JPH0254703B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an FM receiver, and more particularly to an FM receiver capable of receiving traffic information broadcasts.

FM broadcasting has the advantage of having less noise and distortion, as well as having a sufficiently wide audio frequency band, so it can broadcast with excellent sound quality and there is no need to worry about interference.
Furthermore, since it is possible to perform multiple modulation on the same carrier wave, it is used for traffic information broadcasting to send traffic information to drivers. In the case of this traffic information broadcast, a 57KHz traffic information pilot signal indicating that the station is equipped with a traffic information system and various control signals are superimposed and transmitted together with the traffic information program on the same carrier wave, and the receiving side transmits the traffic information pilot signal. Traffic signals and control signals are detected by a traffic information decoder to control various traffic information functions.

Due to its nature, most traffic information broadcasts are received using in-vehicle receivers, but because they are in-vehicle receivers, stable reception conditions cannot be maintained. That is, the antenna input level constantly changes depending on the surrounding situation, and the reception output and S/N change accordingly. In addition, the modulation degree of the 57KHz traffic information pilot signal is kept low to reduce the impact on the main general broadcast program, so the receiver
FM detection output is also small, 57K in white noise
It is not easy to distinguish it from the Hz component. If the sensitivity of the traffic information decoder is increased too much, it is likely to malfunction due to white noise, whereas if the sensitivity is decreased too much, there is a risk that the decoder will not operate. Because,
In an FM receiver, even if an input signal larger than a certain level is applied, the detection output will hardly change due to the limiter in the FM detection circuit, and depending on the variation, the sensitivity level of the decoder may exceed the detection output. It is from.

Furthermore, due to FM detection distortion, harmonics of the 19KHz stereo pilot signal are generated, and among these harmonics, the third harmonic is confused with the regular 57KHz traffic information pilot signal, causing malfunction. Detection distortion tends to increase as the tuning deviation of the receiver increases, and malfunctions occur when the 57KHz component of the harmonics mentioned above exceeds the operation start level of the traffic information decoder. As with the previous example, this malfunction also occurs as the sensitivity of the traffic information decoder increases.
Even a slight synchronization shift will cause malfunction.

In this way, the sensitivity setting of the traffic information decoder is
This is extremely critical, and incorrect adjustment or settings can easily lead to malfunctions or malfunctions.
This was extremely complicated and time-consuming because it had to be done by taking into account variations in the FM detection output level and the sensitivity of the FM receiver.

The present invention has been made in view of the above points, and it is an object of the present invention to provide an FM receiver equipped with a traffic information decoder that does not malfunction due to white noise during weak input or harmonics of the stereo pilot signal due to detuning. purpose.

The FM receiver according to the present invention includes a traffic information decoder that detects reception of traffic information broadcasting, and the traffic information decoder is activated based on a sum signal of a signal corresponding to an antenna input level and a signal corresponding to an FM detection output signal. It is designed to operate selectively.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. In the figure, 1 is the front end,
The front end 1 amplifies the received signal from the antenna 2, converts it into an intermediate frequency signal, and supplies it to the FM detection circuit 3. In the FM detection circuit 3, the intermediate frequency signal from the front end 1 is amplified by a limiter amplifier 4, and then detected by a phase shift circuit 5 and an FM demodulation circuit 6. The detection output is the second
As shown in Figure a, the frequency deviation is derived as a change in DC voltage. This detection output signal is converted by the out-of-band mute signal generating circuit 7 into an inverted trapezoidal out-of-band mute signal as shown in FIG. A level detection circuit 9 is added to the limiter amplifier 4, and the level detection circuit 9 generates a DC voltage according to the antenna input level as shown in FIG. The addition output of addition circuit 8 is a capacitor
Smoothed by a smoothing circuit 10 consisting of C ₁ and resistor R ₁ ,
VCA (voltage control amplifier circuit) with detection output as input
11 via resistor _R2 to control its gain. That is, the output of the smoothing circuit 10 is
As shown in Figure d, when the input is weak or out of tune, the potential becomes high and the gain of the VCA 11 is reduced, and when the input is medium to strong,
At the time of tuning, the potential becomes low and the gain is increased to obtain a so-called soft mute effect outside the band. The output of the FM detection circuit 3 is supplied to a stereo demodulation circuit (MPX) 12 and a traffic information decoder 13.

The MPX 12 demodulates the stereo signal from the detection output and sends it to the left and right speakers 15 via the output amplifier 14.
Drive L and 15R. On the other hand, in the traffic information decoder 13 that detects the reception of traffic information broadcasting, the traffic information pilot detection circuit 16 detects the signal in the input signal.
Detects the 57KHz component. The output of the traffic information pilot detection circuit 16 is supplied to a comparator switch circuit 17 which is turned on/off in response to the addition signal of the addition circuit 8. If the added signal has a potential above a certain level, the comparator switch circuit 17 is turned off and does not supply its output to the subsequent stage even if the pilot detection circuit 16 detects a 57 KHz component. This is because even if a 57KHz component is detected when the addition signal is at a high potential, this 57KHz component is most likely due to white noise at weak input or harmonics of the stereo pilot signal due to detuning. This is to ignore the detection of the 57KHz component in the state. Conversely, when the addition signal is at low potential,
The detection of the 57KHz component can be determined to be almost the 57KHz component of the traffic information pilot signal, and the comparator switch 17 is turned on, driving the subsequent switching circuit 18 to operate the controlled section 19 that is its load. The controlled unit 19 performs reception display of traffic information broadcasting stations, cancellation of mute, switching of low frequency signal system, etc., and obtains functions based on traffic information system reception.

FIG. 3 is a circuit block diagram showing a specific example of the vicinity of the comparator switch circuit 17.
In the figure, parts equivalent to those in FIG. 1 are designated by the same reference numerals. A variable resistor is used as the resistor R ₁ of the smoothing circuit 10 in the FM detection circuit 3 , and the addition output is voltage-divided by the variable resistor and input to the comparator switch circuit 17 . The comparator switch circuit 17 is composed of transistors _Q1 to _Q3 , resistors _R3 to _R8 , and capacitors _C2 and _C3 , and its input signal is passed through a low-pass filter composed of resistor _R3 and capacitor _C2 to transistor Q. It is applied to the base of _Q1 , and when the input is weak or out of tune, it becomes a high potential and turns on the transistor _Q1 . The level at which transistor Q ₁ is turned on is adjusted by changing the voltage division ratio of variable resistor R ₁ .

The output terminal of the traffic information pilot detection circuit 16 is pulled up by a resistor _R4 , and the output terminal is 57K.
When the Hz component is detected, a high level output is generated to turn on transistor Q ₂ and turn off transistor Q ₃ to drive switching circuit 18 . However, if the transistor Q ₁ is turned on by the addition output at this time, the base of the transistor Q ₂ is fixed at approximately zero volts, and the transistor Q ₃ remains on, so the switching circuit 18 does not operate. Here, the time constant circuit consisting of resistors R ₅ to R ₇ and capacitor C ₃ is used to detect short-term loss of the traffic information pilot signal,
This is to provide a delay time so that even if the transistor _Q1 is instantaneously turned on due to the ripple component in the addition output, the transistor _Q3 will not be inverted each time.

The collector of transistor _Q3 is pulled up by resistor _R8 , and when it is off, it is approximately at the power supply voltage Vcc.
A collector output equal to 1 is supplied to the switching circuit 18, and in response, the switching circuit 18 drives the controlled section 19. In this example,
The controlled unit 19 has a circuit configuration consisting of a light emitting diode D ₁ that displays the reception of a traffic information broadcasting station, a transistor Q ₄ that drives it to blink, and resistors R ₉ and R ₁₀ . Needless to say, it also drives and controls circuits that perform system switching.

A resistor is connected between the base of transistor _Q1 and ground.
Transistor Q ₅ is connected through R ₁₁ ,
The transistor Q ₅ is turned on/off in response to the collector output of the transistor Q ₃ supplied via the resistor R ₁₂ to forcibly apply hysteresis to the comparator switch circuit 17, so that the transistor Q 5 closes to the threshold level. This prevents Q ₃ from chattering. That is, in the standby state when transistor _Q3 is on,
Transistor _Q5 is off and VBE _(Q1) volts is at the threshold level of comparator switch circuit 17. Here V _{BE (Q1)} is a transistor
is the base-emitter voltage at which Q ₁ turns on,
For silicon transistors it is about 0.6-0.7 volts. In the so-called system operating state in which the output of the traffic information pilot detection circuit 16 turns on the transistor _Q2 and turns off the transistor _Q3 , the transistor _Q5 turns on, so its collector is equivalent to being grounded, and the resistor R ₃ and R ₁₁
Since a voltage dividing circuit is constructed by , the threshold level becomes R ₁₁ /R ₃ +R ₁₁ ×Q _{BE (Q1)} volts.

In other words, from the perspective of the adder circuit 8, the transistor Q ₁
When operating the system with V _BE(Q1)
It is sufficient to supply a voltage lower than ×K volts, but a voltage higher than V _BE(Q1) ×R ₁₁ /R ₃ +R ₁₁ ×K volts is required to turn on transistor Q ₁ and put the system into a standby state. shall be. (Here, K is the reciprocal of the voltage division ratio by the variable resistor _R1 , and K≧1). Therefore, since the threshold level changes depending on the state of the comparator switch circuit 17, it has hysteresis characteristics.

Conventionally, the operating sensitivity of a traffic information decoder was set by
This was done by changing the gain of the traffic information pilot detection circuit, but in this example, it is configured with a variable resistor _R1 , and since the signal handled here is a DC component, a DC meter can be used for adjustment. It can be done easily. In addition, the FM detection circuit 3 excluding the smoothing circuit 10 in FIG.
If the variation in the output of the adder circuit 8 can be kept within a small range by setting the conditions, the variable resistor can be omitted. In other words, the partial pressure ratio can be fixed and adjustment can be omitted.

FIG. 4 is a circuit block diagram showing another embodiment around the comparator switch circuit 17, in which the same parts as in FIG. 3 are designated by the same reference numerals.
In this embodiment, a fixed resistor is used as the resistor R ₁ to fix the voltage division ratio K to 1, and a diode D ₂ is further connected between the base of the transistor Q ₁ and the collector of the transistor Q ₄ via the resistor R ₁₁ . The configuration is such that connections are made with the polarities shown in the figure, and the other configurations are the same as in FIG. 3. Further, the circuit operation is almost the same as in the case of FIG. 3, and when the system is in standby mode, the threshold level of the comparator switch circuit 17 is V _{BE (Q1)} . The output of adder circuit 8 is
When V _{BE (Q1)} or less and the output of the traffic information pilot detection circuit 16 becomes a high level, the system becomes operational, and the transistor Q ₄ turns on, lighting up the light emitting diode D ₁ and turning on the cathode of the diode D ₂ . Equivalently grounded.

In this state, the output of the adder circuit 8 increases due to a decrease in the antenna input level or detuning, etc.
Even if V _BE(Q1) volts or higher, transistor Q ₁ does not immediately flip from off to on. In other words, in this state, diode D ₂ and transistor Q ₁ form a type of current mirror circuit, and if we consider that their forward characteristics are similar, then the diode
The current flowing through D ₂ and the collector current Ic of transistor Q ₁ are approximately equal. Transistor Q ₁ is used to turn off transistor Q ₂ , so to turn off transistor Q ₂ , Vcc
−Ic×R ₄ <V _BE(Q2) It is necessary to send enough current to flow through the diode D ₂ to satisfy Ic (V _BE(Q2) is the base-emitter voltage at which the transistor Q ₂ turns from on to off. ). Therefore, by appropriately selecting the ratio of R ₃ , R ₁₁ and R ₄ , it is possible to turn on transistor Q ₁ and turn off transistor Q ₂ for the first time at V _{BE (Q1)} volts or higher, resulting in In other words, it can have hysteresis characteristics as in the previous example.

In each of the above embodiments, the operation of the traffic information decoder 17 is controlled according to the sum signal of the signal corresponding to the antenna input level and the signal corresponding to the FM detection output signal (out-of-band mute signal). However, it is also possible to configure the control according to only one of the signals.

As detailed above, in the present invention, the traffic information decoder is configured not to operate during weak input or detuning, so it is possible to prevent malfunctions due to white noise during weak input and harmonics of the stereo pilot signal due to detuning. . Further, the sensitivity adjustment is easy, and if the circuit conditions are sufficient, the sensitivity adjustment can be omitted, which has a great effect.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention;
Figures 2 a to d are waveform diagrams of various parts in Figure 1, Figure 3 is a circuit block diagram showing one embodiment of the periphery of the comparator switch circuit, and Figure 4 shows another embodiment of the periphery of the comparator switch circuit. FIG. Explanation of symbols of main parts, 3...FM detection circuit,
6...FM demodulation circuit, 7...Out-of-band mute signal generation circuit, 8...Addition circuit, 11...Voltage control amplifier circuit, 12...Stereo demodulation circuit, 13...Traffic information decoder, 16...Traffic information Pilot signal detection circuit, 17... Comparator switch circuit, 19... Controlled section.

Claims (1)

[Claims] 1. A traffic information decoder that detects reception of traffic information broadcasting, and a signal and FM according to an antenna input level.
What is claimed is: 1. An FM receiver comprising: an adder circuit for adding a signal corresponding to a detection output signal; and selectively operating the traffic information decoder depending on the output of the adder circuit. 2. The traffic information decoder includes a traffic information pilot detection circuit that detects a traffic information pilot signal indicating that the station is a traffic information broadcasting station, and selectively outputs the output of the traffic information pilot detection circuit according to the output of the addition circuit. 2. The FM receiver according to claim 1, further comprising a transmitting switch means and a controlled section for receiving traffic information activated by the output of said switch means.