JPS61228729A - Input circuit of receiver - Google Patents

Abstract

PURPOSE:To improve the capability excluding an image disturbance signal and a local oscillation disturbance signal by adding a filter having a pole attenuating each of the image disturbing signal and a local oscillation disturbing signal to a desired signal to a receiver input circuit. CONSTITUTION:Filters 1, 2 are added to the input circuit. The local oscillation disturbing signal of an inputted radio wave is blocked by a coil 7 and a capacitor 8 constituting the 1st filter of the filter 1 via a matching coil 4. Further, the image disturbing signal is blocked by a coil 9 and a capacitor 10 constituting the 2nd filter via a matching coil 5. On the other hand, the desired signal passes through matching coils 4, 5, 6 and the band pass filter 2 and reaches a filter output 16. In this case, the coils 7, 9 are adjusted and set so as to minimize a disturbing beat sound caused when the desired signal, the local oscillation disturbing signal and the image disturbance signal are received at the same time.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an input circuit for a receiver. Conventional technology The configuration shown in FIG. 4 has been commonly used as a front-end circuit for a receiver. was. In FIG. 4, 3 is an antenna input terminal, 2 is a bandpass filter that passes the reception band, 20 and 22 are tuning circuits for tuning to the desired signal, 21 is a high frequency amplifier, 25 is a local oscillator,
23 is a mixer, 24 is an intermediate frequency filter, and 26 is an intermediate frequency output terminal. Further, the frequency characteristic of the bandpass filter 2 with a frequency of 27.7 is shown in FIG. fl and f2 in FIG.
is the cutoff frequency of the bandpass filter 2.

Problems to be Solved by the Invention In conventional receivers, the ability to eliminate signals other than the desired signal, that is, image frequency interference signals and local oscillation frequency interference signals, affects the selectivity characteristics of the receiver. However,
In reality, it is difficult to completely eliminate interference signals.

In addition, the selectivity characteristics of a receiver tend to deteriorate as the frequency increases due to the influence of the distributed capacitance of the coil, etc., so that interference signals tend to be easily received in the high range of the receiving frequency.

Furthermore, since broadcasting frequencies vary depending on the country and region, it is necessary to improve the ability to eliminate interference signals in accordance with the local circumstances.

The present invention has been made in view of this problem, and an object of the present invention is to improve the ability to eliminate image interference signals and local oscillation interference signals within the reception band.

31. Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a receiver input circuit with a filter having a pole for attenuating the image interference signal with respect to the desired signal, and a filter for attenuating the local oscillation interference signal. A filter with a pole is added to block the passage of the interference signal.

Function The present invention makes it possible to improve the ability to eliminate image interference signals and local oscillation interference signals by adding the two interference signal elimination filters described above to the receiver input circuit. be.

Embodiment The circuit shown in FIG. 1 is an embodiment of the input circuit of a receiver using the present invention, and FIG. The filter 1 of the present invention is added to the configuration.

Here, an explanation will be given based on the embodiment shown in FIG. The radio waves guided by the receiving antenna are sent to the antenna input terminal 3.
The local oscillation interference signal is blocked from passing through the matching coil 4 by the coil 7 and capacitor 8 that constitute the first filter. Furthermore, the second coil passes through the matching coil 5.
The coil 9 and capacitor 10 that constitute the filter prevent image interference signals from passing through.

On the other hand, the desired signal is generated by the matching coils 4, 5, 6 . and passes through bandpass filter 2 and exits from the filter.

Reach force 16.

FIG. 6 shows the frequency characteristics of the bandpass filter 2, f
l and f3 are its cutoff frequencies.

FIG. 6 shows the frequency characteristics of the filter 1 in the present invention, where f4 is the frequency of the local oscillation interference signal with respect to the desired signal f2, and f5 is the frequency of the image interference signal with respect to the desired signal f2. Here, the f2. f4. f5. The frequency relationship is theoretically f4 = f2 + intermediate frequency f5 = f2 + twice the intermediate frequency.

51<-.

FIG. 7 shows the frequency characteristics of the receiver input circuit in the embodiment of FIG. 1, and shows the overall frequency characteristics when the bandpass filter 2 and the filter 1 of the present invention are used in combination.

In the embodiment of FIG. 1, coils 7 and 9 are adjusted and set to minimize the disturbance beat sound that occurs when the desired signal, local oscillation interference signal, and image interference signal are received simultaneously. It is more practical to leave it there.

FIG. 3 shows another embodiment of the present invention, in which the capacitors 8 and 9 in the embodiment of FIG. The purpose of this is to change the frequency of the desired signal in accordance with changes in the received frequency of the desired signal, thereby improving the ability to eliminate interference signals in all frequency bands.

Effects of the Invention As described above, according to the present invention, the ability to eliminate image interference signals and local oscillation interference signals in a receiver can be improved to a width of 6 pages with an extremely simple circuit configuration. Extremely practical and useful.

Furthermore, it is also possible to add an attenuation pole to the filter of the present invention to eliminate interference signals other than those described above, and the effect can be applied in a very wide range of applications.

[Brief explanation of the drawing]

FIG. 1 is an input circuit diagram of a receiver in an embodiment of the present invention;
Figure 2 is a block diagram of the entire front end circuit of a receiver implementing the present invention, Figure 3 is a circuit diagram of another embodiment of the invention, and Figure 4 is the entire front end circuit of a conventional receiver. FIG. 5 is a frequency characteristic diagram of a bandpass filter in a conventional input circuit, FIG. 6 is a frequency characteristic diagram of a filter added in the present invention, and FIG. 7 is a conventional frequency characteristic diagram showing the characteristics of FIG. 6. FIG. 6 is a diagram of overall frequency characteristics in the so-called embodiment of FIG. 1 in which a bandpass filter and a filter of the present invention having the characteristics of FIG. 6 are used in combination. 1... Filter, 4, 5, 6, 7.9...
... Coil 7, - Le, 8, 1o... Capacitor, 17.19...
・Barrier pull capacitor. Name of agent: Patent attorney Toshio Nakao and one other person
Castle District

Claims (1)

[Claims] What is claimed is: 1. An input circuit for a receiver comprising an attenuation pole for removing an image interfering signal with respect to a desired signal and an attenuation pole for removing a local oscillation interfering signal.