JP2975821B2 - AM / FM 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 an AM / FM radio receiver having a double conversion type AM receiving circuit.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional AM / FM radio receiver. (1) shows an FMRF tuning circuit (2), an FMRF amplifier circuit (3), an FM mixer (4), and an FMIF amplifier circuit (5). ), An FM receiving circuit comprising an FM detecting circuit (6) and an FM local oscillator circuit (7), (8) is an AMRF tuning circuit (9), an AMRF amplifying circuit (10), an AM first mixer (11), AM first IF amplifier circuit (12), AM second mixer (13), AM second IF amplifier circuit (14), AM detector circuit (15), AM local oscillator circuit (16), and first oscillator circuit (17) AM receiver circuit, (19) is a low frequency amplifier circuit, (21) is a PLL frequency synthesizer circuit,
(23) is a second oscillation circuit, (24) is an AM reference divider, (25) is an FM reference divider,
(26) and (27) are switching circuits, (28) and (2)
9) is an amplifier, (30) is a programmable divider,
(31) is a phase comparator, (32) is an AMLPF (low-pass filter), (33) is an FMLPF, and (34) is a control circuit.

Next, the operation of the block diagram shown in FIG. 2 will be described.
At the time of FM reception, the switching circuit (26) outputs the output of the FM reference divider (25) and the switching circuit (27) outputs the amplifier (2) according to a control signal generated from the control circuit (34).
The output of 9) is selected, and the PLL frequency synthesizer circuit operates for FM. Further, at the time of AM reception, the switching circuits (26) and (27) respectively operate the AM reference divider (2) according to the control signal of the control circuit (34).
4) and the output of the amplifier (28) are selected, and the PLL frequency synthesizer operates for AM. An AM reception RF signal received via an antenna (not shown), an AMRF tuning circuit (9), and an AMRF amplification circuit (10)
The first mixer (11) converts the signal into an AM first IF signal. The AM first IF signal is amplified by an IF amplifier (12) and then amplified by an AM second mixer (13).
A signal generated from the M crystal oscillation circuit (17)
It is converted to a second IF signal. Further, the AM second IF
The signal is amplified by an IF amplifier (14), detected by an AM detector (15), and applied to a low-frequency amplifier (19).

[0004]

However, in the circuit shown in FIG. 2, since the oscillation circuit is connected to the PLL frequency synthesizer circuit (21) and the AM second mixer (13), the number of parts is reduced. This has increased the cost of the radio receiver. The oscillation circuit (17)
Is applied to the AM second mixer (13) in both the AM reception and the FM reception. Therefore, the output signal of the oscillation circuit (17) and the AM second mixer (13) is received in the FM reception. Unwanted radiation generated from the wiring between the FM receiver circuit (8)
Had the problem of interfering with the

Further, since the channel step differs depending on the destination, if the multiplication is performed in such a manner that the reference signal of the reference divider corresponds to the channel step, the frequency division ratio must be changed according to the destination. .

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has a first mixer, a first local oscillator for applying a local oscillation signal to the first mixer, and a second mixer. Double conversion type AM receiving circuit having mixer
In an AM / FM receiver provided with an FM receiving circuit having a mixer and a third local oscillator corresponding to the third mixer, a reference oscillation circuit and an output signal of the reference oscillation circuit are divided to generate a plurality of outputs. And a first control signal for comparing the phase of the output signal of the first or third local oscillation circuit with one of the output signals of the frequency division circuit and controlling the frequency of the corresponding local oscillation signal And a gate means for passing the output signal of the reference oscillation circuit only during AM reception.

The frequency dividing circuit is configured to generate four output signals, and one of the four output signals is selected according to a reference oscillation frequency of the reference oscillation circuit and a selected reception band. It is characterized by being performed. Further, the control circuit includes a control circuit, and the control circuit generates a second control signal for controlling the gate unit and a third control signal for selecting an output signal of the frequency dividing circuit.

[0008]

According to the present invention, the output signal of the reference oscillation circuit is divided by the divider circuit, and then one of the plurality of output signals of the divider circuit is combined with the first or third local signal by the phase comparator. A phase is compared with an output signal of the oscillation circuit, and a first control signal is generated according to the comparison difference. The first control signal is applied to a first or third local oscillation circuit that generates a signal applied to the phase comparator, and controls the frequency of a corresponding local oscillation signal. The gate means at the time of AM reception passes the output signal of the reference oscillation circuit to apply it to the second mixer, and the gate means at the time of FM reception shuts off the output signal.

[0009]

FIG. 1 shows an embodiment of the present invention.
(35) is an AND gate constituting a gate means for blocking an output signal of the oscillation circuit (23), (36) is a first AM reference divider, (37) is a second AM reference divider, and (38) is a first and second AM. A switching circuit for switching the output signals of the reference dividers (36) and (37); (39), a first FM reference divider; (40), a second FM reference divider;
1) is the first and second FM reference dividers (3)
This is a switching circuit for switching the output signals of 9) and (40). In the circuit of FIG. 2, the same circuits as those of the conventional circuit of FIG. 1 are denoted by the same reference numerals.

Referring to FIG. 1, when the frequency of the output signal of the oscillation circuit (23) is set to 10.35 MHz, the switching circuits (38) and (41) respectively operate according to the control signal of the control circuit (34). 1AM reference divider (36) and first FM reference divider (39)
Switch to the output signal. When receiving AM, the control circuit (3
The switching circuit (26) switches to the output signal of the first AM reference divider (36) according to the control signal of 4),
The switching circuit (27) switches to the output signal of the amplifier (28), and the AND gate (35) allows the output signal of the oscillation circuit (23) to pass and converts the oscillation signal of 10.35 MHz to A.
M is applied to the second mixer (13).

[0011] The AM signal is received by an AMRF tuning circuit (9) via an antenna. The AMRF signal generated by being selectively tuned in the AMRF tuning circuit (9) is amplified by the AMRF amplifying circuit (10), and is amplified in the AM first mixer (11) by the local oscillation signal of the AM local oscillation circuit (11).
It is converted to an 8 MHz AM first IF signal. Furthermore, A
Amplified by the M first IF amplifier circuit (12)
The signal is converted to a 450 KHz A by the output signal of the 10.35 MHz oscillation circuit (35) in the AM second mixer (13).
It is converted into an M second IF signal. The AM second IF signal is A
The signal is amplified by the M second IF amplifier circuit (14), detected by the AM detector circuit (15), and applied to the low frequency amplifier (19).

On the other hand, the output signal of the AM local oscillation circuit (16) is supplied to the programmable divider (3) via the amplifier (28).
0) and is divided. The output signal of the programmable divider (30) is output to the first AM reference divider (36) in the phase comparison circuit (31).
The phase is compared with a 9 KHz reference signal generated by dividing the frequency of the 35 MHz oscillation signal. The output signal of the phase comparison circuit (31) is applied to the AM local oscillation circuit (16) after being smoothed by the LPF (32). The AM local oscillator circuit (16) changes the frequency of the local oscillator signal based on the smoothed signal.

During FM reception, the switching circuits (26) and (27) select the output signal of the first FM reference divider (39) and the output signal of the amplifier (29), respectively. Then, the AND gate (35) cuts off the oscillation signal applied to the AM second mixer (13) according to the control signal generated from the control circuit (34). The FM signal is applied to an FMRF tuning circuit (2) via an antenna and is selectively tuned. The FM reception RF signal generated from the FMRF tuning circuit (2) is applied to the FM mixer (4) via the FMRF amplification circuit (3). In the FM mixer (4), the FM reception RF signal has a center frequency of 10.
It is converted to a 7 MHz FMIF signal. Furthermore, FMI
Amplified by the F amplifier circuit (5), the FMIF signal is
Detected by the detection circuit (6), the low-frequency amplifier (1
9) is applied.

The output signal of the FM local oscillation circuit (7) is supplied to the programmable divider (3) via the amplifier (29).
0). Programmable divider (30)
Are output from the phase comparison circuit (31) in the phase comparison circuit (31).
By dividing the frequency of the 35 MHz reference signal, the first F
The phase is compared with a 50 KHz reference signal generated from the M reference divider. The output signal of the phase comparison circuit (31) is sent to the FM local oscillation circuit (7) via the FMLPF (33).
And the frequency of the FM local oscillator signal of the FM local oscillator circuit (7) is changed.

The frequency of the output signal of the oscillation circuit (23) is 1
When the frequency is set to 0.25 MHz, the switching circuits (38) and (41) respond to the control signal of the control circuit (34) so that the second AM reference divider (37) and the second AM reference divider (37) respectively.
The signal is switched to the output signal of the FM reference divider (40). At the time of AM reception, the switching circuit (26) switches to the output signal of the second AM reference divider (37) according to the control signal of the control circuit (34), the switching circuit (27) switches to the output signal of the amplifier (28), The AND gate (35) allows the output signal of the oscillation circuit (23) to pass therethrough and converts the 10.25 MHz oscillation signal to the AM second mixer (1).
Apply to 3).

The AM signal is received by an AMRF tuning circuit (9) via an antenna. The AMRF signal generated by being selectively tuned in the AMRF tuning circuit (9) is amplified by the AMRF amplifying circuit (10), and is amplified in the AM first mixer (11) by the local oscillation signal of the AM local oscillation circuit (11).
It is converted to a 7 MHz AM first IF signal. Furthermore, A
Amplified by the M first IF amplifier circuit (12)
The signal is converted to a 450 kHz A by the output signal of the 10.25 MHz oscillation circuit (35) in the AM second mixer (13).
It is converted into an M second IF signal. The AM second IF signal is A
The signal is amplified by the M second IF amplifier circuit (14), detected by the AM detector circuit (15), and applied to the low frequency amplifier (19).

On the other hand, the output signal of the AM local oscillator circuit (16) is supplied via an amplifier (28) to the programmable divider (3).
0) and is divided. The output signal of the programmable divider (30) is output to the second AM reference divider (37) in the phase comparator circuit (31).
The phase is compared with the 10 KHz reference signal generated by dividing the frequency of the 25 MHz oscillation signal. The output signal of the phase comparison circuit (31) is applied to the AM local oscillation circuit (16) after being smoothed by the LPF (32). The AM local oscillator circuit (16) changes the frequency of the local oscillator signal based on the smoothed signal.

The FM reception switching circuits (26) and (27) select the output signal of the second FM reference divider (40) and the output signal of the amplifier (29), respectively. Then, the AND gate (35) cuts off the oscillation signal applied to the AM second mixer (13) according to the control signal generated from the control circuit (34). The FM signal is applied to an FMRF tuning circuit (2) via an antenna and is selectively tuned. The FM reception RF signal generated from the FMRF tuning circuit (2) is applied to the FM mixer (4) via the FMRF amplification circuit (3). In the FM mixer (4), the FM reception RF signal has a center frequency of 10.
It is converted to a 7 MHz FMIF signal. Furthermore, FMI
Amplified by the F amplifier circuit (5), the FMIF signal is
In the detection circuit (6), the signal is detected and the low-frequency amplifier (1) is detected.
9) is applied.

The output signal of the FM local oscillation circuit (7) is supplied to the programmable divider (3) via the amplifier (29).
0). Programmable divider (30)
Are output from the phase comparison circuit (31) in the phase comparison circuit (31).
By dividing the 25 MHz reference signal, the second F
50K generated from the M reference divider (40)
The phase is compared with the reference signal of Hz. Phase comparison circuit (3
The output signal of 1) is applied to the FM local oscillator circuit (7) via the FMLPF (33), and the frequency of the FM local oscillator signal of the FM local oscillator circuit (7) is changed.

Here, the local oscillation signal of the PLL frequency synthesizer circuit (21) corresponds to the channel step of 9 kHz in the AM band and the channel step of 50 kHz in the FM band, and the output signal of the oscillation circuit (23) 450 in the applied AM second mixer (13)
Considering the generation of the AM second IF signal of KHz, the frequency of the output signal of the oscillation circuit (23) is 10.3.
5 MHz. Further, the local oscillation signal is one of the AM bands.
0KHz channel step and FM band 50KH
Considering that the AM second mixer (13) generates an AM second IF signal of 450 KHz as described above corresponding to the channel step of z, the frequency of the output signal of the oscillation circuit (23) becomes 10.25 MHz. Become.

[0021]

According to the present invention, the output signal of the oscillation circuit of the PLL frequency synthesizer is applied to the second AM mixer in the AM receiver circuit of the double conversion type, and the output signal generates the second AM mixer. Therefore, the number of oscillation circuits can be reduced, and the cost of the radio receiver can be reduced.

Further, by blocking the output signal of the oscillation circuit at the time of FM reception by the gate means, it is possible to reduce disturbance to the FM reception circuit due to unnecessary radiation. Furthermore, since the PLL frequency synthesizer circuit has four reference dividers, it is possible to realize a multi-modulated AM / FM radio receiver that can correspond to destinations with different channel steps only by switching the reference dividers.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a block diagram showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 FM receiving circuit 2 AM receiving circuit 21 PLL frequency synthesizer circuit 31 Phase comparison circuit 34 Control circuit 35 AND gate 36 1st AM reference divider 37 2nd AM reference divider 39 1st FM reference divider 40 2nd FM reference divider

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-58-177036 (JP, A) JP-A-3-198435 (JP, A) JP-A-63-37720 (JP, A) 104252 (JP, U) Japanese Utility Model Showa 56-87747 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04B 1/16-1/28 H03L 7/00, 7/26

Claims (3)

(57) [Claims] 1. A double conversion type AM receiving circuit and a third mixer having a first mixer, a first local oscillator for applying a local oscillation signal to the first mixer, and a second mixer, An AM / FM radio receiver comprising: an FM receiving circuit having a third local oscillator corresponding to the third mixer; a reference oscillation circuit; and dividing an output signal of the reference oscillation circuit to generate a plurality of outputs. A phase control circuit that compares a phase of a local signal of the first or third local oscillator with one of output signals of the frequency divider to generate a first control signal for controlling a frequency of a corresponding local signal. And a gate means for passing the output signal of the reference oscillation circuit only at the time of AM reception, and outputting the output of the gate means to the second
AM applied as a local signal to a mixer
/ FM radio receiver. 2. The frequency divider circuit is configured to generate four output signals, and one of the four output signals is selected according to a reference oscillation frequency of the reference oscillation circuit and a selected reception band. A according to claim 1, wherein
M / FM radio receiver. 3. A control circuit, wherein the control circuit generates a second control signal for controlling the gate means and a third control signal for selecting an output signal of the frequency dividing circuit. The AM / FM radio receiver according to claim 2.