JPS58146139A - Noise suppression system - Google Patents

Abstract

PURPOSE:To suppress noised having a high level giving an adverse effect on a normal signal, by operating a squelch circuit when a level change of an input signal is larger than a threshold value in response to an average circuit of the input signal level. CONSTITUTION:An RF signal at a terminal 1 is rectified at a rectifier 2, converted at an A/D converter 3 and latched to a latch 4. Data vn is stored in a latch 4 at a time Tn. A memory 5 is a shift register storing (m+1) sets of data, and (m+1) sets of data vn...vn-m before the time Tn are stored, the data vn... vn-m are added at an average circuit 6, and divided with (m+1) and the average data Xn is picked up. Data Xn is supplied to a reference voltage generator 7, where a positive constant is multiplied into alphaXn=vn and supplied to a comparator 8. In this case, an output Vn+1 of the latch 4 and a latch Vn are supplied to a subtractor and the difference DELTAvn+1-1 is compared with the threshold value vn at a comparator 8.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a noise suppression method, in which the amount of change in the input signal level within a certain period of time is calculated from the average value I of the input signal level within the certain period of time.
To provide a noise suppression method capable of operating a noise suppression function when a signal in which high-level noise that affects a normal signal is superimposed on a normal signal is compared with a corresponding threshold value. The purpose is to

Generally, conventional FM receivers use R to prevent FM noise when there is no signal or low-level noise from being output.
The F level itself is compared with a certain threshold, and when the RF level becomes smaller than the threshold, a squelch circuit is driven to suppress noise.

Incidentally, in recent years, devices such as microcomputers that generate noise in a wide frequency band and at a high level are often used in the vicinity of FM receivers. If an FM receiver is used near a device that generates such high-level noise, the conventional method of comparing the RF level itself with a threshold value, for example, will detect that high-level noise exceeding this threshold level is being input. The problem is that the squelch circuit does not operate when noise occurs, making it difficult to completely suppress this noise.

Therefore, in order to eliminate this drawback, the present applicant proposed and filed a patent application entitled "Noise Suppression Method" on the same date as the present application.

This device detects the level of the input signal at regular intervals to obtain the amount of level change within a certain period of time, and compares this amount of level change with a certain predetermined threshold to determine if the amount of level change is greater than the threshold. This is a method in which the squelch circuit is operated when the noise is clearly distinguished from the normal signal, and only the noise can be reliably suppressed.

By the way, for example, if a signal is superimposed on a normal signal with noise whose level is sufficiently lower than that of the normal signal (no adverse effect on the normal signal), the RF level of the signal superimposed with this noise will change. The amount is approximately the same as that of noise only. However, in the method proposed by the applicant, the amount of level change is simply compared with a certain threshold, so even signals that are superimposed with noise that does not have an adverse effect on the normal signal are considered to be noise and are not squelched. This has the problem of causing the circuit to operate and even suppressing necessary signals.

The present invention solves the above problems, and one embodiment thereof will be described below with reference to the drawings.

FIG. 1 shows a block diagram of an embodiment of the noise suppression method according to the present invention. In the same figure, the second
After being rectified by the RF double signal rectifier 2 as shown in the figure and set to Do level, it is converted to a digital signal by the A/D converter 3 and latched by the latch 4. It is now assumed that data V (FIG. 3(E)) is stored in the latch 4 at time Tn. The memory 5 is of a shift register type that can store (m+1) pieces of data, and as shown in FIG. The data up to (that is, (m+1) pieces of data) Vn% Vn-□ is stored, and this (milli-specific data V.-vn-□
are supplied to the averaging circuit 6 and added, and (m+1
) to extract the average data Xn. Data X. is supplied to the reference voltage generator 7 and multiplied by a positive constant α to obtain αXo−vn (digital value), and this V. (
3(0) is supplied to the comparator 8 as the threshold value 1.

As shown in the third section, when the clock a from the clock generator 9 rises at time T2, the monostable multivibrator (
(hereinafter referred to as mono-multi) 10 and latch 11 are Q in the same figure.
3) The data vn stored in the latch 4 is triggered in the order shown in (0) (both the monomulti 10 and the latch 11 are triggered at the rising edge of the input signal), and as a result, the data vn stored in the latch 4 is triggered as shown in the figure (0). The output data vn of the latch 4 and the output data vn of the latch 11 are both supplied to the subtracter 12 and compared, and the difference Δvn-0 is extracted.The difference ΔvIm-n is
As shown in FIG.
The threshold voltage VQ from the reference voltage generator 7 and the subtractor 12
is compared with the output Δvn−0 from Vn>
Since Δvn-7, an L level signal is taken out.

As a result, the retrigger monomulti 13 will not be triggered,
If this point is within the one-shot time Δ from the time when the trigger was previously fired and its output went to H level, the output remains at H level, and the squelch circuit connected to the output terminal 14 (Fig. (not shown) remains on, while at this point the output goes to H level due to previous triggering, and after one-shot time Δ seconds have elapsed (its output goes to L level and the squelch output goes to H level). (the circuit is turned off), its output remains at the L level, maintaining the off state of the squelch circuit. In either case, the state of the squelch circuit is not reversed.

At time Tn+1, the output b of the monomulti 10 falls, and at this fall, the monomulti 15, latch 4, A/D converter 3, memory 5, and averaging circuit 6 are triggered in order (the monomulti 15 receives the input signal The latch 4, A/D converter 3, memory 5 and averaging circuit 6 are triggered at the rising edge of the input signal (Fig. 3 (to)), and the latch 4, A/D converter 3, memory 5, and averaging circuit 6 are triggered at the rising edge of the input signal. As shown, the output data vn+1 of the A/D converter 3 is loaded into the latch 4 and memory 5 and stored therein. As a result, the memory 5 stores the time Tn
The data vn-□ stored in −□ disappears, and time T
. This means that (m+1) pieces of data vn+1-□ to vn+1 from +l-m to time TIl++1 are stored. Similar to the above case, this data vn+1−m
” vn+1 is added in the averaging circuit 6 and divided to obtain average data Xfl+1, which is then sent to the reference voltage generator 7.
The threshold value vn+1 is then supplied to the comparator 8 as shown in FIG.

At this time, the output vn+1 of latch 4 and the output V of latch 11. is supplied to the subtractor 12, and the difference Δvn+1-11 is calculated as follows, as shown in FIG.
vn(PF?+1) becomes 1. This difference Δvn+t−n
is supplied to the comparator 8 and compared with the threshold ■n+1, and if Δv,1-n > Vn+1, the comparator 8
The output of is set to H level, and the retrigger monomulti 13 is triggered. As a result, the output of the retrigger monomulti 13 becomes H level for one shot time Δ seconds, and the squelch circuit is turned on.

On the other hand, if Δvn+1-n<Vo+1, the output of the comparator 8 is set to L level, and the retrigger monomulti 13 is not triggered. This point is the one-shot time Δ from the point when the trigger was previously fired and its output became H level.
If it is within the pillow, the output will remain at H level and the squelch circuit will remain on, while the one-shot time Δ will be set in seconds from the time when the trigger was previously triggered and the output went to H level. After the elapse of time, the output remains at the L level and the squelch circuit remains in the off state.

Next, when the clock a rises at time T,,+1, the monomulti 10 and the latch 11 are triggered, and the data V stored in the latch 4 is thereby triggered. +1 is loaded into latch 11. Data vn+1 of latch 4 and data vn+1 of latch 11 are supplied to subtracter 12, and the difference between them is (
n++ 1-(n+x l is taken out. This light ΔY
(n+tl-(n+11 is 0 in Figure 3 (as shown in q, Δv(n+1)-in+tl"l vnet(lap 4) n+ll?cute 1).vn+1>Δv(n+11-(.+1) Therefore, as in the case of the time ear above, re-trigger mono multi 1
3 is not triggered and the squelch circuit is not driven.

From then on, time Tn+2 + Tn+21 Tn+31”
The same operation as in the above case 1'1 is repeated, and the difference between the data output of latch 4 and the data output of latch 11 at a certain level observation point is equal to (m+1) data points before that observation point. The squelch circuit is activated when the level is higher than the threshold value corresponding to the average level up to the point in time.

In other words, the present invention provides a threshold value corresponding to the average level of a signal (referred to as a signal person) in which noise of a level that does not affect the normal signal is superimposed, and a point from a certain point in this signal to a certain point. The difference between the amount of level change up to this point and the equal signal (or only high level noise) with high level noise superimposed on the normal signal to the extent that it has a negative effect on this signal (
Focusing on the fact that there is a large difference between the threshold value corresponding to the average level of signal B) and the amount of level change from a certain point in this signal to a certain point, we can calculate the RF level at a certain level observation point. and RF at the previous level observation point
The amount of change in level is compared with a threshold value that corresponds to the average value of the level up to a certain time back from the observation point. Therefore, in the case of the signal A, the amount of change in the level of the signal A is smaller than the threshold value of 4g@A, so that the squelch circuit is not driven, and on the other hand, the signal B
In this case, the amount of change in level of this signal B is greater than the threshold value of this signal B, which can drive the squelch circuit, clearly distinguishing between these two signals, and suppressing noise from the receiver only in the case of signal B. That's what I do.

Note that the period from time T2 to Tn+, and the period from time TI+1 to Tn
During the +2 period, the output of the subtracter 12 is always set to 0 in synchronization with the clock, and the output of the comparator 8 is also set to L level in synchronization with it. Therefore, even when a high level signal such as v<ΔV (output of the subtracter 12) is input, the output of the comparator 8 repeats H level and L level in synchronization with clock a, and , considering that the RF level has an extreme value with respect to time, the subtracter 1 at the extreme value
Since the output of the comparator 2 becomes O, the output of the comparator 8 repeats the H level and the L level. Therefore, if the squelch circuit is switched every time the output of the comparator 8 goes H level or L level, the effect of switching noise on the audio output cannot be ignored. Set the one-shot time Δ to seconds (for example, about 500 times the period of time Tn" Tfill)
is set, and once the squelch circuit is turned on, this state can be maintained.

Further, in this embodiment, the reference voltage generator 7 is configured to obtain the threshold value V by multiplying the output X of the averaging circuit 6 by α, but it may be configured using another relational expression depending on the characteristics of the device Good too.

As described above, the noise suppression method according to the present invention detects the level of an input signal at regular intervals to obtain the amount of level change within a certain period of time, and also detects the amount of change in level within a certain period of time from the point of detection. This method obtains a threshold corresponding to the average level of the input signal up to the point in time, compares the amount of change in level with the threshold, and operates the squelch circuit when the amount of change in level is greater than the threshold. By comparison, in the case of a signal in which noise is superimposed on a normal signal at a level that does not affect this signal, this level change amount is smaller than the threshold in this case; In the case of a signal with high-level noise superimposed on it (or only high-level noise), this level change amount is larger than the threshold in this case, so there is no difference in the normal signal with a level that has a negative effect on this signal. On the same date, the present applicant proposed a method that can suppress only the noise of a signal on which high noise is superimposed or high-level noise, and simply compares the amount of level change with a certain threshold value and drives a squelch circuit according to the comparison result. Unlike the method proposed in , there is no risk that the signal superimposed with noise at a level that does not affect the normal signal will be considered as noise itself, and the squelch circuit will not malfunction. It has a masucho such as.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the method of the present invention, and FIG.
The figure shows the state of change in the 1EtF level, Figure 3 (5)
~ (q is a timing chart for explaining the operation of the method of the present invention. l... input terminal, 2... collector, 3Φ... A/D converter, 4, 11... latch, 5... ...Memory, 6...
・Averaging circuit, 7...Reference voltage generator, 8...Comparator, 9...Clock generator, 10°15...
Monostable multivibrator, 12/1111 subtractor, 1
3... Retrigger monostable multivibrator, 14...
Fist output terminal. Figure 1 Figure 2 n@-1◆

Claims (1)

[Claims] The level of the input signal is detected at regular intervals to obtain the amount of level change within a certain period of time, and the average value of the level of the input signal from the time of detection to the point of time a certain period of time or more is obtained. A noise suppression method whose purpose is to obtain a corresponding threshold value, compare the level change amount with the threshold value, and operate a squelch circuit when the level change amount is larger than the threshold value.