KR19990069209A - Noise Reduction Method of Laser Range Finder Receiver - Google Patents

Abstract

A method for reducing noise of a laser range finder is disclosed. For a laser range finder, a method is provided that eliminates the noise induced by a high voltage circuit in a silent manner and the coupling effect between the transmitter and the receiver. The S / N of the receiver is optimized by the matched filter. Solar noise is measured to adjust the threshold voltage of the comparison circuit and to ensure that the receiver is operating at its optimum. Thus, the amount of noise from any noise source of the laser range finder is also successfully reduced, increasing the range measuring capability of the meter by about 60% and improving the accuracy of the measurement.

Description

Noise Reduction Method of Laser Range Finder Receiver

The present invention relates to a method for reducing received noise on a laser range finder, and more particularly to reducing noise on a receiver to improve the accuracy and ability to measure the distance of a target. It is about a method.

In general, rangefinders based on laser technology have been successfully developed by Laser Tech Co., as disclosed in US Pat. No. 404,779,552, which has a 1 Km distance within 1 m. It has a laser diode as a light source. Two main techniques are used in the prior art. First, a fast charge and slow discharge method is used to achieve the function of extending the reception time. Therefore, the time (about 6.6 ms) from the diode transmitting the light until the receiving circuit receives the corresponding reflected light is enlarged by about 100 times. Time is converted to distance by counting samples (about 8 MHz) with a slow clock. The circuit in the meter preferably uses a highly accurate current source to meet the requirements of fast charge and slow discharge, but device instability remains a chronic problem. Secondly, an automatic threshold adjustment is used to optimize the sensitivity of the receiving circuit. However, the feedback sensitivity is too high to control.

It is an object of the present invention to provide a method for optimizing the sensitivity of a laser range finder so that a high degree of accuracy can be achieved with only a slight adjustment of the threshold voltage of the receiving circuit in the meter. Accuracy according to the invention is within 0.5 m. It is emphasized in the present invention that the threshold voltage is slightly adjusted by solar noise even without feedback operation.

According to the invention, the product has been successfully developed and has the following features:

1. The present invention has the advantage of low power consumption since the time interval for transmitting and receiving the laser is converted to a voltage and then the voltage is converted to the corresponding distance only a 9 V battery is required as the power source.

2. The accuracy can be within 0.5 m.

3. The output power of the semiconductor laser used in the present invention is 24 W to 38 W and the pulse width is 20 ns to 50 ns to measure the concrete building target 1 Km away.

The product of this invention is precise enough to measure a golf ball. To further increase accuracy, when the receiver is operating optimally, the user can assign transmission numbers for different targets so that at least two distance data with accuracy within 3 m for each transmission can be obtained. Average the data to get more accurate distance data. A circuit for reducing reception noise is further described below.

As described above, the technique used to reduce noise in the receiver of the present invention includes three main devices:

1. High voltage silent circuit, which allows the switched power supply controller to shut down to minimize noise while the receiver's detector is receiving.

2. Logarithmic amplifiers, which are used to design the receiver to reduce strong echoes that cause saturation in the receiver due to too short distances, and use matching filters and amplifiers to obtain an optimal signal-to-noise ratio (S / N). To do that.

3. A transresistance amplifier, which optimizes the sensitivity of the receiver by amplifying solar noise and using the amplified signal to adjust the threshold voltage.

The features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings.

1 shows a functional block diagram of a laser range finder in the present invention.

Figure 2 shows a schematic circuit diagram of the transmitter of the meter in the present invention.

Figure 3 shows a schematic circuit diagram of the receiver of the meter in the present invention.

4 shows a schematic diagram of a high voltage power supply in the present invention.

5 shows a timing diagram of noise reduction for solar noise, receiver and transmitter.

Explanation of symbols for main parts of the drawings

10 Laser transmitter 20 Laser receiver

21 log amplifier 30 HV power

40 Precision Charging Part 50 Self-Calibration Part

60 CPU 70 A / D Converter

LD Laser Diode APD Detector

R resistor C capacitor

Q transistor

As shown in FIG. 1, the laser range finder of the present invention includes a laser transmitter 10, a laser receiver 20, a high voltage (HV) power supply 30, a precision charger 40, and a self-calibrating section. 50), a CPU 60, and an analog to digital converter 70.

The laser transmitter 10 receives a predetermined high voltage provided by the HV power supply 30 and a trigger signal from the CPU 60 to cause the laser diode LD to transmit the laser light at a reasonable moment.

The laser receiver 20 receives a predetermined detector bias voltage to receive and amplify the echo laser reflected by the target, and adjusts the maximum operating sensitivity.

The precision charging unit 40 converts the time difference between the transmit pulse and the receive pulse by the internal R / S flip flop (not shown) into the corresponding pulse width, and then converts the above pulse width through the charging circuit having the linear capacitor to the corresponding voltage ratio. To.

The self-calibration unit 50 compensates for variations in current source and capacitance due to temperature.

The CPU 60 provides a predetermined timing signal to the apparatus.

The spirit of the present invention provides a method for reducing noise, which is further described below only for the laser transmitter 10, the laser receiver 20, the HV power supply 30 and the CPU 60.

In order to optimize the operating state of the laser receiver 20, it is very important to handle the noise. There are three main sources of noise:

1. Coupling noise from the SM circuit of the HV power supply 30.

2. White noise from sunlight.

3. Other coupling noise from other devices.

The time from transmission to reception is about 6.6 에 for a distance of 1 Km because the laser range finder operates in synchronous mode. Thus, only noises within 6.6 kHz may affect the laser range finder and other noises outside this time may be ignored. The concept involved in the present invention is to reduce the noise source as much as possible during the measurement period.

In order to achieve the above concept, the present invention reduces the noise generated in the laser transmitter 10 by using a circuit for the laser transmitter as shown in FIG. The circuit of FIG. 2 can be filled in a small box that has a small number of components and can prevent interference of E-M wavelengths. In FIG. 2, capacitors C1, C2, C4 and C5 and resistor R1 form a π filter to remove interference of HV power supply 30. Resistor R2 and capacitor C5 form a charging circuit. The capacitor C5, the laser diode LD, the load resistor R3 and the SCR constitute a discharge circuit. Charge and discharge circuits are used to generate laser light (like the timing diagram shown in FIG. 5). The trigger time is measured by the TTL positive edge signal and applied to resistors R4 and R5 to activate the SCR. Timing is controlled by the CPU 60.

In order to operate the laser receiver 20 at the optimum sensitivity by detecting solar noise and adjusting the threshold voltage, the following circuit is used in this embodiment. In FIG. 3, the laser receiver 20 includes a log amplifier 21, a matched filter 22, a solar noise averaging circuit 23, a high speed comparator 24 and an optical band pass filter 25.

The bias of the detector APD is generated by the π filter, which consists of capacitors C1, C2, C4, C6 and resistor R1, which interferes with the HV power supply 30 and the laser transmitter 10 and the laser receiver. Eliminate high voltage coupling noise from (20).

The optical band filter 25 is placed in front of the detector APD to filter out most of the solar noise.

A log amplifier 21 consisting of a load resistor R7 and a capacitor C8 and a resistor R8 and fast diodes D2 and D3 connected between the resistor R6 and the detector is provided with a dynamic range in the laser receiver 20. is used to provide a range. Thus, similar to AGC, the gain decreases as the target approaches, and increases when the target moves away.

Three transistors Q1, Q2, Q3 (this is a low noise transistor used in the present invention) and five resistors R9, R10, R11, R12, R13 constitute a first stage trans-resistance amplifier 221, This amplifier can transform the laser signal received by the APD into a voltage signal. The first stage trans-resistance amplifier 221 and the log amplifier 21 constitute a band pass filter, which selects appropriate parameters to match the frequency response of the band pass filter and the frequency response of the laser pulse. Thus, a matching amplifier is constructed.

The second stage trans-resistance amplifier 222 is composed of transistors Q4, Q5, and Q6 and resistors R14, R15, R16, R17, R18, and R19, and through the resistor R20 and the capacitor C9, Coupled to the drain of Q3). Therefore, another voltage amplifier with a band pass filter is obtained. Therefore, the matched filter 22 including the log amplifier 21, the first stage trans-resistance amplifier 221, and the second stage trans-resistance amplifier 222 generates a signal corresponding to the laser pulse to obtain an optimal S / N. To get it.

The output of the first stage trans-resistance amplifier 221 is connected to the emitter follower via rectifier diode D4, capacitor C10 and split resistors R21, R22 (ie, solar noise averaging circuit 23). Pass the transistor Q7 as an emitter follower to obtain the average noise for the first stage trans-resistance amplifier 221. The average noise is the white noise of the optical band filter 25 and is induced by sunlight. Regarding the coupling noise generated by the HV power supply unit 30, the HV power supply unit 30 is automatically closed by the voltage feedback circuit (as in the following description) since the high voltage is first established.

The threshold voltage of the high speed comparator 24 is adjusted by the output voltage of the average solar noise and the fixed threshold voltage formed by the resistors R23 and R24. The threshold voltage will increase when solar noise increases, and the threshold voltage will decrease when solar noise decreases.

Before the laser transmitter 10 transmits, the solar noise averaging circuit 23 is configured by the APD, which is provided by the HV power supply 30. Each timing diagram is shown in FIG.

In order to minimize the noise of the APD during reception, the present invention adopts the following design. Referring to FIG. 4, the pulse modulation IC 31 of the HV power supply unit 30 (TL494 is used in the present invention) uses the biases V _LD and V _APD provided for each of the laser diodes _LD and _APD . To control. The high voltage generated by the HV power supply unit 30 is controlled by the negative feedback of the transistors R24 and R25 and V _REF . Due to the very low current consumption for V _APD , the pulse width of the pulse modulation IC 31 when the laser transmitter 10 is not operating will block the high voltage pulse width through the negative feedback (as shown in FIG. 5). The CPU 60 will provide a TTL signal to close the pulse modulation IC 31 for a period longer than 6.6 Hz to keep the oscillator of the HV power supply 30 silent after the laser light has been transmitted.

As mentioned above, the present invention provides each solution to reduce the reception noise of the laser range finder, and furthermore to successfully overcome the conventional drawbacks.

Although the foregoing description merely illustrates preferred embodiments of the invention, it is intended that any modifications or combinations falling within the spirit of the invention be protected.

Claims (6)

(1) providing a laser range finder in a silent manner to eliminate noise generated by the high voltage controller and the coupling effect between the transmitting circuit and the receiving circuit; (2) optimizing the S / N of the receiving circuit using a matched filter; And (3) measuring solar noise to adjust the comparator's threshold voltage so that the receiving circuit operates at the highest sensitivity state; Reducing all noise from any noise source of the laser range finder to increase the range measuring capability of the laser range finder and improve the accuracy of the measurement. The method of claim 1, In step (1), a bias voltage provided to the laser diode and the detector by the high voltage power supply unit generates a negative feedback control, so that the noise of the detector is minimized while the laser receiver is received. and closing the power controller. The method of claim 1, In step (2), a logarithmic amplifier is used in the laser receiver circuit configuration to reduce the strong noise caused by too short a distance that may saturate the laser receiver, so that the S / N Noise reduction method of the laser range finder receiver further comprising the step of optimizing for use. The method of claim 1, The step (3) uses a trans-resistance amplifier in the laser receiver circuit to amplify the solar noise to detect the noise value and adjust the threshold value to adjust the threshold voltage so that the receiver can operate at optimum sensitivity. Noise reduction method of the laser range finder receiver further comprising the step of using. The method of claim 1, The laser receiver according to the steps (2) and (3) comprises a logarithmic amplifier, a matched filter, a solar noise averaging circuit, a high speed comparator and an optical band pass filter; The detector further comprises a π filter used to eliminate interference from the high voltage power supply and the coupling effect between the laser transmitter and the laser receiver; The optical band pass filter is placed in front of the detector to filter out most solar noise; The logarithmic amplifier comprises a plurality of resistors, a capacitor and a fast diode to increase the dynamic reception range for the laser receiver; The first stage trans-resistance amplifier and the logarithmic amplifier, which transform the laser signal received by the detector into respective voltage signals, form a band pass filter, which sets appropriate parameters to determine the frequency response of the band pass filter and the laser pulse. The frequency response is matched and the matched amplifier is formed; A second stage trans-resistance amplifier, the first stage being similar in design to the first stage trans-resistance amplifier and having a resistor and a capacitor in series with the first stage trans-resistance amplifier to obtain another voltage amplifier with a band pass filter. A trans-resistance amplifier and the second stage trans-resistance amplifier are added next to the logarithmic amplifier to form the matched filter to generate a signal for the laser pulse and obtain an optimal S / N; The solar noise averaging circuit comprises an emitter follower, a rectifying diode, a capacitor, and a split resistor, through which the output terminal of the first stage transresistance amplifier passes through and the average noise for the first stage transresistance amplifier. To get; The threshold voltage of the fast comparator is adjusted by the output voltage of the average solar noise and a fixed threshold voltage formed by the split resistor so that the threshold voltage increases when the solar noise increases, and when the solar noise decreases. A method for reducing noise in a laser range finder receiver, characterized in that a threshold voltage is reduced to allow the receiving circuit to operate optimally. The method of claim 1, The bias voltage is provided to the laser diode and the detector in the high voltage power supply according to the step (1); The high voltage generated by the high voltage power supply is controlled by a negative feedback, and in this feedback, the pulse modulation IC controls the feedback path so that the laser transmitter stops the period of time so that the high voltage power supply is kept silent. Noise reduction method for laser range finder receiver.