JP2009212649A - Electronic circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electronic circuit can reduce the occurrence of an interference wave during power off. <P>SOLUTION: In the electronic circuit, when a +B power source is turned off, bias voltage between the gate and the source of a FET becomes zero to turn on the FET. This makes a terminal a2 of a BPF 11 terminated to the ground by an on impedance of the FET, and a reception signal of an ANT 10 is hardly applied to an AMP 12. Consequently, even though an input side of the AMP 12 includes a nonlinear characteristic, the level of an interference wave generated by the nonlinear characteristic is made small, and the interference wave is prevented from affecting one system even though the interference wave is radiated from the ANT 10. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electronic circuit having an active circuit that reduces non-linear distortion caused by the active circuit.

  Conventionally, a film-like FM antenna is installed on a window glass of an automobile, and a reception signal received by the FM antenna is amplified by an amplifier and supplied to an FM receiver. This amplifier is an electronic circuit composed of an active circuit using an active element. By the way, in recent years, the digitization of automobiles has progressed, and various radio waves are used to control various kinds of automobiles. For example, a vehicle often incorporates a keyless entry system. In the vehicle keyless entry system, the door key can be locked and unlocked from the remote control without inserting the key into the cylinder. In the keyless entry system, the door lock control unit is controlled by sending radio waves from a small transmitter installed on the key body or an independent remote controller. In addition to keyless entry systems, wirelessly controlled systems generally use radio waves of a specific frequency.

  In a wirelessly controlled system using radio waves, the control system may not operate normally if there is an interference wave near the frequency used by the system. For example, in a strong electric field area such as directly under Tokyo Tower (FM strong electric field), there is a case where the keyless entry system does not operate normally when the vehicle engine key is turned off. This vehicle is equipped with an FM receiver, and an FM antenna that is a glass antenna and an amplifier that amplifies the received signal of the FM antenna are mounted on the vehicle. When the engine key is turned off, the power supply of the amplifier is also turned off, but the reception signal of the FM antenna is input to the amplifier. Then, frequency components of third-order to fifth-order intermodulation distortion are generated due to the nonlinear characteristics of the active element on the input side of the amplifier. It has been found that this frequency component returns to the FM antenna and is fired, and when the frequency becomes an interference frequency of the keyless entry system of the vehicle, the keyless entry system does not work normally.

  Here, FIG. 11 is a block diagram showing a configuration example of an RF amplifier which is a conventional amplifier mounted on a vehicle and amplifies the FM frequency band. In the RF amplifier 100 shown in FIG. 11, the received signal received by the FM broadcast receiving antenna (ANT) 110 is received by the band pass filter (BPF) 111 in the FM frequency band which is a necessary frequency band of the received signal. A signal is extracted and input to an amplifier (AMP) 112. The FM reception signal amplified by the AMP 112 is removed from a low unnecessary frequency band by a high-pass filter (HPF) 113 and output from an output terminal (OUT) to be supplied to an FM receiver. The AMP 112 is supplied with power from a + B power source.

  FIG. 12 shows the transmission characteristics when the + B power supply of about 13.2 V is turned on in the RF amplifier 100 shown in FIG. In measuring the transmission characteristics, a measurement signal is applied to the input terminal of the BPF 111, and the level of the measurement signal output from OUT is measured. The measurement signal is scanned from 10 MHz to 500 MHz. Referring to FIG. 12, it is amplified to a level of about 5 dB in the FM frequency band of 88 MHz to 108 MHz, and the frequency component level of the frequency 314.4 MHz of the keyless entry system is about −50.5 dB. The level of the frequency component of the frequency 433.9 MHz is about -47.5 dB. FIG. 13 shows transmission characteristics when the RF amplifier 100 is turned off. Referring to FIG. 13, since the power is turned off and is not amplified, the level is reduced to about −11 dB to about −15 dB in the FM frequency band of 88 MHz to 108 MHz, and the frequency component of the frequency component of the keyless entry system is 314.4 MHz. The level is about −46.5 dB, and the level of the frequency component of the frequency of 433.9 MHz of the keyless entry system is increased to about −47.5 dB. As described above, when the power of the RF amplifier 100 is turned off, the level of the frequency component that interferes with the keyless entry system increases. When the power is turned off, no bias is given to the active element of the AMP 112 and the third order. It is also thought that the fifth-order intermodulation distortion component becomes large. As a result, the intensity of the interference wave radiated from the ANT 110 is increased, and the keyless entry system may not operate normally.

  In the conventional RF amplifier, in order to reduce the interference wave radiated from the antenna, it is necessary to cut unnecessary frequency components that cause the interference wave when the power of the RF amplifier is turned off. The impedance of the amplifier differs when the power is on and when the power is off. For this reason, the impedance of the filter is disturbed and hardly functions as a filter, so that there is a problem that unnecessary frequency components cannot be cut when the power is turned off. Also, if a filter is provided inside the amplifier, the impedance changes depending on the length of the power supply line from ANT110 to BPF111, and it is necessary to select the electronic component constant of the filter according to the length of the power supply line. There was a problem of having to.

  Accordingly, an object of the present invention is to provide an electronic circuit that can reduce the generation of interference waves when the power is off.

  In order to achieve the above object, an electronic circuit according to the present invention includes a filter that extracts a signal in a necessary frequency band from a reception signal of an antenna, an active circuit that processes a signal input from the filter, and an active circuit. The main feature is that it comprises switch means that is turned on when the circuit power is turned off and terminates the signal passing through the filter.

  The present invention includes a filter that extracts a signal in a necessary frequency band from a signal received by an antenna, an active circuit that processes a signal input from the filter, and an ON circuit that is turned on when the power of the active circuit is turned off. The switch means for terminating the signal passing through the filter is provided, so that when the power of the active circuit is turned off, the signal applied to the active circuit can be attenuated by the switch means and radiated from the antenna. The interference wave that is generated can be reduced.

FIG. 1 is a circuit diagram showing a configuration of an RF amplifier that is an electronic circuit according to an embodiment of the present invention.
In the RF amplifier 1 shown in FIG. 1, a received signal received by an FM broadcast receiving antenna (ANT) 10 is input to a terminal a1 of a bandpass filter (BPF) 11 in a necessary frequency band. An FM reception signal in a certain FM frequency band is extracted and output from the terminal a3. The output from the terminal a3 is input to an amplifier (AMP) 12 which is an active circuit, and the FM reception signal is amplified with a predetermined gain and output. The amplified FM reception signal from the AMP 12 is supplied to a high-pass filter (HPF) 13 to remove a low frequency band and output from an output terminal (OUT). The FM reception signal output from OUT is supplied to an FM receiver mounted on the vehicle. The AMP 12 is supplied with power from a + B power source.

Further, the RF amplifier 1 according to the present invention includes a switching (SW) circuit 20, in which the terminal a2 of the BPF 11 is an N-channel junction type field effect transistor (FET) via a capacitor C1. Connected to the drain D. This FET operates as a switching element, and the drain D is connected to the + B power supply via the load resistor R1. Further, the gate G of the FET is connected to the ground, and is divided by bias resistors R3 and R4 connected in series between the + B power source and the ground, and this bias voltage is supplied to the source S through the resistor R2. . The source S is connected to a bypass capacitor C2 having one end grounded, and is grounded in an alternating manner.
When the + B power supply is turned on and operating power is supplied to the AMP 12, the FM reception signal is amplified by the AMP 12 with a predetermined gain. In this case, a positive bias voltage is applied to the source S of the FET by the bias resistors R3 and R4, and the gate G of the FET is grounded. Therefore, a reverse bias voltage higher than the pinch-off voltage is applied to the source S of the FET. The FET is off and the FET becomes high impedance and does not affect the operation of the RF amplifier 1.

  Further, when the + B power supply is turned off and the operation power is not supplied to the AMP 12, the AMP 12 does not perform the amplification operation. In this case, the source S of the FET is grounded through a series circuit of the resistor R2 and the bias resistor R4, and the gate G of the FET is grounded, so that the bias voltage between the gate and the source of the FET is zero. The junction type FET is turned on and has a predetermined impedance. Then, the terminal a2 of the BPF 11 is grounded in an alternating manner through a path of the capacitor C1 → the drain-source of the FET → the capacitor C2. That is, the terminal a2 of the BPF 11 is terminated to the ground with the impedance of the FET turned on. As a result, the reception signal received by the ANT 10 is terminated by the SW circuit 20 at the terminal a2 of the BPF 11. Accordingly, since the received signal received by the ANT 10 is hardly output from the terminal a3 of the BPF 11 and is hardly input to the AMP 12, even if the input side of the AMP 12 has a nonlinear characteristic when the + B power supply is turned off, the third order or The level of the interference wave generated by the fifth-order intermodulation distortion becomes extremely small. Also, since the terminal a2 of the BPF 11 is terminated with the impedance of the FET turned on, the impedance of the BPF 11 functions normally without being disturbed. As a result, even if an interference wave is generated due to third-order to fifth-order intermodulation distortion in the AMP 12, the level of the interference wave radiated from the ANT 10 affects a wireless system mounted on a vehicle such as a keyless entry system. There can be no level.

  Next, a detailed circuit example of the BPF 11 is shown in FIG. As shown in FIG. 2, the BPF 11 includes a coil L10, one end of which is a terminal a1, a first series resonance circuit of a capacitor C10, and a second series resonance circuit of a capacitor C11 and a coil L11 connected in series. The output terminal of the second series resonance circuit is a terminal a3. In addition, a parallel resonance circuit including a coil L12 and a capacitor C12 is connected between the connection point of the first series resonance circuit and the second series resonance circuit and the ground, and the connection point of the first series resonance circuit and the second series resonance circuit. Is a terminal a2.

Next, Smith charts showing the input impedance characteristics at the terminal a2 of the BPF 11 in the RF amplifier 1 are shown in FIGS.
The Smith chart shown in FIG. 3 shows the input impedance characteristic of the terminal a2 when the + B power source of the RF amplifier 1 is turned on. Referring to FIG. 3, the real number of impedance at 76 MHz is about 10.98Ω, the imaginary number is about −266.6Ω, the real number of impedance at 88 MHz is about 9.58Ω, and the imaginary number is about −228.6Ω. The real number of impedance at 98 MHz is about 7.09Ω, the imaginary number is about −203.9Ω, the real number of impedance at 108 MHz is about 7.44Ω, and the imaginary number is about −186.4Ω. As described above, when the + B power supply of the RF amplifier 1 is turned on, the FET of the SW circuit 20 is turned off, so that the terminal a2 becomes high impedance in the FM frequency band of 76 MHz to 108 MHz, and the SW circuit 20 is connected to the RF amplifier 1. Even if added, the impedance of the BPF 11 is not disturbed and functions normally.

  The Smith chart shown in FIG. 4 shows the input impedance characteristic of the terminal a2 when the + B power source of the RF amplifier 1 is turned off. Referring to FIG. 4, the real number of impedance at 76 MHz is about 30 Ω, the imaginary number is about 5.21 Ω, the real number of impedance at 88 MHz is about 30.2 Ω, the imaginary number is about 6.17 Ω, and the impedance at 98 MHz The real part is about 30.4Ω, the imaginary part is about 6.78Ω, the real part of the impedance at 108 MHz is about 30.7Ω, and the imaginary part is about 7.49Ω. As described above, when the + B power supply of the RF amplifier 1 is turned off, the FET of the SW circuit 20 is turned on and terminated to the ground with the low impedance of the FET turned on. That is, the signal is terminated to the ground by the SW circuit 20 via the terminal a2 of the BPF 11, and the signal in the FM frequency band of 76 MHz to 108 MHz extracted by the BPF 11 is attenuated.

Next, FIG. 5 shows transmission characteristics when the + B power supply (about 13.2 V) of the RF amplifier 1 shown in FIG. 1 is turned on. In measuring the transmission characteristics, a measurement signal is applied to the input terminal of the BPF 11, and the level of the measurement signal output from OUT is measured. The measurement signal is scanned from 10 MHz to 500 MHz. All transmission characteristics to be described later are also measured in this way.
Referring to FIG. 5, the frequency is amplified to a level of about 5 dB or more in the FM frequency band of 88 MHz to 108 MHz, and the frequency component level of the frequency of 314.4 MHz of the keyless entry system is about −43.1 dB. The level of the frequency component of the frequency of 433.9 MHz is about −53 dB. FIG. 6 shows the transmission characteristics when the + B power source of the RF amplifier 1 is turned off. Referring to FIG. 6, since the power is turned off and the AMP 12 does not operate and the FET of the SW circuit 20 is turned on, the terminal a2 of the BPF 11 is terminated to the ground by the SW circuit 20, and the FM frequency band of 88 MHz to It is greatly reduced to a level of about −24 dB to about −25 dB at 108 MHz, and is attenuated by about 13 dB at the maximum and about 10 dB at the minimum. As a result, when the power of the RF amplifier 1 is turned off, the signal level of the FM frequency band input to the AMP 12 is attenuated, and the level of the interference wave due to the third to fifth intermodulation distortion generated in the AMP 12 is reduced. can do.

  In this case, the level of the frequency component of the frequency 314.4 MHz of the keyless entry system is about −57.1 dB, the level of the frequency component of the frequency 433.9 MHz of the keyless entry system is reduced to about −50.7 dB, and the keyless entry system In the frequency band including this frequency, the maximum frequency is reduced by about 8 dB and the minimum by about 3 dB. Thus, the reception signal received by the ANT 10 is terminated to the ground by the SW circuit 20 at the terminal a2 of the BPF 11, and is hardly output from the terminal a3. As a result, even if the input side of the AMP 12 has a nonlinear characteristic when the + B power supply is turned off, the level of the interference wave caused by the third to fifth intermodulation distortion generated in the AMP 12 becomes extremely small, and the interference wave is generated. Further, the level of the interference wave radiated from the ANT 10 can be a reduced level that does not affect a system mounted on a vehicle such as a keyless entry system.

  Next, for comparison, when the terminal a1 is connected to the drain D of the FET via the capacitor C1 instead of the terminal a2 of the BPF 11, the + B power supply (about 13.2 V) of the RF amplifier 1 is turned on. The transmission characteristics are shown in FIG. Referring to FIG. 7, the frequency is amplified to about 5 dB or more in the FM frequency band of 88 MHz to 108 MHz, and the frequency component level of the frequency 314.4 MHz of the keyless entry system is about -58.6 dB. The level of the frequency component of the frequency of 433.9 MHz is about −54.5 dB. FIG. 8 shows the transmission characteristics when the + B power supply of the RF amplifier 1 is turned off. Referring to FIG. 8, since the power is turned off and the AMP 12 does not operate and the FET of the SW circuit 20 is turned on, the terminal a1 of the BPF 11 is terminated to the ground by the SW circuit 20 and the FM frequency band of 88 MHz to At 108 MHz, the level is reduced to about −16 dB to about −24 dB, and is attenuated by about 5 dB at the maximum and about 2 dB by the minimum. Furthermore, the level of the frequency component of the frequency 314.4 MHz of the keyless entry system is about -62.2 dB, and the level of the frequency component of the frequency 433.9 MHz of the keyless entry system is greatly reduced to about -52.5 dB. The frequency band including the system frequency is reduced by about 20 dB at the maximum and about 9 dB by the minimum.

  Furthermore, when the terminal a3 is connected to the drain D of the FET through the capacitor C1 instead of the terminal a2 of the BPF 11 for comparison, transmission when the + B power supply (about 13.2 V) of the RF amplifier 1 is turned on. The characteristics are shown in FIG. Referring to FIG. 9, it is amplified to a level of about 5 dB in the FM frequency band of 88 MHz to 108 MHz, and the frequency component level of the frequency of 314.4 MHz of the keyless entry system is about −43.6 dB. The level of the frequency component of the frequency 433.9 MHz is about −27.8 dB. FIG. 10 shows the transmission characteristics when the + B power supply of the RF amplifier 1 is turned off. Referring to FIG. 10, since the power is turned off and the AMP 12 does not operate and the FET of the SW circuit 20 is turned on, the terminal a3 of the BPF 11 is terminated to the ground by the SW circuit 20, and the FM frequency band of 88 MHz to At 108 MHz, the level is greatly reduced from about −23.9 dB to about −24.3 dB, and is attenuated by about 12 dB at the maximum and about 9 dB by the minimum. However, the level of the frequency component of the frequency 314.4 MHz of the keyless entry system is about −46.2 dB, and the level of the frequency component of the frequency 433.9 MHz of the keyless entry system is about −44.4 dB. Attenuation.

  As described above, when the terminal a1 of the BPF 11 is terminated to the ground by the SW circuit 20 when the + B power source of the RF amplifier 1 is turned off, the FM frequency band is higher than when the terminal a2 is terminated to the ground by the SW circuit 20. The signal level is increased by about 8 dB at the maximum. Further, when the terminal B3 of the BPF 11 is terminated to the ground by the SW circuit 20 when the + B power source of the RF amplifier 1 is turned off, the frequency component of the keyless entry system is more than the case where the terminal a2 is terminated to the ground by the SW circuit 20. The level becomes larger by about 6 dB or more. From this, when the + B power supply of the RF amplifier 1 is turned off, when the terminal a2 of the BPF 11 is terminated to the ground by the SW circuit 20, the interference wave generated by the third to fifth intermodulation distortion more efficiently. It can be seen that the level of can be reduced.

In the RF amplifier 1 according to the present invention described above, the SW circuit 20 is connected to the terminal a2 of the BPF 11. However, the present invention is not limited to this, and the SW circuit 20 is connected to the terminal a1 of the BPF 11. The terminal a1 may be terminated by the SW circuit 20 when turned off.
The electronic circuit of the present invention is not limited to an RF amplifier, and can be applied to a frequency conversion circuit, a detection circuit, or the like that is an active circuit in the first stage.

It is a circuit diagram which shows the structure of RF amplifier used as the electronic circuit of the Example of this invention. It is a circuit diagram which shows the detailed circuit example of BPF of RF amplifier concerning the Example of this invention. It is a Smith chart which shows the input impedance characteristic in the terminal a2 of BPF of RF amplifier concerning the Example of this invention. It is a Smith chart which shows the other input impedance characteristic in the terminal a2 of BPF of RF amplifier concerning the Example of this invention. It is a figure which shows the transmission characteristic when the power supply is turned on in RF amplifier concerning the Example of this invention. It is a figure which shows the transmission characteristic at the time of turning off a power supply in RF amplifier concerning the Example of this invention. It is a figure which shows the other transmission characteristic at the time of turning on a power supply in RF amplifier concerning the Example of this invention. It is a figure which shows the other transmission characteristic when the power supply is turned off in RF amplifier concerning the Example of this invention. It is a figure which shows the other transmission characteristic at the time of turning on a power supply in RF amplifier concerning the Example of this invention. It is a figure which shows the other transmission characteristic when the power supply is turned off in RF amplifier concerning the Example of this invention. It is a circuit diagram which shows the structure of RF amplifier used as the conventional electronic circuit. It is a figure which shows the transmission characteristic when the power supply is turned on in the conventional RF amplifier. It is a figure which shows the transmission characteristic when the power supply is turned off in the conventional RF amplifier.

Explanation of symbols

1 RF amplifier, 10 ANT, 11 BPF, 12 AMP, 13 HPF, 20 SW circuit, 100 RF amplifier, 110 ANT, 111 BPF, 112 AMP, 113 HPF

Claims (3)

A filter that extracts a signal of a necessary frequency band from the received signal of the antenna;
An active circuit for processing a signal input from the filter;
Switch means for turning on when the power of the active circuit is turned off and terminating the signal passing through the filter;
An electronic circuit characterized in that a signal input to the active circuit is attenuated by the switch means when the power of the active circuit is turned off.   The filter includes two series resonant circuits connected in series and a parallel resonant circuit connected between a connection point of the two series resonant circuits and the ground. 2. The electronic circuit according to claim 1, wherein a connection point of the series resonance circuit of the stage is terminated.   The switch means is composed of a junction type FET, and when the power source of the amplifier is turned on, a reverse bias using the power source is applied between the gate and source of the FET, and the FET is turned off. 2. The electronic circuit according to claim 1, wherein when the power supply of the amplifier is turned off, the gate-source bias of the FET becomes zero and the FET is turned on.

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