JPS6022684Y2 - fm stereo receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an FM stereo receiver, and more particularly to a noise suppression device for an FM stereo receiver.

FM broadcast waves are easily affected by the influence of topography, etc., and the electric field strength changes significantly.

Therefore, in particular, in-vehicle (7) FM stereo receivers have the drawback that skip noise occurs and the signal-to-noise ratio is significantly reduced especially at weak electric field strengths due to the effects of multipath.

Furthermore, even if the average electric field strength is high, pulse noise such as automobile ignition noise and multipath noise in urban areas have an extremely large influence on the S/N ratio, causing audible discomfort.

In order to suppress such noise and improve the audible S/N ratio, an FM stereo receiver as shown in FIG. 1 has been conventionally used.

That is, when the level of the IF signal amplified by the IF (intermediate frequency) amplifier 1 is detected by the W level detector 2 and becomes below a predetermined level, the monaural/stereo mode switching signal generating circuit 3 generates a switching signal. The operation of the MPx (multiplex) recovery circuit 4 is switched from stereo mode to monaural mode to maintain the S/N ratio to a certain extent with respect to weak input.

On the other hand, the output of the IF amplifier 1 is converted into a composite signal by the FM detector 5, and impulse noise is suppressed by the next-stage pulse noise removal circuit 6, which then becomes the MPX demodulation input.

As is well known, the noise removal circuit 6 includes, for example, a bypass filter that detects a pulse noise component from a composite signal, a noise amplifier that amplifies the noise component that is the output of this filter, and a gate signal using the output of this noise amplifier. The generated monostable multi, a gate circuit that uses this gate signal to block transmission of the composite signal to the MPX demodulation circuit, and a hold circuit that samples and holds the level of the composite signal immediately before the gate circuit is closed. When pulse noise is present, the composite signal is cut off by the gate circuit, and the hold output of the hold circuit is transmitted to the MPX demodulation circuit during that time.

With this configuration, it is possible to improve the S/N ratio by removing pulse noise such as ignition pulses.

However, although the noise suppression device shown in Figure 1 can cope with general noise to some extent when the average electric field strength is low, it can cope with noise caused by sudden changes in the electric field and the distortion caused by the multipath described above. It is impossible to completely eliminate components and noise, and if the effects of multipath or rapid changes in electric field strength occur frequently, switching between stereo mode and monaural mode will occur each time, resulting in This is not desirable as it gives the listener a sense of discomfort.

The purpose of the present invention is to eliminate the above-mentioned drawbacks, achieve more complete noise suppression, and provide an F/F that does not give a sense of discomfort to the listener.
M stereo receiver.

The receiver according to the present invention includes an electric field strength detection means that generates a first control signal according to the electric field strength when the electric field strength becomes less than a predetermined value, and a pulse noise removal circuit, thereby making it possible to reduce the FM detection output from the FM detection output. noise detection means for detecting a noise component included in the output after removing pulse noise and generating a second control signal according to the noise level when the noise component exceeds a predetermined value; It operates by inputting each of the first and second control signals, and operates when one or both of these signals is input, and continuously adjusts the degree of separation between both channels of the reproduced signal according to the magnitude of the signal. a degree of separation control means for changing the degree of separation, and each of the first and second control signals as input, and is operated when one or both of these signals is input, and according to the magnitude of the signal. The present invention is characterized in that it includes a high-frequency level control means for continuously changing the level of high-frequency components of the reproduced signal.

The present invention will be explained below with reference to the drawings.

FIG. 2 is a block diagram showing an embodiment of the present invention, and parts equivalent to those in FIG. 1 are designated by the same reference numerals.

An electric field strength detection circuit 10 is provided to detect the electric field strength, and since the IF signal level of the W amplifier 1 is proportional to the electric field strength, the IF signal level is detected by the IF level detector 11. A detection output corresponding to this is generated, and this output is amplified by the DC amplifier 12 and used as a control signal A corresponding to the IF level.

Next, a noise detection circuit 20 is provided to detect various noise components contained in the output of the pulse noise removal circuit 6 which removes pulse noise such as ignition pulses from the composite signal which is the FM detection output.

That is, the FM detection output (composite signal) from which pulse noise has been removed is separated into stereo composite signal components, 38kHz subcarriers, and is removed, and only the noise component is amplified in the next stage noise amplifier 23.

The noise detector 24 detects the level of this amplified output, and the peak hold circuit 25 holds the peak value.The level is controlled by the °C amplifier 26 to a level sufficient to drive the next stage circuit, and the control signal B is output. Become.

As described above, in this embodiment, the output of the pulse noise removal circuit 6 shown in FIG. 1 is used as the FM detection output which is the input of the noise component detection means.

By doing this, not only can pulse noise be removed, but
This prevents an output from appearing in the noise detection circuit 20 every time a pulse noise occurs and malfunctions, and enables removal of distortion and noise components due to multipath, which will be described later, and smoother switching from stereo mode to monaural mode. There is.

The control signal A of the electric field strength detection circuit 10 and the control signal B of the noise component detection circuit 20 are input to the degree of separation control circuit 7 and the high frequency level control circuit 8, respectively.

Both control circuits 7 and 8 receive both control signals A and B, respectively.

The degree of separation control circuit 7 is configured to operate when one or both of the control signals A and B is input, and to generate a degree of separation control signal according to the magnitude of the signal. The separation between the left and right channel signals is continuously changed in the N4PX demodulation circuit 4 according to the signal.

The output of the high-frequency level control circuit 8 operates when one or both of the control signals A and B is input, and generates a high-frequency level control signal according to the magnitude of the signal. The high-frequency characteristics of, for example, voltage-controlled noise filters 9a and 9b inserted into the output lines of the MPX demodulation circuit 4 are continuously controlled.

This control circuit 8 is also configured to have the same configuration and function as the separation degree control circuit 7 described above.

FIG. 3A shows the output spectrum distribution of the pulse noise removal circuit 6, and shows the main channel signal (L + R) up to 15kHz, the pilot signal of 19kHz, and the output spectrum of the 38kHz
The H2 subcarrier is AM-modulated and has a sub-channel signal (L-R) with both sidebands.

Since pulse noise of approximately 100 kHz or more is suppressed by the pulse noise removal circuit 6, distortion components due to multipath including components of 100 kHz or less, noise associated therewith, FM noise peculiar to FM, etc. are represented by the spectrum shown by the dotted line. has been done.

Therefore, in order to detect these noise components, the noise detection circuit 20 has a frequency characteristic as shown in FIG.
38k to remove Hz and main and sub channel signal discontinuities
Hz) wrap 21 and HPF (BPF is also acceptable) 22.

With such a configuration, when the electric field strength decreases to a certain extent and noise becomes noticeable, the IF level decreases and the FM noise increases, so control signals A and B having corresponding levels are output, respectively. A separation degree control signal corresponding to these control signals is generated from the separation degree control circuit 7 to lower the degree of separation and approach the monaural mode, and a high frequency level control signal corresponding to these control signals is generated from the high frequency level control circuit 8. is generated and the filter 9
The high frequency level is lowered by changing each high frequency characteristic of a*9b.

For this purpose, the high cutoff frequency of the filter may be continuously lowered in accordance with the control signal level.
Further, the high-frequency gain may be similarly decreased continuously.

Furthermore, even if the average electric field strength is sufficiently high, if there are many multipaths, distortion components of the composite signal and pilot signal will be detected by the noise detection circuit 20.
Similarly, the S/N ratio is improved by worsening the degree of separation and lowering the high frequency level in accordance with the distortion component.

In this case, it is also effective to provide a difference in sensing level between the separation degree control circuit 7 and the high-frequency level control circuit 8 so that they operate complementary to each other.

When the electric field strength is large and there is no multipath,
It is configured to have good separation and high frequency characteristics.

As described above, according to the present invention, the electric field strength and the noise component are detected respectively, and the rain detection power is used to calculate the S/N ratio at that time.
Since the separation and high frequency level can be controlled by detecting the
An FM stereo receiver can be obtained which prevents deterioration of /N and does not give a sense of discomfort to the listener, and is particularly suitable for a car-mounted receiver.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a conventional FM stereo receiver, Fig. 2 is a block diagram of an embodiment of the present invention, Fig. 3A is a diagram showing the frequency spectrum of composite output, and Fig. 3B is a detection diagram of a noise detection circuit. FIG. 3 is a diagram showing characteristics. Explanation of symbols of main parts, 5...FM detection circuit,
6...Pulse noise removal device, 10...
- Electric field strength detection circuit, 11... Noise component detection circuit.

Claims (1)

[Scope of utility model registration request] an electric field strength detection means for generating a first control signal according to the electric field strength when the electric field strength exceeds a predetermined value; and a pulse noise removal circuit, whereby the pulse noise is removed from the FM detection output; noise detection means for detecting a noise component included in the output of the noise component and generating a second control signal according to the noise level when the noise component exceeds a predetermined value;
Each of the first and second control signals is input, the operation is performed when one or both of these signals is input, and the degree of separation between both channels of the reproduced signal is determined according to the magnitude of the signal. a degree of separation control means for continuously changing the degree of separation; and a degree of separation control means that receives each of the first and second control signals as an input, operates when one or both of the signals is input, and that controls the degree of separation according to the magnitude of the signal. and a high frequency level control means for continuously changing the level of the high frequency component of the reproduced signal accordingly.