JPS6130347Y2 - - Google Patents

Description

[Detailed description of the invention] This invention automatically detects and removes near-field interference from carrier signal components in the high frequency stage or intermediate frequency stage in amplitude modulation receivers such as radio broadcast receivers and television broadcast receivers. In particular, the present invention relates to an interference removal circuit that is capable of easily and sufficiently removing near-field interference waves regardless of frequency and phase, with almost no adjustment.

For example, when interference waves exist in adjacent channels in a medium-wave radio broadcast receiver, an amplitude modulation receiver equipped with an envelope line detector can detect program interference due to cross-modulation, beat interference between carrier waves, and monkey chatter. Unnecessary interfering sounds such as tsk can be heard mixed with the desired signal sound, resulting in proximity interference. The following various circuit configurations have been used as conventional interference removal circuits for this type of near-field interference.
All of them had some serious drawbacks, and a sufficient removal effect could not be obtained. In other words, (1) In a circuit configuration in which the passband width of the intermediate frequency filter is narrowed to eliminate interference from adjacent channels, the audio bandwidth of the desired signal becomes narrower, causing deterioration in the sound quality of the desired signal tone. There were some shortcomings.

(2) In a circuit configuration that reduces the mixed beat sound by inserting a band-removal filter that removes the 9KHz adjacent channel interference beat in the audio signal circuit after the envelope detector, the circuit configuration is simple. However, it is not possible to remove program interference due to cross modulation, the beat sounds that can be removed are limited to those around 9KHz, and furthermore, the removal effect is poor when the level of interference waves is relatively high. It had various drawbacks, such as a small size.

(3) In a circuit configuration that uses a synchronous detection circuit and a wideband 90-degree phase shifter to receive only the sideband where interference waves are not mixed nearby, the interference cancellation performance is Although it is superior to the above two methods, since it uses a synchronous detector and a 90 degree phase shifter, the circuit configuration is complex and the number of circuit components used is large. The drawback was that it could not be used to remove interference from broadcast waves, AM stereo broadcast waves, television broadcast waves, etc.

The purpose of the present invention is to eliminate the various drawbacks of the conventional devices mentioned above, and to provide a simple-configuration interference elimination circuit that can easily and sufficiently eliminate nearby interference waves, regardless of their frequency and phase, with almost no adjustment. It's about doing.

That is, the interference elimination circuit of the present invention divides the amplitude modulated signal component in an amplitude modulation receiver into two, leads one to a subtracter via a delay device, and divides the other into a band elimination filter whose rejection band includes the desired carrier frequency. The carrier frequency component of the interference wave is detected by sequentially guiding the interference wave to an amplitude limiter, and the interference wave frequency component is added to a phase lock loop controlled oscillator to generate a carrier frequency component of the interference wave with a constant amplitude. component is introduced into the subtracter via an automatic gain control amplifier to subtract it from the carrier signal component derived from the delay device, and the output signal of the subtracter is introduced into a synchronous detector to generate a carrier frequency component of the constant amplitude interference signal. By performing synchronous detection and controlling the amplification gain of the automatic gain control amplifier using a signal related to the output signal of the synchronous detector, the amplitude modulated signal component from which the interference carrier frequency component has been removed is obtained from the subtracter. It is characterized by being able to be taken out.

The invention will be explained below by way of example with reference to the drawings.

An example of the configuration of the interference removal circuit of the present invention is shown in FIG.
In the illustrated circuit configuration, a high-frequency or intermediate-frequency amplitude-modulated carrier signal component subjected to interference such as adjacent channel interference waves is used as an input signal. In the figure, reference numeral 1 indicates that the input signal is sent to the main line system which reaches the subtracter 3 via the delay device 2, and the interference component canceling signal generation system which bypasses the band-removal filter 4 and others and also reaches the subtracter 3. This is a distribution amplifier for branching. First, to explain the interference component cancellation signal generation system, 4 is a band eliminator (BEF) for removing the carrier wave component of the desired signal from the input signal. The wave output signal of the wave transmitter 4 contains only the carrier wave component of the interference wave, its sideband component, and the sideband wave component of the desired wave. Then, the wave output signal is supplied to the phase compensator 5 to compensate as much as possible the phase distortion caused by the band-removal waveform 4 within the frequency band to be handled, to improve the linearity of the phase characteristic, and to generate an interference component cancellation signal. The delay time of the input signal in the system is made constant, and a delay device 2 inserted in the main line system prevents a phase shift between the input signals of both systems reaching the subtracter 3. Next, the input signal from which only the phase-compensated desired carrier wave component has been removed is supplied to the amplitude limiter 6, which suppresses and removes sideband components of the desired wave and interference wave that exist as envelope changes of the input signal. , extract only the interference carrier wave component as pure as possible. In addition, when extracting the desired wave, if the level of the sideband component of the desired wave is higher than the level of the interference wave carrier component, it is difficult for the amplitude limiter 6 to suppress and remove the desired wave sideband component, and only the interference wave carrier component is extracted. Therefore, it is necessary to widen the rejection bandwidth of the band-removal filter 4 to a certain extent so that the sideband components of the desired wave can be appropriately attenuated. Then,
Supplying the interference carrier wave component extracted by the amplitude limiter 6 to a phase comparator 7 in a phase lock loop (PLL) controlled oscillator consisting of a phase comparator 7, a low-pass wave generator 8 and a voltage controlled oscillator (VCO) 9, A constant amplitude interference carrier frequency signal whose frequency and phase are almost completely locked to the input interference carrier component is used to control the oscillation state of the voltage controlled oscillator 9 based on the result of phase comparison between the oscillator output and the input, as is well known. to cause it to occur. Note that the oscillation output signal of the phase lock loop controlled oscillator has a phase delay of 90 degrees with respect to the input signal of the phase comparator 7, so the main line system using the delay device 2 described above and the interference component cancellation signal generation system In order to match the phase between the signals, it is necessary to include this 90 degree phase delay. The thus obtained constant amplitude interference wave carrier frequency signal is supplied to the subtracter 3 as an interference component cancellation signal via the automatic gain control amplifier 10,
The interference component in the input signal of the main line system is subtracted and cancelled, but the interference component in the input signal is
In addition to being an amplitude-modulated signal itself, the relative level with the desired wave component changes depending on the propagation state, or because it is affected by the amplitude change of the desired wave component due to cross-modulation, its amplitude constantly changes. On the other hand, the interference carrier frequency signal for cancellation has a constant amplitude, so in order to remove the amplitude deviation between the signals to be canceled, the interference carrier frequency signal that occurs when the interference carrier frequency components to be canceled are mutually subtracted The subtracted output signal of the subtracter 3 containing the residual error is guided to the synchronous detector 11, where it is synchronously detected using the constant amplitude interference carrier frequency signal from the phase locked loop controlled oscillator, and the detected output signal is converted into a low-pass wave. 12, a synchronous detection output signal with a level corresponding to the difference in amplitude between the canceled signals is obtained, and the amplification gain of the automatic gain control amplifier 10 is controlled by the synchronous detection output signal. When loop control is performed such that the level of the interference carrier frequency component contained in the subtracted output signal of subtractor 3 converges to zero, the interference carrier frequency component is automatically canceled out and removed as the subtracted output signal of subtracter 3. It is possible to extract the high frequency signal component or intermediate frequency signal component of the desired wave maintained in this state.

Furthermore, if the pass band of the low-pass wave filter 12 is set narrowly, the amplitude of the canceling interference wave carrier frequency signal changes by following only the slow fluctuation component of the interference wave amplitude due to fading, etc. The generated fluctuations are fully tracked and the interference waves are canceled out, but if the pass band of the low-pass wave filter 12 is set wide, the interference wave frequency signal for cancellation can be canceled by the modulation signal of the interference waves. Since the amplitude is modulated, it is possible to cancel out the interference wave by sufficiently following the interference beat component and the modulation signal component of the interference wave.

However, in the latter case, the same effect as when the intermediate frequency band of the receiver is narrowed occurs, and the frequency band of the detection output signal for the desired wave is also narrowed. Therefore, in order to perform interference cancellation and removal in an appropriate manner depending on the state of occurrence of interference,
For example, it is preferable to make the passband width adjustable by making the capacitance of the capacitor that constitutes the low-pass wave filter 12 variable. In addition, conventionally, it was difficult to make the intermediate frequency bandwidth of the receiver continuously variable, but with the above-mentioned circuit configuration,
It is possible to obtain the same effect as when the intermediate frequency bandwidth of the receiver is made continuously variable.

In addition to matching the amplitudes of the canceling signals mentioned above, matching the phases is also necessary for complete cancellation of the interference carrier frequency component. The phase shift between signals in the system remains constant unless the handled frequency changes, so once the phase compensator 5 and delay device 2 described above are adjusted, other signals can be adjusted as long as the handled frequency does not change. There are no elements that cause phase shifts.

Therefore, if the present invention is applied to the intermediate frequency stage of an amplitude modulation receiver to configure an interference removal circuit, interference caused by nearby interference waves with a frequency slightly distant from the carrier frequency of the desired wave will be eliminated. Regardless of the frequency, it can be canceled out almost completely without adjustment, and even when the present invention is applied to a high frequency stage, the desired signal can be canceled out automatically, such as in a commercial amplitude modulation receiver. If the carrier wave frequency is constant, it is possible to similarly eliminate interference automatically without adjustment. Regarding amplitude modulated carrier signals such as broadcast waves having subcarriers,
It is necessary to insert a band remover for removing the subcarrier into the interference component cancellation signal generation system.

As is clear from the above description, according to the present invention, the following remarkable effects can be obtained. That is, (1) it is possible to perform cancellation cancellation that automatically follows fluctuations in the interference beat frequency due to frequency fluctuations of adjacent interference waves;

(2) When there is no interference, the interference component cancellation signal becomes zero level due to the action of the automatic gain control loop, so it has no effect on the input signal of the main line system, and therefore the reception quality is reduced. There is no risk of deterioration.

(3) It is easy to integrate the interference removal circuit, and a reduction in manufacturing cost can be expected.

In particular, when a desired carrier signal that combines amplitude modulation and PM or FM angle modulation, such as an AM stereo broadcast wave, is subject to close interference interference from an adjacent channel, the desired carrier wave may be distorted by the interference beat component. When amplitude modulation is applied and the program modulation is deep, a phenomenon similar to overmodulation occurs as a result, the desired carrier component disappears, and the PM detector or FM
Strong noise may be generated from the detector.
The generation of such noise can be avoided to some extent by narrowing the intermediate frequency bandwidth, for example, but in that case, the narrower bandwidth will naturally affect the sound quality, stereo separation, distortion characteristics, etc. However, according to the present invention, the close interference interference wave component is canceled out and removed without narrowing the receiving bandwidth, and the generation of intense noise due to isotropic overmodulation as in the conventional method is avoided. It can be prevented. In the case of AM stereo broadcast waves, even if the close interference interference wave is an FM wave, the phase lock loop controlled oscillator can follow the frequency change, so the interference beat can be removed extremely sharply.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of the configuration of the interference removal circuit of the present invention. DESCRIPTION OF SYMBOLS 1...Distribution amplifier, 2...Delay device, 3...Subtractor, 4...Band remover, 5...Phase compensator,
6... Amplitude limiter, 7... Phase comparator, 8... Low pass wave generator, 9... Voltage controlled oscillator, 10...
Automatic gain control amplifier, 11... Synchronous detector, 12
...Low pass wave generator.

Claims (1)

[Scope of utility model registration request] The amplitude modulated signal component in the amplitude modulation receiver is divided into two, one is guided to a subtracter via a delay device, and the other is sequentially guided to a band remover and an amplitude limiter whose removal band includes the desired carrier frequency to prevent interference. detect the carrier frequency component of the interference wave, apply the interference frequency component to a phase lock loop controlled oscillator to generate a carrier frequency component of the interference wave with a constant amplitude, and add the carrier frequency component of the interference wave with a constant amplitude to the above-mentioned interference wave carrier frequency component through an automatic gain control amplifier. The output signal of the subtracter is led to a subtracter and subtracted from the carrier signal component led from the delay device, and the output signal of the subtracter is led to a synchronous detector to perform synchronous detection using the carrier frequency component of the interference wave having the constant amplitude. By controlling the amplification gain of the automatic gain control amplifier using a signal related to the output signal, the amplitude modulated signal component from which the interference carrier frequency component has been removed can be extracted from the subtracter. interference removal circuit.