SU830653A2 - Noise suppressor - Google Patents

Description

(54) DINING SUPPLIER

I

The invention relates to radio engineering and can be used in communication devices to automatically turn on the terminated devices depending on the quality of the input signal, usually assessed by the signal-to-noise ratio. In particular, the proposed noise suppressor can be used in radio receivers to receive signals with a predetermined signal-to-noise ratio when changing, the noise level at its input, caused both by a change in radio reception conditions and by the instability of the linear path of the radio receiver.

According to the main author. St. No. 73488 is known a noise suppressor comprising a driver that converts an analog input signal to a digital one, a counter of the number of periods of the input signal in a time determined by a clocking circuit operated by a master oscillator. The device also has a prohibition element and a delay counter that controls analog to bale, as well as a low-frequency generator and an analog adder, designed to extend the range of adjustment of the threshold signal-to-noise ratio.

The threshold signal / noise ratio of this device is determined by the expression

(is / iy) „. pore VI + (UuLr / Uu.fex) f

where 1 / mg is the voltage of the noise generator,. in is the noise voltage at the input of the device.

Whence it follows that the value of the threshold signal-to-noise ratio in this device depends on the change in noise voltage at its input Um.x, which can be caused both by a change in radio reception conditions and by the instability of the path of the receiving device, which causes a lack of immunity.

The purpose of the invention is to increase the noise immunity of the number.

To achieve the goal in the noise suppressor, which contains a counter for the number of input signal periods, a driver, a clock circuit, a prohibition element, a delay counter, an analog key, a master oscillator, an analog adder and a low-frequency noise generator, the analog adder input is connected to the output of the low-frequency noise generator via serially connected controllers the attenuator and the unit for setting the signal-to-noise threshold ratio, between the device input and the first control unit, its control element is turned on by the input of the controlled attenuator Neny, the other input of which is connected to the output controlled attenuator and the additional barring member, the inputs of which are connected respectively to the outputs zadayush.ego generator, comparing element and barring element connected also to a second control input controlled attenuator.

The drawing shows a structural electrical noise suppressor circuit.

The device contains a driver 1, converting an analog signal into a digital signal, the output of which is connected to the counting input of the counter 2 and the number of periods of the input signal. The zeroing input of the counter 2 is connected to the first output of the clocking circuit 3, working for it from the generator 4. The output of the counter 2 is connected to the first input of the prohibition element 5, the second input of which is connected to the first output of the clocking circuit 3, and the third input of the prohibition element 5 is connected to the output of the counter 6 delay. The counting input of counter 6 is connected to the second output of the clocking circuit 3, and the zeroing input of counter 6 is connected to the second output of prohibition element 5, the first output of which is simultaneously connected to the control, to it the input of the analog switch 7, to the second input of additional prohibition element 8 and to one from the control inputs of the controlled attenuator 9, represented by ush, its a voltage divider, coupled with a pulse counter, which is controlled. The signal input of the Analog Key 7 is simultaneously connected to the first input of the comparison element 10, to the first input of the analog adder 11 and is the input of the device. Comparison element 10 includes detector circuits and a threshold device, such as a comparator, producing an output signal in standard levels of digital circuits on a TTL. The output of the analog adder 11 is connected to the input of the imaging unit 1, the second input of the analog adder 11 is connected to the output of the unit 12 for setting the signal-to-noise threshold ratio, which is, for example, a large-scale amplifier. The input of the signal-to-noise threshold setting unit 12 is simultaneously connected to the second input of the comparison element 10 and to the output of the controlled attenuator 9. The signal input of the attenuator 9 is connected to the low-frequency noise generator 13, and the second control input to the output of the additional prohibition element 8, the first input of which is connected to the output of the master oscillator 4, and the third input to the output of the comparison element 10. The output of the device is the output of the analog switch 7.

The noise canceller works as follows.

The mixture of signal and noise is fed to the input of the noise canceller and simultaneously supplied to the signal input of the analog switch 7, to the first input of the comparison element 10 and to the first input of the analog adder 11, to the second input of which additional noise voltage is supplied from the output of block 12. The resulting mixture from the output of the adder 11 is fed to the input of the former 1, which produces 1M "pulses for each positive crossing of the zero line voltage of the mixture. The pulses from the output of the imaging unit 1 are fed to the counting input of counter 2, which accumulates them over a period of time determined by the follow-up period of the pulses coming to the zero input of the counter 2 from the first output of the clocking circuit 3, to the input of which impulses come from the master oscillator 4. Period following the reset pulses. That is an order of tens of milliseconds and determines the speed of the noise suppressor, and the volume of counter 2 is selected from the condition:

, 9Fu..ep.-To

where Nsch. -the volume of the counter 2;

Fi.tp. -the average frequency of the noise at the input of the device.

If counter 2 overflows in time, then the pulses from its output go to the first input of prohibition element 5, which at the same time prohibits the passage of reset pulses from the first output of the clocking circuit 3 to the zeroing input of counter 6, which begins to accumulate the pulses arriving at its counting input .the second output of the clocking circuit 3 and corresponding to the zero cycles of the counter 2. The volume of the counter 6 is chosen from the condition

bW, VTo,

- counter volume 6;

where the Sword., - y - average duration

pause speech signal.

Claims (1)

If counter 2 overflows by one more time for the number of cycles greater than Ng, then the above described mechanism of operation of prohibition element 5 and counter 6 causes the latter to overflow. The impulse from its output changes the state of the prohibition element 5, which switches the key 7 to the Off position, and the signal from the squelch input does not pass to the output of the device. This happens if the resultant mixture, consisting only of noise, or a signal / noise ratio of less than one, is received from the output of adder II to the input of imaging device 1 for a time greater than T, which indicates that the input to the noise suppressor signal-to-noise ratio is less than the specified threshold value defined by the expression (Uc / Uw) t.r.op. + (K-U "./ U") where and | md is the voltage of the noise generator at the output of the controlled attenuator; Om.jj is the noise input voltage of the device; To the transfer coefficient of the unit setting the threshold signal-to-noise ratio. This expression was obtained taking into account the fact that the threshold signal-to-noise ratio at the input of driver 1 is constant and equal to one. In this case, the pulse frequency from the output of the imaging unit 1 is such that the counter 2 overflows during the time between the two zeroing pulses. Simultaneously with the key 7 being switched to the Off position, the control level from the output of the prohibition element 5 is fed to the second input of the additional prohibition element 8 and the first control input of the attenuator 9. The leading edge of the logical level from the output of the prohibition element 5 is to set the maximum attenuator transfer coefficient 9, at the same time, the noise voltage applied to the second input of the comparison element 10 becomes obviously greater than the maximum possible noise voltage at the input of the device and, accordingly, at the first input comparing element 10 e. In this case, the comparison element 10 outputs a control level to the third input of the inhibiting element 8, which allows the passage of clock pulses from the master oscillator 4 to the second control input of the attenuator 9, the transmission coefficient of which begins to decrease. The noise voltage at the output of the attenuator 9 is reduced until the equality Um is reached. UU.A. Then, the comparison element 10 provides a control level to the third input of the prohibition element 8, which prohibits the passage of clock pulses from the master oscillator 4 to the second control input of the attenuator 9, whose transmission coefficient and voltage of the noise at the output remain fixed, while Uiu holds. The noise voltage from the output of the attenuator 9 is fed to the input of the signal / noise threshold setting unit 12, whose transmission coefficient determines the value of the threshold signal-to-noise ratio, which, taking into account the equality U |, U "y. /, Can be written as (Uc /Ish)vk.por. Gl + K Comparison and adjustment of the noise on the UUI.A voltage. The data noise value at the device input occurs at those times when the key 7 is in the Off state, i.e. during pauses between operating signals When the signal-to-noise ratio at the input of the device is greater than the value determined by the expression (Uc / ish) vk.por. / 1 + K and, accordingly, the signal-to-noise ratio of the resulting mixture at the input of imaging unit 1 is greater than one, the pulse frequency from its output is such that counter 2 overflows during the time between two zeroing pulses. In this case, the prohibition element 5 allows the passage of reset pulses from the first output of the clocking circuit 3 to the obnuyushchy input of the counter 6 and switches the key 7 to the "On" position. In this case, the signal from the device input passes to its output. During natural pauses of a speech signal with a duration of no more than T, the prohibition element 5 does not change its state and maintains key 7 in the "Enabled" state. This occurs because during time T the number of i-pulses less than Nc4 arrives at the counting input of counter 6 from the second output of the clocking circuit 3, and after the end of the pause, it returns again with a pulse from the second output of the clocking circuit 3. Simultaneously with the switch of the key 7 in the "Enabled" position, the control level from the first output of the prohibition element 5 is fed to the second input of the additional prohibition element 8, which prohibits the passage of clock pulses from the master oscillator 4 to the first control input of the attenuator 9. Noise voltage at the output the attenuator 9 remains fixed and equal to the noise voltage at the input of the device. Claims of the invention Noise suppressor St. No. 734884, characterized in that, in order to improve noise immunity, the input of the analog adder is connected to the output of a low-frequency noise generator through a series-connected controlled attenuator and a unit for setting the threshold signal / noise ratio between the input of the device and the first control input of the controlled attenuator is turned on a comparison element, another input of which is connected to the output of the controlled attenuator, and an additional inhibit element, whose inputs are connected respectively to the outputs of the master oscillator, element Comparison element and an apret element, also connected to the second control input of the controlled attenuator. Sources of information taken into account in the examination 1. USSR author's certificate 734884, cl. H 04 B 1/10, 01/23/78.