KR920004375B1 - Circuit for eliminating high frequency impulse noises - Google Patents

Abstract

The noise reduction circuit extracts and eliminates impulse noise included in ASK signal. The circuit includes a first attenuator (10) for attenuating the received serial data using a RC filter, a first comparator (12) for eliminating the impulse noise having a certain level using hysteresis characteristics, a second attenuator (14) for attenuating the output signal of the first comparator (12) using a RC filter, and a second comparator for comparing the output signal of the second attenuator to a second reference voltage using hysteresis characteristics to eliminate the impulse noise having the certain level.

Description

Noise Reduction Circuit of High Frequency Receiver

1 is a noise removing circuit diagram according to the present invention.

2 is an operational waveform diagram of each part of FIG.

3 is a hysteresis characteristic diagram of the comparator of FIG.

* Explanation of symbols for main parts of the drawings

10, 14: first and second signal attenuator 12, 16: first and second comparator

The present invention relates to a noise canceling circuit of a high frequency receiver, and more particularly, to a circuit for removing impulsive noise included in a signal received in an AM high frequency receiver.

Currently, the simplest digital modulation method for modulating digital information is ASK (Amplitude-Shift Keying), which modulates the carrier's amplitude by changing it with a digital signal. In the case of a binary signal (logic signal) on and off of the carrier corresponds to "1", "0", the ASK corresponds to the AM modulation scheme in analog modulation. As a modulation method that is easy to propagate a binary signal, that is, digital data wirelessly, the ASK modulation method is widely used as described above, and wirelessly transmits digital data using the ASK method.

An AM (ASK) high frequency receiver receiving an AM (ASK) high frequency signal modulated in the above manner receives a signal containing noise that is not desired by another medium wave or noise in the atmosphere.

Therefore, the receiver receives the original transmission signal and impulsive noise, which makes it very difficult to demodulate the original data transmitted from the transmitter. Sometimes, the receiver is not able to receive the signal. .

Accordingly, an object of the present invention is to provide a noise removal circuit for receiving only a stable signal by extracting and removing only impulsive noise in a reception device for receiving an ASK modulated signal.

The present invention for achieving the above object is characterized by consisting of a signal attenuator for attenuating the received data by low-pass filtering, and a comparator to remove the impulse by comparing the attenuated signal with reference voltage and hysteresis characteristics.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a noise cancellation circuit diagram according to the present invention, wherein the first attenuator 10 attenuates and outputs serially received data using an RC filter, and a set attenuation output of the first reference voltage VTH1 and the first attenuator 10. , A first comparator 12 for removing the impulse noise signal of a predetermined level by comparing the signal with a hysteresis characteristic, a second attenuator 14 for attenuating and outputting the output of the first comparator 12 with an RC filter, And a second comparator 16 for removing the impulse noise signal having a predetermined level by comparing the set second reference voltage VTH2 with the attenuation output of the second attenuator 14 by hysteresis characteristics. In the first and second attenuators 10 and 14 of FIG. 1, a resistor and a cathode of a diode are connected in series from the power supply voltage VCC to a signal input side, and a capacitor is connected between the anode and the ground of the diode. And the cathode of the diode is filtered out of the input signal and attenuated output. Each of the first and second comparators 12 and 16 is connected between a power supply voltage VCC and a ground GND to divide the power supply voltage VCC to set a reference voltage VTH, and attenuates the voltage. A comparator for inputting a signal to an inverting terminal and inputting the reference voltage VTH to a non-inverting terminal for comparing and outputting an inverted hysteresis; a resistor connected between two input terminals of the comparator and isolating two terminals; A feedback resistor connected on the output terminal of the comparator and the reference voltage VTH, and a resistor connected to the power supply voltage VCC and the output terminal of the comparator to pull up the output of the comparator.

FIG. 2 is an operational waveform diagram of each part of FIG. 1, where Si shows impulsive noise IP as a waveform of received data. V (OP1-) is the output of the first signal attenuator 10 and is compared with the reference voltage VTH1 in the first comparator 12, and V (op10) is the output waveform of the first comparator 12. V (op2-) is the output of the second signal attenuator 14, and VTH2 is the second reference voltage in the second comparator 16. So is the output showing that noise is removed as the output of the second comparator 16.

3 shows the hysteresis characteristics of the first or second comparators 12 and 16 of FIG.

An operation example of FIG. 1 according to the present invention will now be described in detail with reference to the operation waveform diagrams of FIGS. 2 and 3. When the receiving data Si carrying impulsive noise IP is input to the cathode of the diode D1 as shown in FIG. 2A, the diode D1 is " off " at the P1 position in FIG.

Accordingly, in FIG. 2, at the point P1, the time constants of the resistor R1 and the capacitor C1 start to charge both ends of the capacitor C1 with a voltage of V (op1-) as shown in FIG. 3, which is a comparator OP1. Is input to the inverting input terminal (-).

When the input data Si falls to " low " at point P2 in FIG. 2A, the charge potential V (op1-) of the capacitor C1 is rapidly discharged by conduction of the diode D1, so that the waveforms across the capacitor C1 are inputted. According to the data, it is input to the inverting terminal of the comparator OP1 as shown in the second diagram. On the other hand, the non-inverting terminal + of the comparator OP1 is input with the reference voltage VTH1 set as VTH of FIG. 2B by the resistors R2-R3. At this time, the comparator OP1 compares the reference voltage VTH1 and the attenuation signal OP1- voltage with an inverted hysteresis to output the output V (op10) equal to the second c degree. Here, the resistors R2 and R3 are resistors for making the first reference voltage VTH1, R4 is a resistor for isolating the inverting and non-inverting inputs of the comparator OP1, and R5 is an open collector of the comparator OP1. (open collector) type, so it is a pull-up resistor and resistor R11 is a feedback resistor. When the potential V (op−) of the first attenuation portion 10 is equal to that of FIG. 2B, the comparison voltage of the comparator OP1 is as follows.

I) When V (op10) is 0

ii) when V (op10) is VCC

Therefore, the hysteresis waveform is shown as the third degree. Here, if Vref1 in Equation (1) is VTH1 in FIG. 2B, the output V (op10) of the comparator OP1 is the same as the third c degree.

At this time, if impulsive noise such as IP of FIG. 2a is input, impulsive noise IP of FIG. 2b is attenuated to IP1, and IP1 does not reach the first reference voltage VTH1 level, thereby affecting the output of the comparator OP1. Can't reach As such, the unwanted impulsive noise is attenuated and disappeared when the normal signal is input in the middle or standby state.

However, since the pulse width T (FIG. 2a) becomes small as T '(FIG. 2C), it must be compatible with the second signal attenuator 14 to restore it. Similarly, the second signal attenuator 14 has the same operation as that of the first signal attenuator 10, and is composed of a diode D2, a resistor R6, and a capacitor C2. When the output V (OP10) of the comparator OP1 is input together with the 2e degree, the output V (op2-) of the second attenuator 14 becomes the 2d degree and the signal output So becomes the 2e degree. The second comparator 16 includes a comparator OP2 and resistors R7, R8, R9, R10, and R12. The operation is the same as the operation of the first comparator 12

Ⅲ) [When So is 0V]

Ⅳ) [When So is VCC]

to be.

Therefore, if the reference voltage Uref3 of Equation (3) is equal to VTH2 in FIG. In this case, when the plurality of resistors and the capacitors during the first period are R1 = R6, D1 = D2, C1 = C2, R4 = R9, R2 = R7, R3 = R8, R11 = R12, OP1 = OP2, the noise impulse Except for IP, the pulse width is sacrificed as is and Si = So.

As described above, the present invention is a circuit that removes noise only when data is received in an AM high-frequency receiver and is inputted with noise impulses, thereby preventing noise from affecting a malfunction of the receiving system. can do.

Claims (3)

In the noise canceling circuit of a high frequency reception device, a hysteresis is performed on a first attenuator (10) for attenuating and outputting serially received data by an RC filter, a set first reference voltage VTH1, and attenuation output of the first attenuator (10). A first comparator 12 which removes an impulse noise signal of a predetermined level by comparison with a hiss characteristic, a second attenuator 14 which attenuates and outputs the output of the first comparator 12 with an RC filter, and a set first And a second comparator (16) for removing a predetermined level of impulse noise signal by comparing the reference voltage VTH2 with the attenuation output of the second attenuator (14) in hysteresis characteristics. The first and second attenuators 10 and 14 are connected in series with a resistor and a cathode of a diode in the direction of the signal input from the power supply voltage VCC, and a capacitor is connected between the anode and the ground of the diode. And a cathode of the diode is connected to be filtered to operate in attenuating output. 2. The method of claim 1, wherein each of the first and second comparators 12, 16 is connected between a power supply voltage VCC and a ground GND to divide the power supply voltage VCC to set a reference voltage VTH. A voltage divider circuit, a comparator for inputting an attenuation signal to the inverting terminal and a non-inverting terminal for inputting the reference voltage VTH, and an inverted hysteresis comparison output; a two terminal connected between two input terminals of the comparator A resistor connected to the output terminal of the comparator and the reference voltage VTH, and a resistor connected to the power supply voltage VCC and the output terminal of the comparator to pull up the output of the comparator. Characterized by a circuit.

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