JPS5950144B2 - AM/FM stereo radio receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AM-FM stereo radio receiver equipped with an FM receiving circuit configured to supply a demodulating carrier signal generated by a phase-locked loop (PLL) circuit to a stereo demodulating circuit.

First, a conventional AM-FM stereo radio receiver will be explained with reference to FIGS. 1 and 2.

In the AM receiving circuit, A received by AM antenna 1 is
After the M radio wave is amplified by a high frequency amplifier 2, it is supplied to a frequency converter 3, where it is converted into a companion frequency by the output signal of a local oscillator 4.

This intermediate frequency signal is amplified by an AM intermediate frequency amplifier 5, and then supplied to an AM detector 6 and detected.
It is supplied to the fixed contact 8 of the changeover switch 7.

On the other hand, in the FM receiving circuit, the FM radio waves received by the FM antenna 9 are amplified by the high frequency amplifier 10 and then supplied to the frequency converter 11, where they are converted into fellow frequency signals by the output signal of the local oscillator 12. converted.

After this intermediate frequency signal is amplified by the FM intermediate frequency multiplier 13, it is supplied to the FM demodulator 14, where it is demodulated.
It is supplied to the fixed contact 15 of the M changeover switch 7.

And the contact of AM, FM changeover switch 7 is AM, FM.
The signal is switched in accordance with the reception selection of the broadcast, and the signal taken out from the movable contact 16 is supplied to the multiplexer circuit 17.

As a result, when receiving an FM stereo signal, the output terminal 18
．． 19, a stereo signal of left signal and right signal is obtained, and F
When receiving an M monaural signal and an AM signal, the same output signal is obtained at the output terminals 18 and 19.

In the AM and FM receiving circuits, the operating voltage for each circuit is supplied only when that circuit is in operation.

FIG. 2 shows the internal configuration of the multiplexer circuit 17 in FIG.
A terminal 20 connected to the movable contact 16 of the changeover switch 7 is connected to a preamplifier 21 .

The signal amplified by the preamplifier 21 is then supplied to a stereo demodulation circuit 40 having a balanced synchronous detection circuit configuration.
k) h pilot signal is phase-locked loop 24
The signal is supplied to a phase comparison circuit 23 and a pilot signal detection circuit 29 .

The phase-locked loop (PLL) circuit 24 includes a phase comparison circuit 23, a low-pass filter 25, a voltage-controlled oscillator 26 as a variable frequency oscillator, a first frequency divider 27, and a second frequency divider 28. .

The voltage controlled oscillator 26 generates a signal with a frequency of 76 kHz, which is divided into 172 by the first frequency divider 27.
Further, the frequency is divided by 172 by the second frequency divider 28 to produce a signal with a frequency of 19 to 7, and the signal is supplied to the phase comparator circuit 24.

Then, the phase comparison circuit 23 compares the phases of the frequency-divided 19kHz frequency signal and the 19kHz pilot signal of the composite stereo signal, and the output corresponding to the phase comparison error is supplied to the low-pass wave transducer 25. After being converted into a direct current, it is supplied to the voltage controlled oscillator 27 as an oscillation frequency control signal.

22 is a stereo/7-naural changeover switch circuit;
The first signal is detected by the control signal from the pilot signal detection circuit 29.
By switching whether or not to supply the output of the 38-channel stereo demodulation subcarrier signal from the frequency divider 27 to the stereo demodulation circuit 40, the stereo demodulation circuit 40 performs stereo reproduction or seven-naural reproduction (FM monaural and AM (in the case of detected signals).

When stereo reproduction is to be performed, a control signal is supplied from the stereo/monaural changeover switch circuit 22 to the stereo display lamp drive circuit 41, and the stereo reproduction is displayed by the lamp.

By the way, in the above-mentioned receiver, the PLL 24 is always in an operating state, so when receiving AM broadcasting, the 76kHz oscillation signal from the voltage controlled oscillator 26 and its harmonics do not affect the AM receiving circuit. and interfere with AM reception.

Therefore, it would be better to stop the oscillation of this oscillator 26, but
If it is simply stopped, noise will be mixed into the detected output of the AM signal, which is the output of the stereo demodulation circuit, due to the sweep noise of the oscillator 26 and the generation of click noise due to the on/off of the operating voltage.

In view of the above, the present invention provides an AM and FM stereo radio receiver of this type, in which the PL when receiving AM broadcasts as described above.
The purpose of the present invention is to propose a system that is free from interference caused by noise caused by the L variable frequency oscillator.

The present invention will be described in detail below, but since the configurations of the AM and FM receiving circuits are the same as those shown in FIG. 1, their explanation will be omitted.
A portion of the multiplexer circuit 17 will be explained with reference to FIG. 3, and portions corresponding to those in FIG. 2 will be given the same reference numerals and redundant explanation will be omitted.

70 is an AM-FM selection switch, 74 is a stereo
movable contacts 71, 75, respectively, with monaural changeover switches;
It has fixed contacts 72, 76, 73, 77, 73.
74 is a free contact.

The movable contacts 71 and 75 of the switches 70 and 74 are respectively connected to the power supply 1B, and the AM side fixed contact 72 of the switch 70 and the monaural side fixed contact 77 of the switch 74 are connected in common and connected to the resistor 70 and the capacitor 80. It is connected to one end of a resistor 79 of a first time constant circuit (integrator circuit) 78, and the other end of the resistor 79 is grounded via a capacitor 80 and connected to the stereo/monaural changeover switch circuit 22. Ru.

Further, the fixed contact 72 on the AM side and the fixed contact 76 on the monaural side are connected to one end of a resistor 82 of a second time constant circuit (integration circuit) composed of a resistor 82 and a capacitor 83. The other end is connected to the base of a transistor 60 as a switching element.

Note that the time constant τ1 of the first time constant circuit 78 is selected to be smaller than the time constant τ2 of the second time constant circuit 81.

The collector of the transistor 60 is connected to the resistors 62 and 64 of the voltage controlled oscillator 26 and the capacitor 6 via a resistor 61.
The emitter of the transistor 62 is connected to the oscillation control terminal 65 connected to the circuit 36 for determining the oscillation frequency consisting of the transistor 62, and the emitter of the transistor 62 is grounded (reference potential point).

Note that the circuit 36 is connected between the terminal 65 and ground.

With this configuration, in the AM/FM stereo radio receiver of the present invention, when receiving an FM stereo broadcast, the FM
The following operations are performed separately when receiving a seven-day normal broadcast and when receiving an AM broadcast.

That is, first, when receiving an FM stereo broadcast, the movable contact 71 of the AM/FM changeover switch 70 is connected to the fixed contact 73, and the movable contact 75 of the stereo/monaural changeover switch 74 is connected to the fixed contact 77.

Since no circuit is connected to these fixed contacts 73 and 77, the DC voltage from the power supply 10B is not supplied to the first time constant circuit 78 and the second time constant circuit 81.

As a result, only the pilot signal from the pilot signal detection circuit 29 is supplied to the stereo/monaural changeover switch circuit 22, so that the 38k signal from the first frequency divider 27 is
The Hz signal is connected to the stereo monaural changeover switch circuit 22.
The signal is supplied to the stereo demodulation circuit 40 via.

As a result, normal stereo reproduction is performed in the stereo demodulation circuit 40, and demodulated left and right signals are supplied to its output terminals 18 and 19.

Next, when receiving FM monaural broadcasting, the movable contact 71 of the AM/FM changeover switch 70 is connected to the fixed contact 73,
Movable contact 75 of stereo/monaural changeover switch 74
is connected to the fixed contact 76.

As a result, the DC voltage from the power supply 10B is passed through the stereo/monaural changeover switch 74 to the first time constant circuit 78.
and is supplied to the second time constant circuit 81.

Then, since the time constant τ of the first time constant circuit 78 is smaller than the time constant τ2 of the second time constant circuit 81, the stereo/monaural changeover switch circuit 22 is first turned off, and then the transistor 60 is turned on. The oscillation control terminal 65 connected to the circuit 36 that determines the oscillation frequency of the voltage controlled oscillator 26 is grounded, the circuit 36 is short-circuited, and the voltage controlled oscillator 26 stops oscillating.

Furthermore, since the FM monaural broadcast is being received, the stereo/monaural changeover switch circuit 22 is turned off, and the output of the first frequency divider 27 is not supplied to the stereo demodulation circuit 40.

Therefore, the FM demodulated signal passes through the stereo demodulation circuit 40 as it is, and a conductive low frequency signal is supplied to the output terminals 18 and 19.

At the same time, no control signal is supplied from the stereo/monaural changeover switch circuit 22 to the stereo display lamp drive circuit 41, and no stereo display is performed here.

Furthermore, when receiving AM broadcasting, the AM/FM changeover switch 70
The movable contact 71 is connected to the fixed contact 72, and the stereo
A movable contact 75 of the monaural changeover switch 74 is connected to a fixed contact 76 .

As a result, the DC voltage from the power supply 10B is supplied to the stereo/monaural changeover switch circuit 22 via the first time constant circuit 78 as a control signal for monaural demodulation, and is also supplied via the second time constant circuit 81 to the stereo/monaural changeover switch circuit 22. transistor 60
0 base.

First of all, the stereo/monaural changeover switch circuit 2
2 is turned off, and then transistor 60 is turned on.

Therefore, since it is an AM broadcast, the pilot signal is not supplied from the pilot detection circuit 29 to the stereo/monaural changeover switch circuit 22, and the stereo demodulation circuit 40
The detection output of the signal passes through as it is, and the output terminal 18.19
A common output signal can be obtained.

As a result, the stereo/monaural changeover switch circuit 2
2, the signal from the first frequency divider 27 is stopped from being sent to the stereo demodulation circuit signal 40, and the control signal from the stereo/monaural changeover switch circuit 22 is also stopped from being sent to the stereo display lamp drive circuit 41. will be stopped.

Subsequently, a terminal 65 to which a circuit 36 for determining the oscillation frequency of the voltage controlled oscillator 26 is connected is connected to a resistor 61 .
The voltage controlled oscillator 26 is grounded through the transistor 60, and the oscillation operation of the voltage controlled oscillator 26 is stopped.

Note that even if the changeover switch 74 is on the stereo side, the switch circuit 22 is turned off by the detection output of the detection circuit 29 when the FM broadcast is monaural.

Thus, when receiving AM broadcasting, the stereo/monaural selector switch 22 is first turned off, so that the stereo demodulation circuit 40 does not generate noise due to sweep noise of the voltage controlled oscillator 36, click noise when turning on and off the power, etc. Also, the indicator lamp is incorrect and does not display stereo.

Further, since the voltage controlled oscillator 26 then stops oscillating, the AM receiving circuit is not disturbed by the 76 kHz oscillation signal and its harmonics.

Further, in FIG. 4, the transistor 60 is not provided, and the midpoint between the resistors 82 and 61 is connected to the anode of a diode 90, and its cathode is grounded.

With this configuration, when the DC voltage from the power supply 10B is supplied to the anode of the diode 90 via the second time constant circuit 81, the diode 90 becomes conductive, so as in FIG. The voltage-controlled oscillator 26 stops oscillating.

Incidentally, the oscillation may be stopped by applying not only zero voltage (ground potential) but also a power supply potential as a reference potential to the oscillation control terminal of the variable frequency oscillator via a switching element.

Thus, according to the AM and FM stereo receiver of the present invention,
With a simple circuit configuration, the oscillation of the variable frequency oscillator can be reliably stopped when receiving AM broadcasting, and the oscillation of the oscillator, for example, 7
There is no possibility that the high frequency of the 6k) lz oscillation signal will mix into the AM receiving circuit and cause reception interference.

Furthermore, at the same time, it is possible to control the stereo display lamp to ensure that it does not turn on, thereby reliably preventing erroneous display on the lamp.

Furthermore, the demodulation subcarrier signal is no longer supplied to the stereo demodulation circuit before the variable frequency oscillator stops oscillating.
Noise caused by sweep noise of the oscillator, click noise due to power on/off, etc. is not mixed into the output signal of the demodulation circuit.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of an example of a conventional AM/FM stereo receiver, Fig. 2 is a system diagram of a part of the circuit, and Fig. 3 is a main part of an embodiment of the AM/FM stereo receiver of the present invention. FIG. 4 is a system diagram of main parts of another embodiment of the AM/FM stereo receiver of the present invention. 24 is a phase-locked loop, 26 is a voltage-controlled oscillator as a variable frequency oscillator, 22 is a stereo/mono/noral changeover switch circuit, 40 is a stereo demodulation circuit, 6
0 and 90 are transistors and diodes as switching elements, 36 is a circuit that determines the oscillation frequency of the voltage-controlled oscillator 26, 70 is an AM-FM selection switch, and 78 and 81 are first and second time constant circuits. be.

Claims (1)

[Claims] I has an AM reception circuit and an FM reception circuit, and the FM reception circuit includes a stereo demodulation circuit and a phase-locked loop that supplies a demodulation subcarrier signal to the stereo demodulation circuit via a stereo/monaural changeover switch circuit. In the AM and FM stereo radio receiver provided,
AM turns on when receiving M broadcasting and turns off when receiving FM broadcasting.
, the power supply is connected to each input side of the first time constant circuit with a time constant of τ1 and the second time constant circuit with a time constant of τ2 (τ2>τ1) via the FM selection switch, and The output side of the time constant circuit is connected to the control terminal of the stereo/monaural changeover switch circuit, the output side of the second time constant circuit is connected to the control terminal of a switching element, and the switching element is connected to the control terminal of the phase-locked loop. It is connected between the oscillation control terminal of the variable frequency oscillator and the reference potential point, and when receiving an AM broadcast, the ON operation of the AM/FM selection switch first turns off the stereo/monaural selection switch circuit, and then the above switching. An AM/FM stereo radio receiver characterized in that the variable frequency oscillator stops oscillating when the element is turned on.