JPS6159931A - Amplitude modulation stereo broadcast system identification device - Google Patents

Abstract

PURPOSE:To prevent malfunction of a pilot signal frequency identification circuit caused by a received electric field weakened momentarily by interrupting the count of pilot signals when the received electric field is weakened and the identification of the pilot signal is disabled. CONSTITUTION:When a level value signal S(L) reaches a reference voltage value or below momentarily, an output of a comparator 49 goes to an L level and AND gates 47, 48 are closed. Then no pilot signal S(c) is fed to a count section 42 and no reference frequency signal is fed to a gate pulse generator 43. When the signal S(L) resistors to a value over a reference voltage, the output level of the comparator 49 goes again to an H level, and the supply of the pilot signal to the count 42 and the supply of the reference frequency signal to the generator 43 are restarted. Thus, even when the state of radio wave is deteriorated momentarily, the mode is not changed over to the monaural mode and the stereo broadcast is enjoyed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an amplitude modulation (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 systems are known as this AM stereo broadcasting system, such as the AM-PM system of Magnavo7x, the v-CPM system of Harris, the ISB system of Cahn/Haselchin, the C-QUAM system of Motorola, and the C-QUAM system of Vera. 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, the AM-PM method is 5 Hz, the ISB method is 15 Hz, the C-QUAM method is 25 Hz, and the V-CPM method is 55 Hz.

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

On the other hand, when the electric field of the received radio wave is weak, white noise increases, but this white noise is evenly distributed in the frequency band of the pilot signal. Therefore, when the received radio waves are weak, this white noise makes it impossible to identify the pilot signal and therefore the stereo broadcasting system, making it impossible to enjoy stereo broadcasting.

As a way to deal with this, a weak electric field is detected by measuring the S (signal) level and when this voltage level becomes less than the reference voltage, and when the electric field is weak, the mode of the receiver is changed from stereo mode to monaural mode. One possible method is to forcibly switch to the mode to prevent malfunction of the system identification circuit.

However, in car-mounted receivers and the like, the received electric field state tends to be unstable and fluctuate greatly, and instantaneous weak electric fields can frequently occur. For this reason, the above method has the problem of frequently switching between monaural and stereo, making the sound difficult to hear.

[Means for resolving the problem] In order to solve the above-mentioned problem, in the present invention,
A plurality of demodulation circuits for different amplitude modulation stereo broadcast systems, each of which has a different pilot signal frequency for stereo display;
1] A circuit that separates the pilot signal from the output, a frequency identification circuit that identifies the frequency of pilot No. 13 separated by the separation circuit, and demodulation of the plurality of pilot signals based on the pilot signal frequency identified by the frequency identification circuit. In an amplitude modulation stereo broadcast system identification device that is equipped with a circuit for selecting a demodulation circuit corresponding to the pilot signal frequency from among the circuits, a signal level detection circuit for detecting the signal level of a received radio wave is included (lfa), and the frequency identification circuit includes a counter circuit that counts pilot signals and identifies their frequency, and a counter circuit that stops supplying the pilot signal to the counter circuit when the signal level becomes less than a predetermined value.
There is provided an amplitude modulation stereo broadcasting system identification device comprising a circuit that performs control so that the time period during which the pilot signal is supplied to the counter circuit during each measurement is a constant period of time.

[For production]

The pilot signal separated by the pilot signal separating circuit is input to the frequency identification circuit. The frequency identification circuit supplies the input pilot signal to a counter circuit for a certain period of time for each measurement, counts the pilot signal, and identifies its frequency.

At this time, the supply of the pilot signal to the counter circuit is stopped during the period when the signal level detected by the signal level detection circuit is below a predetermined value, and the Pyro 7) signal supply time is the total supply time excluding this stop period. is controlled so that it is constant.

〔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
Each of the input terminals 1 to 14 is dedicated to the input terminals 1 to 14.

Demodulation circuits 11, 12, 13, and 14 are each AM-P
These are demodulation circuits for M system, ISB system, C-QUAM system, and V-CPM system, and each demodulation circuit 11.12.13.1
The 4 pilot signal frequencies are 5Hz and 15Hz, respectively.
, 25Hz, and 55Hz. These demodulation circuits 11 to 14 separate an L channel signal and an R channel signal from the input IF flaw signal and guide them to the input terminal of the system switching circuit 5.

The 5IJB signal (subchannel signal) obtained by the V-CPM demodulation circuit 14 is exclusively sent to the pilot filter 2. The pilot filter 2 is a bandpass 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 the pilot signal component.

The output of the pilot 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 is a circuit that identifies whether the frequency corresponds to 5Hz, 25Hz, or 55Hz. The identification results are 4 for each method.
It is sent to the method switching circuit 5 in the form of an identification signal that sets one of the book output cottons 6 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.

A detection circuit 7 for detecting the signal level of received radio waves is connected to the frequency identification circuit 4.

A block configuration of the frequency identification circuit 4 in the device shown in FIG. 1 is shown in FIG. In FIG. 2, the pyro 71 signal from the waveform shaping circuit 3 is guided to one input terminal of an AND gate 47. The comparison output signal from the comparator 49 is sent to the other input terminal of the AND gate 47. Comparator 4
9 has the level value signal S (L) from the signal level detection circuit 7 delivered to its comparison side input terminal, and converts the level value signal S (L) into the reference voltage value V (r
ef), and the comparison output signal S (a) is applied to the input terminal of the AND gate 47 and also to one input terminal of the AND gate 48 .

The output of AND gate 47 is applied to one input terminal of AND gate 41. The other input terminal of the AND gate 41 receives the gate signal S(g) from the gate pulse generator 43.
is guided. The gate pulse generator 43 is an AND gate 4
It is connected to a reference oscillator 44 via a reference oscillator 44, and generates a gate signal S (gl, a reset signal S (rl), a launch signal 5 (1), etc. at a predetermined timing based on a reference frequency signal provided from the reference oscillator 44. The pulse width of the gate signal s tg+ is made to be a unit time width (1 second).These signals S(g), 5(11, 5(
The signal waveform and generation timing of r) are shown in Figure 3 (1).
, (2) and (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, and calculates the pilot signal frequency 5 of each method.
．． 15.25.55 Hz,
The corresponding output line of the four output lines is set to the "1" level and sent to the latch circuit 46.

A recent signal S (rl) is led from a gate pulse generator 43 to a recent terminal of the counting section 42, and the count value is reset by an erroneous sesor signal S (r).A launch control terminal of a latch circuit 46 A latch signal S(1) is led from the gate pulse generator 43, and the latch timing is controlled by the latch signal 5(1).The output of the launch circuit 46 is used to switch the method via the output line 6. Dedicated to circuit 5.

An example of the configuration of the counting section 42 is shown in FIG. Fourth
In the figure, the output from the 1 and AND gate 41 is led to the input terminal of the 175 frequency divider 420. The divided output of the 0 frequency divider 420 is diluted to the input terminal of the AND gate 427, and each of the counters 421 to 423 led to the input terminal. Counters 421 to 423 are circuits that output rlJ level output signals when the number of input pulse signals is 2 to 4.4 to 6.9 to 13, respectively.

The output of the counter 423 is led to the input terminal of the latch circuit 46, and is also connected to the ant gate via the inverter 426.
1-427 to 429 input terminals.

Similarly, the output of the counter 422 is led to the input terminal of the AND gate 429, and also to each input terminal of the AND gate 427 and 42B via the inverter 425, and the output of the counter 421 is led to the input terminal of the AND gate 428. At the same time, it is guided to the input terminal of AND gate 427 via inverter 424 . and gate 427
The output of ~429 is sent to the latch circuit 46 via four output lines.
are respectively guided to each input terminal of.

In the counter shown in FIG. 4, the manually input pilot signal is once frequency-divided by frequency divider 420 to 115. Therefore, the pilot signal frequency to be identified is 5H
2 becomes IHz, 15Hz becomes 3Hz, 25Hz becomes 5Hz
, 55H2 is converted to 11Hz. counter 421
When the number of input pulses is 2 to 4, the counter 422
is 4 to 6, and the counter 423 sends an output to the latch circuit when it is 9 to 13.

When each counter 421 to 423 sends an output,
By closing the AND gates 427 to 429 via an inverter connected to the output terminal, a lower counter having a lower number of counters than itself is prevented from sending an output to the latch circuit. This can prevent a situation in which the lower counter also outputs an integer number of counts even though the upper count is transmitting an output. If the pilot signal is once frequency-divided by 175 and then counted, the number of connected stages of binary counters forming the counters 421 to 423 can be significantly reduced.

The operation of the FIG. 1 apparatus will now be described.

The received radio wave is converted into an IF signal by a high frequency receiving section (not shown), and the IF4Ts signal is input to demodulation circuits 11 to 14, respectively. The SUB signal obtained by the demodulation circuit 14 is input to a pilot filter 2 to extract a pilot signal, which is shaped into a pulse waveform by a waveform shaping circuit 3 and then inputted to a frequency identification circuit 4.

In the frequency identification circuit 4, when the signal level of the received radio wave is sufficiently large, a high level output is sent from the comparator 49 and the AND gates 47 and 48 are opened, so that the manually input pilot signal is not detected. passes through AND gates 47 and 41 and is input to the counting section 42. In this case, the opening time of the AND gate 41 is adjusted to 1 second by the gate signal S (gl) from the gate pulse generator 43. Therefore, the number of pulses of the pilot signal counted by the counter 42 during this 1 second is the pilot signal frequency.

The counting unit 42 determines whether the frequency of the input pilot signal is 5Hz, 15Hz, 25Hz, or 35Hz.
When it is identified, the identification result is sent to the latch circuit 46. The latch circuit 46 has a latch signal S
At the same time as latching the identification result at timing (L),
The identification result is sent to the method switching circuit 5. As a result, the system switching circuit 5 selects a demodulation circuit suitable for the stereo broadcasting system of the received radio waves.

Next, the operation of the frequency discrimination circuit 4 when the signal level of the received radio wave momentarily becomes weak will be explained below with reference to FIG. FIG. 5 is a No. 43 waveform diagram of each part of the frequency identification circuit 4 of FIG. 2. In FIG. 5, S (L) is the level value signal from the signal level detection circuit 7, S fa) is the comparison output signal of the comparator 49, and S Ftel is the reference frequency signal from the reference oscillator 44 that has passed through the AND gate 48. , S fcl are pilot signals that have passed through the AND gate 47.

While the level value signal S (L) from the signal level detection circuit 7 is larger than the reference voltage value V (ref) of the reference power supply 45, the comparison output signal S (11 is at high level and The gates 47 and 48 are opened, and the above-described operation is being performed.

The level value signal S (L) momentarily changes to the reference voltage value V (r
ef), it becomes impossible to identify the pilot signal. In this case, the comparison output signal S (a) of the comparator 49 becomes low level, and the AND gates 47 and 48 are closed. As a result, the pilot signal S fc) is no longer supplied to the counting section 42, and the reference frequency signal S (bl) is no longer supplied to the gate pulse generator 43.

The gate pulse generator 43 determines the pulse length of the gate signal S (gl) by counting the reference frequency signal 5 (b1), but this counting is stopped while the reference frequency signal S (b) is cut off. Therefore, the gate signal S (gl) does not go to low level even if the pulse width exceeds 1 second.

The level value signal S (L) is again changed to the reference voltage value V (ref
), the comparison output signal 5(a
l becomes high level again, opens the AND gate 47°48, and sends the pilot signal S (C) to the counting section 42.
and the supply of the reference frequency signal S (bl) to the gate pulse generator 43 is resumed. When 1 second has passed, the gate signal S[g] is set to low level and the AND gate 41
will be closed.

As a result of the above operation, the received electric field becomes weak and the level value signal S (1
) is below the reference voltage value V, (ref), the counting section 42 interrupts counting of pilot signals and can restart counting again after the received electric field becomes strong, so that the received electric field is instantaneously It is possible to prevent malfunctions in frequency identification caused by weak frequencies.

〔Effect of the invention〕

According to the present invention, even when the received radio waves momentarily fluctuate to a weak electric field, the identification of the pyro/) signal frequency, and therefore the identification of each stereo broadcasting system, can be performed properly without error, and the radio waves monaural even if reception conditions are poor.
You can enjoy stereo broadcasting without switching modes. This is especially true when this device is used on a company radio where radio wave reception conditions are not always good.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an amplitude modulation stereo broadcast system as an embodiment of the present invention, FIG. 2 is a block diagram of a frequency identification circuit in the device shown in FIG. 1, and FIG. 3 is a gate pulse generator in the circuit shown in FIG. FIG. 4 is a block diagram of a part of the circuit in FIG. 2, and FIG. 5 is a signal waveform diagram of each part of the circuit in FIG. 11-14... Demodulation frequency f/s, 2... Pilot filter, 3... Waveform shaping circuit, 4... Frequency identification circuit, 5
...Method switching circuit, 7.Signal level detection circuit, 42..Count section, 43..Gate pulse generator, 45..Reference power supply, 46..Launch circuit, 4.
9... 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 comprising a circuit includes a signal level detection circuit for detecting a signal level of a received radio wave, the frequency identification circuit includes a counter circuit that counts pilot signals and identifies their frequency, and
When the signal level is below a predetermined value, the supply of the pilot signal to the counter circuit is stopped, and control is performed so that the time period during which the pilot signal is supplied to the counter circuit is a fixed time in one measurement. An amplitude modulation stereo broadcast system identification device comprising a circuit.