JPS6159932A - Amplitude modulation stereo broadcast system identification device - Google Patents

Abstract

PURPOSE:To prevent a frequency identification circuit from identifying an erroneous system just after application of power supply by initializing the frequency identification circuit just after power supply of an AM stereo broadcast identification device is applied. CONSTITUTION: When power of a power supply leading detection circuit 7 is applied, a voltage source rises rapidly to a voltage VCC and then a voltage dividing voltage V1 dividing the voltage VCC by resistors R72, R73, rises also rapidly. On the other hand, a voltage across a capacitor C71 rises gradually to a voltage V2 with a delay of a time constant of C71.R73. Thus, a pulse signal going to a high level just after application of power and going to a low level when a terminal voltage of the capacitor C71 exceeds the voltage dividing voltage V1 is outputted from a comparator 71. The pulse signal is fed to a reset terminal of a frequency identification circuit 4 to reset binary counters or the like. Thus, erroneous identification of the broadcast system by the identification circuit 4 is prevented just after application of power.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a variable amplitude 'J (AM) stereo broadcast system identification device.

The AM stereo broadcast system identification device of the present invention receives broadcast radio waves transmitted from broadcast stations with different stereo broadcast systems, identifies the broadcast system, selects a demodulation circuit according to the broadcast system, and broadcasts stereo broadcasts. It can be applied to, for example, a car radio installed in a car.

[Conventional technology]

In the United States, Canada, etc., AM is the stereo broadcasting system.
A stereo broadcast system is used. Various AM stereo broadcasting systems are known, including Magnavo7x's AM-PM system, Harris' V-CPM system, Kahn/Haselchin's ISB system, Motorola's C-QUAM system, and Vera's There are AM-FM systems, etc. In the United States, the first four of these systems are currently approved, and broadcast stations are currently operating and broadcasting in stereo, but stereo broadcasting using each of these systems overlaps in some areas. The current situation is that

On the other hand, although the configuration of the receiver differs depending on each of the above stereo broadcasting systems, the receiver of one of the above systems cannot receive stereo broadcasting of other systems. For this reason,
Despite the fact that various stereo broadcast programs are being broadcast in these areas, the stereo broadcast systems for these programs are different, so of these programs, only the programs that are compatible with the system of the receiver you own are available. The current situation is that you can't enjoy it.

[Problem that the invention seeks to solve]

In order to be able to receive all stereo broadcast programs of each stereo broadcast system with a single receiver, the receiver must be equipped with a demodulation circuit for each system, and the receiver must be able to identify the stereo broadcast system of the broadcast program and convert it according to that system. The demodulation circuit may be selected appropriately.

A method using pilot signals has been proposed as a method for automatically identifying each method. In other words, the broadcast radio waves of each system include a pilot signal to indicate that it is a stereo broadcast with a stereo indicator, and the frequency of this pilot signal differs depending on the system. . That is, A M −P
M method is 5Hz, ISB method is 15H2, C-QU
The AM method uses 25 Hz, and the V-CPM method uses 55 Hz.

Therefore, each method can be identified by identifying the pilot signal frequency.

The frequency identification circuit for identifying this pilot signal frequency includes a latch circuit, a counter, etc.
These latch circuits, counters, etc. are all composed of binary elements such as flip-flops. When the power is turned on, it is unclear whether these elements are set to the output Q or the inverted output.

Therefore, there is a problem in that when the device is powered on, the frequency identification circuit randomly identifies the broadcasting system and malfunctions until the first identification operation in the frequency identification circuit is completed.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention provides a plurality of demodulation circuits for different amplitude modulation stereo broadcasting systems, each of which has a different pilot signal frequency for stereo display; a circuit for separating a pilot signal from the demodulated output of the circuit, a frequency identification circuit for identifying the frequency of the pilot signal separated by the separating circuit, and a plurality of demodulation circuits based on the pilot signal frequency identified by the frequency identification circuit. The amplitude modulation stereo broadcast system identification device includes a circuit for selecting a demodulation circuit corresponding to the pilot signal frequency from among the demodulation circuits. There is provided an amplitude modulation stereo broadcast system identification device characterized in that a binary element constituting the frequency identification circuit is initialized by a rising edge detection signal.

[For production]

When the device is powered on, the power supply voltage rises rapidly, so a detection circuit detects the rise of the power supply voltage when the power is turned on, and the rise detection signal is used to detect binary elements such as flip-flops in the frequency identification circuit. Initialize.

This can prevent the frequency identification circuit from malfunctioning when the power supply voltage is turned on.

〔Example〕

An AM stereo broadcast system identification device as an embodiment of the present invention is shown in FIG. In FIG. 1, received radio waves are received and detected by a high frequency receiver (not shown) and converted into an intermediate frequency (IF) signal.

Four demodulation circuits 1 with different IF flaw signals and methods
They are led to input terminals 1 to 14, respectively.

Demodulation circuits 11, 12, 13, and 14 are AM-PM, respectively.
The demodulation circuits are for ISB, C-QUAM, and VCPM systems, and the pilot signal frequencies of each demodulation circuit 11, 12, 13, and 14 are 5Hz and 15Hz, respectively.
, 25Hz, and 55Hz. These demodulation circuits 1
1 to 14 separate the input IF defective signal-like channel signal and R channel signal and send them to the input terminals of the system switching circuit 5.

The SUB signal (
subchannel signal) is guided to a pilot filter 2. The pilot filter 2 is a band pass filter that passes a frequency band including four types of pilot signals, that is, a band of 5 Hz to 55 Hz, and removes L and R channel signal components to extract a pyro node signal component.

The output of the pyro filter 2 is guided to a waveform shaping circuit 3. The waveform shaping circuit 3 is a circuit that shapes the pilot filter output signal as the signal to be identified into a pulse waveform. This waveform shaping circuit 3 can be configured with a so-called hysteresis comparator, and thereby can perform waveform shaping by removing the influence of low voltage level noise components superimposed on the pilot signal. The output signal of the waveform shaping circuit 3 is guided to the input terminal of the frequency discrimination circuit 4.

The frequency identification circuit 4 selects a pulse-like pilot signal inputted via the pilot filter 2 and the waveform shaping circuit 3, which has a frequency of 4 types of pilot signals of 5Hz and 1.
This circuit identifies which one of 5H2, 25H2, and 55H2 corresponds to. The identification result is sent to the system switching circuit 5 in the form of an identification signal that sets one of the four output lines 6 corresponding to each system to a high level. The system switching circuit 5 is composed of, for example, an analog switch, and selectively switches one of the four systems of demodulation circuits 11 to 14 based on an identification signal.

The frequency identification circuit 4 has an electric current St when the device is powered on.
A power supply rise detection circuit 7 for detecting a rise in pressure is connected.

The configurations of the frequency identification circuit 4 and power supply rise detection circuit 7 in the device shown in FIG. 1 are shown in FIG.

In the frequency discrimination circuit 4 shown in FIG. 2, the pilot signal from the waveform shaping circuit 3 is guided to one input terminal of an AND gate 41. A gate signal S (gl) from a gate pulse generator 43 is introduced to the other input terminal of the AND gate 41. The gate pulse generator 43 is connected to a reference oscillator 44, and a reference Gate signal stn and reset signal S based on the frequency signal
(rl, latch signal 5(1), etc. are generated at predetermined timing, and the pulse width of gate signal S(g) is made to be a unit time width (1 second).These signals S(g)
, 5(1), and 5(r) are shown in FIG. 3(1) and (21°(3)), respectively.

The output of the AND gate 41 is led to the input terminal of the counting section 42. The counting unit 42 counts the number of pulses of the input pilot signal, identifies which of the pilot signal frequencies of 5.15 and 25.55 Hz for each method, and selects the corresponding one of the four output lines. The output line is set to the "1" level and sent to the launch circuit 46.

An example of the configuration of the counting section 42 in the circuit of FIG.
As shown in the figure. The counting unit 42 includes a frequency divider 420 that divides the input pilot signal by 175, counters 421 to 423 to which the output signal of the frequency divider 420 is input, inverters 424 to 426, and AND gates 427 to 429. Ru. Counters 421 to 423 are circuits that output "1" level output signals when the number of manually input pulse signals is 2 to 4.4 to 6, and 9 to 13, respectively. Inverters 424-426 and AND gates 427-42
Reference numeral 9 is for preventing output signals of "1" level from being simultaneously output from two or more of the four output lines from the counter section 42.

An example of the configuration of the counter 422 in FIG. 4 is shown in FIG. 5. As shown in FIG. 5, counter 422 consists of three binary counters (or flip-flops)
I'-Q3 are connected in cascade, and the inverted output s (direction z) of binary counter Q2 and the output 5 (Qs) of binary counter Q are led to each input terminal of AND gate Q4. . The basic configuration of the counters 421 and 423 is the same except that the number of connected stages of the binary counters is different.

Frequency divider 420 and counter 4 in counting section 42
A reset signal S (r
) is derived, and the count value is reset by the reset signal S (r). A rising edge detection signal from the power rising detection circuit 7 is introduced to the other input terminal of the OR gate 45 . This rising detection signal is also guided to the reset terminal of the latch circuit 46. Furthermore, a latch signal 5(1) is led from the gate pulse generator 43 to the latch control terminal of the latch circuit 46, and the latch signal S(1)
The latch timing is controlled by - In the power supply rise detection circuit 7 shown in Fig. 2, the comparator 71
A voltage divider circuit consisting of resistors R0+R, □ is connected to the non-inverting input terminal of , and a resistor Rff3 is connected to the inverting input terminal of
An integrating circuit consisting of a capacitor C7,1 and a capacitor C7,1 is connected.

One end of these voltage dividing circuit and integrating circuit is connected to a voltage source that supplies power supply voltage VCC to each circuit of the device. The rising edge detection signal output from the comparator 71 is sent to the frequency identification circuit 4 as a reset pulse.

The operation of the apparatus of FIG. 1 will be described below with reference to FIG. FIG. 6 is a diagram showing the signal waveforms of various parts when the power is turned on in the power rise detection circuit of FIG.
(2) shows the voltage waveform of resistors Rt+, R
? ! The divided voltage output waveform at point a is a solid line, and the capacitor C? The terminal voltage at point b of I is shown by the dashed line, and (
3) shows the output waveform of the comparator 71.

When the power of the device is turned on, the voltage source suddenly rises to the power supply voltage Vcc as shown in FIG.
1 also rises rapidly as shown by the solid line in FIG. 6(2). Note that ■1 is as follows.

On the other hand, the terminal voltage of the capacitor 75 is determined by the time constant C'll·R?, as shown by the broken line in FIG. 6(2). After a delay of 3, the voltage V gradually rises to (V□-Vcc).

Therefore, from the comparator 71, the terminal voltage of the capacitor Ct+ becomes high level immediately after the power is turned on, and the terminal voltage of the resistor R□, R
A pulse output signal that becomes low level is output when the divided voltage of 12 exceeds 1.

This pulse output signal is applied as a reset pulse to the reset terminal of the frequency identification circuit 4, whereby all the binary counters and the like constituting the frequency identification circuit 4 are reset. Therefore, it is possible to prevent the frequency identification circuit 4 from randomly identifying the broadcasting system immediately after the power is turned on.

〔Effect of the invention〕

According to the present invention, the frequency identification circuit in the AM stereo broadcast identification device is initialized immediately after the power is turned on, thereby preventing the frequency identification circuit from identifying an incorrect system immediately after the power is turned on. can.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an AM stereo broadcast system identification device as an embodiment of the present invention, FIG. 2 is a block diagram of a frequency identification circuit and a power supply rise detection circuit in the device shown in FIG. 1, and FIG. A waveform diagram of the signal output from the gate pulse generator in the circuit, FIG. 4 is a block diagram of the counter section in the circuit in FIG. 2, and FIG.
A block diagram of the 4-176° counter, and FIG. 6 is a signal waveform diagram of each part of the power rise detection circuit shown in FIG. 2 immediately after the power is turned on. 11-14... Demodulation circuit, 2... Pilot filter, 3... Waveform shaping circuit, 4... Frequency identification circuit, 5
...Method switching circuit, 7...Power supply rise detection circuit,
42... Count section, 46... Latch circuit, 7
1... Comparator.

Claims (1)

[Claims] A plurality of demodulation circuits for different amplitude modulation stereo broadcasting systems, each of which has a different pilot signal frequency for stereo display, a circuit that separates a pilot signal from the demodulated output of the demodulation circuit, and a circuit that separates the pilot signal. a frequency identification circuit that identifies the frequency of the pilot signal separated by the frequency identification circuit; and selecting a demodulation circuit corresponding to the pilot signal frequency from among the plurality of demodulation circuits based on the pilot signal frequency identified by the frequency identification circuit. An amplitude modulation stereo broadcast system identification device equipped with a circuit includes a detection circuit that detects the rise of the power supply voltage when the power supply voltage of the device is turned on, and a binary frequency identification circuit that configures the frequency identification circuit by a rise detection signal from the detection circuit. 1. An amplitude modulation stereo broadcast system identification device, characterized in that the device is configured such that an element is initialized.