JPS5921132B2 - High sensitivity receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a highly sensitive receiving device that can be used in equipment that handles signals with a lot of external and internal noise, such as photoelectric switches and ultrasonic switches.

Photoelectric switches and ultrasonic switches are often used for crime prevention and control purposes, but due to their nature, they generate a lot of external disturbance and internal noise.
Simply increasing the degree of amplification in an attempt to obtain a highly sensitive receiver has not been effective.

The present invention uses an oscillator that modulates the amplitude of a high frequency signal with a low frequency signal, and uses a phase synchronized circuit (hereinafter referred to as PL) that follows the frequency and phase of the input signal in the receiving circuit.
The aim is to obtain a receiving device with extremely high sensitivity.

In other words, the gist of the present invention is to increase the signal-to-noise ratio using a tuned amplifier tuned to the high-frequency signal of the oscillator, perform detection to extract a low-frequency signal, and use the PLL section to determine whether or not it is a predetermined low-frequency signal. This system attempts to make a judgment and drive an output circuit, making it possible to detect a regular signal buried in irregular noise and increasing the sensitivity of the receiving device.

Examples of the present invention will be described below.

FIG. 1 is a block diagram of an infrared warning device for crime prevention according to the present invention, in which 1 is a light receiving element, 2 is a tuning type amplifier tuned to the high frequency signal of the projector 8, and 3 is a detector, and 3 is a tuning type amplifier 2.
The output is detected and a low frequency signal is extracted.

An amplifier 5 amplifies the low frequency signal output from the detector 3 and supplies it to the next PLL section 6.

The PLL section 6 is a circuit section mainly composed of a semiconductor integrated circuit element that has an internal phase comparator and a voltage (or current) controlled oscillation circuit (hereinafter referred to as vCO), and when there is no input signal, the frequency at which vCO is When an input signal is given, a phase comparator compares the input signal and the oscillation frequency of vCO, almost independently of the input signal amplitude, and outputs a voltage (or current) according to the difference. , which results in v
The oscillation frequency and phase of the CO are changed so that they match or have a certain relationship with the input signal (hereinafter simply referred to as "match"), and when they match, a match signal is output.

Similarly, the phase and frequency comparisons can be performed by determining an arbitrary fixed time and frequency range.

That is, it outputs a matching signal when an input signal in a certain frequency range is applied for a certain period of time.

Reference numeral 7 denotes an output circuit which performs signal processing such as driving a relay and turning on or off an indicator lamp in response to a coincidence signal from the PLL section 6.

A projector 8 includes a low frequency oscillator 81 and a high frequency oscillator 82, which is modulated by a modulator 83 and applied to a light source 84 to project infrared rays toward a light receiving device.

In the above configuration, when the emitter is not operating, that is, when no signal light is given to the light receiving element 1, the light receiving element 1
The output is an irregular electrical signal due to noise f caused by ambient light and noise generated inside the light receiving element 1 (especially noticeable when external light is strong).

This electric signal is amplified by a tunable amplifier 2, and its tuning frequency, that is, a frequency component tuned to the high frequency signal of the projector is selectively amplified and given to a detector 3.

This detection output is amplified by the amplifier 5 and given to the PLL unit 6, but since the noise is mostly composed of random pulses, it contains low frequency components and the frequency is not constant, so the PLL unit 6 is synchronized. The same frequency is not maintained for the time required to make the signal match, and the PLL section 6 does not output a matching signal.

Therefore, no output is output from the output circuit 7.

When a modulation signal (100% amplitude modulated, i.e., intermittent) of a high frequency signal with a low frequency signal as shown in FIG. Internally generated noise appears as an electrical signal in the light receiving element 1, and as shown in FIG. 2, when the input signal is weak, it appears as if the noise component has completely filled the signal component.

When this is applied to the tunable amplifier 2, signals in a frequency range approximating the tunable frequency, that is, a high frequency signal including noise, are selectively amplified, and components other than the tunable frequency are significantly cut off.

That is, as shown in FIG. 2C, noise components are largely removed and signal components are emphasized.

When this wave is detected by the wave detector 5, a wave is emitted as shown in Fig. 2d.

This becomes a signal of the same frequency as the low frequency signal of the optical device 8, which is amplified by the amplifier 5 and given to the next PLL section 6.

When this signal is given to the PLL section 6, the VCO inside the PLL section 6 starts to follow it in synchronization with it, and when the frequency and phase match for a certain period of time continuously, the PLL section 6 outputs a coincidence signal.

Therefore, the output section 7 is driven and a desired output is output.

Since noise is generally random, if a low level but regular input signal from a projector is added to it, regularity appears as a whole.

As described above, according to the present invention, it is possible to detect the regularity, and as a result, an extremely sensitive receiving device that can detect the presence or absence of a target input signal from an input signal buried in noise can be obtained.

In addition, even if regular noise is mixed in, the vCO
Since the frequency range that can be tracked can be set to an arbitrary range, there is extremely little risk that a matching signal will be output from the PLL section 6 due to noise, and the reliability of the receiving device will be extremely high.

The PLL section 6 is mainly composed of a semiconductor integrated circuit including a voltage controlled oscillation circuit and a phase comparator, such as BA567.
A PLL application integrated circuit such as the following is used.

In FIG. 1, reference numeral 4 denotes an automatic gain control circuit, which controls the amplification degree of the synchronous amplifier 2 based on the average value of the output voltage of the detector 3.

This is used to prevent the amplifier from becoming saturated with an input signal that is more than necessary. When only noise is input to the detector 3, the synchronous amplifier is is operating but a normal input signal is input, the output voltage of the detector 3 increases, and the amplification degree of the synchronous amplifier decreases by that amount.

At the same time, the noise component that was input together with the normal signal is further reduced relatively, and the signal-to-noise ratio is improved.

Conventionally, an infrared warning device using an optical system (lens) with a light diameter of 60111 m-f: 150 mrIt had a maximum reachable distance of 600 meters with infrared modulated light (IKHz), but now it uses the same optical system and has a maximum reachable distance of 20 KHz. When the present invention was implemented in a light receiving device using double modulated infrared pulsed light obtained by amplitude modulating the modulated light at 500 Hz, the maximum reachable distance was 1200 meters.

Furthermore, using the double modulated infrared pulsed light, the light diameter is 11.
It was confirmed that by using an optical system of 6 mm" f: 300 mvn, the maximum reach distance was 4000 meters or more.

The above explanation was about an example using a projector that uses infrared rays as the signal medium and intermittents a high frequency signal with a low frequency signal, but it is also possible to use light beams or ultrasonic waves as the signal medium. It goes without saying that the present invention is applicable even when the degree of modulation of the low frequency signal with respect to the high frequency signal is changed.

As explained above, according to the present invention, an oscillator that modulates the amplitude of a high frequency signal with a subharmonic signal is used, and a tunable amplifier, a detector, and a PLL section are continuously connected in this order, and the oscillator is By making the oscillation frequency of the VCO inside the PLL section track the low-frequency signal of the device, and outputting a matching signal when these match for a certain period of time, extremely high sensitivity is achieved that can reliably detect even input signals buried in noise. It is possible to obtain a receiving device that is

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an infrared warning device for crime prevention which is an embodiment of the present invention, and FIG. 2 is a diagram of internal operation waveforms of the device shown in FIG. 1... Light receiving element, 2... Tunable amplifier, 3... Detector, 4... Automatic gain control circuit, 5... Amplifier 6...PLL section,
7...Output circuit, 8...Light emitter.

Claims (1)

[Claims] 1. In a receiver used in opposition to an emitter that outputs double-modulated infrared pulsed light in the form of a low-frequency amplitude modulated high-frequency modulated light, a synchronous amplifier, a detector, and phase synchronization that follow the input signal are used. circuit, these are connected in this order, and the frequency and phase of the internal oscillation of the phase synchronized circuit are made to follow the low frequency signal of the double modulated infrared pulsed light, and both coincide for a certain period of time or have a certain relationship. a photoelectric switch receiver configured to output a coincidence signal when