JPH11234098A - Pulse signal demodulation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of a malfunction pulse due to the effects of disturbance light being a background noise component, in the reception circuit of an infrared data communication equipment demodulating a pulse signal. SOLUTION: A signal light 3 and disturbance light 4 are converted photoelectrically in a photodiode 32, are amplified in an amplifier 33, are edge- detected in a coupling capacitor 34, are inputted to a comparator 37 from an amplifier 36 and are shaped into a rectangular wave pulse. The output of the amplifier 33 is fed back to the input side of the amplifier 33 by an automatic bias control circuit 40 provided with a primary low-pass filter 41 with a sufficiently low interrupt frequency with respect to the frequency of signal light 3 and with a current source 42 which voltage/current-converts the output. Then, the component of disturbance light 4 is compensated. In the input/output of the amplifier 33, a signal is differentiated once, the undesired vibration of output is prevented, and the occurrence of the malfunction pulse can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse signal demodulation circuit which is suitably implemented in an infrared data receiving apparatus or the like and shapes an input pulse signal current from a photoelectric conversion element or the like into a rectangular wave pulse.

[0002]

2. Description of the Related Art In recent years, various standards for infrared data communication have been enacted by the IrDA (Infrared Data Communication Association), and due to its high convenience, peripheral devices, mainly personal computers and portable information terminals, have been established. Products equipped with a transmission / reception device conforming to the IrDA standard for connection of the above have been put on the market. In such an infrared data communication device, as shown in FIG.
, The signal light 3 is transmitted spatially to the receiver 2, so that disturbance light 4 such as sunlight or illumination light having a lower frequency than the frequency of the signal light also enters the receiver 2. . Therefore, it is necessary to remove the influence of the disturbance light 4 serving as background noise and extract only the signal light 3.

FIG. 7 is a block diagram showing an electrical configuration of a typical conventional receiving circuit 11 in the receiver 2. As shown in FIG. The signal light 3 and the disturbance light 4 from the transmitter 1 are photoelectrically converted by the photodiode 12, and a current corresponding to the input light level is output from the photodiode 12 to the amplifier 13. The amplifier 13 converts the output current of the photodiode 12 into a voltage and performs amplification.
The output from amplifier 13 is coupled to coupling capacitor 14
And input to the amplifier 16 via the pull-up resistor 15. The output from the amplifier 16 is supplied to a comparator 17, which performs level discrimination with a detection voltage Vth which is predetermined in accordance with the pull-up voltage, and outputs a square wave pulse as a discrimination result to an output terminal 1.
8 is output.

The output voltage of the amplifier 13 is also supplied to an auto bias control circuit 20, which extracts a low frequency component corresponding to the disturbance light 4 and corresponds to the low frequency component. The current is fed back to the input side of the amplifier 13. Thus, the amplifier 13 is not saturated with respect to the large disturbance light 4 and only the signal light 3 can be extracted. The auto bias control circuit 20 includes secondary low-pass filters 21 and 22 and a current source 23 that performs voltage / current conversion.

FIGS. 8 and 9 are waveform diagrams for explaining the operation of the receiving circuit 11 configured as described above.
FIG. 8 shows a state where the disturbance light 4 is relatively small, and when the waveform of the signal light 3 is shown in FIG.
As shown in FIG. 8B, a differential waveform of the signal light 3 is output from the amplifier 16 by the coupling capacitor 14. The level is discriminated by the comparator 17 based on the detection voltage Vth, and an output as shown in FIG. That is, when the disturbance light 4 is small, the current fed back from the auto bias control circuit 20 to the input side of the amplifier 13 is small, and the coupling capacitor 1
From 4, a high-frequency component corresponding to the signal light 3 is extracted.

[0006]

On the other hand, when the disturbance light 4 is relatively large, the input light to the photodiode 12 includes the signal light 3 as shown in FIG.
At the same time, the disturbance light 4 is superimposed, and a current corresponding to the disturbance light 4 is fed back to the input side of the amplifier 13. Therefore, an apparent second-order differentiation is performed between the input and output of the amplifier 13, and the output from the amplifier 16 after passing through the coupling capacitor 14 oscillates as shown in FIG. Will have
The output derived from the comparator 17 to the output terminal 18 includes a malfunction pulse as indicated by reference numerals α1 and α2 in FIG. 9C.

An object of the present invention is to provide a pulse signal demodulation circuit capable of reducing the occurrence of malfunction pulses due to background noise components.

[0008]

A pulse signal demodulation circuit according to the present invention is a circuit for demodulating a pulse signal from an input pulse signal current, wherein the amplifier amplifies the input pulse signal current and the output of the amplifier. A coupling capacitor for extracting a high-frequency component from the input signal, a comparator for demodulating the pulse signal by discriminating the output of the coupling capacitor at a predetermined level, a primary low-pass filter, and a voltage / current conversion circuit. By extracting a background noise component having a lower frequency than the pulse signal to be demodulated from the output of the amplifier, and feeding back a current corresponding to the background noise component to the input side of the amplifier, It includes an auto bias control circuit that demodulates the pulse signal with the noise component suppressed. To.

According to the above arrangement, a high frequency component corresponding to the pulse signal is extracted from the input pulse signal current by the coupling capacitor, and the pulse signal is demodulated by waveform shaping by the comparator.
For an amplifier that amplifies the input pulse signal current, a current corresponding to the background noise component is created by an auto bias control circuit, and the current is fed back to the input side of the amplifier. Is removed.

At this time, by configuring the auto bias control circuit with a primary low-pass filter and a voltage / current conversion circuit, the input and output of the amplifier can be
The signal is differentiated once, so that the occurrence of undesired vibrations in the pulse signal to be demodulated can be suppressed, and the occurrence of malfunction pulses can be reduced.

Further, in the pulse signal demodulation circuit according to the invention of claim 2, the auto bias control circuit includes:
A high-frequency cut capacitor interposed in parallel with the signal line, and a first transistor in an output stage for performing current amplification by applying an output voltage of the high-frequency cut capacitor to a base.

According to the above configuration, current amplification is performed by the first transistor, and the impedance on the base side of the first transistor, that is, the resistance r which is hfe times the emitter resistance of the first transistor is large. And a cutoff frequency fc (= 1 / 2πCr) determined from the resistance r and the capacitance C of the high-frequency cut capacitor,
Even if the capacitance C is small, it can be made sufficiently lower than the frequency of the pulse signal, and the occurrence of a malfunction pulse can be prevented.

Furthermore, in the pulse signal demodulation circuit according to the third aspect of the present invention, in the auto bias control circuit, a signal current is applied to an emitter, and a base side is connected to the high-frequency cut capacitor and a base of the first transistor. And a second transistor to be provided.

According to the above configuration, the signal current supplied to the first transistor and the high-frequency cut capacitor is reduced to 1 / hfe by the second transistor, and the base-side impedance of the first transistor is increased. , The cutoff frequency fc can be further reduced.

Further, in the pulse signal demodulation circuit according to the invention of claim 4, the auto bias control circuit comprises:
It further includes a third transistor for amplifying an output current of the first transistor, and a fourth diode-connected transistor for supplying a current to an emitter of the third transistor.

According to the above configuration, the current fed back from the first transistor to the amplifier can be multiplied by hfe of the third transistor, and even if the level of the background noise component is large, the current corresponding thereto can be reduced. You can return. Further, even if the emitter potential of the third transistor decreases, the fourth transistor can sufficiently supply the emitter current to the third transistor, so that the current supply capability can be increased.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described.
The following is a description based on FIGS. 1 to 3.

FIG. 1 is a block diagram showing a schematic configuration of a receiving circuit 31 in an infrared data communication apparatus according to one embodiment of the present invention. The signal light 3 and the disturbance light 4 from the transmitter 1 are photoelectrically converted by the photodiode 32,
From the photodiode 32, a current corresponding to the input light level is output to the amplifier 33. The amplifier 33 converts the output current of the photodiode 32 into a voltage,
Perform amplification. The output from the amplifier 33 is input to the amplifier 36 via the coupling capacitor 34 and the pull-up resistor 35. The output from the amplifier 36 is provided to a comparator 37, which performs level discrimination by a detection voltage Vth which is predetermined in accordance with the pull-up voltage, and outputs a square wave pulse as a discrimination result from an output terminal 38. Is output. The output of the amplifier 33 is also supplied to an auto bias control circuit (ABCC).
40, a low frequency component corresponding to the disturbance light 4 is extracted, and a current corresponding to the low frequency component is output to the amplifier 3.
3 is fed back to the input side. The auto-bias control circuit 40 extracts a low-frequency signal component corresponding to the disturbance light 4 from the output of the amplifier 33, and converts the output of the low-pass filter 41 into a voltage / current signal. And a current source 42 that feeds back to the input side of the amplifier 33.

FIG. 2 is an electric circuit diagram showing a specific configuration of the auto bias control circuit 40. The output from amplifier 33 is provided to the base of transistor Q2. The collector of this transistor Q2 is connected to a power supply line 43 of a high level Vcc, and the emitter is connected to a power supply line 44 of a low level GND via a resistor R2. The connection point between the transistor Q2 and the resistor R2 is connected to the base of the transistor Q3, and the collector of the transistor Q3 is connected to the power supply line 43 via a high frequency cut capacitor C. The emitter of the transistor Q3 is connected to the power supply line 44 via a resistor R3, whereby the output voltage of the amplifier 33 is voltage / current converted by the resistor R3, and the connection point a between the transistor Q3 and the capacitor C Appears in

The connection point a is also connected to the base of a transistor Q1, which is a first transistor. The emitter of the transistor Q1 is connected to the power supply line 43 via a resistor R1. It is provided to the input of the amplifier 33. The transistor Q2,
Q3, resistors R2 and R3 and capacitor C constitute the low-pass filter 41, and transistor Q1 and resistor R1 constitute the current source.

In the automatic bias control circuit 40 configured as described above, the cut-off frequency fc of the low-pass filter 41 represents the capacitance of the capacitor C with the same reference numeral, and the connection when the capacitor C is not connected. Fc = 1 / 2πCr, where r is the impedance at point a, and the parallel resistance of the combined resistance of the emitter resistance and the resistance R1 of the transistor Q1 to the resistor hfe times the transistor Q1 and the collector resistance of the transistor Q3 is r. ... (1)

Accordingly, the output voltage of the amplifier 33 appears as a voltage / current conversion at the connection point a, and a component equal to or lower than the cutoff frequency fc expressed by the above equation (1) is h of the transistor Q1.
It is multiplied by fe and fed back to the input side of the amplifier 33.
As a result, a sufficient blocking ability can be obtained with the primary low-pass filter 41.

For example, the cutoff frequency of the coupling capacitor 34 is 40 kHz corresponding to the signal light 3, and the cutoff frequency fc is 10 kHz in the auto bias control circuit 20 of the conventional receiving circuit 11 shown in FIG. On the other hand, the frequency can be set to about 100 Hz in the automatic bias control circuit 40 of the present invention. Therefore, even for incident light which is greatly affected by the disturbance light 4 as shown in FIG. 3A, the output waveform of the amplifier 36 has the above-mentioned waveform shown in FIG. 8B as shown in FIG.
Similarly to the case described above, there is no undesired vibration, so that the output pulse from the comparator 37 to the output terminal 38 can be free of a malfunction pulse as shown in FIG.

Another embodiment of the present invention will be described below with reference to FIG.

FIG. 4 is an electric circuit diagram of an auto bias control circuit 50 according to another embodiment of the present invention. The auto bias control circuit 50 is similar to the above-described auto bias control circuit 40, and the corresponding portions are denoted by the same reference numerals and description thereof will be omitted.
In the low-pass filter 51 of the auto bias control circuit 50, the output of the amplifier 33 is provided to the base of a transistor Q11. The emitter of the transistor Q11 is connected to a resistor R11 for current / voltage conversion and a diode-connected transistor. It is connected to the power supply line 44 via Q12. The collector of the transistor Q11 is connected to the power supply line 43 via a transistor Q13 and a resistor R12. The transistor Q13 forms a current mirror circuit with the transistor Q14, and its emitter is
The power supply line 43 is connected via a resistor R13, and the collector is connected to the emitter of the transistor Q15. The collector of the transistor Q15 is connected to the power supply line 44, and the base is connected to the base and the collector of the transistor Q16 constituting the current mirror circuit and the base of the transistor Q17. The emitters of the transistors Q16 and Q17 are connected to the power supply line 44, respectively, and the collector of the transistor Q17 is connected to the capacitor C and the base of the transistor Q1.

Therefore, when the capacitor C is not connected to the connection point a between the collector of the transistor Q17 and the base of the transistor Q1, the impedance of the connection point a is the emitter resistance of the transistor Q1 (r _e =
(A _{V T = kT / Q, I} E is the collector current.) V _T / I _E) and the hfe times the resistance of the transistor Q1 of the combined resistance value of the resistor R1, the collector resistance of the transistor Q17 The cut-off frequency fc of the low-pass filter 51 is determined by the parallel resistance value, and can be obtained by Expression (1). In the low-pass filter 51, the emitter current of the transistor Q1 is set to 1 / hfe of the transistor Q15 by using the transistor Q15. Therefore, the impedance at the connection point a is further increased, the cutoff frequency fc is further reduced, and the ability to remove the disturbance light 4 can be further increased.

Regarding still another embodiment of the present invention,
The following is a description based on FIG.

FIG. 5 is an electric circuit diagram of an auto bias control circuit 60 according to still another embodiment of the present invention. The auto bias control circuit 60 is similar to the above-described auto bias control circuit 50, and the corresponding portions are denoted by the same reference numerals and description thereof will be omitted. In this auto bias control circuit 60,
Another output transistor Q21 is provided for the output transistor Q1 of the current source 62, and the base of the transistor Q21 is
1 and a connection point between one end of the resistor R1 and one end of the resistor R1.
The emitter, together with the other end of the resistor R1, is connected to a resistor R21.
Is connected to the power supply line 43 via the An output current is supplied to the input of the amplifier 33 from the collector of the transistor Q21. Further, the transistor Q2
1 and a connection point b between the resistor R1 and the resistor R21 are connected to the power supply line 43 through a diode-connected transistor Q22 and a resistor R22.

Therefore, even if the emitter current of the transistor Q1 is reduced by the transistor Q15, the emitter current of the transistor Q1 is multiplied by hfe of the transistor Q21 and output to the amplifier 33.
The current supply capability can be increased, and even if the intensity of the disturbance light 4 is high, the disturbance light 4 can be removed and the occurrence of a malfunction pulse can be prevented. Further, even if the intensity of the incident light increases, the emitter current of the transistor Q21 increases, and the potential at the connection point b decreases, the current is supplied from the resistor R22 and the transistor Q22. And the occurrence of malfunction pulses can be prevented.

[0030]

As described above, the pulse signal demodulation circuit according to the first aspect of the present invention extracts a high-frequency component corresponding to the pulse signal from the input pulse signal current by a coupling capacitor and shapes the waveform by a comparator. When demodulating a pulse signal by the auto-bias control circuit including a primary low-pass filter and a voltage / current conversion circuit, a current corresponding to a background noise component is supplied to an amplifier for amplifying the input pulse signal current. Is created and fed back to the input side of the amplifier to remove the background noise component from the output of the amplifier.

Therefore, the signal is differentiated once between the input and output of the amplifier, thereby suppressing the occurrence of an undesired vibration and the occurrence of a malfunction pulse with respect to the pulse signal to be demodulated. be able to.

In the pulse signal demodulation circuit according to the second aspect of the present invention, as described above, the auto-bias control circuit includes a high-frequency cut capacitor interposed in parallel with a signal line, and a high-frequency cut capacitor. A first transistor in an output stage for applying current to the base to perform current amplification.

Therefore, by the first transistor,
The impedance on the base side of the first transistor, that is, the resistance r which is hfe times the emitter resistance of the first transistor increases, and a cutoff frequency determined from the resistance r and the capacitance C of the high-frequency cut capacitor. fc (= 1
/ 2πCr) can be sufficiently reduced with respect to the frequency of the pulse signal even when the capacitance C is small, and the occurrence of a malfunction pulse can be prevented.

Furthermore, in the pulse signal demodulation circuit according to the third aspect of the present invention, as described above, the auto bias control circuit includes a signal current supplied to the emitter, a base side having the high-frequency cut capacitor and the first A second transistor connected to the base of the transistor.

Therefore, by the second transistor,
The signal current applied to the first transistor and the high-frequency cut capacitor becomes 1 / hfe, the impedance on the base side of the first transistor increases, and the cutoff frequency fc can be further reduced.

In the pulse signal demodulation circuit according to the fourth aspect of the present invention, as described above, the auto bias control circuit includes the third transistor for amplifying the output current of the first transistor, and the third transistor for amplifying the output current of the first transistor. And a diode-connected fourth transistor for supplying a current to the emitter of the third transistor.

Therefore, the current fed back from the first transistor to the amplifier can be multiplied by hfe of the third transistor, and even if the level of the background noise component is large,
The corresponding current can be fed back. Further, even if the emitter potential of the third transistor decreases, the fourth transistor can sufficiently supply the emitter current to the third transistor, so that the current supply capability can be increased.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a receiving circuit in an infrared data communication device according to an embodiment of the present invention.

FIG. 2 is an electric circuit diagram of an auto bias control circuit according to the embodiment of the present invention in the receiving circuit shown in FIG. 1;

FIG. 3 is a waveform chart for explaining an operation of the auto bias control circuit shown in FIG. 2;

FIG. 4 is an electric circuit diagram of an auto-bias control circuit according to another embodiment of the present invention in the receiving circuit shown in FIG. 1;

FIG. 5 is an electric circuit diagram of an auto bias control circuit according to still another embodiment of the present invention in the receiving circuit shown in FIG. 1;

FIG. 6 is a diagram schematically showing a configuration of an infrared data communication device.

FIG. 7 is a block diagram showing an electrical configuration of a receiving circuit of a typical conventional infrared data communication apparatus.

8 is a waveform chart for explaining an operation of the receiving circuit shown in FIG. 7 in a state where disturbance light is relatively small.

9 is a waveform chart for explaining an operation of the receiving circuit shown in FIG. 7 in a state where disturbance light is relatively large.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Transmitter 2 Receiver 3 Signal light 4 Disturbance light 31 Receiving circuit 32 Photodiode 33 Amplifier 34 Coupling capacitor 35 Pullup resistor 36 Amplifier 37 Comparator 40 Auto bias control circuit 41 Low-pass filter 42 Current source (voltage / current conversion circuit) Reference Signs List 50 auto bias control circuit 51 low-pass filter 60 auto bias control circuit 62 current source (voltage / current conversion circuit) C capacitor Q1 transistor (first transistor) Q2, Q3; Q11 to Q14, Q16, Q17 transistor Q15 transistor (second Transistor Q21 Transistor (third transistor) Q22 Transistor (fourth transistor) R1 to R3; R11 to R13; R21, R22 Resistance

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI H04B 10/22

Claims (4)

[Claims] 1. A circuit for demodulating a pulse signal from an input pulse signal current, comprising: an amplifier for amplifying the input pulse signal current; a coupling capacitor for extracting a high-frequency component from an output of the amplifier; It comprises a comparator for demodulating the pulse signal by level discriminating the output at a predetermined level, a primary low-pass filter and a voltage / current conversion circuit. An automatic bias control circuit for extracting a low-frequency background noise component and feeding back a current corresponding to the background noise component to the input side of the amplifier, thereby demodulating a pulse signal in which the background noise component is suppressed. A pulse signal demodulation circuit characterized in that: 2. The automatic bias control circuit according to claim 1,
2. A high-frequency cut capacitor interposed in parallel with a signal line, and a first transistor in an output stage for performing current amplification by applying an output voltage of the high-frequency cut capacitor to a base. A pulse signal demodulation circuit according to any one of the preceding claims. 3. The auto bias control circuit according to claim 2,
3. The pulse signal demodulation circuit according to claim 2, wherein a signal current is applied to an emitter, and the base side further includes a second transistor connected to the high-frequency cut capacitor and a base of the first transistor. 4. The automatic bias control circuit according to claim 1,
4. The semiconductor device according to claim 3, further comprising: a third transistor for amplifying an output current of the first transistor; and a diode-connected fourth transistor for supplying a current to an emitter of the third transistor. A pulse signal demodulation circuit according to any one of the preceding claims.