JPH0336120Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Field of industrial application The present invention relates to an improvement of an AM radio receiver, and particularly to an AM radio receiver that can eliminate beat interference from adjacent stations. (b) Prior art In AM radio receivers, when a beat occurs between the desired station and an adjacent station, an audible frequency beat component is mixed into the detected output, causing unpleasant noise to the listener. Occur. The beat interference can be removed by using a narrow band filter as an IF (intermediate frequency) filter to prevent signals from stations other than the desired receiving station from being added to the detection circuit.
However, the use of the narrowband filter is not preferable because it degrades the sound quality of the signal of the desired station, particularly cutting out high-frequency components. On the other hand, on pages 97 to 102 of the May 1979 issue of "Radio Science" published by the Japan Broadcasting Publishing Association on May 1, 1979, there was an article titled "Joint Report on Hot New Products." On pages 101 and 102, there is an explanation about ``a beat canceller that takes advantage of the characteristics of synchronous detection.'' According to the above description, the beat canceller includes a synchronous detection circuit that detects an AMIF signal, a quadrature synchronous detection circuit that detects orthogonal components of the AMIF signal, and output signals of the synchronous detection circuit and the quadrature synchronous detection circuit. a phase shifter that performs a phase shift such that the phase shifters have a phase difference of 90 degrees from each other, and matrixing the two output signals that have passed through the phase shifter, and outputting an upper sideband signal to a first output terminal;
It is composed of a matrix circuit that generates a lower sideband signal at the second output terminal, and a changeover switch that manually selects either the upper sideband signal or the lower sideband signal. By manually selecting sideband waves that are expected to cause less beat interference, listening with less noise is attempted. (c) Problems to be solved by the invention However, the manual switching of the changeover switch is performed according to the auditory sense of the listener, so the accuracy is not very good. Since the method has disadvantages such as cumbersome operation, an improvement has been desired. (d) Means for Solving the Problems The present invention has been made in view of the above points, and includes a third detection circuit that detects the beat component contained in the first output terminal of the matrix circuit, and a third detection circuit that detects the beat component contained in the first output terminal of the matrix circuit. a fourth detection circuit that detects a beat component included in a second output terminal of the circuit; a comparison circuit that compares the levels of the output signals of the third and fourth detection circuits and generates a control signal circle accordingly; The present invention is characterized by comprising a switch connected to the first and second output terminals of the matrix circuit and switched in accordance with the control signal. (E) Effect According to the present invention, it is detected which of the upper and lower sideband signals obtained at the first and second output terminals of the matrix circuit contains the most beat components, and the switch is activated accordingly. Since the switching is automatic, sideband signals with less beat interference can be automatically received without relying on the listener's audibility. (F) Embodiment Figure 1 shows an embodiment of the present invention.
2 is an IF amplifier circuit that generates an IF signal, and 2 is a first circuit that synchronously detects the IF signal obtained from the IF amplifier circuit 1.
A detection circuit 3 is a second detection circuit that performs orthogonal synchronous detection of the orthogonal component of the IF signal, and 4 is a PLL (phase locked loop) that generates a 0 degree synchronization signal and a 90 degree synchronization signal synchronized with the carrier frequency of the IF signal. ) circuit, 5 is a first phase shift circuit that shifts the phase of the output signal of the first detection circuit 2 by +45 degrees, 6 is a second phase shift circuit that shifts the phase of the output signal of the second detection circuit 3 by -45 degrees, 7 is a matrix circuit for matrixing the output signals of the first and second phase shift circuits 5 and 6; 8 is a matrix circuit for matrixing the output signals of the first and second phase shift circuits 5 and 6; A first high-pass filter is taken out, 9 is a third detection circuit for detecting the level of the output signal of the first high-pass filter 8, and 10 is a detection circuit near 9 KHz included in the lower sideband signal obtained at the second output terminal of the matrix circuit 7. 11 is a fourth detection circuit that level-detects the output signal of the second high-pass filter 10; 12 is a fourth detection circuit that compares the output signal levels of the third and fourth detection circuits 9 and 11; 13 is a comparator circuit that generates a control signal; 13 is an adder circuit that adds the upper and lower sideband signals obtained at the first and second output terminals of the matrix circuit 7; , is a switch that switches and outputs signals obtained at the first and second output terminals of the matrix circuit 7 and the output terminal of the adder circuit 13. Next, the operation will be explained. The amplified IF signal obtained at the output terminal of the IF amplifier circuit 1 is sent to the PLL circuit 4.
, a 0 degree synchronization signal synchronized with the carrier frequency (approximately 455KHz) of the IF signal is generated at the first output terminal of the PLL circuit 4 by PLL operation.
A 90 degree synchronization signal is generated at the second output terminal. In general, the AM signal is Acosω _t +A/2cos(ω+P _U )t +A/2cos(ω-P _L )t...(1) [However, A is a constant, ω is the carrier angular frequency P _U is the upper sideband signal, P _L is a lower sideband signal], so in the first detection circuit 2, the above 0
When the AMIF signal expressed by the above equation (1) is synchronously detected using the frequency synchronization signal, the output terminal of the first detection circuit 2 receives A/4cos(P _U )t+A/4cos(P _L )t...(2 ) is generated. In addition, the second detection circuit 3
When the AMIF signal expressed by equation (1) is quadrature synchronously detected using the 90-degree synchronization signal, the output terminal of the second detection circuit 3 receives A/4sin(P _U )t-A/4sin(P _L )t...(3) An output signal is generated. The signals shown in equations (2) and (3) above, which have been phase-shifted by the first and second phase shift circuits 5 and 6 to have a phase difference of 90 degrees, are matrixed by the matrix circuit 7. An upper sideband signal is generated at the first output terminal of the circuit 7, and a lower sideband signal is generated at the second output terminal. Then, the beat component near 9KHz included in the upper sideband signal passes through the first high-pass filter 8,
The level is detected by the third detection circuit 9 and the comparison circuit 12
9K applied to and contained in the lower sideband signal
Beat components near Hz are passed through the second high-pass filter 10
The signal is level-detected by the fourth detection circuit 11 and applied to the comparison circuit 12. In the comparison circuit 12, the levels of the output signals of the third and fourth detection circuits 9 and 11 are compared, and a control signal corresponding to the result of the level comparison is generated at the output terminal of the comparison circuit 12. now,
If the upper and lower sideband signals do not contain beat components, the output signal levels of the third and fourth detection circuits 9 and 11 will be equally zero, and the output of the comparison circuit 12 will also be "0". In that case, the movable terminal 14a of the switch 14 is switched to contact the second fixed terminal 14c by the "0" control signal of the comparator circuit 12, and the sum signal of the upper and lower sideband signals from the adder circuit 13 is applied to the switch 14. Output terminal 15 through
occurs in Furthermore, when the beat component in the upper sideband signal increases due to beat interference from the adjacent station, the output signal level of the third detection circuit 9 becomes higher than the output signal level of the fourth detection circuit 11, and the comparison circuit 12 outputs "H". ” is generated, and the movable terminal 14a of the switch 14 comes into contact with the third fixed terminal 14d. As a result, the lower sideband signal obtained at the second output terminal of the matrix circuit 7 is generated at the output terminal 15 via the switch 14 . Furthermore, when the beat component in the lower sideband signal increases due to beat interference from the adjacent station, the output signal level of the fourth detection circuit 11 becomes higher than the output signal level of the third detection circuit 9, and the comparison circuit 1
A control signal of "L" is generated from switch 14 .
The movable terminal 14a contacts the first fixed terminal 14b. As a result, the upper sideband signal obtained at the first output terminal of the matrix circuit 7 is generated at the output terminal 15 via the switch 14 . Therefore, as shown in FIG. 1, the levels of the beat components contained in the upper and lower sideband signals obtained at the first and second output terminals of the matrix circuit 7 are compared with each other to generate a control signal. If you change the switch,
Beat interference-free reception can be achieved automatically. Note that as the first detection circuit 2, an envelope detection circuit may be used instead of the synchronous detection circuit. Furthermore, instead of the first and second high-pass filters 8 and 10, band-pass filters having a center frequency of 9 KHz may be used. Furthermore, if the adder circuit 13 is omitted and the switch 14 is used as two contacts, and the output signal levels of the third and fourth detection circuits 9 and 11 are approximately equal, the movable contact of the switch 14 is connected to one of the fixed contacts. They may also be in contact. FIG. 2 shows another embodiment of the present invention.
A differential switch 16 is used as the comparison circuit 12 and switch 14 in FIG.
and 11, the differential switch 1
6. Therefore, the differential switch 16 has a base that is connected to the matrix circuit 7.
a first transistor 1 connected to a first output terminal of
7, a second transistor 18 whose base is connected to the second output terminal of the matrix circuit 7, third and fourth transistors 19 and 20 whose bases are connected to the third detection circuit 9, and a second transistor 18 whose base is connected to the second output terminal of the matrix circuit 7; It consists of fifth and sixth transistors 21 and 22 connected to the fourth detection circuit 11, the emitters of the third and fifth transistors 19 and 21 are commonly connected to the collector of the first transistor 17,
The emitters of the fourth and sixth transistors 20 and 22 are commonly connected to the collector of the second transistor 18. Now, assuming that the output signal levels of the third and fourth detection circuits 9 and 11 are equal, the base voltages of the third to sixth transistors 19 to 22 are equal, and the voltage from the first output terminal of the matrix circuit 7 to the first transistor 17 becomes equal. The upper sideband signal applied to the base of is passed through the fifth transistor 21 to the output terminal 23.
and the second one of the matrix circuit 7.
A lower sideband signal applied from the output terminal to the base of the second transistor 18 is led out to the output terminal 23 via the fourth transistor 20. Therefore, a mixed signal of upper and lower sideband signals is generated at the output terminal 23. Further, when the beat disturbance of the upper sideband signal becomes large and the output signal level of the third detection circuit 9 becomes higher than the output signal level of the fourth detection circuit 11, the third and fourth transistors 19 and 20 are turned on. The fifth and sixth transistors 21 and 22 are turned off, producing a lower sideband signal at the output terminal 23 which is applied to the base of the second transistor 18 . Furthermore,
When the beat disturbance of the lower sideband signal becomes large and the output signal level of the fourth detection circuit 11 becomes higher than the output signal level of the third detection circuit 9, the fifth and sixth transistors 21 and 22 are turned on, and the third and the fourth transistors 19 and 20 are turned off, generating an upper sideband signal at the output terminal 23 which is applied to the base of the first transistor 17. Note that when the difference in the output signal levels of the third and fourth detection circuits 9 and 11 is not very large, upper and lower sideband signals are generated that are mixed at a ratio corresponding to the level difference. In that case, the sideband signal on the side where there is less beat interference can be obtained at the output terminal 23 at a higher level, so the influence of the beat interference is reduced, and the sideband signal on the opposite side can also be obtained at the output terminal 23. Therefore, reception with a good signal-to-noise ratio is achieved. (g) Effects of the invention As described above, according to the invention, it is possible to automatically select and receive the signal on the side where there is less beat interference among the upper and lower sideband signals. Eliminated AM reception can be achieved. Also,
When the output signal levels of the third and fourth detection circuits are substantially equal as in the embodiment, AM reception with an improved SN ratio can be achieved by making it possible to obtain the summed signal of the upper and lower sideband signals at the output terminal.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, and FIG. 2 is a circuit diagram showing another embodiment of the present invention. Explanation of main drawing numbers, 2...1st detection circuit, 3...
2nd detection circuit, 4... PLL circuit, 7... Matrix circuit, 9... Third detection circuit, 11... Fourth detection circuit, 12... Comparison circuit, 14 ... Switch.

Claims (1)

[Scope of utility model registration request] a first detection circuit that detects the AMIF signal;
A second detection circuit detects the orthogonal component of the AMIF signal, and the output signals of the first and second detection circuits are matrixed, and the upper sideband signal is output to the first output terminal, and the upper sideband signal is output to the second output terminal.
a matrix circuit that generates a lower sideband signal at an output terminal; a third detection circuit that detects a beat component in a signal obtained at the first output terminal; and a third detection circuit that detects a beat component in a signal obtained at the second output terminal. a fourth detection circuit that performs detection; a comparison circuit that compares output signals of the third and fourth detection circuits and issues an output signal;
An AM radio receiver comprising: a switch connected to first and second output terminals of the matrix circuit and controlled by an output signal of the comparison circuit.