JPS6219012Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to an FM stereo to AM stereo receiver, in which a single switch can be used to switch between stereo and monaural in the FM band and between stereo and monaural in the AM band. I made it
FM Stereo-AM Stereo Receiver.

An embodiment of the present invention used in an FM stereo-AM stereo receiver capable of receiving FM stereo broadcasts and AM stereo broadcasts (for example, Magnabox AM stereo broadcasts) will be described below with reference to FIG.

1 is an FM antenna, 2 is an FM front end section that includes an FM high frequency amplification circuit and a frequency conversion circuit, 3 is an AM front end section that includes an AM antenna circuit and a frequency conversion circuit, and 4 is an FM-AM
Common intermediate frequency amplifier circuit, 5 is FM detection circuit, 6 is
Main signal L+R of AM stereo broadcast signal
or an envelope detection (AM detection) circuit for detecting an AM monaural signal; 7 is an FM stereo demodulation circuit; It consists of The pin of IC8 is a forced monaural terminal, and when a voltage is applied to the forced monaural terminal, the PLL circuit (not shown) inside IC8
The operation of the voltage-controlled oscillator that makes up the signal stops, and the signal is forced into monaural reception mode.

Reference numeral 11 denotes an AM stereo demodulation circuit section, and the AM stereo demodulation circuit section includes a block 12 for AM stereo demodulation processing, which includes a limiter circuit and a phase detection circuit for detecting sub-signals LR of the AM stereo broadcast signal. It consists of IC13 (LA 1900) and others. The IC13 for AM stereo demodulation processing includes:
A matrix circuit 14, a PLL (phase locked loop) circuit 15 constituting a stereo identification signal (ID signal) processing circuit, a display trigger circuit 16, and the like are built-in. The pin of the IC 13 is a forced monaural terminal, and when a voltage is applied to the forced monaural terminal, the voltage controlled oscillator VCO in the PLL circuit 15 is stopped, and the setting is made so that a monaural reception state is forced.

S is a one-circuit stereo/monaural changeover switch shared by the FM band and AM band, which connects the common terminal COM to the +B power supply path 17, and makes the fixed terminal STEREO on the stereo side an idle terminal. And monaural side fixed terminal MONO
is connected to the forced monaural terminal pin of IC 8 for FM stereo demodulation via diode D ₁ and resistor R ₁ , and to the forced monaural terminal pin of IC 13 for AM stereo demodulation processing via diode D ₂ and resistor R ₂ . are doing. 18 is resistance R ₃ , R ₄
and a first light emitting diode LED ₁ .
A stereo display device for FM stereo display; 19 is a stereo display device for AM stereo display, which is composed of resistors R ₅ and R ₆ and a second light emitting diode LED ₂ ;
SW ₁ , SW ₂ , SW ₃ , and SW ₄ are band changeover switches.

The operation of the circuit configured in this manner will be explained next.

(A) When band selection switches SW ₁ to _{SW 4} are set to the AM side.

(i) When the stereo/monaural selector switch S is set to the monaural side (as shown)
Since the +B voltage is applied to the pin of the AM stereo demodulation processing IC 13 via the power supply path 17 → stereo/monaural changeover switch S → diode D ₂ → resistor R ₂ , the voltage of IC 13 is
The operation of the VCO constituting the PLL circuit 15 is stopped. Therefore, even if an AM stereo broadcast signal is received at this time, the stereo identification signal (ID signal) is not demodulated and the output from the pin of IC13 becomes high level, so the phase detection circuit 12
The detected sub-signal L-R is muted to force a monaural reception state, and the second light emitting diode LED ₂ for AM stereo display also does not emit light.

(ii) When the stereo/monaural changeover switch S is set to the stereo side, the power supply path 17 and the pin of IC13 are opened by the stereo/monaural changeover switch S, so that +B voltage is applied to the pin of IC13. Not done. Therefore, the PLL circuit 15 in the IC 13
Since the VCO operates, when an AM stereo broadcast signal is received, the ID signal is demodulated in the PLL circuit 15, and the display trigger circuit 16 operates.
The output of the pin of IC13 becomes low level. Therefore, the sub-signal L-R detected by the phase detection circuit 12 is input to the matrix circuit 14 without being muted, and the main signal L+R and the sub-signal L-R are matrixed in the matrix circuit 14, and the left channel signal is The L signal and the right channel signal R are separated and output to the output terminal pins of the IC 13. At this time, the second light emitting diode LED ₂ emits light to indicate that AM stereo broadcasting is being received. Also, at this time, the +B voltage is not applied to the pin of the FM stereo demodulation IC8, so the FM side is also in stereo reception mode, but the band selection switch _SW1 ,
Due to SW ₂ , the FM broadcast signal is not input to the FM stereo demodulation IC 8, so there is no influence.

(B) When band selection switches SW ₁ to _{SW 4} are set to the FM side.

(i) When the stereo/monaural changeover switch S is set to the monaural side, the power supply path 17→stereo/monaural changeover switch S
→ Diode D ₁ → Resistor R ₁ Since the +B voltage is applied to the pin of IC8 for FM stereo demodulation, the VCO that constitutes the PLL circuit of IC8
operation stops and is forcibly set to monaural reception mode. At this time, the output from the pin of IC8 becomes high level, so the first light emitting diode _LED1 for stereo display does not emit light.

(ii) When the stereo/monaural changeover switch S is set to the stereo side, the power supply line 17 and the pin of IC8 are opened by the stereo/monaural changeover switch S, so the +B voltage is applied to the pin of IC8. Not done. Therefore, since the VCO of the PLL circuit in IC8 operates, when an FM stereo broadcast signal is received, this signal is stereo demodulated into left channel signal L and right channel signal R in IC8. And at this time, the FM stereo demodulation IC
The stereo pilot signal is demodulated at 8.
Since the output of the pin of IC8 is low level, the first light emitting diode for stereo display
LED ₁ will light up to indicate that FM stereo broadcasting is being received. Also, at this time, the +B voltage is not applied to the pin of the AM stereo demodulation processing IC 13, so the AM side is also in stereo reception mode, but the AM broadcast signal is switched to AM by the band selection switches SW ₁ and SW ₂ .
Since it is not input to the stereo demodulation processing IC 13, there is no influence.

Note that the diodes D ₁ and D ₂ are diodes for preventing backflow, so they may be unnecessary depending on the circuit. Further, the resistors R ₁ and R ₂ are used to adjust the voltages applied to the pins of IC8 and IC13, respectively, and may be unnecessary if the +B voltage is low.

Furthermore, in the embodiment of FIG.
Although an example has been described in which a switch with one circuit and two contacts is used as a monaural changeover switch, the present invention is not limited to this embodiment. For example, as shown in _{FIG .} In that case, the stereo/monaural switching switches S ₁ and S ₂ connect each common terminal COM to the power supply path 17, and connect the fixed terminal on the monaural side to the power supply path 17.
MONO is connected to each IC8 and 1 through resistors R ₁ and R ₂ respectively.
All you have to do is connect it to the forced monaural terminal pins and pins of 3, and make each stereo side fixed terminal STEREO an idle terminal.

As described above, in the FM stereo-AM stereo receiver according to the present invention, a single switch is used to switch between stereo and monaural in the FM band and to switch between stereo and monaural in the AM band. , the number of parts can be reduced, and costs can be reduced. Furthermore, the number of wirings is reduced, and the number of assembly steps can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram showing an FM stereo-AM stereo receiver according to the present invention, and FIG. 2 is a circuit diagram of main parts showing another embodiment of the present invention. 7...FM stereo demodulation circuit section, 11...AM
Stereo demodulation circuit section, 15...PLL circuit, S,
S ₁ , S ₂ ... Stereo/monaural changeover switch.

Claims (1)

[Scope of utility model registration request] An FM stereo-AM stereo receiver in which an FM stereo demodulation circuit section and an AM stereo demodulation circuit section are each provided with a voltage controlled oscillator constituting a PLL circuit, wherein the control terminal of the voltage controlled oscillator of the FM stereo demodulation circuit section is provided. and connecting the control terminal of the voltage controlled oscillator of the AM stereo demodulation circuit section to the monaural side terminal of one stereo/monaural changeover switch whose common terminal is connected to the control voltage supply path,
An FM stereo-AM stereo receiver characterized in that the stereo/monaural changeover switch serves both for switching between stereo and monaural in the FM band and between stereo and monaural in the AM band.