detecting the output amplitude of the damping means, and the amplitude change for detecting the change in both amplitudes detected by the both amplitude detecting means and outputting a signal corresponding to the detected change. It is equipped with a detection means.</p><p> According to the present invention having the above configuration, it is possible to extend the upper limit of the frequency of the input FM signal, and to realize low power consumption and low price.</p>

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The configuration of the embodiment of the FM demodulation device of the present invention will be described with reference to FIGS. 1 and 2. As shown in FIG. 1, the FM demodulator according to this embodiment includes a voltage amplitude detector 1, an attenuator 2, a voltage amplitude detector 3, and an amplitude change detector 4.

The voltage amplitude detector 1 detects the amplitude (voltage amplitude) of the input FM signal. When the amplitude of the input FM signal is V1 at the peak / peak value as shown in FIG. 1, the voltage amplitude detector 1 preferably detects the peak / peak value. The attenuator 2 inputs an FM signal, reduces the amplitude of the FM signal in proportion to the frequency, and outputs an FM signal whose amplitude has been reduced. An example of the frequency characteristics (frequency-output voltage characteristics) of the attenuator 2 is shown in FIG. The attenuator 2 is composed of, for example, a transmission line having the characteristics shown in FIG.

The voltage amplitude detector 3 detects the amplitude (voltage amplitude) of the FM signal attenuated by the attenuator 2. When the amplitude of the output signal of the attenuator 2 is V2 as shown in FIG. 1, the voltage amplitude detector 3 preferably detects the peak / peak value. The amplitude change detector 4 obtains the amplitude value detected by the voltage amplitude detector 1 and the amplitude value and the ratio detected by the voltage amplitude detector 3, and on the time axis according to the changed amount of the obtained ratio. An output signal that changes (increases or decreases) is generated as an FM demodulated signal and output.

Next, an operation example of the embodiment having such a configuration will be described with reference to FIGS. 1 and 2. As shown in FIG. 1, for example, the frequency of the FM signal currently input is f1, and the amplitude thereof is V1. In this case, the FM signal is input to the voltage amplitude detector 1 and the attenuator 2, respectively.

The FM signal is directly input to the voltage amplitude detector 1 and its amplitude value is detected. Therefore, the detection value detected by the voltage amplitude detector 1 is V1, which is input to the amplitude change detector 4. On the other hand, the amplitude of the FM signal input to the attenuator 2 decreases to V2 according to its frequency f1 (see FIGS. 1 and 2), and this is input to the voltage amplitude detector 3 to detect its amplitude value. .. Therefore, the detection value detected by the voltage amplitude detector 3 is V2, which is input to the amplitude change detector 4.

The amplitude change detector 4 obtains the ratio V2 / V1 of the detected value V1 and the detected value V2, and generates and outputs a signal corresponding to the obtained ratio. Next, it is assumed that the amplitude of the input FM signal remains V1 and the frequency changes (decreases) from f1 to f2 (f1&gt; f2). In this case, the detection value detected by the voltage amplitude detector 1 does not change with V1, and this is input to the amplitude change detector 4.

On the other hand, the output from the attenuator 2 increases its amplitude from V2 to V2'as the frequency of the FM signal changes from f1 to f2 (see Fig. 2), which is input to the voltage amplitude detector 3. And the amplitude value is detected. Therefore, the detection value detected by the voltage amplitude detector 3 changes from V2 to V2', and this is input to the amplitude change detector 4. Therefore, the ratio detected by the amplitude change detector 4 changes from V2 / V1 to V2'/ V1, and the output signal generated in response to this change also changes (increases or decreases) on the time axis. Therefore, the output signal output from the amplitude change detector 4 is a demodulated signal obtained by demodulating the FM signal.

Here, the output characteristic of the attenuator 1 is proportional to the frequency as shown in FIG. Therefore, if the relationship between the frequencies f1 and f2 of the FM signal is f1 = 2 × f2, the relationship in Eq. (1) below holds. 2 × (V2 / V1) = (V2'/ V1) (1) According to the equation (1), when the frequency of the FM signal changes (decreases) from f1 to f2 and becomes 1/2, the amplitude The above ratio obtained by the change detector 4 doubles. Therefore, the amplitude change detector 4 can easily generate a signal that changes on the time axis by utilizing a large change in the ratio.

As described above, according to this embodiment, it is possible to extend the upper limit of the frequency of the input FM signal, and also to realize low power consumption and low price. In the amplitude change detector 4 shown in FIG. 1, the ratio of both amplitude values detected by the voltage amplitude detector 1 and the voltage amplitude detector 3 is obtained, and the time axis is calculated according to the change in the obtained ratio. The output signal that changes above is generated and output as an FM demodulated signal.

However, instead of this, the difference between the two amplitude values detected by the voltage amplitude detector 1 and the voltage amplitude detector 3 is obtained, and the output signal that changes on the time axis according to the obtained difference is the FM demodulated signal. It may be generated and output as.

<figref num="1">It is a block diagram which shows the structure of embodiment of this invention.</figref><figref num="2">It is a figure which shows an example of the output characteristic of an attenuator.</figref>

Code description

1 ... Voltage amplitude detector, 2 ... Attenuator, 3 ... Voltage amplitude detector, 4 ... Amplitude change detector.