JPH0129084B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field] The present invention relates to an improvement in a receiver for radio control in a radio control system.

[Conventional technology]

When a model airplane or the like is remotely operated using a radio control method, the electric field strength at the position of the airplane varies greatly depending on the distance between the airplane and the transmitter and the terrain. However, the receiver installed inside the device is required to operate stably regardless of the strength of the electric field. Therefore, receivers are usually provided with an automatic gain control circuit (hereinafter referred to as an AGC circuit). FIG. 1 is a block diagram showing an example of a conventional multi-channel digital proportional receiver. In this figure, an antenna 1 is connected to a high frequency amplification circuit 3 via a high frequency tuning circuit 2. The output signal of the high frequency amplifier circuit 3 is sent to the mixer 4
It is once converted to an intermediate frequency through 5 is a local oscillator. The intermediate frequency signal is amplified by an intermediate frequency amplification circuit 6 and demodulated by a wave detector 7.
The obtained signal is converted into a sharp square wave through a waveform shaping circuit 8, and converted into each channel output by a decoder 9. Here, from the output of detector 7
The AGC voltage is taken out by the AGC circuit 10 and applied to the intermediate frequency amplification circuit 6 and the high frequency amplification circuit 3. This reduces the gain of the receiver in strong electric fields and ensures stable operation.

By the way, in the digital proportional system, there is no need to faithfully reproduce the amplitude component of a transmitted signal, and it is important that "0" and "1" be completely distinguished. Therefore, it is preferable that the output signal of the amplifier is somewhat saturated in order to eliminate interference and noise. For this reason, it is necessary to keep the AGC in a state where it maintains a certain minimum gain. Figure 2 shows the conventional example in Figure 1.
It shows the output waveform of the detector 7 for various electric field intensities when the AGC intensity setting is changed, and the subscripts a, b...e indicate weak electric field, weak electric field, weak electric field,
Medium electric field, strong electric field, and extremely strong electric field are shown, and subscripts 1 and 2 indicate cases where AGC is made stronger and cases where AGC is made weaker. the second one
). Also, Fig. 3 is a waveform diagram of each detection output when there is noise, Fig. 4 is a diagram of the output waveform of the detector 7 when there is interference from a pulse signal of an adjacent channel, and Fig. 5 is an output waveform diagram of the detector 7 when there is strong interference. The meanings of the subscripts are the same as in FIG. Here, if AGC is set weakly so as to maintain a constant minimum gain, as shown in Figure 3 a-1, b-1, c-1.
As shown in FIG. 3 a-2, b-2, and c-2, the influence of noise can be reduced. Also, because saturation occurs inside the receiver, Fig. 4 b-1, d-1 and Fig. 4 b-2, d-2, as well as Fig. 5 d-1, e-1 and Fig. 5 d. -2,e-
As shown in 2, the influence of interference can be reduced. Also, Figure 2 a-1, b-1 and Figure 2 a-2,
As shown in b-2, high sensitivity can be obtained in weak electric fields.

[Problem to be solved by the invention]

However, if AGC is set weakly,
As shown in FIG. 2, d-2 and e-2, extreme saturation occurs in a strong electric field, and as a result, the detection output voltage decreases, resulting in the disadvantage that a desired pulse signal cannot be obtained. Conversely, if the AGC is set strongly, the output voltage will not drop due to extreme saturation, but as mentioned above, it has the disadvantage of low sensitivity due to weak electric fields and susceptibility to noise and interference.

The present invention aims to eliminate all of these conventional contradictory drawbacks, and includes:
The technical challenge is to be able to obtain highly sensitive and always stable output pulse signals.

[Means for Solving the Problems] The present invention is a radio control receiver that receives radio waves using pulses as modulated signals, and includes a high frequency tuning circuit connected to an antenna, and a radio frequency tuning circuit connected to the output side of the high frequency tuning circuit. an attenuator, which has a capacitor connected between input and output terminals, and a diode connected to one end of the capacitor and whose other end is grounded for high frequency, and attenuates a high frequency input signal by applying a voltage to the other end of the diode. , a tuning circuit connected to the output side of the attenuator, an amplifier circuit that amplifies the signal that has passed through the tuning circuit, a detector that demodulates the amplified output of the amplifier circuit, and a signal that exceeds the saturation level of the amplifier circuit. An AGC circuit that attenuates a high frequency input signal by applying a DC voltage to a diode of an attenuator according to the level and making the diode conductive;
It is characterized by comprising the following.

[Effect]

According to the present invention having such characteristics, an attenuator consisting of a capacitor and a diode is connected to the output end of the high frequency tuning circuit, and a tuning circuit is connected to the input and output ends of the high frequency tuning circuit to form a detuning circuit. There is. The output of the tuning circuit is then amplified by an amplifier circuit and detected by a detector. Since the AGC circuit and attenuator do not operate under a weak electric field, signals can be received with high sensitivity by making the amplification factor of the amplifier circuit sufficiently large. Also, under strong electric field strength, the amplifier circuit reaches the saturation level, but when the signal exceeds this level, it
A DC voltage is applied to the attenuator diode from the AGC circuit. This will cause the diode to gradually conduct and bypass high frequencies. Therefore, the input signal will be attenuated according to the DC signal level provided by the AGC circuit.

[Explanation of Examples]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below with reference to the drawings. FIG. 6 is a block diagram of a receiver showing one embodiment of the present invention. In this figure, a high frequency tuning circuit 2 is connected to an antenna 1 as in the conventional example shown in FIG. The high-frequency tuning circuit 2 may be constructed by using a coupling coil as shown in the figure, or may be one in which the antenna is directly connected to a resonant circuit. Now, an attenuator 11 is connected to the output end of the high frequency tuning circuit 2. The attenuator 11 attenuates the output signal of the high frequency tuning circuit 2 and transmits it to the next stage high frequency amplification circuit 3 when the input signal is above a predetermined value. The high frequency amplification circuit 3 is provided as necessary to amplify the input high frequency signal, and its output is given to the mixer 4. Here, a tuning circuit is connected to the output side of the attenuator 11 as described later. The mixer 4 receives the output of the local oscillator 5 and converts the input signal into an intermediate frequency signal, and supplies the output to the intermediate frequency amplification circuit 6 at the next stage. In this embodiment, a high frequency amplification circuit 3 and an intermediate frequency amplification circuit 6 constitute an amplification circuit of a receiver. The intermediate frequency amplification circuit 6 amplifies the intermediate frequency signal, and also extracts a signal from the middle of the signal and supplies it to the second AGC circuit 13. No.
The 2AGC circuit 13 is a novel AGC circuit according to the present invention, which obtains a frequency corresponding to the signal level when the signal exceeds the saturation level of the amplifier circuit, and is applied to the attenuator 11 as an attenuation signal.
The output of the intermediate frequency amplification circuit 6 is given to a detector 7, demodulated, and waveform shaped by a waveform shaping circuit 8, as in the conventional example. The output of the waveform shaping circuit 8 is given to a decoder 9. The decoder 9 decodes the signal and converts it into a control signal for each channel. The first AGC circuit 12 is similar to the conventional example.
The AGC circuit is an amplifier circuit that extracts the AGC voltage from the detector 7, and in this embodiment, a high frequency amplifier circuit 3.
and intermediate frequency amplification circuit 6. This AGC circuit 12 is set to be weak as in the second conventional example.

FIG. 7 shows an example of a specific circuit diagram of a main part of an embodiment of the present invention, and the same parts as in FIG. 6 are shown using common symbols. In this figure, an antenna 1 is connected to a high frequency tuning circuit 2 made of LC, and one end of the high frequency tuning circuit 2 is provided to an attenuator 11. In the attenuator 11, a series connection body of coupling capacitors C1 and C2 of minute capacitance is connected between the input and output terminals, and the cathode of the diode D1 and the anode of the diode D2 are connected to the midpoint thereof. The other end of the diode D1 is connected to the power supply, and the other end of the diode D2 is connected to the second AGC circuit 13. FIG. 7 shows an example of the circuit excluding the high frequency amplifier circuit 3, and the signal from the attenuator 11 is applied to the mixer 4.
The mixer 4 has a tuning circuit on the output side of the attenuator 11, and is an emitter injection type mixer in which the local signal of the local oscillator 5 is injected into the emitter of the mixing transistor TR1, and only intermediate frequency signals are input. is applied to the next stage intermediate frequency amplification circuit 6. A part of the intermediate frequency signal is also given to the second AGC circuit 13.
The second AGC circuit 13 has a transistor TR2 that converts the signal level into a voltage.
The intermediate frequency signal is applied to the base of transistor TR2. A capacitor C3 is connected between the collector of the transistor TR2 and ground to smooth out fluctuations in collector voltage. Capacitor C3 is connected to capacitor C4 via a resistor. Capacitor C4 is a high frequency bypass capacitor, and is connected to the cathode of diode D2 of attenuator 11.

Next, the operation of the receiver of this embodiment will be explained with reference to the waveform diagrams of FIGS. 2 to 5. In each figure, the subscript 3 indicates the waveform of the receiver of this embodiment, and the meanings of the other subscripts are the same as those described above. In this embodiment, as mentioned above, the first AGC
Since the AGC of the circuit 12 is set to be weak as in the second conventional example, the sensitivity does not decrease in weak electric fields and weak electric fields as shown in FIG. 2 a-3 and b-3. Also, since moderate saturation occurs in a weak electric field, the influence of noise can be reduced as shown in Figure 3 a-3 and b-3, similar to the second conventional example shown in Figure 3 a-2 and b-2. It is possible to do so. When the electric field strength increases, the first AGC circuit 12 starts working, and the gain of the intermediate frequency amplifier circuit 6 gradually decreases to keep the output level of the receiver constant. When the electric field strength becomes even stronger, the first AGC circuit 12 reaches its operating limit. However, in the present invention, the second AGC circuit 13 starts operating. and transistor TR
The base current of 2 increases and the collector current flows,
The potential of the collector decreases. Then, current begins to flow from the power source through the diodes D1 and D2 of the attenuator 11, and the diodes D1 and D2 become conductive. Therefore, a part of the high frequency signal obtained from the high frequency tuning circuit 2 is grounded at high frequency through the diode D1 and through the diode D2 and the capacitor C4, so that the high frequency signal is attenuated. Therefore, even if the electric field strength becomes stronger than a certain level, extreme saturation does not occur as in the second conventional example, as shown in Figure 2 d-2, d-3, e-2, and e-3, and the output The pulse signal remains constant. Further, in the present invention, the attenuator 11 is provided before passing through the active element. Therefore, Figure 4b-
1, b-3, d-1, d-3 and Figure 5 d-1,
As shown in d-3, e-1, and e-3, cross-modulation caused by the nonlinear characteristics of the active element can be effectively prevented.

In the embodiment shown in FIG. 7, the attenuator 11 is composed of a capacitor and a diode, but other attenuators such as a varicap may be used.

Further, the present invention can be applied not only to a heterodyne receiver but also to a homodyne receiver.

In addition, this embodiment and the circuit example embodying it also show a first AGC circuit that applies AGC to the amplifier circuit in the same way as in conventional radio control receivers, but this is necessary for AM receivers.
An FM receiver is not required. The present invention is
Cross-modulation is prevented by operating the attenuator using the second AGC circuit regardless of the presence or absence of the first AGC circuit.

〔Effect of the invention〕

As described above in detail, the present invention uses an AGC circuit (second AGC circuit in the embodiment) that starts operating from a range that sufficiently exceeds the output saturation level. Therefore, high sensitivity can be obtained in a weak electric field, and since the influence of noise is reduced, a stable waveform can be obtained. Also, under strong electric field
Since the AGC circuit operates and activates the attenuator, extreme saturation is eliminated and an output signal of a constant level is obtained. The present invention thus provides the first,
It has the advantages of the second conventional example, but
Furthermore, since the AGC signal is applied to the attenuator 11 before the amplifier circuit, cross-modulation characteristics are also significantly improved. This is particularly effective when operating several adjacent channel transmitters in a strong electric field, and can greatly reduce malfunctions caused by cross modulation.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of a conventional receiver, and FIGS. 2 to 5 are waveform diagrams of the detection output in different states. When there is noise, FIG. 4 shows a case where pulse signals of adjacent channels interfere, and FIG. 5 shows a case where this interference is strong. In each figure, subscripts a, b...e indicate a weak electric field, a weak electric field, a medium electric field, a strong electric field, and an extremely strong electric field, respectively. Also, subscript 1 indicates the case where strong AGC is applied in a conventional receiver (first conventional example), subscript 2 indicates when weak AGC is applied in the conventional receiver (second conventional example), and subscript 3 indicates the case in which the present invention is applied. receivers are shown respectively. FIG. 6 is a block diagram showing an embodiment of a receiver according to the present invention, and FIG. 7 is a main circuit diagram showing a specific example of the present invention. DESCRIPTION OF SYMBOLS 1... Antenna, 2... High frequency tuning circuit, 3... High frequency amplifier circuit, 4... Mixer, 6... Intermediate frequency amplifier circuit, 7... Detector, 10... AGC circuit, 11... Attenuator, 12... First AGC circuit, 13 ...Second AGC circuit.

Claims (1)

[Scope of Claims] 1. A radio control receiver that receives radio waves with pulses as modulated signals, comprising: a high frequency tuning circuit connected to an antenna; and an input/output circuit connected to the output side of the high frequency tuning circuit. an attenuator that includes a capacitor connected between terminals and a diode connected to one end of the diode and the other end of which is grounded in terms of high frequency, and that attenuates a high frequency input signal by applying a voltage to the other end of the diode; a tuning circuit connected to the output side of the tuning circuit, an amplifier circuit that amplifies the signal that has passed through the tuning circuit, a detector that demodulates the amplified output of the amplifier circuit, and a signal that exceeds the saturation level of the amplifier circuit. A radio control receiver comprising: an AGC circuit that attenuates a high frequency input signal by applying a DC voltage to a diode of the attenuator and making the diode conductive according to the level. 2. The radio control according to claim 1, further comprising a frequency conversion section that converts the output of the attenuator into an intermediate frequency, and the amplifier circuit is an intermediate frequency amplification circuit that amplifies the intermediate frequency. receiver.