JPS5821448B2 - synthesizer fm receiver - Google Patents

Description

[Detailed description of the invention] The present invention relates to a synthesizer FM receiver.

Generally, in a synthesizer FM receiver that performs a tuning operation using a frequency divider with a variable frequency division ratio, the frequency division ratio of the frequency divider is varied to perform a frequency sweep, and when reception is received during the sweep, the A synthesizer FM receiver in which the sweep is stopped is known.

By the way, in a conventional synthesizer FM receiver, in order to stop the above-mentioned sweep, the carrier wave output taken out from the intermediate frequency amplifier circuit becomes high, and the output of the DC voltage detection circuit that detects the DC voltage of the output of the FM detection circuit increases. (So-called S-curve) It is detected that both the level becomes low and the occurrence of the same occurs at the same time, and when this is detected, it is assumed that the signal has been received and the upward sweep is stopped.

In the above-mentioned conventional synthesizer FM receiver, for example, when two FM broadcast waves are received in close proximity to each other at the same level, the above-mentioned carrier wave output 1 becomes high due to the influence of interference between the two signals. Also, since the output level of the DC voltage detection circuit becomes low, the above-described sweeping stops.

In such a case, a low quality signal resulting from the interference is received.

That is, the conventional synthesizer FM receiver has the drawback that the above-mentioned sweep stops even when the low-quality signal is received.

The present invention eliminates the above-mentioned drawbacks by separating inaudible high-frequency components caused by the above-mentioned interference (interference) from the signal after passing through FM detection, and detecting the high-frequency components. The above-mentioned sweep is not stopped when there is an error.

An embodiment of the present invention will be described in detail below with reference to the drawings.

The figure shows a main part related to the present invention in a synthesizer FM receiver.

In the figure, 1 is an intermediate frequency amplification circuit, 2 is an FM detection circuit, and 3 is an input terminal.

Reference numeral 5 denotes a carrier wave detection circuit, which is composed of a transistor Q1, an intermediate frequency amplifier 6, a Schmitt circuit T, etc., and detects the carrier wave output that has not been taken out from the intermediate frequency/amplification circuit 1, and when this is detected, the carrier wave output is activated by the Schmitt circuit. T
output will be at a low level.

Reference numeral 8 denotes a DC voltage detection circuit (detection amplifier), which is composed of transistors Q2, Q3, Q4, etc. so as to detect the DC voltage output from the FM detection circuit 2.

This circuit 8 is well known, and when the output of the FM detection circuit 2 is zero, the output is zero, and when the output of the FM detection circuit 2 is positive or negative, the output is high level.

Reference numeral 9 denotes a high frequency component detection circuit, which includes a transistor Q5 and a bypass through which inaudible high frequency components pass, so as to detect the level of the high frequency component contained in the output signal from the FM detection circuit 2. Filter 10, amplifier 11
and a Schmitt circuit 12, etc., and the output (output of the Schmitt circuit 12) becomes high level due to the above-mentioned high frequency component.

In the synthesizer FM receiver described above, the carrier wave detection circuit 5, the DC voltage detection circuit 8, and the high frequency component detection circuit 9
Since the above-mentioned sweep is stopped only when all the outputs of the carrier wave detection circuit 5 are at a low level, there is no synchronization difference between stations where the output of the carrier wave detection circuit 5 is at a high level, and where the output of the DC voltage detection circuit 8 is at a high level. In this case, the above-mentioned sweep does not stop, and the sweep does not stop even in the case of the above-mentioned interference in which the output of the high-frequency component detection circuit 9 becomes high level, so that the above-described low-quality signal reception can be prevented.

Incidentally, the signals from the outputs 13 of the circuits 5, 8, and 9 can also be used to prevent erroneous lighting of the stereo display lamps.

[Brief explanation of the drawing]

The figure is a block diagram showing one embodiment of the present invention. 1...Intermediate frequency amplification circuit, 2...FM
Detection circuit, 5...Carrier detection circuit, 8...
...DC voltage detection circuit, 9...High frequency component detection circuit.

Claims (1)

[Claims] 1. In a synthesizer FM receiver that performs a tuning operation using a frequency divider with a variable frequency division ratio, a frequency sweep is performed by varying the frequency division ratio of the frequency divider, and when reception is received during the sweep, the above A DC voltage detection circuit configured to stop the sweep and characterized by detecting the DC voltage of the output of the FM detection circuit, a carrier detection circuit detecting the carrier output taken out from the intermediate frequency amplification circuit, and the FM detection circuit. a high frequency component detection circuit that detects the level of high frequency components included in the output signal of the carrier wave, the level of the carrier wave supplied to the carrier wave detection circuit is high, and the signal is supplied to the high frequency component detection circuit. The synthesizer FM receiver is configured to stop the above-mentioned sweep only when the level of the high frequency component of the above-mentioned DC voltage detection circuit is low and the output level of the above-mentioned DC voltage detection circuit is also low.