KR950011707B1 - Noise detecter of handy phone - Google Patents

Abstract

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Description

Car noise-free background noise detector

1 is a block diagram of a general hands-free unit.

2 is a conventional background noise detector circuit diagram.

3 is a time chart diagram showing conventional noise characteristics.

4 is a noise characteristic detection characteristic table.

5 is a noise detector circuit diagram of the present invention.

* Explanation of symbols for main parts of the drawings

10: noise monitor 20: detector

C1, C2: capacitors D1-D6, DN: diode

U1, U2: Op amp U5, U6: Comparator

U7: Delay U8: Analog Switch

LPF: Low pass filter R1 to R4: Resistance

Background of the Invention The present invention provides a background noise detector for a hands-free unit of a car phone to remove frequent disconnection caused by impulse noise in a hands-free unit used for safe driving when using a car or a hand-held phone (HHP) in a vehicle. It is about.

In general, hands-free unit operation is not a simultaneous call between two handsets, but a one-way call that continuously monitors each volume level of transmission and reception and opens only the path with the larger level, and distinction between background noise and sound is absolutely required. . In other words, if a caller or a caller makes a call in an environment where background noise is very high, if there is no circuit for detecting the amount of background noise, the call can be made by selecting only one path from the beginning to the end of the call. It is self-evident.

The configuration of the hands-free unit can be shown in FIG. That is, the signal from the microphone 1 to the amplifier 2 is provided to the switch or attenuator 3, the background noise detector 4, and the song and reception level comparators 5, respectively, and the background noise detector 4 and the song. The reception level comparator 5 controls the switch or attenuator 3 so that the microphone output is provided to the transmitter through the amplifier 6, and the signal from the receiver is transmitted through the amplifier 2 'to the background noise detector 4'. And a switch or attenuator 3 'and a send and receive level comparator 5, respectively, and the background noise detector 4' and the send and receive level comparator 5 receive by controlling the switch or attenuator 3 '. The signal is provided to the speaker 1 'via the amplifier 6'. In this case, each volume level of the transmission and reception is compared by the transmission and reception level comparators 5, and the background noise is detected by the background noise detectors 4 and 4 'to operate the path of the transmission or reception level smoothly. do. The configuration of the background noise detectors 4 and 4 'can be shown in FIG. That is, the noise monitor unit 10 includes resistors R1-R4, capacitors C1 and C2, diodes DN, and op amps U3 and U4 so as to gradually change their levels in response to noise levels; The input level is detected and consists of op amps U1 and U2, diodes D1-D6, resistors R6 and R7, and capacitors C4 and C5, and the op amps U1 and U2 are arranged in parallel. A detection unit 20; The noise monitor unit 10 receives the output of the op amp U2 of the detector 20 as a non-inverting terminal through the low pass filter LPF, and monitors the output of the op amp U1 of the detector 20. Comparator (U5) is provided to receive the output of the inverting terminal. When the input level is applied in this state, the output terminals of the op amps U1 and U2 are detected by the diodes D1 and D2 and the diodes D3 and D4, respectively. The input level detected by the op amp U1 is provided to the op amps U3 and U4 in turn to provide an inverting terminal of the comparator U5, and the input level detected by the op amp U2 is a low pass filter LPF. By providing the non-inverting terminal of the comparator U5 through the comparator U5, the comparator U5 compares these levels with each other to determine whether a user's voice is heard or general noise.

That is, when the level applied to the non-inverting terminal (+) side is greater than the level provided to the inverting terminal (-) of the comparator U5, the channel is opened (see FIG. 3).

In other words, when there is only noise on the line and an audio signal is momentarily applied, one side slows down the input level (noise monitor section 10) and the other side makes the output faster. It opens at the high level and opens the talk path, and if there is no talk sound through the diode DN at the output of the op amp U4, it immediately returns to the original noise level so as to respond quickly to the next audio sound input. will be. This monitor configuration does not have a big problem when the background noise of a certain level or the vehicle attempts to make a call while the vehicle stops, but when an impulse noise such as a third degree that occurs irregularly when the level of the instantaneous background noise or the vehicle moves is generated. Since the level of the noise monitor 10 is higher than the set level of the noise monitor 10, the output of the operational amplifier (U5) is low level, there is a disadvantage that the call sound disconnection phenomenon (off) (call disconnection) occurs.

The inventors note that the characteristics of the impulse noise have a characteristic that the level is large and the duration is extremely short, unlike the general background noise, and immediately recognizes the occurrence of the impulse noise by using an op amp and delay, and for a preset time It prevents the impulse noise from entering the background noise monitor, and prevents unnecessary rise of the background noise level to prevent the blocking of the transmission path.

That is, an analog switch in a nomarion state is connected between the noise monitor unit and the detection unit, and the analog switch is made to be turned off by a delay output for a predetermined time corresponding to the interval of the impulse noise, and the delay is detected at the detection unit. It is controlled by a comparator that compares the output provided by the low pass filter with a setting level that varies with a potential of 50% or more above the maximum value of general noise.

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

The background noise detector of the hands-free unit of the car phone of the present invention can be exemplified as shown in FIG. 5, and corresponds to the noise level, so as to gradually change the level of the resistors R1-R4, capacitors C1 and C2, diodes DN and A noise monitor unit 10 comprising op amps U3 and U4; Detecting the presence or absence of an input level, the diodes D1-D6, resistors R6 and R7, and capacitors C4 and C5; A detector 20 comprising op amps U1 and U2 that receive input levels in parallel; A comparator U5 for receiving the input / output through the op amp U2 of the detector 20 as a non-inverting terminal through the low pass filter LPF, and receiving and comparing the output of the noise monitor unit 10 as an inverting terminal; In the comparator U6 and the detector 20, the output provided from the detector 20 to the low pass filter LPF is commonly provided as a non-inverting terminal and the variable potential V1 is provided as an inverting terminal. An analog switch (U8) for switching the output provided to the noise monitor unit (10), and being turned off only while the control level for switching control is applied to the control terminal in the nomarion state; In accordance with the output of the comparator (U6) is composed of a delay (U7) for providing a control level signal for a time corresponding to the interval of the normal impulse noise to the control terminal for switching control of the analog switch (U8).

At this time, the initial state of the analog switch U8 is on. In this state, the input signal is detected through the detector 20 and is DC-directed through the low pass filter by the resistor R1 and the capacitor 1. This DC input level is appropriately amplified by the op amp U3 and applied to the non-inverting terminal of the op amp U4. The potential of the output terminal Vn of the op amp U4 does not immediately rise, and the resistor R4 And gradually increase due to the time constant of the condenser C2. If the amount of noise is constant at this time, the potential of the output terminal Vn is maintained at a constant value by the charging and discharging action by the capacitor C2 and the resistor R4. In this state, when the audio signal mixed with the background noise is applied, the non-inverting terminal potential of the op amp U3 is increased by the amount of the audio signal, so that the potential of the output terminal Vn is out of equilibrium, and thus the resistance R4 and The charging and discharging action of the capacitor C2 causes a new equilibrium state and gradually rises. However, at this time, the path by the op amp U2 of the detector 20 immediately rises to a new level (the level at which the audio signal is applied), so that the output of the op amp U4 (potential of the output terminal Vn) rises completely. Before, the potential higher than the output of the operational amplifier U4 is applied to the non-inverting terminal side of the comparator U5, thereby making the output of the comparator U5 high level to open the talk path.

Here, when the application of the audio signal is stopped, both the potential by the op amp U2 (non-inverting terminal side potential of the comparator U5) and the potential by the op amp U4 (inverting terminal side potential of the comparator U5) are fast. The speed is lowered, but the discharge of the capacitor C2, that is, the sink current, is absorbed by the op amp U4 directly by the op amp U4 and the diode DN, not directly by the resistor R4. The potential of Vn) drops rapidly. Therefore, the output of the comparator U5 is at the low level and is in the reception standby state.

The above has described the general operation in the normal state in which there is no impulse noise in the noise.

Now when the impulse noise is mixed with the background noise and applied to the op amps U1 and U2, the op amp U2 immediately reacts to apply the pulse to the comparator U6, and the comparator U6 is set to the preset potential ( The pulse is output to delay U7 in comparison with V1) (which is set to 50% higher than normal noise by experiment), and delay U7 receives the rising pulse and receives 20-30 msec (typical). When the high level output is applied to the control terminal of the analog switch U8 during the impulse noise interval or change), the analog switch U8 is turned off during the output period of the delay U7 and the operational amplifier U1. By preventing the impulse output of the output from being applied to the low pass filter composed of the resistor R1 and the capacitor C1, the output terminal Vn caused by the impulse noise prevents the potential rise, thereby preventing the transmission path from being blocked. This is the disconnection area as shown in FIG. It can be seen that close to the ideal curve is a (b) characteristics as compared with the conventional (A). At this time, as the potential of the output terminal Vn rises, if the rising factor is an increase due to impulse noise, the transmission path is opened only when a larger level audio signal is applied, which in turn raises the average level of the output terminal Vn. Eventually, the disabling state (one-sided state) continues. As described above, the present invention can prevent frequent transmission path interruption caused by impulse noise when using the hands-free unit while the vehicle is in operation, and high reliability can be obtained when the hands-free unit is actually used by a simple configuration such as a general logic amplifier and an op amp.

Claims (1)

A noise monitor unit 10 comprising resistors R1 to R4, capacitors C1 and C2, diodes DN, and op amps U3 and U4 so as to gradually change their levels in response to noise levels; Op amps (U1, U2) diodes (D1-D6), resistors (R6, R7), and capacitors (C4, C5) that detect the input level and receive the input levels in parallel. The output through U1) includes: a detector 20 for providing the noise monitor 10 with the output of the op amp U2 to the low pass filter LPF; Comprising a comparator (U5) receives the output through the op amp (U2) of the detector 20 through a low pass filter (LPF) as a non-inverting terminal, and receives the output of the noise monitor unit 10 as an inverting terminal. In detecting the background noise of the hands-free unit of the car phone, the output provided from the detector 20 to the noise monitor unit 10 through the op amp U1 is turned on and off, and is separately controlled in the normally-on state. An analog switch (U8) which is turned off while the control input is applied through the terminal to block the output signal to the noise monitor unit (10); The detector 20 outputs the detector 20 output from the detector 20 to the low pass filter (LPF) through the op amp U2 in common to the non-inverting terminal, and is 50% or more than the maximum value of general noise in the inverting terminal. The comparator U6 receives the set voltage V1 and the output of the comparator U6 receives the output of the comparator U6 and controls the control terminal of the analog switch U8 for a set period corresponding to the impulse noise interval when the output is high level. A background noise detector of a car phone's hands-free unit, wherein a delay (U7) for providing an input is added to block the impulse noise during the set period of the delay.