JPH0326695Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a pilot signal detection circuit for use in an AM stereo receiver that uses a plurality of low frequency pilot signals.

Prior art and problems Currently, in the United States, Magnavox, Kahn,
AM using four types of methods: Motorola and Harris
Stereo broadcasting has been commercialized, and in order to identify these systems, 5Hz, 15Hz, 25Hz, and 55Hz are used in the same order.
pilot signals are used.

Conventionally, in order to identify each of these pilot signals, four resonant circuits for each pilot signal frequency were provided in parallel, and the output of each resonant circuit was detected.

However, the conventional detection circuit described above not only requires a large number of relatively large resonance elements (especially inductances) at low frequencies and occupies a large space, but also takes a long time to detect when the Q is increased to increase detection sensitivity. There was a problem that required .

Purpose of the Invention The present invention aims to improve the above-mentioned drawbacks of the conventional circuit and provides a pilot signal detection circuit which can be miniaturized and which can detect pilot signals at high speed and with high sensitivity.

Structure of the invention The present invention, which achieves the above objects, includes a low-pass filter that receives a received signal including a pilot signal and passes only the pilot signal; a limiting circuit, a frequency/voltage conversion circuit that converts the output of the amplitude limiting circuit into a signal with a voltage value corresponding to the frequency and outputs the signal;
A plurality of comparison circuits that compare the outputs of the voltage conversion circuits with reference to the intermediate value of the frequency-corresponding voltage values of each adjacent pilot signal, and a decoder that combines the comparison results of the respective comparison circuits to determine the pilot signal currently being received. It is configured to be equipped.

Further details of this configuration will be explained below using examples.

Embodiment of the invention FIG. 1 is a block diagram of an embodiment of the invention, in which 10 is a reception input terminal, 20 is a low-pass filter, 30 is an amplitude limiting circuit, 40 is a frequency/voltage conversion circuit, 50 is a comparison circuit group, and 60 is a logic circuit.

Reception input terminal 10 connected to a reception circuit (not shown)
The above received signal is supplied to a low pass filter 20, and only the low frequency pilot signal that has passed through this filter is supplied to an amplitude limiting circuit 30. The pilot signal whose amplitude has been limited here is supplied to the frequency/voltage conversion circuit 40 at the next stage. The pilot signal supplied to this frequency/voltage conversion circuit 40 is made up of an input resistor 41, an operational amplifier 42 with a gain of 1, and a feedback capacitor 43, and passes through a low-pass filter having a delay time of about 1 Hz, and then passes through a diode. 44 and a smoothing capacitor 45. The frequency/voltage conversion characteristic of this frequency/voltage conversion circuit 40 is such that the output voltage decreases linearly as the frequency increases, as illustrated in FIG.

The pilot signal converted into a voltage is supplied to a group of comparison circuits 50 at the next stage. This comparison circuit group is composed of four comparison circuits 51, 52, 53, and 54, and each reference voltage V1 to V4 is set to be an intermediate value of the frequency-corresponding voltage values of each adjacent pilot signal. There is. That is, as shown in FIG. 2, the reference voltage V1 of the comparator circuit 51 is
The lowest frequency of the seed pilot signal frequency is 5Hz (Magnavox method) and the adjacent 15Hz.
(Kahn method) is set to a value corresponding to a voltage of 10Hz, which is the intermediate frequency. In addition, the comparison circuit 5
The reference voltage V2 of No. 2 is set to a value corresponding to a voltage of 20Hz, which is an intermediate frequency between 15Hz (Kahn method) and the adjacent first-stage high frequency 25Hz (Motolora method). Reference voltages V3 and V4 of 53 and 54 are set to voltage values corresponding to frequencies of 40Hz and 70Hz, respectively.

Therefore, when this receiver receives broadcast waves of the Magnavox system using a 5 Hz pilot signal, the outputs of all comparison circuits 51 to 54 become high. Furthermore, when this receiver receives a Kahn system broadcast wave that uses a 15Hz pilot signal, only the output of the comparison circuit 51 becomes low, and all the outputs of the other three comparison circuits 52 to 54 become low. Get high. Similarly, when this receiver receives Motorola broadcast waves that use a 25Hz pilot signal, the outputs of comparison circuits 51 and 52 become low, and the outputs of comparison circuits 53 and 54 become high. .
This receiver uses a 55Hz pilot signal.
When a Harris system broadcast wave is received, only the output of the comparison circuit 54 becomes high, and the outputs of the other three comparison circuits all become low.

The high/low outputs of the four comparison circuits 51-54 are decoded by a decoder 60 consisting of three AND gates 61-63 and three inverters 64-66, and detected at four terminals 67-70. Output the results. That is, if a high signal is output only to the output terminal 67, reception of a Magnavox broadcast wave is detected, and if a high signal is output only to the output terminal 68, reception of a Kahn broadcast wave is detected. If a high signal is output only to output terminal 68, reception of Motorola system broadcast waves is detected, and if a high signal is output only to output terminal 69, reception of Harris system broadcast waves is detected. Ru.

In the above embodiment, a combination of a low-pass filter and a rectifier circuit is used as the frequency/voltage conversion circuit, but other appropriate frequency/voltage conversion circuits may be used instead.

Effects of the Invention Since the present invention has the above-described configuration, it has the advantage of being miniaturized and being able to detect pilot signals at high speed and with high sensitivity.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.
FIG. 2 is a conceptual diagram for explaining the operation of the above embodiment. 10... Reception input terminal, 20... Low pass filter, 30... Amplitude limiting circuit, 40... Frequency/voltage conversion circuit, 50... Comparison circuit group, 60... Decoder.

Claims (1)

[Claims for Utility Model Registration] In an AM stereo receiver for receiving AM stereo broadcasting using a plurality of low frequency pilot signals, a low frequency receiver that receives a received signal including the pilot signal and allows only the pilot signal to pass through. A pass filter, an amplitude limiting circuit that limits the amplitude of the output of the low pass filter, a frequency/voltage conversion circuit that converts the output of the amplitude limiting circuit into a signal with a voltage value corresponding to the frequency and outputs the signal, and the frequency. /a plurality of comparison circuits that compare the outputs of the voltage conversion circuits with reference to the intermediate value of the frequency-corresponding voltage values of adjacent pilot signals, and a decoder that combines the comparison results of the respective comparison circuits to determine the pilot signal currently being received. A pilot signal detection circuit comprising: