JP3107503B2 - Double superheterodyne AM radio receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double superheterodyne AM receiver, and more particularly to a first frequency converter in which the frequency of an intermediate frequency signal is converted to be higher than the reception frequency.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram of a conventional double superheterodyne AM radio receiver. In a conventional double superheterodyne AM radio receiver, an amplitude modulated wave taken from an antenna 1 is asynchronously amplified by a field effect transistor 2 of a high frequency amplifier circuit, and then input to a low pass filter 3. The output of the low-pass filter 3 is
The signal is added to the first frequency mixer 4 of the first frequency converter together with the oscillation signal of the first local oscillator 5. Then, the signal is converted into a first intermediate frequency signal having a frequency higher than the reception frequency (for example, 10.7 MHz). This first frequency mixer 4
Is input to the first intermediate frequency amplifier 6 and amplified. The first intermediate frequency signal amplified by the first intermediate frequency amplifier 6 is added to the second frequency mixer 7 of the second frequency converter together with the oscillation signal of the second local oscillator 8 and, for example, a second intermediate frequency of 450 KHz. It is converted to a frequency signal. The second intermediate frequency signal of the second frequency mixer 7 is input to the second intermediate frequency amplifier 9 and amplified. And the second
The second intermediate frequency signal amplified by the intermediate frequency amplifier 9 is input to a subsequent detection circuit. Reference numeral 10 denotes a resistor for adjusting the amplification of the field effect transistor 2 and matching impedance, and reference numeral 11 denotes a coil for equalizing the amplification of the field effect transistor 2.

The low-pass filter 3 of this double superheterodyne AM radio receiver has a circuit diagram shown in FIG. 5, and attenuates an amplitude-modulated wave having a frequency higher than the frequency band to be received. Between the input terminal 51 and the output terminal 52, a coil L5 and a coil L6 are connected in series. The capacitor C10 is connected between the connection point of the coil L5 and the coil L6 and the ground, and the input terminal 51
The capacitors C11 and C12 are respectively connected between the output terminal 52 and the ground. The input terminal 51 is connected to the field effect transistor 2 and the output terminal 5
2 is connected to the first frequency mixer. Reference numeral 53 denotes a DC voltage supply terminal, which is connected to a power supply.

[0004] Such a double superheterodyne AM
The radio receiver does not have a tuning circuit in a circuit between the antenna 1 and the first frequency mixer 4. For this reason, if there is an input of an amplitude modulated wave of a desired radio station and an amplitude modulated wave of another radio station in the same band, and the low-pass filter 3 cannot sufficiently remove it, the second frequency mixer mixes the signals. Is done. Therefore, the amplitude modulated wave signal of the desired radio station is obstructed by the amplitude modulated wave signals of other radio stations, and cannot be clearly received. This phenomenon is particularly noticeable in the mid-wave band (520 KHz
-17 KHz), and a double superheterodyne AM radio receiver capable of clearly receiving a desired radio station in the medium wave band has been desired.

[0005]

SUMMARY OF THE INVENTION According to the present invention, the amplitude modulated wave of a desired radio station in the medium wave band is less likely to be disturbed by the amplitude modulated wave of another radio station in the same band, and the present invention is not limited to this. Double superheterodyne A that can receive
It is intended to provide an M radio receiver.

[0006]

SUMMARY OF THE INVENTION A double superheterodyne AM radio receiver according to the present invention comprises a high-frequency amplifier circuit for amplifying an amplitude-modulated wave from an antenna in a non-tuned manner and a first frequency converter for obtaining a first intermediate frequency signal. A switching circuit forming a low-pass filter or a high-frequency tuning circuit is connected between them. The switching circuit includes a coil electrically coupled to the high-frequency amplifier circuit, a first capacitor connected between one end of the coil and the ground, a first transistor connected in parallel to the first capacitor, and another end of the coil. A transformer formed by a series circuit composed of a variable capacitance diode and a second capacitor and a second transistor connected between the power supply and the ground, or one end of a primary-side coil connected to a high-frequency amplifier circuit; Capacitor connected between one end of the side coil and ground, a first transistor connected in parallel with the first capacitor, a variable capacitance diode connected between the other end of the secondary side of the transformer and ground And a second capacitor formed by a second transistor connected between the other end of the primary coil of the transformer and one end of the secondary coil. It is one in which the low-pass filter or a high-frequency tuning circuit is formed by the conductive state of the first and second transistors. The switching circuit is switched to a high-frequency tuning circuit when a medium-wave band amplitude modulated wave is received, and to a low-pass filter when a long-wave band amplitude modulated wave is received.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a double superheterodyne AM radio receiver according to the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram of a double superheterodyne AM radio receiver of the present invention, and FIG. 2 is a circuit diagram of a switching circuit of the double superheterodyne AM radio receiver of the present invention. The same parts as those in FIG. 4 are denoted by the same reference numerals. Amplitude modulated waves from a plurality of broadcasting stations are transmitted to antenna 1
Taken from. The plurality of amplitude-modulated waves introduced from the antenna 1 are amplified by the field-effect transistor 2 of the high-frequency amplifier circuit in a non-tuned manner and input to the switching circuit 13. Then, the output of the switching circuit 13 is added to the first frequency mixer 4 together with the oscillation signal of the first local oscillator 5, and
The signal is converted into a 10.7 MHz first intermediate frequency signal and amplified by the first intermediate frequency amplifier 6.

[0008] The switching circuit 13 of this double superheterodyne AM radio receiver is a circuit as shown in FIG. In the switching circuit 13, the coil L2 is electrically coupled to the coil L1 of the high-frequency amplification circuit connected to the drain of the field effect transistor 2. One end of the coil L2 is grounded via the first capacitor C1. First
The collector of the first transistor Q1 is connected to the side of the capacitor C1 connected to the coil L2. The ground side of the first capacitor C1 is connected to the first transistor Q1.
Are connected. The other end of the coil L2 is connected to the output terminal 21 of the switching circuit 13 via a series circuit composed of capacitors C2 and C3 for blocking DC current. The connection point between the capacitors C2 and C3 is
Are connected to each other via a series circuit including a capacitor C4 and a second transistor Q2 and a variable capacitance diode D1. The variable capacitance diode D1 is connected to a DC voltage supply terminal 22 to the variable capacitance diode D1 via the resistor R1. The second transistor Q2 has a collector connected to the second capacitor C4, an emitter grounded, and a base connected to the resistor R2. A third connection point between the base of the second transistor Q2 and the resistor R2
Of the transistor Q3. The third transistor Q3 has an emitter grounded. In addition,
A bias current flows through the base of the second transistor Q2 via the resistor R2. Then, the base of the first transistor Q1 and the base of the third transistor Q3 are connected to the terminal 23. Note that the first transistor Q
1, second transistor Q2, third transistor Q3
Is an NPN transistor. Further, the capacitor C5 is a stray capacitance when the medium wave band is being received.

The switching circuit 13 has a medium-wave band (520 KH
z to 1710 KHz), the base of the first transistor Q1 and the third
Current is supplied to the base of the transistor Q3. Then, the current supplied to the base of the second transistor Q2 is blocked. Therefore, the switching circuit 13 uses the coil L
2 and a variable capacitance diode D1 are connected in parallel to form a high-frequency tuning circuit. This high-frequency tuning circuit has a reception frequency f
_It is tuned to the amplitude modulation wave of the radio station ₀ , and attenuates the amplitude modulation waves of other radio stations in the medium wave band. Further, by changing the DC voltage applied to terminal 22, by varying the capacitance of the variable capacitance diode D1, it is possible to change the reception frequency f _0.

In the switching circuit 13, the long wave band (15
When receiving an amplitude modulation wave of 0 kHz to 320 kHz, supply of current from the terminal 23 to the base of the first transistor Q1 and the base of the third transistor Q3 is stopped. Then, at the base of the second transistor Q2,
Current is supplied. Therefore, the switching circuit 13 uses the coil L
2 is grounded via a first capacitor C1,
The other end of the coil L2 becomes a low-pass filter grounded by the second capacitor C4 and the variable capacitance diode D1. This low-pass filter passes the amplitude modulation wave with the reception frequency f ₀ best. Then it is provided an attenuation pole at the frequency f ₁ of the same band giving interference. Also,
This reception frequency f ₀ can be changed by changing the DC voltage applied to the terminal 22 to change the capacitance of the variable capacitance diode D1.

Another embodiment of the switching circuit 13 of the double superheterodyne AM radio receiver is a circuit as shown in FIG. The switching circuit 13 has a transformer T connected to the drain of the field-effect transistor 2 of the high-frequency amplifier circuit.
One end of the primary side coil L3 is connected. One end of a secondary coil L4 of the transformer T1 is grounded via a first capacitor C6. First capacitor C6
The collector of the first transistor Q4 is connected to the secondary side connected to the coil L4. Further, the ground side of the first capacitor C6 is connected to the emitter of the first transistor Q4. The other end of the secondary coil L4 is connected to the output terminal 31 of the switching circuit 13 via a series circuit composed of capacitors C7 and C8 for blocking DC current. The connection point between the capacitors C7 and C8 is grounded via the variable capacitance diode D2 and the second capacitor C9, respectively. The variable capacitance diode D2
Is connected to the DC voltage supply terminal 32 via the resistor R3. The collector of the second transistor Q5 is connected to the other end of the primary coil L3.
The emitter of the second transistor Q5 is connected to a connection point between one end of the first transistor 4 and the first capacitor C6. The base of the second transistor Q5 is connected to a terminal 33 via a resistor R4.
Connected to. Further, the connection point between the other end of the primary coil L3 and the collector of the second transistor Q5 is connected to the collector of the third transistor Q6. Further, the connection point between the base of the second transistor Q5 and the resistor R4 is
Of the transistor Q7 is connected. This third
The emitter of the transistor Q6 and the emitter of the fourth transistor Q7 are grounded. Then, the base of the first transistor Q4 and the third transistor Q
6 and the base of the fourth transistor Q7 are connected to the terminal 33 via the switch SW1 and the resistor R5.
Note that the first transistor Q4 and the second transistor Q
5, the third transistor Q6, the fourth transistor Q7
Are NPN transistors. The resistances R4 and R5 are set to the same resistance value.

When receiving the amplitude modulation wave in the medium wave band, the switching circuit 13 turns on the switch SW1 to turn on the base of the first transistor Q4, the base of the third transistor Q6, and the fourth transistor Q7. Current is supplied to the base of the. Then, current to the base of the second transistor Q5 is blocked. Accordingly, the switching circuit 13 forms a high-frequency tuning circuit including the secondary coil L4, the variable capacitance diode D2 connected in parallel with the secondary coil L4, and the second capacitor C9, and the reception frequency f It is tuned to the amplitude modulation wave of radio station ₀ .

When receiving an amplitude-modulated wave in the long-wave band, the switch SW1 is turned off to connect the base of the first transistor Q4, the base of the third transistor Q6, and the base of the fourth transistor Q7. Stop supplying current. As a result, a current is supplied to the second transistor Q5. Therefore, the switching circuit 13 has the primary side coil L
3 and the secondary side coil L4 are connected in series, the connection point is grounded via the first capacitor C6, and the other end of the secondary side coil L4 is connected to the variable capacitance diode D2 and the second coil L4.
A low-pass filter grounded via the capacitor C9 is formed. The switching circuit 13 in which the low-pass filter is formed passes the amplitude modulated wave of the radio station having the reception frequency f ₀ and attenuates the amplitude modulated wave of another radio station in the long wave band that causes interference. Switching circuit 13 of this embodiment
It is to gently attenuate frequencies other than the reception frequency f ₀ is passed through the occupied bandwidth of the radio station receiving frequency f _0, and it is possible to absorb variations of the electronic components constituting the switching circuit 13, FIG. 2 It can be more clearly received than that of the embodiment.

Although the embodiments of the double superheterodyne AM radio receiver of the present invention have been described above, the present invention is not limited to these embodiments. For example, the polarity of each transistor of the switching circuit may be connected so as to be switched to a low-pass filter or a high-frequency tuning circuit.
Further, each transistor may be of a PNP type. Furthermore, the base of the first transistor Q4 and the third
Of the transistor Q6 and the fourth transistor Q7
May be connected to another DC current supply terminal via a resistor.

[0012]

As described above, the double superheterodyne AM radio receiver of the present invention comprises a high-frequency amplifier circuit for amplifying an amplitude-modulated wave from an antenna in a non-tuned manner and a first frequency conversion circuit for obtaining a first intermediate frequency signal. A switching circuit forming a low-pass filter or a high-frequency tuning circuit is connected between the sections. Therefore, it is not disturbed by the amplitude modulated wave of another radio station in the same band.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of a double superheterodyne AM radio receiver of the present invention.

FIG. 2 is a circuit diagram of a switching circuit of the embodiment of the double superheterodyne AM radio receiver of the present invention.

FIG. 3 is a circuit diagram of another switching circuit of the embodiment of the double superheterodyne AM radio receiver of the present invention.

FIG. 4 is a block diagram of a conventional double superheterodyne AM radio receiver.

FIG. 5 is a circuit diagram of a low-pass filter of a conventional double superheterodyne AM radio receiver.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Antenna 2 Field effect transistor 4 1st frequency mixer 5 1st local oscillator 6 1st intermediate frequency amplifier 7 2nd frequency mixer 8 2nd local oscillator 9 2nd intermediate frequency amplifier 13 Switching circuit

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takeshi Kasahara 18th Gomigaya, Oaza, Tsurugashima-shi, Saitama Toko Co., Ltd., Saitama Office Inside the Saitama Works Co., Ltd. (72) Inventor Yukio Suzuki 18th Gomigaya, Tsurugashima-shi, Saitama Prefecture Toko Co., Ltd. Saitama Works (56) References JP-A-3-276924 (JP, A) JP-A Sho 62- 13129 (JP, A) JP-A-52-135609 (JP, A) JP-A-7-2833753 (JP, A) JP-A-7-283693 (JP, A) JP-A-7-297743 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) H04B 1/26 H04B 1/10 H03J 5/24

Claims (4)

(57) [Claims] In a double superheterodyne AM radio receiver in which a frequency of an intermediate frequency signal is converted to be higher than a reception frequency in a first frequency conversion section for obtaining an initial intermediate frequency signal, an amplitude modulated wave from an antenna is converted. A double superheterodyne AM radio receiver, wherein a switching circuit forming a low-pass filter or a high-frequency tuning circuit is connected between a high-frequency amplifier circuit that amplifies in a non-tuned manner and the first frequency conversion unit. 2. A switching circuit comprising: a coil electrically coupled to a high-frequency amplifier circuit; a first capacitor connected between one end of the coil and the ground; and a first capacitor connected in parallel to the first capacitor. A transistor, a series circuit including a second capacitor and a second transistor connected between the other end of the coil and the ground, and a variable capacitance diode;
The double superheterodyne AM radio receiver according to claim 1 , wherein a low-pass filter or a high-frequency tuning circuit is formed by a conduction state of the first and second transistors. 3. The transformer according to claim 1, wherein the switching circuit comprises: a transformer having one end of a primary coil connected to a high-frequency amplifier circuit;
A first capacitor connected between one end of the secondary coil and ground; a first transistor connected in parallel to the first capacitor; a first capacitor connected between the other end of the secondary coil of the transformer and ground. A variable capacitance diode and a second capacitor, and a second transistor connected between the other end of the primary coil and one end of the secondary coil of the transformer. 2. A low-pass filter or a high-frequency tuning circuit is formed by the conduction state of the transistor.
2. A double superheterodyne AM radio receiver according to 1. 4. The switching circuit comprises a high-frequency tuning circuit when a medium-wave band amplitude modulated wave is received, and a low-pass filter when a long-wave band amplitude modulated wave is received. A double superheterodyne AM radio receiver according to any one of claims 1, 2 and 3.