JPS6322739B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a receiver, and particularly to a receiver that reduces interference signals by shifting the tuning frequency of an antenna input circuit in a direction in which the interference signals are reduced.

A receiver commonly used in the past has a superheterodyne configuration as shown in FIG. In the figure, reference numeral 1 denotes an antenna input circuit including a tuning circuit, which selects and outputs only a target frequency signal from antenna signals supplied from the antenna. 2 is a high frequency amplification circuit that amplifies the output signal of the antenna circuit 1;
3 is a local oscillation circuit; 4 is a mixing circuit that mixes the output signal of the high frequency amplifier circuit 2 and the output signal of the local oscillation circuit 3 to output an intermediate frequency signal; 5 is a mixing circuit 4
6 is a detection circuit that detects the intermediate frequency signal and inputs the audio signal. Note that 1a is a variable capacitance diode provided in the tuning circuit of the antenna input circuit 1.

In the receiver configured in this way, the antenna input circuit 1 and the high frequency amplification circuit 2 are tuned to a desired signal frequency d. Here, the desired signal received at the antenna input circuit 1
Fd is amplified by the high frequency amplifier circuit 2 and then supplied to the mixing circuit 4. On the other hand, the local oscillation circuit 3 oscillates a frequency o that is higher than the desired signal frequency d by an intermediate frequency i (or a frequency lower by i) and inputted to the mixing circuit 4. The mixing circuit 4 receives the desired signal frequency input from the high frequency amplifier circuit 2.
By mixing d and the local oscillation frequency o supplied from the local oscillation circuit, the intermediate frequency signal i
It is converted into and supplied to the intermediate frequency amplification circuit 5. In this case, the tuning of the tuning circuit provided in the antenna input circuit 1 is performed by varying the tuning voltage V _T applied to the variable capacitance diode 1a, and the high frequency amplifier circuit 2 and local oscillation circuit 3 are also tuned in this way. It is designed to be variable in conjunction with the tuning voltage _VT .

However, since the conventional receiver having the above configuration employs the superheterodyne system, there is a problem in that spurial interference, intermodulation interference, etc. occur due to the presence of the mixing circuit.

An object of the present invention is to provide a receiver that can reduce the effects of spurial interference and intermodulation interference.

FIG. 2 is a circuit showing an embodiment of the receiver according to the present invention, and the same parts as in FIG. 1 are indicated using the same symbols. In the figure, reference numerals 7 and 8 are bandpass filters that receive the intermediate frequency signal i output from the mixing circuit 4, and the passband of the bandpass filter 7 is higher than the intermediate frequency i.
The passband of bandpass filter 8 is intermediate frequency i
is set lower than. 9 and 10 are detectors for detecting the outputs of the bandpass filters 7 and 8; 11;
is a comparator that compares the outputs of the wave detectors 9 and 10, and this comparison output is supplied as a tuning control signal to the variable capacitance diode 1a provided in the tuning circuit for the antenna input signal 1.

In the circuit configured as described above, in a normal radio wave receiving state without interference, the output from the bandpass filters 7 and 8 is not sent out, so the output from the comparator 11 becomes zero. As a result, comparator 11
No tuning control is performed on the antenna input circuit 1 by the output of the first antenna.
The desired broadcast is received by performing the same operation as the conventional circuit shown in the figure.

Next, if other signals exist near the receiving frequency or if intermodulation interference occurs, the output of the mixing circuit 4 will contain interference signals other than the intermediate frequency signal i. For example, if an interference signal exists on the higher frequency side than the intermediate frequency signal i, an output is generated only from the bandpass filter 7, and the output of the bandpass filter 7 is transmitted to the detector 9.
The signal is detected at and supplied to the negative input terminal of the comparator 11. As a result, the input signal of the comparator 11 becomes negative, and this negative signal is supplied to the variable capacitance diode 1a of the antenna input circuit 1 as a tuning control signal. Therefore, the tuning frequency of the tuning circuit of the antenna input circuit 1 is shifted to a lower side, and the occurrence of interference is accordingly reduced.

Further, contrary to the case described above, when an interference wave having a frequency lower than that of the intermediate frequency signal i occurs, an output is generated only from the bandpass filter 8. The output signal of the bandpass filter 8 is detected by the detector 10 and then supplied to the positive input terminal of the comparator 11. As a result,
A positive tuning signal corresponding to the output of the bandpass filter 8 is sent from the comparator 11, and the variable capacitance diode 1a is controlled by this tuning control signal, thereby adjusting the tuning provided in the antenna input circuit 1. The tuning frequency of the circuit will be shifted slightly to the higher side. Therefore, the intermediate frequency signal i output from the mixing circuit 4 is a signal with reduced interference waves, and accordingly, good reception without interference can be performed.

In the above embodiment, a case has been described in which the tuning circuit provided in the antenna input circuit 1 is configured with a twin type variable capacitance diode, but the present invention is not limited to this, and the tuning circuit provided in the antenna input circuit 1 is configured with a single type variable capacitance diode. Needless to say, it may be configured.

As explained above, according to the receiver according to the present invention, an interference signal other than the intermediate frequency signal included in the output of the mixing circuit is detected, and the tuning frequency of the antenna input circuit is adjusted in a direction in which the interference signal level is reduced. Since it is configured to shift the signal, it has an excellent effect of reducing the effects of adjacent interference, intermodulation interference, etc.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a conventional receiver, and FIG. 2 is a circuit diagram showing an embodiment of the receiver according to the present invention. DESCRIPTION OF SYMBOLS 1... Antenna input circuit, 1a... Variable capacitance diode, 2... High frequency amplifier circuit, 3... Local oscillation circuit, 4... Mixing circuit, 5... Intermediate frequency amplifier circuit, 6... Detection circuit, 7, 8... Band pass filter, 9, 10... Detector, 11... Comparator.

Claims (1)

[Claims] 1. In a superheterodyne receiver that mixes the output of the antenna input circuit and the output signal of the local oscillation circuit in a mixing circuit, extracts the difference signal as an intermediate frequency signal, and detects this intermediate frequency signal to obtain a received output signal. , a first bandpass filter that receives the output of the mixing circuit as an input and passes only frequency components higher than the frequency of the intermediate frequency signal; and a second bandpass filter that passes only frequency components lower than the frequency of the intermediate frequency signal. and comparing the detection outputs of the first and second bandpass filters and shifting the tuning frequency of the antenna input circuit according to the difference between the two, thereby reducing the influence of adjacent interference waves and intermodulation interference waves. Receiver with comparator.