JPH07235885A - Radio reception circuit - Google Patents

Abstract

PURPOSE:To reduce reception disturbance due to electromagnetic induction from a power supply circuit or the like. CONSTITUTION:An antenna tuning circuit is formed by connecting two varactor diodes 11,16 whose characteristic is matched to have the same characteristic in terms of DC and to have the opposite characteristic in terms of AC. Concretely cathodes of the varactor diodes 11,16 are connected to an output terminal of a low pass filter 4 of a PLL circuit used for frequency control in terms of DC, an anode of the varactor diode 11 and a cathode of the varactor diode 16 are connected via a capacitor 15, an anode of the varactor diode 16 connects to ground and an anode of the varactor diode 11 is connected to a high voltage side terminal of a primary coil 18a of an antenna coil 18. Since the two varactor diodes 11, 16 are connected to have the opposite characteristic in terms of AC in this way and voltage fluctuation from a power supply circuit or the like due to electromagnetic induction is cancelled, the reception disturbance is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PLL (Phase Locked Loop) type radio receiving circuit for use in a portable radio, a cassette tape recorder with a radio, or the like, for receiving an amplitude modulation broadcast.

[0002]

2. Description of the Related Art In recent years, portable audio equipment such as a cassette tape recorder with a radio is required to be combined with a compact disk or other new media, and further downsized. An example of the above-described conventional radio receiving circuit will be described below with reference to the drawings.

FIG. 3 shows a conventional PLL type radio receiving circuit for receiving amplitude modulated broadcasting of a single band.
In FIG. 3, reference numeral 1 is a reference oscillation circuit that outputs a reference frequency oscillation signal. Reference numeral 2 is a frequency dividing circuit for dividing the reference frequency oscillation signal. Reference numeral 3 is a phase comparison circuit, 4 is a low-pass filter, and 5 is a high-frequency amplifier circuit. Reference numeral 31 is a frequency divider circuit for dividing the output signal of the high frequency amplifier circuit 5. 6 is a high frequency mixer circuit, 7 is an intermediate frequency amplifier circuit, and 8 is a detection circuit. Reference numeral 9 denotes a coil block for a local oscillation circuit, which includes a primary coil 9c, a secondary coil 9d, and two capacitors 9a and 9b connected to the primary coil 9c. 10,
Reference numeral 11 is a variable capacitance diode. Reference numeral 13 is a resistor, 14 is a capacitor, and 30 is a resistance element. Reference numeral 17 is an adjusting capacitor. Reference numeral 18 denotes an antenna coil, which includes a primary coil 18a and a secondary coil 18b.

Normally, the block Z surrounded by the alternate long and short dash line is composed of one integrated circuit. The local oscillator circuit coil block 9 and the variable capacitance diode 10 form a local oscillator circuit for receiving amplitude modulation broadcast. The signal induced in the secondary coil 9d of the local oscillator circuit coil block 9 is
The phase comparison circuit 3 is inputted via the high frequency amplification circuit 5 and the frequency division circuit 31 and the phase comparison is performed with the reference frequency oscillation signal generated by the reference oscillation circuit 1 and the frequency division circuit 2. Output of variable capacitance diode 10, 1
Frequency lock is applied by adding to 1. The PLL circuit is configured with the above circuit configuration.

The frequency is changed by changing the frequency division ratio of the frequency dividing circuit 31. The frequency set by the frequency dividing circuit 31 is the minimum frequency interval of normal received broadcast or 1 / integer thereof. Normally, in the case of medium-wave broadcasting, the minimum frequency interval is set, so for example, in Japan,
With 9 kHz as the reference frequency, the frequency can be set to an integral multiple. In addition, the low pass filter 4
Is set to a constant such that a frequency sufficiently lower than the reference frequency becomes the cutoff frequency.

The variable capacitance diode 11 constitutes an antenna tuning circuit together with the antenna coil 18 and the adjusting capacitor 17. In a portable radio or a cassette tape recorder with a radio, a so-called ferrite antenna in which a coil is wound around a ferrite core is usually used. A primary side coil 18a and a secondary side coil 18b are wound around the ferrite core, and a secondary side is formed by mutual induction. The resonance voltage of the primary coil 18b induced in the coil 18b is converted into an intermediate frequency by the high frequency mixer circuit 6, and demodulated into a low frequency signal by the intermediate frequency amplifier circuit 7 and the detection circuit 8.

In the case of medium-wave broadcasting in Japan, the intermediate frequency is usually set to 450 kHz, and each constant is set so that the oscillation frequency of the local oscillation circuit is around +450 kHz with respect to the frequency of the antenna tuning circuit within the reception band. Is set. In the circuit configuration of FIG. 3, the oscillation frequency of the local oscillation circuit is exactly + with respect to the frequency of the antenna tuning circuit at three points in the reception band due to the action of the capacitors 9b and 9a.
It becomes 450 kHz. At other points, this frequency relationship shifts, so the reception sensitivity decreases.

Next, FIG. 5 shows a configuration of a conventional example of a PLL type radio receiving circuit for receiving amplitude-modulated broadcasting of a plurality of bands (two bands as an example). In FIG. 5, the local oscillation circuit side commonly uses the variable capacitance diode 10,
The local oscillation circuit coil blocks 9 and 32 are connected to the variable capacitance diode 10 in parallel with the transistor 33 by the band switching signal X, or the series circuit of the local oscillation circuit coil blocks 9 and 32 is changed. Band switching is performed by switching whether or not the capacitor diode 10 is connected in parallel.

On the other hand, on the antenna tuning circuit side, each band constitutes a separate antenna tuning circuit, and the secondary side of the antenna coil 18 has band switching signals X and / X (meaning an inverted signal of X). Based on the transistors 34, 35
The band is switched by switching with. Since the antenna coil 18 has two bands, in addition to the primary side coil 18a and the secondary side coil 18b, another set of the primary side coil 18d and the secondary side coil 18c.
Is wound around a ferrite core, and each coil 18a-
18d is separated. Similarly to the primary coil 18a, the primary coil 18d is also provided with the variable capacitance diode 19 and the adjusting capacitor 20, and the cathode of the variable capacitance diode 19 outputs the output of the low-pass filter 4 via the resistor 13. Connected to the end. The variable-capacitance diode 19 having the same characteristics as the variable-capacitance diodes 10 and 11 is used. Regarding the circuit configuration in each band, the configuration is similar to that of the single band radio receiving circuit shown in FIG.

[0010]

However, in the conventional PLL type radio receiving circuit for receiving the amplitude modulation broadcast as shown in FIG. 3, the local oscillator circuit coil block 9 and the variable capacitance diode 10 are used. A frequency PLL lock is applied on the oscillation circuit side, and a DC voltage determined on the local oscillation circuit side is applied to the variable capacitance diode 11 on the antenna tuning circuit side regardless of the state on the antenna tuning circuit side. Therefore, when the antenna tuning circuit side receives electromagnetic induction due to some disturbance factor, the induced voltage due to the induction is applied to the variable capacitance diode 11 on the antenna tuning circuit side. As a result, the capacitance of the variable capacitance diode 11 changes, and when a broadcast is received, the received signal is amplitude-modulated. At the reception frequency at which the frequency difference between the antenna tuning circuit and the local oscillation circuit is exactly the intermediate frequency, as shown by the solid line A in FIG. 4, ideally, the selectivity characteristic is symmetrical with respect to the reception frequency. The shake due to is almost canceled.

However, at a reception frequency with a tracking deviation, as shown by a broken line B, the selectivity characteristic with respect to the operating point is not symmetrical, so the received signal is amplitude-modulated by the induced voltage, and the induced voltage is changed. It is demodulated as a low frequency signal. If the frequency of this induction is within the audible band, the demodulated signal by this induction will be heard as a hum and will interfere with reception.

50H for equipment with a built-in power transformer
The power supply frequency of z or 60 Hz, and harmonic leakage flux induction due to its distortion are interference factors that enter the audible band. Therefore, the layout inside the device must be determined so that this guidance does not pose a problem. However, this problem of induction has been a hindrance to the market demand for more compact portable audio equipment in recent years.

The radio receiving circuit shown in FIG. 5 has the same problem as the radio receiving circuit shown in FIG. 3, and the antenna tuning circuit has a variable capacitance diode for each band and each variable capacitance diode has a variable capacitance diode. Both of them are affected by induction, and it is necessary to implement the countermeasure for each band, and there is a problem that the countermeasure becomes difficult as the number of bands increases.

An object of the present invention is to provide a P for amplitude modulation broadcast reception which is not affected by reception interference due to electromagnetic induction from a power supply circuit or the like.
The purpose of the invention is to provide an LL radio receiving circuit. Another object of the present invention is to provide a radio receiving circuit capable of easily taking measures against reception interference due to electromagnetic induction from a power supply circuit or the like even in a radio receiving circuit capable of receiving in a plurality of bands.

[0015]

According to a first aspect of the present invention, there is provided a radio receiving circuit in which the cathodes of the first variable capacitance diode and the second variable capacitance diode are frequency-controlled PL.
The output terminal of the low frequency pass filter of the L circuit is connected in a direct current manner, the anode of the first variable capacitance diode and the cathode of the second variable capacitance diode are connected via a capacitor, and the second variable capacitance is connected. The antenna tuning circuit is configured by grounding the anode of the capacitance diode and connecting the anode of the first variable capacitance diode to the high voltage side terminal of the primary coil of the antenna coil.

A radio receiving circuit according to a second aspect of the present invention is the radio receiving circuit according to the first aspect, wherein a plurality of primary side coils of antenna coils that can be tuned to a plurality of bands are connected in series, and the plurality of primary side coils are provided. It is characterized in that the switching means is connected to and the switching means is controlled according to the band switching signal so that the combined inductance value of the primary side coil can be set to the inductance value according to the reception band.

[0017]

According to the structure of claim 1, the first and second
By adjusting the characteristics of the variable-capacitance diodes described above, the capacitance change of the first variable-capacitance diode and the second
The capacitance change of the variable capacitance diode of is just the opposite,
It is possible to eliminate a capacitance change due to electromagnetic induction in the antenna tuning circuit, and it is possible to provide a PLL-type radio receiving circuit for receiving amplitude-modulated broadcasting that does not receive reception interference due to electromagnetic induction from a power supply circuit or the like.

According to the second aspect of the present invention, the composite inductance value of the primary side coil can be set to the inductance value corresponding to the reception band by controlling the switching means according to the band switching signal. Therefore, the number of variable capacitance diodes on the antenna tuning circuit side is 2 regardless of the number of bands, and when receiving in multiple bands, electromagnetic waves from the power supply circuit etc. can be used with circuit components equivalent to or less than the conventional circuit. It is possible to provide a PLL type radio receiving circuit for receiving amplitude-modulated broadcasting that is not affected by induction interference, and even in a radio receiving circuit capable of receiving in multiple bands, reception interference due to electromagnetic induction from a power supply circuit or the like can be prevented. Measures can be taken easily.

[0019]

Embodiments of the present invention will now be described in detail with reference to the drawings. [First Embodiment] FIG. 1 is a block diagram showing a configuration of a PLL type radio receiving circuit for receiving a single band amplitude modulation broadcast according to a first embodiment of the present invention. In FIG. 1, 1
Is a reference oscillation circuit that outputs a reference frequency oscillation signal.
Reference numeral 2 is a frequency dividing circuit for dividing the reference frequency oscillation signal. Three
Is a phase comparison circuit, 4 is a low-pass filter, and 5 is a high-frequency amplifier circuit. Reference numeral 31 is a frequency divider circuit for dividing the output signal of the high frequency amplifier circuit 5. 6 is a high frequency mixer circuit, 7 is an intermediate frequency amplifier circuit, and 8 is a detection circuit. Reference numeral 9 denotes a local oscillator circuit coil block, which includes a primary side coil 9c, a secondary side coil 9d, and two capacitors 9a and 9b connected to the primary side coil 9c. Reference numerals 10, 11, and 16 are variable capacitance diodes having uniform characteristics. 12 and 13 are resistors,
Reference numerals 14 and 15 are capacitors, and 30 is a resistance element. 17
Is an adjusting capacitor. 18 is an antenna coil,
It is composed of a primary coil 18a and a secondary coil 18b.

Usually, the block Z surrounded by the alternate long and short dash line is composed of one integrated circuit. The local oscillator circuit coil block 9 and the variable capacitance diode 10 form a local oscillator circuit for receiving amplitude modulation broadcast. The signal induced in the secondary coil 9d of the local oscillator circuit coil block 9 is
The phase comparison circuit 3 is inputted via the high frequency amplification circuit 5 and the frequency division circuit 31 and the phase comparison is performed with the reference frequency oscillation signal generated by the reference oscillation circuit 1 and the frequency division circuit 2. Output of variable capacitance diode 10, 1
Frequency lock is applied by adding to 1,16. The PLL circuit is configured with the above circuit configuration.

The frequency is changed by changing the frequency division ratio of the frequency dividing circuit 31. The frequency set by the frequency dividing circuit 31 is the minimum frequency interval of normal received broadcast or 1 / integer thereof. Normally, in the case of medium-wave broadcasting, the minimum frequency interval is set, so for example, in Japan,
With 9 kHz as the reference frequency, the frequency can be set to an integral multiple. In addition, the low pass filter 4
Is set to a constant such that a frequency sufficiently lower than the reference frequency becomes the cutoff frequency.

The variable capacitance diodes 11 and 16 together with the antenna coil 18 and the adjusting capacitor 17 constitute an antenna tuning circuit. In a portable radio or a cassette tape recorder with a radio, a so-called ferrite antenna in which a coil is wound around a ferrite core is usually used. A primary side coil 18a and a secondary side coil 18b are wound around the ferrite core, and a secondary side is formed by mutual induction. The resonance voltage of the primary coil 18b induced in the coil 18b is converted into an intermediate frequency by the high frequency mixer circuit 6, and demodulated into a low frequency signal by the intermediate frequency amplifier circuit 7 and the detection circuit 8.

In the case of medium-wave broadcasting in Japan, the intermediate frequency is usually set to 450 kHz, and each constant is set so that the oscillation frequency of the local oscillation circuit is around +450 kHz with respect to the frequency of the antenna tuning circuit within the reception band. Is set. In the circuit configuration of FIG. 1, the oscillation frequency of the local oscillation circuit is exactly + with respect to the frequency of the antenna tuning circuit at three points in the reception band due to the action of the capacitors 9b and 9a.
It becomes 450 kHz. At other points, this frequency relationship shifts, so the reception sensitivity decreases.

The configuration and operation of the radio receiving circuit of this embodiment constructed as above will be described in detail below. First, the cathode of the variable capacitance diode 11 is connected via the resistor 13, and the cathode of the variable capacitance diode 16 is connected via the resistor 12 to the output end of the low frequency pass filter 4 of the PLL circuit for frequency control. , The anode of the variable capacitance diode 11 and the cathode of the variable capacitance diode 16 are connected via the capacitor 15, and the anode of the variable capacitance diode 16 is grounded,
The anode of the variable capacitance diode 11 is connected to the antenna coil 1
An antenna tuning circuit is configured by connecting the primary side coil 18a of 8 and the adjusting capacitor 17 to each other. That is, the variable-capacitance diodes 11 and 16 are connected under the same condition in terms of direct current and in reverse connection in terms of alternating current. Therefore, when the antenna tuning circuit side receives electromagnetic induction due to some disturbance factor, the capacitance change due to the applied voltage fluctuation of the variable capacitance diodes 11 and 16 due to the induced voltage due to the induction has an inverse characteristic, and the characteristics of the variable capacitance diodes 11 and 16 are changed. If they are used, the influences of disturbances will cancel each other out and will not be affected.

The variable-capacitance diode 10 constituting the local oscillation circuit has its anode connected to the primary side of the coil block 9 for the local oscillation circuit and its cathode frequency-controlled via the resistor 13, as in the conventional example. It is connected to the output terminal of the low frequency pass filter 4 of the PLL circuit in a direct current manner, and has a configuration in which the capacitance changes in conjunction with the variable capacitance diodes 11 and 16.

In this embodiment, the variable capacitance value of the variable capacitance diodes 11 and 16 on the antenna tuning circuit side is twice the variable capacitance value of the variable capacitance diode 10 on the local oscillation circuit side. The constants are different from conventional circuits. In addition, an antenna tuning circuit using a ferrite antenna usually has a high Q, so
Needs to be set to a sufficiently high resistance value so as not to affect the antenna tuning circuit. In addition, the capacitor 14,
15 is set so that the impedance is sufficiently low in the receiving frequency band. The resistor 13 and the capacitor 14
The filter circuit is connected to the cathode side of the diode 11, and this cathode side is an AC ground side. Therefore, the resistance 13 does not have to be set as high as the resistance 12.

As described above, according to this embodiment, even when the antenna tuning circuit side receives electromagnetic induction due to some disturbance factor, the variable capacitance diode 1 due to the induction is generated.
The capacitance changes of 1 and 16 cancel each other, and the combined capacitance of the variable capacitance diodes 11 and 16 has no capacitance change.
Not interfere with reception. [Second Embodiment] FIG. 2 is a block diagram showing the configuration of a PLL type radio receiving circuit for receiving a plurality of bands of amplitude modulation broadcast according to a second embodiment of the present invention.

In the multi-band radio receiving circuit as shown in FIG. 5 described above, a circuit configuration which does not receive the reception interference by the electromagnetic induction from the power supply circuit or the like is realized as in the first embodiment (see FIG. 1). In this case, two variable capacitance diodes must be used on the antenna tuning circuit side for each band. And all these variable capacitance diodes are all in order to realize a circuit that is not subject to reception interference due to electromagnetic induction from the power supply circuit etc. which is the object of the present invention, and to obtain good tracking characteristics in each reception band. It is necessary that the characteristics of the varactor diode are matched.

However, even the minimum two-band receiving circuit shown in FIG. 5 requires five variable capacitance diodes having the same characteristics, which is technically and costly. It is difficult to take measures against reception interference due to electromagnetic induction from the system. On the other hand, in the radio receiving circuit of the second embodiment shown in FIG.
By connecting the primary coils 18a and 18d for two bands in series, connecting the secondary coils 18b and 18c in series, and turning on / off the transistor 21 by the band switching signal X, only the primary coil 18a is formed. The case where the antenna tuning circuit is configured, and the primary coil 18
By switching between the case where the antenna tuning circuit is configured with a and 18d connected in series, the configuration of the radio receiving circuit in which the variable capacitance diode 19 is omitted corresponds to two bands, and the case of FIG. Similarly, a variable capacitance diode 16, a capacitor 15 and a resistor 12 are provided.

Therefore, the present invention can be realized only by using the same number of variable capacitance diodes as in the conventional circuit shown in FIG. In FIG. 2, the diode 22 is provided to reduce the adverse effect of the junction capacitance of the transistor 21 entering in parallel with the primary coil 18d and the capacitor 20 when the transistor 21 is off. 23
Is resistance.

Although the circuit configuration for receiving two bands is shown in the embodiment of FIG. 2, a receiving circuit for three or more bands may be configured. Even in this case, the present invention can be realized with three variable capacitance diodes, and even if the number of bands increases,
The number of required varactor diodes does not increase. Further, although the secondary coils 18b and 18c of the antenna coil 18 are connected in series in the same manner as the primary coils 18a and 18d in the embodiment, the configuration is not limited to this embodiment.

A circuit for improving spurious characteristics and image rejection characteristics may be added if necessary.

[0033]

According to the radio receiving circuit of the first aspect, the two first and second variable capacitance diodes having the same characteristics have the same DC condition and opposite AC characteristics. By configuring the antenna tuning circuit by connecting them in the same manner, the capacitance change of the first variable capacitance diode and the capacitance change of the second variable capacitance diode due to electromagnetic induction are just opposite, and the capacitance change due to electromagnetic induction in the antenna tuning circuit Can be eliminated, and reception interference due to electromagnetic induction from the power supply circuit or the like can be prevented.

According to the radio receiving circuit of claim 2,
By controlling the switching means according to the band switching signal, the combined inductance value of the primary coil can be set to the inductance value according to the reception band, so that the variable capacitance diode on the antenna tuning circuit side is independent of the number of bands. Therefore, when receiving in multiple bands, it is possible to prevent reception interference due to electromagnetic induction from the power supply circuit, etc. with multiple circuit components equivalent to or less than the conventional circuit when receiving in multiple bands. Even in a possible radio receiving circuit, it is possible to easily take measures against reception interference due to electromagnetic induction from a power supply circuit or the like.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a radio receiving circuit according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a radio receiving circuit according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of an example of a conventional radio receiving circuit.

FIG. 4 is a characteristic diagram showing an example of high frequency selection characteristics in a conventional radio receiving circuit.

FIG. 5 is a block diagram showing the configuration of another example of a conventional radio receiving circuit.

[Explanation of symbols]

 1 Reference Oscillation Circuit 2 Frequency Division Circuit 3 Phase Comparison Circuit 4 Low Pass Filter 5 High Frequency Amplifier Circuit 6 High Frequency Mixer Circuit 7 Intermediate Frequency Amplifier Circuit 8 Detection Circuit 9,32 Local Oscillation Circuit Coil Block 10, 11, 16 Variable Capacitance Diode 12, 13 Resistance 14, 15 Capacitor 17, 20 Adjustment capacitor 18 Antenna coil

Claims (2)

[Claims] 1. A cathode of a first variable capacitance diode and a cathode of a second variable capacitance diode are connected in direct current to an output terminal of a low frequency pass filter of a PLL circuit for frequency control, and the first variable capacitance diode is connected. Is connected to the cathode of the second variable capacitance diode via a capacitor, the anode of the second variable capacitance diode is grounded, and the anode of the first variable capacitance diode is the primary coil of the antenna coil. Radio receiving circuit characterized in that an antenna tuning circuit is configured by connecting to the high-voltage side terminal of. 2. A plurality of primary side coils of an antenna coil that can be tuned to a plurality of bands are connected in series, switching means is connected to the plurality of primary side coils, and the switching means is controlled according to a band switching signal. The radio receiving circuit according to claim 1, wherein the composite inductance value of the primary side coil can be set to an inductance value according to a reception band by performing the above.