JP3270904B2 - Infrared remote control sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared remote control device for performing remote control or the like using infrared light.
Infrared remote control used as an infrared light receiving device
It relates to a troll sensor .

[0002]

Conventionally, the remote control device using radio waves as a remote control device, remote with remote controller and infrared light using ultrasonic
Control devices and the like are known. Of these, remote control devices that use radio waves are subject to the effects of urban noise, are difficult to provide directivity, and are difficult to maintain confidentiality. It had disadvantages such as difficulty in handling. In addition, the remote control device using ultrasonic waves also has disadvantages such as a large influence of city noise and a change in directivity due to wind.

For this reason, general remote control
Less susceptible to urban noise as equipment, making it possible to have a predetermined directivity with a simple structure, an infrared remote controller with easy infrared light handling inexpensive
Roll devices are exclusively employed.

[0004] Conventional general infrared remote control
A block diagram of a Le device shown in FIG. 10. In FIG.
The infrared remote control device includes a transmitting device 200 for transmitting infrared light and a light receiving device 3 for receiving the transmitted infrared light.
Reference numeral 101 denotes a control signal generator for generating a control signal for controlling the control circuit 110; 102, a coding circuit for coding the control signal into a pulse signal; 103, a modulator (MOD) for amplitude-modulating the pulse signal. , 104 is MOD
Oscillator (OS) that generates a carrier to be applied to 103
C) and 105 are LEs for transmitting infrared light according to the modulation output.
D, the control signal generator 101, the coding circuit 1
02, the MOD 103, and the OSC 104 form an infrared transmission device 200.

Next, reference numeral 106 denotes a photodiode for receiving infrared light transmitted from the LED 105, and 107 denotes an amplifier (AM) for amplifying an output current of the photodiode 106.
P), 108 are demodulation circuits (DEMOD) for demodulating the modulated signal and shaping the waveform, 109 is a decoder for decoding the coded signal, 110 is a control circuit controlled by the control signal, and is a control circuit 120 surrounded by a dotted line. Is an infrared remote control sensor comprising a photodiode 106, an AMP 107 and a DEMOD 108, and 300 is an infrared remote control sensor.
2 shows a light receiving device including a remote control sensor 120, a decoder 109, and a control circuit 110.

An infrared remote control shown in FIG.
When the operator operates, for example, a television or a VTR provided with the light receiving device 300, the transmitting device 2
For example, when a button or the like provided on a remote controller is operated, the control signal generator 101 generates a control signal corresponding to the operated button.
In step 2, a predetermined code signal pulse is generated.

[0007] The coded pulse signal is the OSC 104
The pulse signal P amplitude-modulated by the MOD 103 by the carrier generated at the MOD 103 as shown in FIG.
Becomes This pulse signal P is applied to the LED 105 and becomes infrared light, which is transmitted from the LED 105.

[0008] The infrared light transmitted from the LED 105 is received by the photodiode 106 of the light receiving device 300, and a photocurrent corresponding to the amount of received light is generated by the photodiode 1 by a photoelectric effect.
06. The photocurrent induced in the photodiode is amplified by the AMP 107, applied to the DEMOD 108, demodulated, and shaped.

The demodulated signal whose waveform has been shaped is supplied to a decoder 109.
Is decoded and applied to the control circuit 110, and the control circuit 110 performs a desired operation such as a television or a VTR. The oscillation frequency of the OSC 104 is a low frequency, and for example, the oscillation frequency is generally selected from a frequency of 30 to 40 kHz.

[0010] Such an infrared remote control
Infrared Li used as a part of the light receiving device 300 of the apparatus
FIG. 5 shows a block diagram of the mote control sensor 120. In FIG. 5, reference numeral 1 denotes a photodiode that receives infrared light and converts it into a current corresponding to the amount of received light, 2 denotes an amplifier,
A signal processing circuit comprising a band-pass filter 5 and a demodulation circuit 6 for amplifying and shaping the output signal of the photodiode 1 to output a pulse waveform. An amplifier (AMP) 4 for amplifying the output of the photodiode 1 and 5 for amplification. A band-pass filter (BPF) for extracting a signal component in a desired band from the output of the photodiode 1;
Output signal is detected by an envelope and a predetermined reference level V
This is a demodulation circuit that obtains a pulse waveform output signal by shaping the waveform using ref.

An infrared remote control shown in FIG.
The infrared light incident on the sensor is infrared light transmitted from the transmission device 200 as shown in FIG. The transmitting apparatus 200 transmits the above-described pulse signal P shown in FIG. 9 as infrared light, and the pulsed infrared light transmitted from the transmitting apparatus 200 as shown in FIG. The photodiode 1 outputs a photocurrent according to the amount of incident light by the photoelectric effect.

A photocurrent signal obtained from the photodiode 1 is amplified by an amplifier 4 and applied to a band-pass filter 5, and a signal having a carrier frequency component for amplitude-modulating the pulse is extracted from the photocurrent signal. The bandpass filter 5 removes the noise component having no carrier frequency component from the photocurrent signal applied to the bandpass filter 5, but the noise component included in the pass band of the bandpass filter 5 is It cannot be removed.

Such noise includes, for example, shot noise generated from a photodiode, noise generated from an element used, and the like. In addition, the photocurrent signal has a waveform whose rising and falling are slightly attenuated due to the frequency characteristics of the transmission space and the frequency characteristics of the elements used in the light receiving device, so that the output of the bandpass filter 5 eventually becomes as shown in FIG. In addition, the rising and falling edges are gently inclined, and the waveform is superimposed with noise.

Such a photocurrent signal whose rising and falling are rounded and on which noise is superimposed has a pulse waveform which is shaped by the demodulating circuit 6 so that the rising and falling is steep and the noise is also removed. You. That is, the demodulation circuit 6 is a circuit that performs envelope detection on the output of the band-pass filter 5 and compares the envelope-detected photocurrent signal with a predetermined reference level Vref to perform waveform shaping. Therefore, when the photocurrent signal taken out of the band-pass filter 5 is applied to the demodulation circuit 6, the photocurrent signal is subjected to envelope detection to become an envelope photocurrent signal as shown in FIG. This envelope-detected photocurrent signal is compared with a predetermined reference level Vref, and FIG.
As shown in the figure, the level of the photocurrent signal and the reference level Vr
When ef coincides with each other, the output signal becomes a pulse shaped pulse waveform whose waveform rises or falls sharply.

The reference level Vre of the demodulation circuit 6
The smaller the value of f, the higher the light receiving sensitivity can be, but the lower the value of f, the easier it is to pick up noise. Therefore, the environment in which the infrared photosensor is used and the amount of noise generated by the infrared photosensor itself are taken into consideration. Meanwhile, the reference level Vref is set to a predetermined value. This output signal is applied to the decoder 109 as a demodulated signal as shown in FIG.

[0016]

The infrared ray shown in FIG.
Consider a case where the amount of disturbance light increases in the remote control sensor . The magnitude of the noise current generated in the photodiode 1 changes according to the amount of incident light. This noise current is a noise current _ipn called shot noise, and is proportional to the square root of the photocurrent io flowing through the photodiode 1 as shown in the following equation.

(Equation 1) Here, q: elementary charge, B: bandwidth, and k ₁ are constants.
The characteristic represented by the above equation 1 is shown in the graph of FIG. As can be understood from FIG. 8, shot noise (noise current i
_pn ) gradually increases according to the magnitude of the photocurrent io.

As described above, since the general photodiode 1 has such characteristics, when the amount of disturbance light increases, the shot noise also increases in accordance with the amount of disturbance light. When the amount of disturbance light increases and the generated shot noise increases, the level of the noise current is reduced to the reference level Vref of the demodulation circuit 6 as shown in FIG.
Will be exceeded. When the level of the noise current exceeds the reference level Vref of the demodulation circuit 6, the output of the demodulation circuit 6 falls, and conversely, when the level of the noise current falls below the reference level Vref, the output of the demodulation circuit 6 rises. When the photocurrent signal when is large is applied to the demodulation circuit 6, an output signal having chattering as shown in FIG. 7B is output from the demodulation circuit 6.

Since the output signal with chattering shown in FIG. 7b should be an output signal as shown in FIG. 6b, when the output signal shown in FIG. 7b is used, this signal is applied, for example. The decoder circuit 109 as shown in FIG. 10 outputs an erroneous decoded output.

Therefore, in order to prevent malfunction when the amount of disturbance light increases, it is only necessary that the level of the noise current due to the disturbance light does not exceed the reference level Vref. It is only necessary to lower the amplification degree so that the noise current does not exceed the reference level Vref.

However, if the amplification degree of the amplifier 4 is reduced, erroneous data will not be output when the amount of disturbance light increases, but this time the photodiode 1
Since the photocurrent signal cannot exceed the reference level Vref unless the light amount of the signal component of the infrared light incident on the infrared remote control sensor is large, the light receiving sensitivity of the infrared remote control sensor decreases.

Therefore, the infrared remote control of the present invention
In the sensor , the amplification degree is controlled according to the amount of disturbance light so that the magnitude of the noise current in the photocurrent signal applied to the demodulation circuit is constant regardless of the amount of disturbance light. To suppress the effect of noise current without lowering the light receiving sensitivity.

[0022]

In order to achieve the above object, in the infrared remote control sensor according to the present invention, an input matching circuit having a function proportional to the square root of the photocurrent is provided after the photodiode so as to be demodulated. The magnitude of noise current such as shot noise included in the photocurrent signal applied to the circuit is made substantially constant regardless of the amount of disturbance light.

[0023]

By providing an input matching circuit having a function proportional to the square root of the photocurrent to the photodiode, an output in which the magnitude of shot noise proportional to the square root of the photocurrent is constant regardless of the amount of disturbance light. Since it can be obtained from the input matching circuit, it is possible to suppress the influence of the noise current without lowering the light receiving sensitivity.

[0024]

A block diagram of an infrared remote control sensor <br/> of EXAMPLES present invention shown in FIG. 1, the infrared remote of the present invention in FIG. 2
FIG. 2 shows a detailed circuit diagram of an input matching circuit used in a port control sensor . In FIG. 1, blocks with the same reference numerals as those in FIG. In this figure, reference numeral 3 denotes an input matching circuit having a function proportional to the square root of the photocurrent of the photodiode 1.

In the infrared light remote sensor shown in FIG. 1, the infrared light incident on the photodiode (PD) 1 is transmitted from, for example, a transmitting device 200 shown in FIG.
This is a pulse signal amplitude-modulated with a carrier of 30 to 40 kHz as shown in FIG.

The infrared light of the pulse signal is received by the photodiode 1, and the photodiode 1 outputs a photocurrent io corresponding to the amount of incident light. The optical current io is applied to the input matching circuit 2, is the output current i _m as shown in equation (2) that is proportional to the square root of photocurrent io.

(Equation 2) Here, k ₂ is a constant.

The output current i _m of the input matching circuit 2 is applied to a band pass filter (BPF) 5 is amplified by the amplifier (AMP) 4. This bandpass filter 5
In this way, only a pulse signal having a carrier frequency component that modulates the amplitude of the pulse is extracted from the output of the amplifier 4.

A pulse signal having a carrier frequency component, which is the output of the band-pass filter 5, is applied to a demodulation circuit 6 and is first subjected to envelope detection. Next, the pulse signal from which the carrier detected by the envelope detection is removed is compared with a predetermined reference level Vref as shown in FIG. 6A to obtain a pulse signal whose waveform is shaped as shown in FIG. 6B. You. The baseband pulse signal shaped by the demodulation circuit 6 is applied to, for example, a decoder as shown in FIG.

Next, the infrared remote control shown in FIG.
A description will be given focusing on how noise occurs in the troll sensor . The noise current i _pn of the shot noise generated by the photodiode 1 that receives the infrared light is proportional to the square root of the photo current io flowing through the photodiode 1 as shown in the above equation (1).

[0030] Thus noise current i _pn is an AC signal, is input to the input matching circuit 3 noise current i _pn
Is operated by the dynamic characteristics of the input matching circuit 3.
Since the dynamic characteristic of the input matching circuit 3 is obtained by differentiating the function shown in the above equation (2), the dynamic characteristic G becomes as shown in the following equation (3).

(Equation 3)

The noise current i _mn appearing at the output of the input matching circuit 3 is expressed by the product of the noise current i _pn input to the input matching circuit and the dynamic characteristic G of the above _{equation (} 3). Become like

(Equation 4) However, a _{k 3 = k 1 · k 2} /2.

That is, the noise component appearing at the output of the input matching circuit 3 has a constant magnitude irrespective of the magnitude of the photocurrent io, as shown in the above equation (4). Therefore, even if the disturbance light increases and the photocurrent io increases, the noise current _imn output from the input matching circuit 3 becomes constant, so that the amplification degree of the amplifier circuit 4 following the input matching circuit 3 does not decrease. In both cases, the phenomenon that the noise current exceeds the reference level as shown in FIG.
Does not output an output in which chattering occurs.

Next, a detailed circuit diagram of the input matching circuit 3 shown in FIG. 2 will be described. In FIG. 2, the cathode of the photodiode 1 is connected to the emitter of an NPN-type first transistor T1, the anode is connected to ground, and the collector of the first transistor T1 is connected to the cathode of the first diode D1. And its base is connected to the collector of a fourth transistor T4 of the NPN type. The emitter of the fourth transistor T4 is connected to the ground, the collector is connected to the power supply Vcc via the resistor R1, and the anode of the first diode D1 is also connected to the power supply Vcc.

The collector of the first transistor T1 and the first
The base of a PNP-type second transistor T2 is connected to the connection point of the diode D1 with the cathode, the emitter of the second transistor T2 is connected to a power supply Vcc via a resistor R2, and the collector thereof is connected to the power supply Vcc. By being connected to the cathode of the second diode D2, it is connected to ground via a series circuit of the second diode D2 and the resistor R3.

The collector of the second transistor T2 and the second
The base of a third transistor T3 of NPN type is connected to a connection point of the diode D2 of the third transistor T2, the emitter of the third transistor T3 is connected to the ground via a resistor R5, and the collector thereof is connected via a resistor R4. It is connected to the power supply Vcc.

The connection point between the collector of the third transistor T3 and the resistor R4 is connected as an output terminal to the subsequent amplifier 4.

The operation of the input matching circuit 3 shown in FIG. 2 is as described below. A photocurrent is induced in the photodiode 1 by the infrared light incident on the photodiode 1, and this photocurrent flows through the emitter of the first transistor T1. so that the substantially equal currents i ₁ and induced photocurrent in the photodiode 1 flows.

When the current i ₁ flows through the first diode D1, a voltage drop occurs across the first diode D1. The voltage generated between both ends of the first diode D1 is applied between the base and the emitter of the second transistor T2 and to the resistor R2. This voltage becomes the base bias voltage of the second transistor T2,
Of the collector of the transistor T2 the current i ₂ corresponding to the voltage generated at both ends of the first diode D1 flows.

The collector current i ₂ of the transistor T2 flows to the ground via the series circuit of the second diode D2 and the resistor R3, and the voltage generated in the series circuit of the second diode and the resistor R3 is equal to the voltage of the third transistor T3. The voltage is applied between the base and the emitter and to the resistor R5. The second diode and the voltage generated in the series circuit of the resistor R3 is the base bias voltage of the third transistor T3, a current i ₃ in accordance with the base bias voltage flows to the collector of the third transistor T3.

The collector current of the third transistor T3 flows through the resistor R4, and the voltage i ₃ .multidot.
R4 is output from the output terminal as the output voltage of the input matching circuit 3. The relationship between the AC currents i ₁ and i ₂ and the AC currents i ₂ and i ₃ is represented by the AC currents i ₁ and i ₂ for simplicity.
And i ₃ as direct currents I ₁ , I ₂ and I _3, are given by the following equations (5) and (6).

(Equation 5)

(Equation 6) Where k is Boltzmann's constant, T is absolute temperature, I _S is P
The reverse saturation current of the NP transistor, I _s ′ is the reverse saturation current of the NPN transistor, x is the coefficient of current proportional to the emitter area of the PNP transistor, and y is the coefficient of current proportional to the emitter area of the NPN transistor.
The relationship between the currents I ₁ and I ₂ and the relationship between the currents I ₂ and I ₃ shown in the above formulas (5) and (6) are approximately represented in a graph as shown in FIG.

[0041] In FIG. 3, the current I ₂ when the vertical axis when the horizontal axis and current I ₁ is the current I ₂ becomes the current I ₁ becomes larger a characteristic to be saturated. The curvature of the saturation characteristic can be changed by the current coefficient x and the resistance R2, which are proportional to the emitter area of the second transistor T2.

In FIG. 3, if the horizontal axis is the current I ₂ , the vertical axis is the current I ₃ , and the current I ₃ has a characteristic that the current I ₂ becomes saturated as the current I ₂ increases. The curvature of the saturation characteristic can be changed by the current coefficient y and the resistances R3 and R5, which are proportional to the emitter area of the third transistor T3. Therefore, the input current I ₁ of the input matching circuit is
If, when finding the relationship between the output current I _3, since the circuit that indicates the characteristic of the graph as shown in FIG. 3 is connected to 2-stage cascade, the relationship between the current I ₁ and I ₃ in Fig. 3 The graph of the saturation characteristic is more saturated than the graph of the saturation characteristic shown. After all, the graph showing the relationship between the currents I ₁ and I ₃ approximates the graph of the square root.

Further, the coefficients x and y and the resistances R2 and R
3 and R5 can change the curvature of the saturation characteristic shown in FIG.
2, R3, R5 are adjusted curvature of the saturation characteristics by appropriately changing, so is represented approximately a current I ₃ as approximately the square root of the current I _1.

As a result, the characteristics of the input matching circuit 3 are substantially as shown in Expression 2, so that the shot noise generated in the photodiode 1 becomes constant as described above regardless of the magnitude of the disturbance light, and the amplifier 4. The signal is applied to the demodulation circuit 6 via the band-pass filter 5, so that the demodulation circuit 6 can output a shaped output without being affected by shot noise. Moreover, when the disturbance light is small, the gain of the input matching circuit 3 is high, so that the light receiving sensitivity can be kept high.

In the circuit shown in FIG. 2, the NPN type fourth transistor T4 is a negative feedback transistor for improving the frequency characteristics. This fourth
The operation of the transistor T4 is as follows. Assuming that the amount of infrared light incident on the photodiode 1 increases and the photocurrent induced on the photodiode 1 increases,
An increase in the base current of the fourth transistor T4, and thus an increase in the emitter current thereof, lowers the collector-emitter voltage of the fourth transistor T4 so that the base bias of the first transistor T1 does not increase. .

That is, the fourth transistor T4 is connected to the first transistor T4.
Of the transistor T1. When negative feedback is applied, the gain decreases and the GB product (the product of the gain and the frequency band) is constant, so that the operating frequency band of the circuit is widened and the frequency characteristics are improved.

The infrared remote control described above
Figure a photodiode and signal processing circuit Rusensa 4
Can be integrated on one chip as shown in FIG. 4, reference numeral 1 denotes a photodiode, and 2 denotes a signal processing circuit as shown in FIG. 1, for example. Like this infrared
When the remote control sensor is integrated as a single chip, further advantageous effects such as direct connection to a microcomputer, resistance to power supply noise due to electromagnetic noise and the like, and reduction in size, reliability and cost can be further achieved.

[0048]

The infrared remote control cell of the present invention
Since capacitors are configured as described above, the infrared remote
Be greater amount of ambient light incident on the bets control sensor, it is possible to suppress the influence of the shot noise or the like generated in the photodiode without sacrificing the light receiving sensitivity of the infrared remote control sensor.

[Brief description of the drawings]

FIG. 1 is a diagram showing a block diagram of an infrared remote control sensor of the present invention.

FIG. 2 is a circuit diagram of an input matching circuit used for the infrared remote control sensor of the present invention.

FIG. 3 is a diagram showing input-output current characteristics of a current circuit in an input matching circuit.

FIG. 4 is a schematic diagram showing an integrated infrared remote control sensor .

FIG. 5 is a diagram showing a block diagram of a conventional infrared remote control sensor .

FIG. 6 is a diagram illustrating a waveform shaping operation of the demodulation circuit.

FIG. 7 is a diagram showing a waveform shaping operation of a conventional demodulation circuit.

FIG. 8 is a diagram showing a photocurrent-shot noise characteristic of a photodiode.

FIG. 9 is a diagram showing a modulated pulse waveform.

FIG. 10 is a block diagram of a general infrared remote control device.

[Explanation of symbols]

 Reference Signs List 1,106 photodiode 2 signal processing circuit 3 input matching circuit 4,107 amplifier 5 band pass filter 6 demodulation circuit 101 control signal generator 102 coding circuit 103 modulator 104 oscillator 105 LED 108 demodulation circuit 109 decoder 110 control circuit 200 transmission Device 300 Light receiving device T1, T2, T3, T4 Transistor D1, D2 Diode R1, R2, R3, R4, R5 Resistance Vcc Power supply

Continued on the front page (51) Int.Cl. ⁷ Identification code FI H04B 10/28

Claims (1)

(57) [Claims] An emitter of a first transistor of a first type having a predetermined bias applied to a base is connected to an infrared ray.
Is connected to a first power supply through a photodiode to which light is incident, a collector of the first transistor is connected to a second power supply through a first diode, and a second type opposite to the first type is connected. Connected to the base of the second transistor, the emitter of the second transistor is connected to the second power supply via the first resistor, and the collector of the second transistor is connected to the second diode and the second resistor. while connected to the first power supply via a series circuit, connected to the base of the third transistor of the first type, before the emitter of the third transistor via a third resistor
Connected to the serial first power supply, the collector of the third transistor as well as connected to a second power supply through the fourth resistor, taking out an output corresponding to the incident light of the photodiode from the collector, the first The second transistor has a current saturation characteristic of the second transistor.
A coefficient proportional to the emitter area of the transistor or the first
And the current saturation characteristic of the third transistor is changed by the third transistor.
A coefficient proportional to the emitter area of the transistor or the second
Or by changing the resistance by the third resistance.
And the current of the third transistor is supplied to the photodiode.
An infrared remote control sensor characterized in that it is set to approximate a square root of a current flowing through the sensor.