JPS6216044Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a receiver for receiving stereo broadcasts, which uses an inexpensive circuit configuration to improve the actual hearing sensation when receiving weak stereo broadcasts.

Generally, in FM stereo broadcasting, a main signal consisting of the sum of the left and right channel components of the stereo signal and a sub signal consisting of the difference between the left and right channel components are transmitted using the sum-difference method, and the receiver receives the FM stereo broadcast. The automatic frequency control circuit (AFC)
A stereo multiplex demodulation circuit that demodulates and outputs a stereo signal from a main signal and a sub signal is provided.

For example, when receiving a weak FM stereo broadcast with a signal strength of 30 dBμ or less, the frequency control effect by the AFC circuit will not be as effective, and the noise components received by the aforementioned sub-signals will be transmitted to the left and right of the demodulation circuit. They have the disadvantage that they appear at the channel output terminals in opposite phases to each other, and the high-frequency noise called sah, which is characteristic of FM stereo broadcasting, is output from speakers, etc., making it very harsh on the ears.

This invention has been made with the above-mentioned points in mind, and next, this invention will be explained in detail with reference to FIGS. 1 to 3 showing one embodiment thereof.

In FIGS. 1 and 2, 1 is an antenna;
2 is a high frequency amplification circuit that amplifies the received signal from the antenna 1, and 3 is a mixing circuit that mixes the output frequency of the high frequency amplification circuit 2 and the oscillation frequency of the local oscillation circuit 4, and performs frequency exchange of the received signal. 5 is an intermediate frequency amplification circuit that amplifies the output of the mixing circuit 3;
6 is a stereo multiplex demodulation circuit into which the output of the intermediate frequency amplification circuit 5 is input, and when receiving FM stereo broadcasting, demodulates the stereo signal from the above-mentioned main signal and sub signal, and demodulates the left channel signal and right channel signal. Outputs . OL and OR are left and right output terminals to which left and right channel signals of the demodulation circuit 6 are input, respectively.

Q1 is an NPN type transistor, the base of which is grounded through the first resistor R1, connected to the negative voltage power supply terminal -B through the second resistor R2, and the emitter connected to the negative voltage power supply terminal -B through the third resistor R3. It is connected to the power supply terminal -B, the collector is connected to the mixing circuit 3, and the first capacitor C is connected between the collector and the base.
1 is connected. C2 and C3 are second and third capacitors provided in parallel between the collector of the transistor Q and the ground point, a trimmer capacitor for adjustment is used for the second capacitor C2, and a local oscillation capacitor is used for the third capacitor C3. Variable capacitors are used. L is the third capacitor C3
A local oscillation coil C4, which is provided in parallel with
D is a fourth capacitor connected in series and a variable capacitance diode, which is provided in parallel to the coil L. V is an AFC voltage input terminal connected to the connection point between the fourth capacitor C4 and the variable capacitance diode D via the fourth resistor and the fifth resistor R4 and R5,
Connected to an AFC circuit (not shown). 7 is
It is the first switch for connecting and disconnecting the AFC circuit, and includes the first to third contact terminals 7a, 7b, 7c and the switching piece 7s.
For example, it consists of one circuit of a two-circuit type changeover switch, and the first contact terminal 7a is connected to the connection point of the fourth and fifth resistors R4 and R5, and the second contact terminal 7b is grounded. . C5 is a fifth capacitor provided between the first and third contact terminals 7a and 7c of the first switch 7.

R6 is a sixth resistor provided between one output end of the demodulation circuit 6 and the ground point, and 8l is a left channel whose input end is connected to one output end of the demodulation circuit 6 via the sixth capacitor C6. The output terminal is connected to the left output terminal OL, and the ground terminal is grounded. R7 is a seventh resistor provided between the other output end of the demodulation circuit 6 and the ground point, and 8r is a right channel whose input end is connected to the other output end of the demodulation circuit 6 via the seventh capacitor C7. The output terminal is connected to the right output terminal OR, and the ground terminal is grounded. One end of C8 is the left output terminal
The eighth capacitor for high blend connected to OL, 9 is the first to third contact terminals 9a, 9b, 9
High blend circuit 10 equipped with c and switching piece 9s
This is a second switch for connecting and disconnecting, and is made up of the other circuit of the aforementioned two-circuit type changeover switch, with the first contact terminal 9a connected to the other end of the eighth capacitor C8, and the second contact terminal 9b connected to the right output terminal. Connected to OR.

Next, the operation of the above embodiment will be explained.

First, the operations of the first and second switches 7 and 9 formed by two-circuit type changeover switches will be explained.

First and second contact terminals 7a, 7 of the first switch 7
b is connected, the AFC voltage input terminal V of the local oscillation circuit 4 is grounded via the fifth resistor R5 and the first switch 7, the AFC circuit is disconnected, or turned off, and the first and second switches of the second switch 9 are connected. The two contact terminals 9a and 9b are connected, the eighth capacitor C8 is connected between the left and right output terminals OL and OR, and the high blend circuit 10 is connected, that is, turned on.

Conversely, the second and third contact terminals 7 of the first switch 7
b, 7c are connected, the first contact terminal 7a of the first switch 7 is opened, the AFC circuit is turned on, and the second and third contact terminals 9b, 9c of the second switch 9 are connected, and the second The first contact terminal 9a of the switch 9 is opened, and the high blend circuit 10 is turned off.

When receiving a weak FM stereo broadcast, the first and second contact terminals 7a of the first switch 7,
By connecting 7b, the AFC circuit is turned off, the first and second contact terminals 9a and 9b of the second switch 9 are connected, and the high blend circuit 1 is connected.
0 turns on.

Furthermore, the received signal from the antenna 1 is amplified by the high frequency amplifier circuit 2, the amplified received signal is input to the mixer circuit 3, the mixer circuit 3 mixes the frequency of the received signal with the oscillation frequency of the local oscillator circuit 4, the frequency of the received signal is converted to an intermediate frequency, the output of the mixer circuit 3 is amplified by the intermediate frequency amplifier circuit 5, the output of the intermediate frequency amplifier circuit 5 is input to the demodulator circuit 6, and the demodulator circuit 6 demodulates the main signal and sub signal of the received signal into a stereo signal.
The left channel signal of the stereo signal is outputted to a left output terminal OL via a low pass filter 8l, and the right channel signal of the stereo signal is outputted to a right output terminal OR via a low pass filter 8r.

Further, the noise components generated in the sub-signal are outputted from both output ends of the demodulation circuit 6 in opposite phases, and at this time, by turning on the high blend circuit 10, the left and right output terminals
OL and OR are coupled by the eighth capacitor C8 of the high blend circuit 10, and high frequency noise peculiar to FM stereo broadcasting is canceled out and reduced, improving the S/N ratio.

Furthermore, since the left and right output terminals OL and OR are coupled by the eighth capacitor C8, the high-frequency components of the left and right channel signals are also mixed according to the capacitance of the eighth capacitor C8, and the left and right channel signals are combined. The frequency response characteristic and the degree of separation characteristic change, and the frequency response characteristic at a specific capacitance value of the eighth capacitor C8 and the degree of separation characteristic when the capacitance of the eighth capacitor C8 is changed are shown in FIG.

In the figure, the horizontal axis shows the frequency, the vertical axis shows the frequency response amount and degree of separation, the solid line a shows the frequency response characteristic when the capacitance of the eighth capacitor C8 is 0.001μF, and the solid lines b, c, d The capacitance of the eighth capacitor C8 is 0.01μF and 0.0047μ, respectively.
F, 0.001μF, solid line e shows high blend circuit 9 turned off, left,
The isolation characteristics are shown when the right output terminals OL and OR are not coupled by the eighth capacitor C8, and the isolation is the best when the left and right output terminals OL and OR are not coupled by the eighth capacitor C8. 8 capacitor C
As the capacity of 8 increases, the degree of separation deteriorates.

By selecting the capacitance value of the eighth capacitor C8, it is possible to improve the actual hearing sensation when receiving a weak FM stereo broadcast.

Next, when receiving an FM stereo signal with sufficient signal strength, the S/N ratio is sufficiently high and the frequency control effect by the AFC circuit is sufficiently obtained. When the three contact terminals 7b and 7c are connected and the AFC circuit is turned on, the second switch 9 switches in conjunction with the second and third contact terminals 9 of the second switch 9.
b and 9c are connected, the high blend circuit 10 is turned off, and the high frequency components of the left and right channel signals are output without being mixed.

In addition, if the received signal from antenna 1 is an FM monaural signal, turn on high blend circuit 10,
Even if it is turned off, there will be no change in the noise component.

Therefore, according to the embodiment, the first switch 7 for disconnecting the AFC circuit and the high blend circuit 10
A second switch 9 for connecting and disconnecting is formed by a two-circuit type changeover switch, and connects the AFC circuit when receiving FM stereo broadcasts with sufficient signal strength, and disconnects the high blend circuit 10 to control weak FM stereo broadcasts. At the time of reception, in order to disconnect the AFC circuit and connect the high blend circuit 10,
With an inexpensive circuit configuration, it is possible to improve the actual hearing sensation when receiving weak stereo broadcasts.

As described above, the receiver of this invention includes a stereo signal demodulation circuit, a high blend circuit that reduces noise components included in the output signal of the demodulation circuit, and a first switch for disconnecting the automatic frequency control circuit. By providing a second switch for disconnecting and connecting the high blend circuit in conjunction with the first switch, it is possible to improve the actual hearing sensation when receiving weak stereo broadcasts with an inexpensive circuit configuration. .

[Brief explanation of the drawing]

Figures 1 to 3 show the first receiver of this invention.
An example is shown, and FIG. 1 is a partial block diagram, and FIG. 2 is a partial block diagram.
The figure is a partial wiring diagram, and FIG. 3 is a diagram of a frequency response characteristic curve and a separation characteristic curve. 6... Demodulation circuit, 7... First switch for disconnection, 9...
2nd switch for disconnection, 10...high blend circuit.

Claims (1)

[Scope of utility model registration request] A stereo signal demodulation circuit, a high blend circuit for reducing noise components included in the output signal of the demodulation circuit, a first switch for controlling on/off operation of the high blend circuit, and a first switch for controlling a local oscillation frequency. and an automatic frequency control circuit that operates in conjunction with the first switch to turn off the operation of the automatic frequency control circuit at the same time as the on operation of the high blend circuit, and also connects the automatic frequency control signal supply path of the automatic frequency control circuit and the reference potential. A receiver comprising a second switch disposed between the points.