JPS6350215A - Radio receiver - Google Patents

Abstract

PURPOSE:To reduce the output distortion by adding an input limiting circuit, which consists of a series circuit of a diode or a transistor TR to which a diode is connected and a resistance, between the input terminal of a high frequency amplifying circuit and the ground. CONSTITUTION:If an input voltage (c) lower than a breakdown voltage (b) is applied to an input terminal 1, the reverse voltage (c) is applied to a diode 6, but the input signal is amplified by a high frequency amplifying circuit 2 as it is because the voltage (c) is lower than the breakdown voltage, (b). If an input voltage (d) higher than the breakdown voltage (b) is applied to the input terminal 1, the voltage exceeding the breakdown voltage (b) is applied to the diode 6. A divided path passing the input terminal, the diode 6, a resistance 7, and the ground is formed besides the path passing the input terminal 1 and the high frequency amplifying circuit 2. Consequently, the signal level inputted to the high frequency amplifying circuit 2 is changed by a ratio of the input impedance of the high frequency amplifying circuit 2 to the value of the resistance 7 to limit the input signal to the high frequency amplifying circuit 2.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a radio receiver capable of receiving FM radio broadcast signals or MU radio broadcast signals.

Conventional technology In recent years, the sensitivity and other characteristics of radio receivers have improved, but when receiving strong input in areas with strong electric fields, they are subject to cross-modulation and intermodulation, making reception difficult. There is.

An example of a conventional radio receiver will be described below with reference to the drawings.

FIG. 7 shows a block diagram of an input circuit of a conventional radio receiver. In FIG. 7, a signal input from an input terminal 1 is amplified by a high frequency amplifier circuit 2, frequency-converted by a local oscillation signal from a local oscillation circuit 4 and a mixing circuit 3 to become an intermediate frequency signal, and then converted to an intermediate frequency signal by an intermediate frequency amplifier circuit 5. amplified.

Problems to be Solved by the Invention However, in conventional radio receivers, when a strong input signal is input to the input terminal 1, the same input signal is also input to the high frequency amplifier circuit 2 and amplified, but the signal components are Due to its large size, the power supply line of the high frequency amplifier circuit 2 and mixing circuit 3,
There is a problem in that the signal affects the local oscillation circuit 4 through the bias line, the ground line, etc., the local oscillation frequency fluctuates, and the output is distorted when there is a strong input compared to when there is a weak input.

In the present invention, when the powerful input that conventional radio receivers have enters the input terminal, the signal enters a high single-wave amplifier circuit, is amplified, and changes the local oscillation frequency by passing through the power line and ground line. This solves the problem that the output is distorted.

Means for Solving the Problems The radio receiver of the present invention is provided with an input limiting circuit consisting of a diode or a series connection of a diode-connected transistor and a resistor between the input terminal of the high frequency amplifier circuit and the ground. This is a characteristic feature.

According to the above-described structure, when a signal voltage higher than the breakdown voltage of the diode or diode-connected transistor is applied to the input terminal, the input signal is connected to the high-frequency amplification circuit and the diode or diode-connected transistor. It is possible to limit signal input to prevent excessive input signals from entering the high frequency amplification circuit by dividing the circuit into two series circuits, ie, a series circuit and a resistor. Therefore, when a strong input is applied to the input terminal, the input signal above a certain level is restricted, the input to the high-frequency amplifier circuit is suppressed, and the fluctuation of the local oscillation frequency is suppressed to reduce output distortion at the time of strong input. This means that you can do it.

Embodiment Hereinafter, a radio receiver according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of a radio receiver having an input limiting circuit according to the present invention. FIG. 2 shows the voltage-current characteristics of the diode. The radio receiver of this example is provided with an input limiting circuit constituted by a series circuit consisting of a diode 6 and a resistor connected to the anode side of the diode 6 between the input terminal 1 and the ground.

In such a configuration, if an input voltage C smaller than the breakdown voltage shown in Fig. 2 is applied to the input terminal 1, a reverse voltage C is applied to the diode 6, but since it is smaller than the breakdown voltage, the input The signal is directly amplified by the high frequency amplification circuit 2. Next, when an input voltage d greater than the breakdown voltage shown in Figure 2 is applied to the input terminal 1, a voltage d75 exceeding the breakdown voltage shown in Figure 2 will be applied to the diode 6, and the conventional signal path will be reversed. In addition to the path from input terminal 1 to high frequency amplifier circuit 2, a divided path from input terminal 1 to diode e to resistor 7 to ground is formed. Therefore, the level of the signal input to the high frequency amplification circuit 2 can be changed by proportionality between the value of the resistor 7 and the input impedance of the high frequency amplification circuit 2, and the input signal to the high frequency amplification circuit 2 can be restricted. In other words,
The resistor A connected in series with the diode 6 prevents the input from being shorted when the input limiting circuit operates, and its resistance value can change the input limited voltage depending on the ratio with the input impedance of the high frequency amplifier circuit 2 and beyond. can.

In the above embodiment, the input limiting circuit was configured to have a diode 6 on the input terminal 1 side and a resistor 7 on the ground side. , the input limiting circuit may be configured to have a diode 6 on the ground side.

Furthermore, the diode 6 constituting the input limiting circuit may be constructed by connecting a plurality of diodes in series, or by using all diodes having different breakdown voltages in the reverse direction. As an example, FIG. 4 shows an input limiting circuit using diodes 8 and 9 connected in the second diagonal row. At this time, assuming that the diode characteristics of each of the diodes 8 and 9 are the same as those of the diode 6, the total voltage-current characteristics of the diodes 8 and 9 will be K as shown in FIG. Therefore, if the circuit is as shown in Figure 4,
The input limiting circuit operates when the input voltage reaches b' of 5 or more. That is, as shown in FIG. 1 or 3.

It can be seen that the input limiting circuit does not operate unless a voltage larger than that of the circuit is applied to the input terminal.

Further, as shown in FIG. 6, it can be seen that when a diode with a low voltage withstand voltage in the reverse direction is used, the input limiting circuit operates with a smaller input voltage. Further, it goes without saying that the diode may be a diode-connected transistor.

Effects of the Invention As described above, the radio receiver of the present invention has the advantage of adding an input limiting circuit consisting of a diode or a series circuit of a diode-connected transistor and a resistor, thereby reducing the input to the high frequency amplifier circuit of the radio receiver. This is extremely useful in practice as it can limit output distortion and reduce output distortion.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the radio receiver of the present invention, Fig. 2 is a voltage-current characteristic diagram of a diode used in the radio receiver, and Figs. 3 and 4 are diagrams of the radio receiver of the present invention. Fig. 5 is a voltage-current characteristic diagram of diodes used in the same radio receiver, Fig. 6 is a voltage-current characteristic diagram of diodes with different reverse breakdown voltages, and Fig. 7 is a diagram of the conventional FIG. 2 is a block diagram of a radio receiver. 1...Input terminal, 2...High frequency amplifier circuit, 3...Mixing circuit, 4...Local oscillation circuit, 6...Intermediate Frequency amplification circuit, 6,8.9・
...Diode, 7...Resistor. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 Figure 5 Figure 6 Rotation 7 Figure

Claims (1)

[Claims] A radio receiver characterized in that an input limiting circuit consisting of a diode or a series connection of a diode-connected transistor and a resistor is provided between an input terminal of a high-frequency amplifier circuit and ground.