JPS58146138A - Noise suppression system - Google Patents

Abstract

PURPOSE:To suppress noises having steep level change, by operating a squelch circuit, when a level change of an input signal deteced at a fixed period is larger than a fixed threshold value predetermined. CONSTITUTION:After an RF signal at a terminal 1 is rectified at a rectifier 2, the signal is converted at an A/D converter and latched to a latch 4. Data v0 is stored in the latch 4. When a clock (a) from a clock generator 5 rises at a time T0.5, a monostable multivibrator 6 and a latch 7 are triggered, and the data v0 stored in the latch 4 is loaded to the latch 7. At a time T1.0, the output (b) of the monostable multivibrator 6 falls down, a monostable multivibrator 3, the latch 4 and the A/D converter 3 are triggered and the data v1 of the latch 4 and the output v0 of the latch 7 are supplied to an attenuator 8. The difference DELTAv1-0 is compared with a threshold value VTH at a comparator 9 and when DELTAv1-0>VTH, then a retriggerable multivibrator 11 is triggered, goes to an H level for DELTAtsec and the squelch circuit is turned on.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a noise suppression method, which compares the amount of change in input signal level within a certain period of time with a certain threshold value, clearly distinguishes between noise and normal signals, and reliably suppresses only noise. The purpose is to provide a noise suppression method that can suppress noise.

In general, conventional FM receivers compare the RF level itself with a certain threshold in order to prevent noise when there is no signal or low-level noise from being output, and squelch when the RF level becomes lower than the threshold. The noise was suppressed by driving the circuit.

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. Do not install an FM receiver near equipment that generates such high-level noise.
With the conventional method of comparing the RF level itself with a threshold value, for example, when high-level noise exceeding the threshold level comes in, the squelch circuit does not operate and the noise cannot be completely eliminated. had drawbacks that were difficult to suppress.

The present invention eliminates the above-mentioned drawbacks, and an 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
The signal is rectified into a DC level by an RF double signal rectifier 2 as shown in the figure, converted into a digital signal by an A/D converter 3, and latched by a latch 4. Now, data V is in latch 4. Suppose that (Fig. 3 @) is trying to store. At the 9th time shown in Figure 3, time T. When the clock signal a from the clock generator 5 rises at step 5, the monostable multivibrator (hereinafter referred to as monomulti) 6 and latch 7 are activated as shown in FIG.

(The data VO stored in the latch 4 is triggered in the order shown in q (both the monomulti 6 and the latch 7 are triggered by the rising edge of the input signal), and the data VO stored in the latch 4 is triggered as shown in the figure (
It is loaded into latch 7 as shown in Q.

Latch 4 output data V. and output data v of latch 7
o are both supplied to the subtractor 8 and compared, and the difference Δv
oo is taken out. The difference Δv0−〇 is shown in Figure 3 (G)
As shown in , ΔVO-0=l VO (latch 4) - vO (latch 7) is 0, and is supplied to the comparator 9. Comparator 9
A constant threshold voltage VTR (
(digital value) and the output Δv o-o from the subtractor 8 are compared, and in this case, since vTH>ΔvO-0, an L level signal is taken out from the comparator 9.・Thus,
The re-trigger monomulti 11 is not triggered, and if this point is within the one-shot time Δ from the time when the trigger was previously activated and its output went to H level, its output remains at H level and the output terminal While maintaining the on state of the squelch circuit (not shown) connected to 12, one-shot time Δ seconds has elapsed from the time when the trigger was previously fired and its output became H level ( Its output is L
level and the squelch circuit is turned off), the output remains at the L level and the squelch circuit is kept in the off state. In either case, the state of the squelch circuit is not reversed.

At time T 1.0, the output of the mono multi 6 falls, and at this fall, the mono multi 13, latch 4 and A/Di
The converter 3 is triggered on the negative side (the monomulti 13 is triggered on the falling edge of the input signal (Fig. 3 (g)), and the latch 4 and A/D converter 3 are triggered on the rising edge of the input signal). ,
The output data v1 of the A/D converter 3 is loaded into the latch 4 and stored there. At this time, the output v1 of the latch 4 and the output vo of the latch 7 are subtracted. 8, and the difference Δv1-(, is shown in Figure 3T) becomes ΔVl-o = I Vx (9y 4) - Vo (yy ty) 1. This difference ΔV
l-0 is supplied to the comparator 9 and compared with the dark value VTR, and if ΔVl-0>VTH, the output of the comparator 9 is set to H level, and the re-trigger monomulti 11 is triggered. As a result, the output of the Go trigger monomulti 11 becomes I (level) for one shot time Δ seconds, and the squelch circuit is turned on.

On the other hand, if ΔVl-0<VTH, the output of the comparator 9 is set to L level, and the retrigger monomulti 11 is not triggered. If this point is within the one-shot time Δ from the point when the trigger was previously fired and the output went to H level, the output will remain at H level and the squelch circuit will remain on, while at this point If the one-shot time Δ seconds has elapsed since the trigger was previously fired and the output became H level, the output remains at L level, and the squelch circuit remains in the OFF state.

Next, when clock a rises at time T1.5, the monomulti 6
, latch 7 is triggered, causing data v1 stored in latch 4 to be loaded into latch 7. Data v1 of latch 4 and data v1 of latch 7 are reduced (
8, and the difference Δv1-1 is taken out. This difference Δv1-1 is expressed as ΔVt-x ''I vtDy<l-v
In this case, since VTH>Δv1-1, the red trigger mono multi 11 is not triggered and the squelch is not driven once, as in the case of time To5.

From then on, time T2.0 + T2.5 + T3.0 +
The same operation as in the above case is repeated, and the difference between the output of latch 4 and the output of latch 7 is Δvn-(n-1).
``When n-vn-1 is greater than one value vTH, the squelch circuit is driven.

In other words, this invention focuses on the fact that noise level changes are generally more rapid than regular signal level changes, and compares the LF level change (within a certain period of time) with a certain threshold of 11 m. are doing. Therefore, in the case of a regular signal, the amount of level change is small compared to the 1ml value, so the squelch circuit will not be activated.On the other hand, in the case of noise, including high-level ones, the amount of level change will be the threshold value. Since the signal is large compared to the normal signal, this can drive a squelch circuit to clearly distinguish high-level noise from a normal signal, thereby reliably suppressing high-level noise.

Note that the period from time 'ro,s to T1.0, time Tt,
s~Tz.

During the period, the output Δvn-11 of the subtracter 8 is always set to 0 in synchronization with the clock, and the output of the comparator 9 is also set to the L level in synchronization with it. For this reason, VTH〈Δvn
Even when a high-level signal such as -in-11 = vn-vn-□ is input, the output of the comparator 9 repeats H level and L level in synchronization with clock a, and RF Considering that the level value has an extreme value with respect to time, the output of the subtracter 8 becomes O at the extreme value, so the output of the comparator 9 changes for each extreme value (level and L level are repeated). Therefore, the output of this comparator 9 is
If the squelch circuit is switched for each level and L level, the effect of switching noise on the audio output cannot be ignored. ””' T
For example, about 500 times the period of n+1),
- It is constructed so that this state can be maintained if the squelch circuit is turned on.

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 compares this amount of level change with a certain predetermined threshold. Since the squelch circuit operates when the amount of change in the lever is greater than the threshold, it is possible to clearly distinguish between noise, which generally has relatively rapid level changes, and regular signals, which generally have relatively slow level changes. For example, when applied to an FM receiver, etc., it is possible to distinguish between high-level noise from a computer, etc. and a regular signal of the same level, and to operate the squelch circuit reliably only in the case of noise generation.
Compared to the conventional method in which a squelch circuit is operated by comparing the level itself with a fixed threshold value every certain period, this method has the advantage of being able to dramatically suppress base level noise.

[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 a state of change in the RF level, and FIGS. 3-3 are timing charts for explaining the operation of the system of the present invention. 1... Φ input terminal, 2 @... Rectifier, 3... A/D converter, 4, 7 @ II, latch, 5, fist, clock generator i
, 6, 13... Monostable multivibrator, 8.0 subtractor, 9... Comparator, 10... Reference voltage generator, 11... Retrigger monostable multivibrator, 1
2...Output terminal.

Claims (1)

[Claims] Detect the level of the input signal at regular intervals to obtain the amount of level change within a certain period of time, compare the amount of level change with a certain predetermined threshold, and when the amount of level change is greater than the threshold A noise suppression method whose characteristic is operating a squelch circuit.