JPS60233950A - System discriminating device in am stereo receiver - Google Patents

Abstract

PURPOSE:To discriminate quickly and accurately the system by detecting an incoming pilot signal of each system in an AM stereo broadcast and discriminating its frequency. CONSTITUTION:A filter 8 detects a low frequency pilot signal included in a difference signal of the AM broadcast and it is shaped into a rectangular wave by a Schmitt ciruit 9. Then an output of the Schmitt circuit and an output of a reference frequency generator 10 are inputted to an AND circuit 11, its logical output is counted by a counter 12 and its count output is stored by a latch circuit 13. A holding signal in the latch circuit 13 is outputted to a logical circuit 14 by using a latch pulse (j) of a pulse generating circuit 16 and the counter circuit 12 is reset by a reset pulse (k) of the pulse generating circuit 16. The logical circuit 14 discriminates a pilot signal frequency from the output value of the latch circuit 13 and outputs a type identification signal to a latch circuit 15.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to a system identification device used for identifying different pilot signal frequencies for each system in AM stereo broadcasting and identifying the system.

Conventional Structure and Problems Various AM stereo broadcasting systems have been proposed, and an AM stereo receiver that can support each system is required. This requires a system identification device that selects demodulated signals from different demodulation means for each system.

In the system currently being proposed in the United States, a pilot signal indicating stereo broadcasting is superimposed on the difference signal between the left and right channel signals. A conventional method identification device will be described below with reference to the drawings. FIG. 1 is a block diagram of a pilot signal detection device that detects the presence or absence of one type of pilot signal. The filter 1 that extracts the pilot signal superimposed on the difference signal a is composed of a biloft, a band pass filter or a low pass filter that passes the frequency of the signal, and the pilot signal selected by the filter 1 is sent to the amplifier 2.
The signal is amplified and input to the Schmitt circuit 3. The pilot signal inputted to the Schmitt circuit 3 is converted into a rectangular wave C and inputted to the CR integration circuit 4. The CR integration circuit 4 sequentially performs integration, and the integral output d is input to the level detection circuit 6, where it is determined whether the integrated value exceeds a specified value. If it exceeds the specified value, it is determined that a pilot signal exists. It outputs a detection signal e indicating that it has occurred.

The operation of the pilot signal detection device configured as described above will be explained. FIG. 2 is a timing chart for detecting a biloft signal.

In FIG. 2, the horizontal axis (1) indicates the passage of time, and when stereo broadcasting starts at time T1, a difference signal a on which a pilot signal is superimposed is output. difference signal a
The pilot signal is extracted by passing through the filter 1, and a pilot signal amplified by the amplifier 2 is obtained. In the amplifier 2, the detection level of the Schmitt circuit 3 ■1. Amplify to a level suitable for v2. In the Schmitt circuit 3, when the pilot signal becomes larger than the level of ■1, it outputs H (high level), and the level of ■2
’, outputs L (low level) and generates a rectangular wave C.
Convert to The rectangular wave C is integrated by the CR integrating circuit 4, and the integrated output d is sent to the level detecting circuit 5. If it becomes larger than the vU level, H (or L) is output as the pilot detection signal e. At time T2 in Fig. 2, the integral output d
is larger than the vU level, indicating that the pilot detection signal e becomes H. On the other hand, if time changes from stereo broadcasting to monaural broadcasting, the pilot signal will no longer be detected, so neither the square wave C nor the output will be output, and the level of the integral output d will decrease with the discharge time constant of OR. When the signal becomes lower than the L level, the pilot detection signal e becomes L at time 74 in FIG. In this way, the pilot signal can be detected.

FIG. 3 is a block diagram of a system identification device using a pilot signal detection device. Filter 110°120.13
0,140 is composed of a bandpass filter whose center frequency is the frequency of the pilot signal superimposed on the difference signal of each method, and the selected pilot signal is amplified by amplifiers 210, 220, 230 and 240. The signal is converted into a square wave by Schmitt circuits 310, 320, 330, and 340. The converted rectangular wave is passed through a CR integration circuit 41 having an OR time constant suitable for the frequency of the pilot signal of each method.
o.

420, 430, and 440, and the integrated outputs are input to level detection circuits 510, 520, 530, and 540, which detects which type of pilot signal is present, and outputs a pilot detection signal. The pilot detection signal is held in the latch circuit 6 and output as a system identification signal. On the other hand, the latch signal of the latch circuit 6 is outputted from the launch pulse generation circuit 7 at the rising edge of the pilot detection signal of each system. The pilot signal detection operation in the moxibustion method is the same as that described in FIGS. 1 and 2.

However, in the method identification device having the above-described configuration, each filter is required to have a steep selectivity characteristic. The pilot signal for each system uses an extremely low frequency, for example, the Magnavox system uses 5 kHz, the Kern system uses 15 kHz, and the Motorola system uses 25 kHz.
In the Harris/Harris method, the ratio is 55. Since the pilot signal frequencies of each method are close to each other, there may be an inconvenience that pilot signal detection devices of different methods may operate erroneously.

In addition, if the time constants of C and H in the CR integration circuit are small, the output of the pilot signal detection device will be an intermittent output corresponding to the pilot signal. Even if a signal is input, the detection output is sent out with a delay of a time constant, which poses a problem in that a quick detection operation cannot be performed.

OBJECT OF THE INVENTION The object of the present invention is to provide an AM stereo receiver that can quickly and accurately identify the system by detecting the arrival of pilot signals of each system in AM stereo broadcasting and identifying the frequency. An object of the present invention is to provide a method identification device for use in a computer.

Structure of the Invention The system identification device of the present invention includes a filter that selects a low-frequency pilot signal included in a difference signal of AM broadcasting, a seamit circuit that rectangles the signal after passing through the filter, and a signal that selects a reference frequency. a reference signal generator that generates a reference signal generator, an AND circuit that takes the logical product of the output of the Schmitt circuit and the output of the reference signal generator, a counter circuit that inputs the output of the AND circuit, and an output state of the counter circuit. a first latch circuit for holding, a logic circuit for inputting the output of the first latch circuit, a second latch circuit for holding the output state of the logic circuit, and an output of the Schmitt circuit for controlling the counter circuit. A first pulse generation circuit that generates a reset pulse and a latch pulse of the first latch circuit, and a reset pulse of a counter circuit in the first pulse generation circuit and the output of the logic circuit are inputted, The second one generates a latch pulse to the latch circuit.
This pulse generation circuit is used to identify each type of AM stereo broadcasting.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 4 shows a block diagram of an automatic method identification device according to an embodiment of the present invention. In FIG. 4, the difference signals of each method are added together and input to a filter 8. Here, as for the frequency characteristics of the filter 8, if method 1 is the Magnavox method, method 2 is the Kahn method, method 3 is the Motorola method, and method 4 is the Harris method, the respective pilot signal frequencies are the Magnavox method. Since the Cahn type filter has a cutoff frequency of 16L, the Motorola type has a cutoff frequency of 25L, and the Harris type has a cutoff frequency of 66L, a low-pass filter having a cutoff frequency of 66L is sufficient. However, since 50 Hz or higher is a region where broadcast signals exist, it is desirable that the filter characteristic be as steep as possible.

Also, since the signal level differs depending on the system, it is desirable to have amplitude characteristics such that the pilot signal level at the output of the filter 8 is the same level. The pilot signal f obtained by passing through the filter 8 is converted into a rectangular wave q by a Schmitt circuit 9 and then sent to an AND circuit 11.
is input. On the other hand, the signal from the reference frequency generator 1o is also input to the AND circuit 11, where it is ANDed with the rectangular wave q.

The ANDed symbol i is input to the counter circuit 12, and its output is held in the first latch circuit 13. or,
The latch pulse j of the first latch circuit 13 is outputted from the pulse generating circuit 16 in large numbers as the rectangular wave q falls, and the reset pulse k of the counter circuit 12 is output as the latch pulse j falls. The logic circuit 14 determines the pilot signal frequency based on the value held in the latch circuit 13, and its output is held in the latch circuit 16 and becomes a system identification signal. The timing at which this latch circuit 16 latches is such that only when the pilot signal frequency of one of the systems is detected in the logic circuit, the second A latch pulse is output from the pulse generating circuit 17. 1. Therefore, the method identification signal is always in a state where one of the methods is selected.

The operation of the method identification device of this embodiment configured as described above will be described below.

FIG. 5 shows a timing chart for the pilot signal f, the rectangular wave q, the signal of the reference frequency generator 1o, the output i of the AND circuit 11, the latch pulse j, and the reset pulse. If the pilot signal f passed through the filter 8 becomes higher than the level of vH of the Schmitt circuit 9, the output q becomes H (high level), and if it becomes lower than the level of VL, the output q becomes L (low level selection). Yoshi output q
becomes an i-shaped wave. On the other hand, the output of the reference frequency generator 10 is input to the counter circuit 12 only when the rectangular wave q is H. The number of outputs is counted during a half cycle of the sipirosoto signal. On the other hand, when the rectangular wave q falls, a launch pulse j is output to the latch circuit 13, which holds the counter value, and then, using the fall of the latch pulse J, a reset pulse k of the counter circuit 12 is output. Output. From the above, period detection is performed in half the period of the pilot signal, so even if the detection time is long, it is 100 m' with the Magnavox method.
ieC, and the fastest is )・9m5eC of squirrel method
It is.

In FIG. 6, the waveform of the signal amount is different between the first half and the second half, but this indicates a difference in the method and indicates that the operation is the same.

Next, the algorithm of the logic circuit will be explained.

In particular, we will explain the case where the reference frequency is set to 680±10) (,.
The reason for choosing 1z is that the configuration of the logic circuit is the simplest, as will be described later.

It should be noted that the logic circuit is configured to take into account fluctuations within the range of ±2° for the pilot signal and to prevent malfunctions. Table 1 shows the decimal values of the counters for each method.

Table 1 FIG. 6 shows the conversion of this counter decimal value into Kubinoto's binary value. In FIG. 6, the characteristic parts for identifying each method are enclosed in squares. Range A, where one of the upper 2 bits is 1, is the Magnavox method; range B, where the upper 2 bits are 0 and the 3rd bit is 1, is the Kahn method; the upper 3 bits are 0, and the upper 4.5 bits are 1. If the range C where both bits are 1 is the Motorola method, and the range where the upper bit is 0 and the 6th bit is 1 is the Harris method, the result will be the detection range as shown in Table 2.

An embodiment of the logic circuit 14 is shown in FIG. 7 of Table 2. The same parts as in the block diagram of FIG. 4 are given the same numbers. FIG. 7 shows a circuit configuration in which characteristic parts of each system of counter binary values shown in FIG. 6 can be identified.

Although the operation has been described above, the logical sum of the pilot signal detection signals output from the logic circuit 14 can also be used for one piece of information on a monaural/stereo switching signal. Furthermore, it is possible to use a microcomputer with a built-in counter circuit, and to replace all of the Schmitt circuit 9 and later with microcomputer software, and even more accurate method identification can be performed.

Effects of the Invention As is clear from the above description, the present invention can reduce the time required to identify the different pilot signal frequencies for each AM stereo broadcast system in a half period of the pilot signal frequency, and The configuration of the reference signal generator and logic circuit makes it possible to improve the frequency identification accuracy and to configure a system that does not malfunction. Furthermore, it can be said that the system is versatile in that it can be adapted to different detection frequencies by changing the reference signal generator and logic circuit. Furthermore, since the system can be automatically identified, the operator does not have to worry about changing the system every time he or she tunes in.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional pilot signal detection device.
FIG. 2 is a timing chart for detecting a pilot signal, FIG. 3 is a block diagram of a method identification device using a conventional pilot signal detection device, and FIG. 4 is a block diagram of a method identification device in an embodiment of the present invention. FIG. 6 is a timing chart of the method identification device of the present invention, FIG. 6 is a diagram showing the relationship between the decimal value and the binary value of the counter value, and is a diagram showing the characteristics of each method, and FIG. 7 is an embodiment of the present invention. It is a logic circuit diagram in an example. 8... Filter, 9... Schmitt circuit, 1°... Reference frequency generator, 11...
...AND circuit, 12... Counter circuit, 13
．． 15...Lunch circuit, 14...Logic circuit, 16.17...Pulse generation circuit 0 Agent's name Patent attorney Toshi Nakao Haka1 persong
Metzuka City's currency '1 ゛) Responsibility

Claims (1)

[Claims] a filter that selects a low-frequency pilot signal included in a difference signal of AM broadcasting; a Schmitt circuit that shapes the waveform of the signal after passing through the filter; a reference frequency generator that generates a reference frequency; an AND circuit that takes the logical product of the output of the circuit and the output of the reference frequency generator, a color/recircuit that inputs the output of the AND circuit, and a first launch circuit that maintains the output state of the counter circuit; a logic circuit that determines the output state of the first latch circuit; a second latch circuit that holds the output state of the logic circuit; and a reset pulse of the counter circuit and the first a first pulse generation circuit that generates a latch pulse of the latch circuit; a reset pulse of the counter circuit in the first pulse generation circuit and the output of the logic circuit are inputted, and the latch pulse is inputted to the second latch circuit; 1. A system identification device for an AM stereo receiver, comprising: a second pulse generation circuit that generates a pulse; and identifying a system based on an output state of the second launch circuit.