KR19990046244A - Novel electrical circuits for background light noise rjection in an optical range finder - Google Patents

Abstract

In a system that irradiates a light wave (LASER Diode or infrared LED) to a transmitting device and receives the reflected light, a fatal error is caused by a sudden flash or background light. Compensation for this is generally compensated by modulating the transmission light source or by adding an optical filter in front of the sensor of the receiver.

In general, the method of removing background light noise (flash or sunlight) using the optical filter of the receiving device using the reflected light cannot use a relatively inexpensive LED and uses an expensive laser diode due to the reduction of the received light amount due to the use of the optical filter. The high cost of the filter itself raises the price of the entire system.

According to the present invention, a method and a circuit capable of eliminating the background light noise, which is pointed out as a disadvantage in a receiving apparatus using light waves, instead of an optical method, are proposed. In addition, since the receiver does not use an optical filter, the cost of the receiver is low, and since it is possible to use an infrared LED that is easy to drive a transmission light source and is not sensitive to temperature effects, it is cheaper than a transmitter that uses a laser diode. The driving circuit is simple and a reliable transmission device can be realized.

Description

Novel electrical circuits for background light noise rjection in an optical range finder

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit arrangement capable of electronically removing background optical noise, which is a fatal problem in a receiving device using a light wave (particularly a device using reflected light).

In general, in the case of a distance measuring device using light waves, as shown in FIG. 1, in order to prevent a malfunction caused by background light noise (flash or sunlight), the light source of the transmitting device is pulsed and the receiving device is driven by background light noise. In order to remove the DC component of the PSD sensor, an optical filter that passes only a certain frequency component and removes other frequency components is mounted in front of the receiving lens. By attaching an optical filter, the light source of the transmitting device should use a laser diode with a narrow spectral width and relatively high power. Laser diodes have the advantages of faster response time, narrower emission spectrum width, and higher output than infrared LEDs. However, they require a separate temperature control circuit because they are sensitive to temperature, and are also quite expensive. Therefore, in the case of the system as shown in FIG. 1, the driving circuit becomes complicated because the light source must use the laser diode, and the temperature control circuit of the laser diode must be attached, and the optical filter must be attached to the receiver. There is this.

The present inventors studied a method of eliminating background noise, which is a problem in a system of irradiating light waves and receiving the reflected light by an electronic circuit method rather than an optical method. Highly reliable infrared LEDs can be used, and the receiving side has the effect of removing the optical filter. When using the present invention, the same effect can be configured at a much lower price point, and also has the advantage of building high reliability.

In the background light noise removing circuit of FIG. 3, the ADD-1 output value is mixed with an original signal (LED modulation signal) and background light noise. The signal mixed with the background optical noise is applied to the positive terminal of IC241 (subtraction circuit) and the positive terminal of IC242 (Sample & Hold circuit). The ADD-1 waveform input to the IC242 outputs a waveform as shown in (2) of [Fig. 4]. When this output waveform is applied to and subtracted from the negative terminal of IC241, it is finally reduced to (2) in [Fig. 5]. As such, the PSD output waveform obtained by removing only background optical noise can be obtained. In the same way, the background light noise (IC242, IC245) is removed for the SUB-1 output value in the same way as above. Output only waveforms.

A block diagram of the present invention is shown in FIG. In the present invention, as shown in the block diagram of FIG. 2, the light source is used as an infrared LED instead of a laser diode, and an optical filter is used by adding an electronic circuit background optical noise filter instead of deleting the optical filter of the receiver. To achieve the same effect as the system.

EXAMPLE

4 and 5 add background optical noise reduction circuits to compensate for changes in PSD output (affected by distance measurement) due to the effects of sunlight or sudden flash, which are weaknesses in using light waves. One result is shown.

In FIG. 4, (1) shows that the background optical noise is loaded at the LED modulation frequency (1.2KHz) at the ADD output. Figure 2 shows the ADD output without the background optical noise. Subtracting these two signals outputs only the original signal from which the curved portion disappears, that is, the background optical noise has been removed, as shown in (2) of FIG.

As shown in the above embodiment, according to the method of the present invention, an inexpensive, easy to purchase and highly reliable component can be used as a light source of the transmitter, and an expensive optical filter by adding a background optical noise canceling circuit to the receiver side. It has the effect of deleting it. Therefore, according to the present invention, since the price of the entire system can be lowered to 1/20 or less than the existing price, not only the price competitiveness but also the system manufacturing is easier than the existing apparatus.

Claims (1)

In distance measuring devices and other applications using light waves, Add & Sub output signals containing background light noise are sampled & held to remove only the data part, and signals from which only the data part is removed and signals containing background light noise are mixed. A circuit method that passes through a subtractor and outputs an original signal with only background optical noise removed.