JPS6098714A - Circuit for preventing malfunction of radio receiver - Google Patents

Abstract

PURPOSE:To prevent malfunction at an image frequency in the automatic sweep operation by providing a frequency comparator circuit, a discrimination circuit, an AND gate circuit and an automatic sweep operation stop circuit in case of the upper side heterodyne reception system. CONSTITUTION:When a reception signal is inputted to an antenna 1, the frequency of the reception signal amplified by a high frequency stage 2 and an amplifier 18 and the frequency of a local oscillation signal via a buffer amplifier circuit 8 are compared (19), and only when the local oscillating frequency is higher than the reception frequency, a high level output is generated from a discrimination circuit 20. In case of the upper side heterodyne receiving system, the image frequency is higher than the local oscillation frequency by an intermediate frequency but the output of the circuit 20 goes to a high level only when the local oscillation frequency is higher than the reception frequency. Thus, the output of the circuit 20 does not go to high level by the image frequency and th AND gate circuit 21 is not conducted. Thus, malfunction such that the automatic sweep operation is stopped through the operation of the automatic sweep operation stop circuit 17 due to the image frequency is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention is directed to a malfunction prevention circuit for a radio receiver, particularly for a radio receiver having a single super-heterodyne short wave automatic sweep operation function. This invention relates to a circuit that prevents malfunctions at image frequencies during automatic sweep→operation.

(b) Prior art A conventional single super-heterodyne PLL radio receiver having an automatic sweep operation function, when receiving an automatic sweep operation signal, as shown in the pro-riff diagram in Fig. 1, The AGCg pressure obtained from the detection circuit has been used as a stop signal to stop the sweep operation.

In Figure 1, (1) is an anti+, '+2) is a high frequency stage including an antenna tuning circuit and a high frequency amplification circuit, and (3) is a high frequency stage including an antenna tuning circuit and a high frequency amplification circuit.
) is a mixed circuit, (4) is a voltage-side local oscillation circuit with a variable capacitance semiconductor, (5) is an intermediate frequency amplification circuit, (
6) is a detection circuit, (7) is a tuning detection circuit, (8) is a buffer amplifier circuit, (9) is a prescaler, and αω is P
In the LL circuit section, a reference oscillator αυ using a crystal oscillator, a phase comparator (14) for comparing the phases of the reference station wave, and a low voltage control circuit provided between the phase comparator and the pressure-controlled local oscillation circuit (4) are used. A sweep counter α6) that performs sweeping operation by changing the division ratio of the programmable frequency divider αJ, a tuning detection circuit (7
) is provided with an automatic sweep operation stop circuit αη that is controlled by the output from the automatic sweep operation stop circuit αη and stops the sweep counter output during synchronization and stops the automatic sweep operation.

However, in shortwave reception that requires wide-range reception, it is difficult to obtain a sufficient image frequency interference ratio due to the deterioration of q in the antenna tuning circuit. (20M
5 to 1 (about 1 dB) at Hz. Therefore, in a single super-heterodyne type radio receiver with shortwave automatic sweep function, there was a risk of a malfunction in which the sweep operation would stop at the current 7 image frequency during automatic sweep operation. In order to prevent such malfunctions, a double super-hetero gain reception system may be considered, but this has the disadvantage of complicating the circuit configuration and increasing costs.

Purpose of the Invention In view of the above, the present invention provides a radio receiver having an automatic sweep operation function, such as a PLL radio receiver with a short wave of a single super-heterodyne system. The purpose is to prevent malfunctions.

B) Structure and Embodiment of the Invention FIG. 2 is a block diagram showing an embodiment of the present invention used in a single super-0 heterodyne shortwave PLL radio receiver.

In FIG. 2, the same figure numbers as in FIG. 1 are used for the same circuit parts as in FIG. 1.

In Figure 2, α$ is an amplifier circuit that amplifies the received signal taken out from the high frequency stage (2), and αω is the frequency (reception frequency) of the received signal from the amplifier circuit Ql and the buffer amplifier circuit (8).
■ is a frequency comparison circuit that compares the frequency of the local oscillation signal (local oscillation frequency) from
! This is a discrimination circuit that is controlled by 1 and discriminates whether the reception frequency is high or low between the receiving frequency and the local oscillation frequency.In the case of an upper heterodyne reception method such as in a short wave band, only when the local oscillation frequency is higher than the reception frequency, the discrimination circuit High level (“1”
) is now generated. (21) receives the output from the tuning detection circuit (7) and the discrimination circuit (output from the lees), and other configurations are the same as in FIG.

In Figure 2, when a received signal is input to the antenna (1) during shortwave band reception, the frequency of the received signal amplified by the high frequency stage (2) and the amplifier circuit (inhibitor) and the buffer amplifier circuit (
The frequency comparison circuit compares the frequency of the local oscillation signal that has passed through step 8), and only when the local oscillation frequency is higher than the reception frequency, the discrimination circuit (a) outputs a high level (
a first output) is generated.

Further, a high level output (second output) is generated from the tuning detection circuit (7) only during tuning.

Therefore, only when the local oscillation frequency is higher than the receiving frequency at the same time, the AND gate circuit (21)
becomes conductive and a high level output (third output) is generated. This high level output (third output) is applied to the automatic sweep operation stop circuit (1η), and the automatic sweep operation stop circuit 0η is activated, stopping the sweep counter 00 and stopping the automatic sweep operation.

By the way, in the case of the upper heterodyne reception method, the image frequency is higher than the local oscillation frequency by the intermediate frequency, but in the case of Fig. 2, the output of the discrimination circuit ■ is only when the local oscillation frequency is higher than the reception frequency. Not at a high level. Therefore, the output of the discrimination circuit (■) will not become high level depending on the image frequency, and the AND gate circuit +211
There is no conduction. Therefore, depending on the image frequency, it is possible to prevent a malfunction in which the automatic sweep operation stop circuit αη operates and the automatic sweep operation is stopped.

In the embodiment shown in Fig. 2, the configuration is such that a high level output is generated from the discrimination circuit ■ only when the local oscillation frequency is higher than the reception frequency, but in the case of the lower heterodyne reception method, Conversely, the configuration may be such that the discrimination circuit generates a high-level output only when the receiving frequency is higher than the local oscillation frequency.

Furthermore, although the present invention is extremely suitable for use in short wave bands, it goes without saying that it can also be applied to reception bands other than short wave bands.

Effects of the Invention As described above, according to the present invention, in a radio receiver having an automatic sweep operation function, such as a single super heterodyne ε-wave PLL radio receiver, during automatic sweep operation, Malfunctions at image frequencies can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a conventional radio receiver, and FIG. 2 is a schematic diagram showing a malfunction prevention circuit for a radio receiver according to the present invention. (171...Self-excited sweep operation stop circuit, (1g)...
Frequency comparison circuit, ■...discrimination circuit, <211...and gate circuit. Figure 1 PLL Figure 2 LL

Claims (3)

[Claims] (1) In a radio receiver having automatic sweeping 1J, 11 operation function, there is a frequency comparison circuit that compares the frequency of the received signal and the frequency of the local oscillation signal, and a frequency comparison circuit that compares the frequency of the received signal and the frequency of the local oscillation signal. a discrimination circuit that generates a first output only when the frequency of the received signal is higher (or lower) than the frequency of the received signal; a tuning detection circuit that generates a second output during tuning; and a first output from the discrimination circuit. and a gate circuit that generates a sixth output when the second output from the tuning detection circuit is applied together; and an automatic gate circuit that stops the automatic sweep operation when the third output from the gate circuit is applied. A malfunction prevention circuit for a radio receiver, comprising a sweep operation stop circuit. (2) The malfunction prevention circuit for a radio receiver according to claim 1, wherein the radio receiver is a single super-hetero gain radio receiver with short waves. (3) The malfunction prevention circuit for a radio receiver according to claim 1, wherein the first to third outputs are high-level outputs, and the gate circuit is an AND gate circuit.