JPH0533086Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to a signal discrimination circuit that discriminates the presence of an identification signal of a predetermined frequency, and particularly relates to a signal discrimination circuit that discriminates the presence of an identification signal using a counter. It is an object of the present invention to provide a signal discrimination circuit designed to prevent the circuit from malfunctioning due to signal interruption.

(b) Conventional technology FMX stereo broadcasting has been proposed as a way to improve the S/N ratio of FM stereo broadcasting and expand the service area. The FMX stereo broadcasting simultaneously transmits a compressed stereo difference signal in addition to the conventional FM stereo broadcast transmission signal, and the compressed stereo difference signal is a 38KHz subcarrier on which the stereo difference signal is AM modulated. are modulated in an orthogonal relationship. Additionally, the transmission signal for FMX stereo broadcasting includes a 10Hz identification signal to distinguish it from normal FM stereo broadcasting. Therefore, in order to receive FMX stereo,
It is necessary to detect the identification signal and switch the reception mode of the receiver to be suitable for FMX stereo reception.

Regarding FMX stereo broadcasting, please refer to the magazine "JASJOURNAL" September 1986 issue, pages 11 to 15.
Details are given on page.

Incidentally, in order to detect the 10 Hz identification signal, a signal discrimination circuit as shown in FIG. 2 may be used. In FIG. 2, a 19 KHz stereo pilot signal applied to the first input terminal 1 is frequency-divided by a first frequency dividing circuit 2 to approximately 74 Hz, and is applied to a counter 3 as a clock signal. On the other hand, the 10Hz identification signal applied to the second input terminal 4 is passed through the bandpass filter 5.
Since the signal is applied to the pulse generating circuit 6 via the pulse generating circuit 6, a pulse signal having the same frequency as the identification signal is generated from the pulse generating circuit 6. The pulse signal is frequency-divided by a second frequency dividing circuit 7 and supplied to the counter 3 as an operation signal. Therefore, in the counter 3,
During the "H" period of the pulse signal, the clock signal is counted, and the detection circuit 8 detects whether the count value of the counter 3 is a predetermined value.

The signal discrimination circuit shown in FIG. 2 includes a level detection circuit 9 that detects the level of the signal obtained at the output end of the bandpass filter 5. The level detection circuit 9 generates an output signal of "L" when the level of the signal is above a predetermined value, and generates an output signal of "H" when the level of the signal is below a predetermined value. For that reason,
If the level of the signal decreases for some reason,
The output signal of the level detection circuit 9 becomes "H", and the detection circuit 8 is reset.

(c) Problems to be solved by the invention By the way, when receiving a radio broadcast having an identification signal, if multipath interference or external noise is mixed in, the identification signal will be distorted and its level will drop. Therefore, even if the level of the identification signal decreases, the condition of the receiver may change while the radio broadcast having the identification signal continues to be received. However, when the level detection circuit 9 as shown in FIG. 2 is used, even if the level of the identification signal drops instantaneously, the detection circuit 8 is reset and the state of the receiver changes. For example, when receiving an FMX stereo broadcast, if the level of the 10Hz identification signal momentarily drops, the receiver will be switched to receive the FM stereo broadcast, causing fluctuations in the noise level, etc., which may make the listener uncomfortable. There was a problem with giving a sense of feeling.

(d) Means for Solving the Problems The present invention has been made in view of the above points, and includes a pulse generation circuit that generates a pulse according to the frequency of an identification signal, and a pulse generation circuit that generates a pulse according to the frequency of the identification signal, and a pulse generation circuit that generates a pulse according to the frequency of the identification signal. a detection circuit that detects the presence of the identification signal based on the count value of the counter; and a level detection circuit that detects the level of the identification signal and generates a reset signal for the detection circuit. and a gate circuit that cuts off the reset signal depending on the state of the output signal of the detection circuit.

(E) Effect According to the present invention, the gate circuit is cut off in response to the first output signal generated from the detection circuit when a broadcast signal including an identification signal is received, and the level detection circuit is reset to the detection circuit. The signal is prohibited from being applied. Therefore, it is possible to prevent the detection circuit from being reset even if the identification signal is cut off for a short time or its level drops. Furthermore, when a broadcast signal that does not include an identification signal is being received, the gate circuit opens in response to the second output signal generated from the detection circuit. Therefore, the detection circuit continues to be reset while receiving a broadcast signal that does not include an identification signal. Then, when the tuning state changes from receiving a broadcast signal that does not include an identification signal to receiving a broadcast signal that includes an identification signal, and an identification signal of a predetermined level or higher is applied to the level detection circuit accordingly, the reset signal stops. Then, the detection circuit detects the count value of the counter.

(F) Embodiment Figure 1 is a circuit diagram showing an embodiment of the present invention.
Reference numeral 10 denotes an AND gate to which the output reset signal of the level detection circuit 9 is applied to the first input, the output signal of the detection circuit 8 is applied to the second input, and the output is applied to the reset terminal of the detection circuit 8. Note that the other circuit blocks in FIG. 1 are designated the same as in FIG. 2, are given the same reference numerals, and will not be described further.

By the way, broadcasting stations that can transmit FMX broadcasts always transmit FMX broadcasts, and there is always a 10Hz ID signal in the signal. on the other hand,
Some stations can only transmit FM broadcasts, and these stations are randomly placed within a given band at a given frequency. Therefore, FM and
A receiver capable of receiving FMX broadcasts must determine whether the received signal is an FM broadcast or an FMX broadcast each time it is tuned, and a signal discrimination circuit as shown in Figure 1 is essential for this determination. It is. However, if a certain station is received and it is determined to be an FMX broadcasting station, for the reasons mentioned above, the status of receiving FMX broadcasting should not change unless the tuning status is changed, and the level will not change. There is no need for the signal discrimination circuit to have strict judgment capabilities such as detection.

The signal discrimination circuit according to the present invention was created based on the above-mentioned concept, and its operation will be explained next in accordance with the reception state.

If you are currently receiving FM broadcasts, the first
A 19KHz stereo pilot signal applied to input terminal 1 is frequency-divided by first frequency dividing circuit 2 and applied to counter 3 as a clock signal. At that time, F.M.
Since the broadcast is being received, the 10Hz identification signal is not applied to the second input terminal 4, and the second frequency dividing circuit 7 outputs the 10Hz identification signal to the counter 3.
No operating signal is applied. Therefore, counter 3
does not perform a counting operation, and the output of the detection circuit 8 becomes "H". The “H” output signal of the detection circuit 8 is transmitted from the output terminal 11 to a usage circuit (not shown) such as a display circuit, and is applied to the second input of the AND gate 10. Therefore, the AND gate 10 becomes open.

On the other hand, since no identification signal is applied to the second input terminal 4, the input of the level detection circuit 9 becomes "L" and its output becomes "H". Then, the "H" output passes through the open AND gate 10,
Since the signal is applied to the reset terminal of the detection circuit 8, the detection circuit 8 is reset and the output terminal 11 is maintained in the "H" state.

When the tuning state is changed and FMX stereo broadcasting is received, a 19KHz stereo pilot signal is applied to the first input terminal 1 and a 10Hz identification signal is applied to the second input terminal 4. If the level of the 10Hz identification signal is sufficiently large, the output of the level detection circuit 9 becomes "L", and the "L" signal is output to the AND gate 1.
0 to the detection circuit 8, the reset of the detection circuit 8 is released. And the second
The counter 3 counts the output clock signal of the first frequency dividing circuit 2 in accordance with the output operation signal of the frequency dividing circuit 7, and the counting result is detected by the detecting circuit 8. If the count value of the counter 3 is a predetermined value, the FMX is output from the detection circuit 8.
An "L" output signal indicating broadcast reception is generated. The "L" output signal is transmitted from the output terminal 11 to the circuit to be used, and is also applied to the second input of the AND gate 10. Therefore, the AND gate 10 is closed, its output becomes "L", and resetting of the detection circuit 8 is prohibited. In this state, the detection circuit 8 is not reset;
The output of the detection circuit 8 changes only depending on the count value of the counter 3. Therefore, once the signal discrimination circuit shown in FIG. 1 determines that FMX broadcast reception is being received, it does not respond to changes in the level of the identification signal, thereby preventing erroneous switching.

When the tuning state is changed again and FM stereo broadcasting is received, the 10Hz identification signal disappears and the counter 3 stops operating. At that time, the detection circuit 8
Maintain the state at the time of previous FMX reception. In order to cancel this, as described in Japanese Patent Application No. 139238/1983 filed earlier by the same applicant as the present invention, it is necessary to detect that the 10Hz identification signal does not exist for a predetermined period of time,
The detection circuit 8 may be reset. Then, the output of the detection circuit 8 becomes "H", the AND gate 10 becomes open, and the state returns to the initial state in which the "H" output of the level detection circuit 9 is applied to the detection circuit 8.

The level detection circuit 9 has a predetermined threshold level, detects the signal level applied from the bandpass filter 5, and outputs "L" if the signal is above the threshold level, and "L" if the signal is below the threshold level. For example, it generates an "H" output signal, but in order to prevent malfunctions due to noise etc., redundancy may be provided so that the output signal changes only after multiple detections are performed. .

In addition, although this invention has explained the relationship between FMX broadcasting and FM broadcasting, it is also important to note that the relationship between FMX broadcasting and FM broadcasting has been explained.
It can be applied to a variety of broadcasting systems, such as FM broadcasting, in which stations that include identification signals and stations that do not include them coexist.

(g) Effects of the invention As described above, according to the invention, it is possible to provide a signal discrimination circuit that can reliably discriminate identification signals included in broadcast signals. In particular, according to the present invention, once an identification signal is detected, the gate is shut off and the output of the level detection circuit is cut off, thereby preventing misjudgment of a station transmitting a broadcast signal including an identification signal. Can be prevented.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a signal discrimination circuit which is an object of improvement of the present invention. 3...Counter, 8...Detection circuit, 9...Level detection circuit, 10...And gate.

Claims (1)

[Claims for Utility Model Registration] (1) A pulse generation circuit that generates pulses according to the frequency of an identification signal, a counter that counts clock signals according to the output signal of the pulse generation circuit, and the count value of the counter. a detection circuit that detects the presence of the identification signal by detecting the level of the identification signal;
A signal discrimination circuit comprising: a level detection circuit that generates a reset signal for the detection circuit; and a gate circuit that cuts off the reset signal depending on the state of the output signal of the detection circuit. (2) The detection circuit detects that the count value of the counter reaches a predetermined value and generates an output signal of a first level, and the gate circuit detects that the count value of the counter reaches a predetermined value.
2. The signal discrimination circuit according to claim 1, wherein the output signal of said level detection circuit is cut off in accordance with the output signal of the level of said level detection circuit.