JPH0345035A - Fm receiver - Google Patents

Abstract

PURPOSE:To provide both broadcasts with their respective optimum receptions by corresponding separation control to a general FM stereo broadcast and an FMX stereo broadcast to each other. CONSTITUTION:A signal from a detection circuit 6 is fed to a terminal Ts through resistors R7, R8 and fed to a terminal Th through a diode D1. The collector and the emitter of a transistor(TR) Q1 are connected in parallel with a resistor R8 and a detection output Sd is extracted from a terminal Td and the signal Sd is fed to the base of the TR Q1 via a common emitter TR Q2. Thus, the operation start point of a stereo noise control circuit 17 and a high-cut control circuit 18 with respect to an antenna input level is automatically changed to an optimum value at the reception of an FM broadcast and of an FMX broadcast. Thus, the optimum separation characteristic or frequency characteristic is obtained in the reception of any broadcast.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an FM receiver.

[Summary of the invention]

The present invention enables an FM receiver to perform separate lane control for general FM stereo broadcasting and so-called FM This is what I did.

[Conventional technology]

FMX is one of the noise reduction systems in FM stereo, and aims to improve the S/H by focusing on the triangular noise characteristics in the FM signal.

That is, assuming that stereo left and right channel audio signals are LSR, in general FM stereo broadcasting, the baseband signal Sfm is expressed as Sfm=M+5sin ωt+Sp as shown in FIG. 4A.

On the other hand, in FMX stereo broadcasting, the baseband signal Sfx is shown as shown in FIG. 4B and is expressed as follows.

Sfx=M+5sina+t+Xcoscut
+ Sp= S fm + Xcos act l, -1-te, signal x is -22d of difference signal (L-R)
Point B is the knee point, and anything below this knee point is 1.
Boost the signal uniformly by 4 dB and add 1 dB to the signal.
This is a signal obtained by adding the identification signal S1 of 0 losses (strictly speaking,
The frequency of the signal S1 is 1/1920 of the frequency of the pilot 1 word Sp.

Therefore, this FMX broadcast can be received by a general FM receiver. In addition, when receiving with a dedicated FMX receiver, signal X is used for stereo demodulation, meaning that signal However, at this time, the level of noise contained in signal X also decreases and the S/N of signal can expand its service area.

FIG. 5 shows an equalization circuit of an IC that demodulates the audio signal R from the signals Sfm and Sfx.

That is, in this figure, the circuit (11) surrounded by a chain line
~ (19) is one chip I as decoder IC (10)
It has been converted into C. Then, the signal Sfm or Sfx is demodulated from the intermediate frequency signal in the FM demodulation circuit (1),
This signal Sfm or Sfx is sent to the gain correction circuit (3)
The subcarrier signal sinωt 5cosωt is supplied to the stereo demodulation circuit (12) through the phase correction circuit (2), and is supplied to the PLL (11) through the phase correction circuit (2).
are formed, and these subcarrier signals are sent to the demodulation circuit (12
) from the signal Sfm or Sfx to the signals M, S
(and signal X) is demodulated and extracted.

Then, the signal X is supplied to the trap circuit (5) to remove unnecessary signal components, and the signal (13), the signal X is a difference signal (L-
R), and this difference signal (L-R) is supplied to the level control circuit (14) to perform level correction (level down) complementary to the level boost at the time of transmission. The signal (LR) is supplied to the switch circuit (15>). At this time, the level of the noise component included in the signal X (=LR) also decreases at the same time.

Further, the signal S is supplied to the switch circuit (J5), and the signal X from the demodulation circuit (12) is supplied to the filter (4).
), the identification signal Si is taken out, and this signal Si is supplied to the detection circuit (19), which sets the level to "1" when the broadcast is FM broadcast, and to "0" when the broadcast is FMX broadcast.
The detection signal Sd that becomes the level is extracted, and this signal Sd
is supplied to the switch circuit (15) as its control signal, and from the switch circuit (15), a difference signal (L-R) of the signal S is taken out when receiving FM broadcasting, and F M
When receiving a broadcast, a difference signal (LR) based on signal X is extracted.

Then, this difference signal (L-R) is transmitted to the matrix circuit (1
6), and the signal M from the demodulation circuit (12) is also supplied to the matrix circuit (16).
R is taken out and 1. This signal R is taken out to the terminal T1.Tr through the stereo noise control circuit (17) and the high cut control circuit (18).

In this case, the control circuits (17) and (18) are equivalently configured as shown in FIG. 6, for example.

That is, the stereo noise control circuit (17) is configured by connecting a capacitor C1 and a variable resistance circuit R1 in series between the signal line of the signal R and the signal line of the signal R. Then, a signal Sa indicating the antenna input level as shown in FIG. 7, for example, a signal Sa for the S meter obtained by detecting the level of the intermediate frequency signal in the forming circuit (6), is further transmitted through the resistor R6. The signal is supplied as a control signal to the variable resistance circuit R1 through the terminal Ts, and the resistance value of the variable resistance circuit R1 is set to a value corresponding to the level of the signal Sa.

Therefore, if the antenna input level is sufficiently large, the S/
When N is sufficiently good, the resistance value of variable resistance circuit R1 is large, and the signal R is used as it is in the next stage control circuit (18).
supplied to However, the antenna input level is low,
When the S/N is poor, the resistance value of the variable resistance circuit R1 becomes small, and the high-frequency noise contained in the signal L1R is added to each other and canceled out. Therefore, the high-frequency separation decreases, but the antenna input level increases. Even if it is small, a signal LSR with a relatively good S/N ratio can be obtained.

In addition, the high-cut control circuit (18) has resistors R2 and R3 connected in series to the signal line of the signal LSR, and capacitors C2 and C3 and variable resistance circuits R4 and R5 on their output sides, respectively. Configured by connecting in series. Then, the signal 3a from the resistor R6 is supplied as a control signal to the variable resistance circuits R, , Rs through the diode D and further through the terminal Th, and the resistance value of the variable resistance circuit R, , Rs is determined by the signal Sa. The size corresponds to the level of

Therefore, if the antenna input level is large enough, S
/ When N is sufficiently good, the variable resistance circuit R,, R3
Since the resistance value of R is large, the signal R is output as is.

However, when the antenna input level is low and the S/N is poor, the resistance values of variable resistance circuits R1 and R5 become small, the high-frequency noise included in the signal LSR is bypassed, and the high-frequency characteristics deteriorate. However, even if the antenna input level is small, the signal L with relatively good S/N
You can get SR.

Literature: FMXf Cor';' I: Cr LA-
3440J (7) Manual [Problems to be Solved by the Invention] However, with the above configuration, the features of FMX broadcasting cannot be fully demonstrated.

That is, FIG. 8A shows an example of static characteristics during reception of FM broadcasting, and the separation of signals RI and H is as follows.
As shown by the chain line, the antenna input level is 55 (18 μ
When the antenna input level is above 55 dBμ, it is about 40 dB, but as the antenna input level decreases from 55 dBμ, it gradually becomes worse due to the movement of the stereo noise control circuit (17), and when the antenna input level reaches about 30 dBμ,
OdB, that is, monaural mode.

The noise level gradually increases as the antenna input level decreases, as shown by the broken line.
The rate of increase in the noise level is due to the stereo noise control circuit (17), compared to when the stereo noise control circuit (17) does not work.
It has been improved. When a stereo broadcast is received in monaural mode, the S/N is approximately 23 dB (theoretical value) better than when received in stereo mode, so the antenna input level becomes approximately 30 dBμ and the signal is switched to monaural mode. Once that happens, the noise level will improve.

On the other hand, as shown in Figure B, when the stereo noise control circuit (17) is operated so that the noise level in FMX broadcasting becomes equal to the noise level in FM broadcasting, the separation characteristics at that time are as follows. Figure B
The antenna input level is 25dBμ.
It will not decrease until it reaches a certain level.

In other words, as mentioned above, the boosted signal X
However, when the signal is corrected (leveled down) to its original level during reception, the level of noise contained in the signal X also decreases, improving the S/N of the signal The required S/N ratio can be obtained without operating the stereo noise control circuit (17) until this point.

Therefore, as shown in FIG. 8A, if the stereo noise control circuit (17) is operated in the same way as when receiving FM broadcasts, the S
Even though /N is good, the separation becomes poor.

The same applies to the high-cut control circuit (18).

Therefore, the stereo noise control circuit as shown in Fig. 6 (
17), the high-cut control circuit (18), or the detection circuit (6) cannot fully utilize the features of FMX broadcasting.

This is especially true in car stereos, where the antenna input level changes as the car travels.

This invention attempts to solve these problems.

[Means to solve the problem]

Therefore, in this invention, when receiving FM broadcasting,
The operation start point of the stereo noise control circuit 1at (17>high-cut control circuit (18)) with respect to the antenna input level is different from when receiving FMX broadcasting.

[Effect]

Stereo noise control circuit (17) for antenna input level when receiving FM broadcasting and when receiving FMX broadcasting.
The operation start point of the high-cut control circuit (18) automatically changes to its respective optimum value.

[Example] In FIG. 1, the signal Sa from the detection circuit (6) is
It is supplied to the terminal Ts through the resistors Ri and Re, and is further supplied to the terminal Th through the diode D+. Note that, for example, Rq + Ra = R6.

Also, the collector of transistor Q1 is connected to resistor R8.
The emitters are connected in parallel, and the detection output Sd is taken out from the terminal Td, and this signal Sd is supplied to the base of the transistor Q through the emitter-grounded transistor Q2.

According to this configuration, when receiving FM broadcast, Sd
="1", transistor Q is turned off, and transistor Q1 is also turned off.

Therefore, at this time, the signal Sa is applied to the resistor Rff1R
6 to the variable resistance circuit R1, the signal Sa supplied to the variable resistance circuit R1 is
It becomes equal to the signal Sa supplied through the resistor R8, and has the same characteristics as in FIG. 7, as shown by the solid line in FIG. 2A. Therefore, the separation characteristic of the stereo noise control circuit (17) becomes as shown by the solid line in FIG. 8 and FIG. Similarly, the frequency characteristics of the high-cut control circuit (18) also become the same as in the prior art.

On the other hand, when receiving FMX broadcasting, 5d=60",
Transistor Q2 turns on and transistor QI
is also turned on.

Therefore, at this time, the signal Sa is supplied to the variable resistance circuit R1 only through the resistor R1, so the signal Sa supplied to the variable resistance circuit R1 is transmitted through the A+, m 631 line in FIG. As shown, the characteristics are shifted to the smaller antenna input level. Therefore, the separation characteristic at this time is a characteristic shifted toward the lower antenna input level, as shown by the chain line in FIG. 2B, for example, and when receiving FMX broadcasting,
Separation will not drop to an antenna input level that is, for example, 15 dB lower than when receiving FM broadcasts,
Excellent separation properties can be obtained.

Similarly, the operation start level of the high-cut control circuit (18) has a characteristic shifted to the lower antenna input level, and when receiving SMX broadcasting, it is possible to obtain better frequency characteristics even in weak electric fields than when receiving FM broadcasting. I can do it.

Moreover, at that time, the noise characteristics are equivalent to those of the conventional method.

Thus, according to the present invention, when receiving FM broadcasting and
When receiving X broadcast, the operating point of the stereo noise control circuit (17) or high cut control circuit (18) for the antenna input level is automatically changed to the respective optimum value, so it is possible to receive either broadcast. Optimal separation characteristics or frequency characteristics can be obtained at any time.

Moreover, for that purpose, transistors Q,...Q are required.

It is only necessary to add a number of parts such as , and the cost is low.

In the example shown in FIG. 3, the output signal Sa of the detection circuit (6) is supplied to the terminal Ts through a resistor R8. Further, the signal Sd from the terminal Td is transmitted to the common emitter transistor Q3. Q is supplied to the base of transistor Q through resistor R4 and to the input of resistor R5.

The collector and emitter of each are connected in series.

According to such a configuration, when receiving FM broadcast, Sd
=″l″, so transistor Q3. Q.

is turned off, and transistor Q is turned on.

Therefore, since the resistor R7° becomes a load on the detection circuit (6), the level of the signal Sa supplied to the control circuits (17) and (18) has the characteristics shown by the solid line in FIG. 2A, and the control circuit ( 17) and (18) have the same characteristics as before.

However, when receiving FMX broadcasting, Sd="0", so transistors Q, , Q, are turned on and transistor Q5 is turned off. Therefore, the resistor RIG
is released from the load of the detection circuit (6), so the signal Sa supplied to the control circuits (17) and (18) is
The level increases, resulting in the characteristics shown by the chain line in FIG. 2A, and therefore the separation characteristics and frequency characteristics are improved.

〔Effect of the invention〕

According to the present invention, the stereo noise control circuit (17) or the high-cut control circuit (17) for the antenna input level is controlled when receiving FM broadcasting and when receiving FMX broadcasting.
Since the operating points 8) are automatically changed to their respective optimum values, optimum separation characteristics or frequency characteristics can be obtained when receiving either broadcast.

Moreover, for this purpose, it is only necessary to add a few components such as transistors Q, Q2, and the cost is low.

[Brief explanation of drawings]

Figures 1 and 3 are connection diagrams of an example of this invention; Figure 2;
FIGS. 4 to 8 are diagrams for explaining the same. (1) is an FM demodulation circuit, and (10) is an I for stereo demodulation.
C1 (16) is a matrix circuit, (17) is a stereo noise control circuit, (18) is a high cut control circuit, (1
9) is a detection circuit. Agent Hidemori Matsukuma's assistant room (X-L-R) Academic error circuit diagram Figure 6 7 Site T input station A.

Claims (1)

[Scope of Claims] A stereo demodulation circuit that performs stereo demodulation for FM stereo broadcasting and FMX stereo broadcasting; a first detection circuit that detects an identification signal indicating the FMX stereo broadcast; Based on the detection output, the stereo signal demodulated from the FM stereo broadcast and the FMX
a circuit that selectively outputs a stereo signal demodulated from a stereo broadcast; a second detection circuit that detects an antenna input level; and a circuit that selectively outputs a stereo signal demodulated from a stereo broadcast; and a control circuit that performs noise reduction by bypassing and not mixing the high-frequency components thereof, and the control circuit starts operating with respect to the antenna input level based on the detection output of the first detection circuit. An FM receiver that shifts the level to a lower level when receiving the FMX stereo broadcast than when receiving the FM stereo broadcast.