JPS5895444A - Sn ratio improving circuit - Google Patents

Abstract

PURPOSE:To improve the SN ratio of the output signal of a stereo multiplex (MPX) circuit, by controlling the MPX circuit in accordance with the level of a noise signal included in an FM demodulation signal. CONSTITUTION:The demodulation signal of an FM broadcast wave received through a front end 2, IF amplifier 3, and demodulating circuit 4 is separated to left and right signals by an MPX circuit 5, and these signals are applied to speakers 8 and 9 through an amplifier 67. The MPX circuit 5 is controlled by a subcarrier, which a PLL circuit 10 consisting of a phase comparator 11, a low pass filter 12, a voltage control oscillator 13, and frequency dividers 14 and 15 generates on a basis of a pilot signal obtained from a band pass filter 16, to perform the separating operation. Noise components of 15-23kHz appearing in the output of the phase comparator 11 are applied to the MPX circuit 5 through an amplifier 17, a rectifier 18, and a control signal generator 19 to control a stereo separation degree adjusting circuit and a high-band component attenuating circuit included in this circuit 5, thereby improving the SN ratio of the output signal.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to the interference noise of a1, especially the interference multiplier 9 with shallow modulation.
It is an object of the present invention to provide an 8H ratio modification circuit that can effectively modify the perceptual SR ratio in response to co-channel interference caused by the 8H ratio modification circuit.

Conventionally, the electric field strength of a received signal is detected, and depending on the electric field strength, the degree of separation of a stereo MPX (multiplex) circuit is adjusted to 1, or the degree of separation obtained at the input side or output till of the stereo MPX circuit is adjusted. A method of modifying the Sol ratio by attenuating the frequency components is known. This method is effective when the field strength is reduced, but is completely ineffective against multipath interference, adjacent channel interference, co-channel interference, etc. that do not correspond to the field strength and occur depending on the reception conditions. Met.

Furthermore, there is also a conventionally known method of detecting high-frequency (for example, 75 ICHg or higher) noise components in the output signal of an FM demodulation circuit, and adjusting the degree of stereo separation to 1 or attenuating the high-frequency components accordingly. . This method prevents multipath interference and
Although it is effective against adjacent channel interference, it is not effective against co-channel interference caused by interference signals with shallow modulation and small frequency & 2 shift.

The present invention has been made in view of the above-mentioned points, and will be described in the following embodiments with reference to basic drawings.

FIG. 1 shows the spectrum of miscellaneous noise generated due to co-channel interference contained in the output signal of the FM demodulation circuit. The case of FIG. 1 shows the noise caused by co-channel interference when an interference signal having a frequency shift of about 4QKBz is mixed with an unmodulated desired signal. Figure 2 shows an embodiment of the present invention.
(1) is the antenna, (2) is the FM front end, (3) is the intermediate frequency amplifier circuit, and (4) is the FM front end.
demodulation circuit, (5) is a stereo MPX circuit, (6) is a left signal amplification circuit, (7; is a right signal amplification circuit, (8) is a left speaker, and (9) is a right speaker. Also, aa is 1
Phase comparator Uυ, low-pass filter/DC amplifier a3.
Voltage controlled oscillator α3. Digital filter 57 for the stereo MP1 circuit (5) consisting of the first frequency divider α4 and the second frequency divider
The PLL circuit that generates the signal (FM demodulation circuit 4) and about f PLL times lil! A band pass filter with a center cylinder wave number of 19 and 2 is inserted between the phase comparator I and αD is a band amplifier that amplifies the output signal of the phase comparator αυ of the PLLI circuit described in fiO, aa
is a rectifier circuit that galvanizes the output signal of the band amplifier 110, and U] is a rectifier circuit that galvanizes the output signal of the band amplifier 110;
This is a control gi generation output path that generates a signal.

Discounts received on the antennaill are sent to the front end (
2), the signal is converted into an F signal, amplified by the F amplification circuit (3), and then demodulated by the 1Mui modulation circuit (4). stop'
CsFMuLm output is FL/1M P X1gMf
The left and right stereo signals are separated by the action of the 33KHz multiplication carrier multiplier obtained from the W11 frequency divider α-hiro of the 5Jt'PLL circuit, and the left stereo signal is amplified by the left signal amplification circuit (6). The right stereo signal is processed by the right signal amplification circuit (
After being amplified by step 7), the signal is applied to left and right speakers (8) and (9), respectively.

The first input terminal of the phase comparator αυ of PLL b path ■ has %.
rw revenge! i! ! The output signal of the circuit (4) is applied through a bandpass filter (LE).
The second input terminal of is connected to the oscillation output (
76Ki1m)'! - The gi number of 19KF1s obtained by the first and second frequency divisions e, a and cts is applied. When the aforementioned input signals are applied to the first and second input terminals of the phase comparator αυ, a signal equal to the phase difference by 5 is generated at the output of the phase comparator 1uucD. A signal corresponding to this phase difference is transmitted to a low-pass filter/DC m-width filter 13.
After being amplified with 1! applied to the suppression oscillator [13,
The output signal of the voltage controlled oscillator 0 is correctly 76z, and the output of the first divider w4 cI4 is correctly synchronized with the output signal of the FM demodulation circuit (4).

At this time, the output of the bandpass filter rLB is 19 to 11.
zWhen noise occurs along with the stereo pilot signal.

The instantaneous phase of the stereo pilot signal changes due to noise, resulting in a phase difference between the 19 KHz signal and the second frequency divider 1151. When noise occurs and a phase difference occurs, the output of the phase comparator αυ is:

An alternating current signal is generated according to the phase wave. This AC signal is
It is amplified by the band amplifier ll'b and rectified by the rectifier circuit. Therefore, at the output terminal of the rectifier circuit αδ, a DC output corresponding to the noise state is obtained, and this is transmitted to the stereo mpxl path (
5) By being applied to the control signal generation circuit (11) that controls the stereo separation degree adjustment circuit and the 18+ range component attenuation circuit included therein, the BH ratio in (5) is achieved.

The miJ stereo separation degree circuit is as shown in FIG. 6, for example, and has a left double path (7) and a right double path c! from which left and right stereo signals are obtained, respectively. In the darkness with v.

A variable resistor is operated, and the value of the variable resistor @ is changed by a drive circuit (c) that operates in response to a control signal from the control signal generating circuit α9. By using this stereo separation degree adjustment circuit, the noise in the signal increases,
When the output of the rectifier circuit becomes large, it is possible to worsen the stereo separation, move it closer to monaural, and increase the 8W ratio.

At this time, since the degree of stereo separation corresponds to the output level of the rectifier circuit G8, the modification of the 8N ratio is performed in accordance with the amount of noise.

The high-frequency component attenuation circuit is, for example, as shown in FIG. 4, and first and second low-pass filters ＼ and ＠ are inserted into the left and right signal paths Q4 and (c) from which left and right stereo signals are obtained, respectively. Yes, that W! Control the amount of attenuation of high-frequency signals of J1 and the second low-pass filter and □□□! Il signal generation times W! ! The performance is changed by a drive circuit that operates in response to a control signal from σ9. The amount of attenuation of the high frequency signal depends on the output signal of the rectifier circuit.

That is, it can be changed according to the amount of noise in the signal, and the 8H ratio can be changed continuously according to the amount of noise.

FIG. 5 shows another embodiment of the invention. Fifth
In the figure, instead of amplifying and rectifying the output signal of the phase comparator 1υ as shown in Figure 2, the noise is detected by pulse count detection of the 19111m signal obtained from the second minute 5419. What makes it special is that it rectifies it and generates a control signal.

In FIG. 5, the same figure number is not given to the [2J road block that is the same as in FIG. 2, and the explanation is omitted.

The 19-section 1g signal obtained at the output of the second frequency divider αS is as follows.

Since the input signal applied to the first input terminal of the phase comparator I via the bandpass filter 161 undergoes a phase change mt due to noise, strictly speaking, it has a frequency slightly different from 191 Hz in positive and negative directions when noise occurs. There is.

Therefore, if the output of the second frequency divider +151 is detected by a pulse count detector 6D consisting of a monostable multivibrator (support) and an integrating circuit (end), the detected output will be 19KIIg. A signal corresponding to the frequency IC that changes positively and negatively around the center is obtained, and this is amplified by the band amplifier αD and then rectified by the rectifier circuit [18], a DC output corresponding to the noise is generated, and the DC output is By applying this to the control signal generation circuit 0, a control signal T is generated at the output terminal □□□. If this control signal is applied to the stereo MPx circuit (5) in the same way as in the case of Fig. 2, it is possible to adjust the degree of stereo separation and perform secondary attenuation of high frequencies, improving the 8N ratio. can vomit.

There are many types of noise mixed into the signal 8, such as noise corresponding to the electric field strength of the signal, noise caused by multipath, noise caused by adjacent channel interference, and noise caused by co-channel interference. The above SN ratio improvement circuit that improves the 81 ratio is effective for all of these. In particular, the SN ratio improvement method according to one aspect of the present invention eliminates co-channel interference.
Same channel interference due to shallow jamming signal of 7R fiber, which could not be dealt with in the past (noise occurs as shown in Figure 1)
It has the great advantage of being able to generate a large effect even between regions where broadcasting stations of the same channel exist at geographically close points. It has a great effect when used in a beautiful stereo receiver.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram showing noise due to co-channel interference, FIG. 2 is a circuit block diagram showing an embodiment of the present invention, FIGS. 5 and 4 are circuit block diagrams showing specific circuit examples thereof, and FIG. FIG. 5 is a circuit block diagram showing another embodiment of the present invention. Explanation of raw drawing numbers (5)...Stereo MP! Circuit, -... PI, L circuit, αD... Phase comparison ti, ne... Bandpass filter, αD... Bandwidth amplifier, (181... Rectifier circuit, Control signal generation circuit Figure 1 (KHz3 Figure 3

Claims (1)

[Claims] (From 15KIIg to 25K during the output of the IIFM demodulation circuit)
Detects noise components included in the band up to Hz, and detects them depending on the Fk noise component. The feature is that the stereo multiplex circuit for separating the output of the Reifuran circuit into left and right stereo signals is controlled, thereby improving the 81 ratio of the output signal of the stereo multiplex circuit. do87
1 ratio conversion circuit.