JPS6268334A - Optical pfm signal demodulation circuit - Google Patents

Abstract

PURPOSE:To miniaturize a circuit by constituting an optical PFM demodulation circuit with an optical signal converting element and plural passive elements only so as to simplify a circuit constitution remarkably more than a conventional circuit constitution in spite of having the same degree of the PFM demodulation characteristic. CONSTITUTION:An optical PFM signal is irradiated to an optical signal converting element D constituting a part of a series resonance circuit 20 through an optical fiber 11. The said series resonance circuit 20 is constituted by connecting a coil L and the 1st capacitor C1 sequentially between the anode and cathode of the element D. A capacitor charge circuit 21 is connected to the series resonance circuit 20, the capacitor charging circuit 21 is connected across the 1st capacitor C1 and the 1st capacitor C1 is charged via the 1st resistor R1 from a power supply E0 such as a battery. Further, the 2nd resistor R2 and the 2nd capacitor C2 are connected across the capacitor C1 from the connecting point between the coil L and the 1st capacitor C1 sequentially and the 2nd resistor R2 and the 2nd capacitor C2 constitute an integration circuit 22.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical PFM signal demodulation circuit that demodulates a PFM-modulated optical signal and converts it into an electrical signal.

(Prior art) Conventionally, this type of optical PFM signal demodulation circuit has been published in the literature:
There is one disclosed in "Optical Communication System", edited by Yoshiharu Shigei, published by Television Society, Shokodo, pp. 243-253). FIG. 2 is a block diagram showing a configuration example of a conventional optical PFM signal demodulation circuit. In the figure, 11 is an optical fiber, 12
is a light receiving diode optically coupled to an optical fiber, 1
3 is a preamplifier, 14 is a pulse shaping circuit, and 15 is a low frequency F.
16 is an output terminal.

The optical PFM modulation signal is composed of a pulse signal with constant amplitude and pulse width, and is an optical pulse signal in which the pulse interval is proportional to the amplitude of the modulation signal. This optical PFM signal is generally used in a modulation method for optical communications, mainly because demodulation can be performed by a combination of band limitation using an optical fiber and a receiving low-band P-wave device.

Next, the operating method of the conventional optical PFM demodulation circuit will be briefly explained.

The optical PFN signal is transmitted by optical fiber 11 and illuminates light receiving diode 12 . The light receiving diode 12 converts the optical PFM signal into an electrical PFM signal 17 corresponding to the optical PFM signal. The electrical PFM signal 17 is sufficiently amplified by the preamplifier 13, and is then configured with a pulse vibrator, a Schmitt trigger circuit, and the like. Only the low frequency components of the PFM signal 18 having a high amplitude and pulse width are extracted by the low frequency filter 15, and a modulated signal 19 is extracted from the output terminal 16.

(Problems to be Solved by the Invention) However, in the conventional demodulation circuit configured as described above, it is necessary to convert the optical PFM signal into an electrical PFM signal, and perform amplification, waveform shaping, and low-frequency waveforming. However, there was a problem that the circuit configuration was complicated, and therefore, the circuit could not be made smaller.

Furthermore, since active elements are provided in these circuit configurations, power consumption is large, a large power source is required, and they are unsuitable for nine-electronic integration (0KIC).

The purpose of the present invention is to eliminate the above-mentioned drawbacks of complication of the conventional demodulation circuit, and to provide an optical PF that has a simple circuit configuration and can be miniaturized.
An object of the present invention is to provide an M demodulation circuit.

(Means for Solving the Problem) In order to achieve this object, the optical PFM demodulation circuit of the present invention uses an optical signal conversion element having an S-shaped negative characteristic that changes depending on the amount of incident light of the optical signal. The series resonant circuit, the capacitor charging circuit, and the integrating circuit are composed of only passive elements. It is characterized by

In carrying out this invention, a resonant circuit is constructed by connecting a photoelectric conversion element, a coil, and a first capacitor in series, and a capacitor charging circuit is constructed by connecting a capacitor charging circuit between both terminals of the first CO/D/S. A series circuit of one resistor and a power supply is configured, and an integrating circuit is connected between the connection point of the coil and the first capacitor, or the connection point of the optical signal conversion element and the coil, and the connection point of the first capacitor and the power supply. Preferably, a second resistor and a second capacitor are sequentially connected in between, and the output signal is extracted from a connection point between the second resistor and the second capacitor.

(Function) With this configuration, since the optical PFM demodulation circuit of the present invention is configured only by the optical signal conversion element and a plurality of passive elements, it has the same 22M demodulation characteristics as the conventional one. First, the circuit configuration is significantly simpler than the conventional one, and therefore the circuit can be miniaturized.

Furthermore, since the optical PFM demodulation circuit of the present invention does not include any active elements, power consumption is extremely low. Therefore, a battery can be used as a power source, making it possible to miniaturize the circuit and achieve 0E
I (The circuit configuration is suitable for 3).

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention.
The FM signal irradiates an optical signal conversion element D (shown as a diode in the figure) forming a part of the series resonant circuit 20 through the optical fiber 1. This series resonant circuit 20 is constructed by sequentially connecting a coil L and a first capacitor C0 between an anode and a cathode of an optical signal conversion element.

Furthermore, a capacitor charging circuit 2 is added to this series resonant circuit 20.
Connect 1. A capacitor charging circuit 21 is connected between both terminals of a first capacitor C, and this first capacitor C is connected to a power source E such as a battery.

The structure is such that charging can be performed from the first resistor R through the first resistor R.

Furthermore, in the illustrated embodiment, the second resistor R2 and the second capacitor C are sequentially connected between both terminals of the first capacitor C from the connection point side of the coil L and the first capacitor C, and these second An integrating circuit 22 is constituted by the resistor R2 and the second capacitor C2.

Note that the output terminal 16 of this integrating circuit 22 is formed at the connection point between the second resistor R2 and the second capacitor C2.

Therefore, the voltage signal generated between the terminals of the first capacitor C of the series resonant circuit 20 is the voltage signal generated between the terminals of the second resistor R2 and the second capacitor C.
2 and an integrating circuit 2 having a low-frequency P reduction effect.
2 as a PFM demodulated output signal.

Next, the optical signal conversion element used in the present invention will be explained.

The optical signal conversion element is a semiconductor element that electrically has an S-shaped negative resistance and exhibits a negative resistance characteristic that changes depending on the amount of incident light. Its structure and electrical and optical characteristics are shown below.

FIG. 3 is a cross-sectional view showing an example of the structure of an optical signal conversion element (hereinafter referred to as an optical element), in which N-Al! σaaS cladding layer 31, p-type G, A8 curable layer 32, n-type GaA, active layer 33, P-type AAG, A8 cladding layer 34, p IEJ caAf3 contact layer 3
5, on the p-type GaA3 contact layer 35.
Ohmic electrode (anode) 36, n-type GaAs substrate 30
It has a structure in which an n-type ohmic electrode (cathode) 37 is attached on top. The optical PFM signal is irradiated through the light receiving window 38 formed in the p-type contact layer 35 through the optical fiber 11.

- When a voltage is applied to this optical element so that the anode 36 becomes a positive voltage with respect to the cathode 37, an S as shown in FIG.
It exhibits a shape-shaped negative resistance characteristic. This will be briefly explained below. FIG. 4 shows the applied voltage (V) on the horizontal axis and the current (mA) flowing through the optical element on the vertical axis. Initially, even if the applied voltage is increased above Ov, a high resistance state occurs in which almost no current flows.

However, when the voltage becomes equal to the turn voltage vt, the resistance of this optical element decreases rapidly and becomes conductive.

Furthermore, the turn voltage vt decreases depending on the amount of light of the optical signal incident on the optical element. An example of its characteristics is shown in FIG.

Figure 5 shows the amount of incident light (μW) on the horizontal axis and the turn voltage (V) on the vertical axis, and the wavelength λ of the optical signal in this case
For example, let it be 818 nm.

As shown in the figure, the turn voltage V exhibits a characteristic of monotonically attenuating as the amount of incident light increases.

Next, the principle of operation of the circuit of the present invention shown in FIG. 1 will be explained.

First, the optical element D1 coil L, the first resistor Ro and the power source E
. Consider a closed circuit consisting of.

FIG. 6 shows voltage-current characteristic curves I and 11. of the optical device. The voltage value at the intersection with E is E. It is. here,! , :lr
D is the internal resistance of the optical element, and the internal resistance of the coil L is ignored. The negative soda line ■ in this circuit is the 6th
As shown in the figure, the voltage vF at the intersection point a between the voltage-current characteristic curve I of the optical device and the load line ■ is O<<VF<V
, the following conditions are satisfied. Under this condition, the terminal voltage of the optical element becomes V, and the optical element is in a cut-off state.

Next, consider the case where light is incident on the optical element.

As described above, since the turn voltage V of the optical element exhibits a characteristic of decreasing in proportion to the amount of incident light, the operating state of the optical element is controlled by the amount of incident light. That is, in a state where the amount of incident light is small and therefore the amount of decrease in V is small and Vt>V, the optical element is in a cut-off state. However, when the amount of incident light increases and the state becomes V, "VF," the optical element becomes conductive, and the voltage-current characteristic of the optical element changes to point a in Figure 6.
It becomes 2. Let the voltage corresponding to this point a2 be vF'.

Next, it is determined by a circuit obtained by adding the first capacitor C□ to the aforementioned closed circuit, that is, the optical element D, the coil L, and the first capacitor C□. In this case, the terminal voltage of the optical element is the time constant τ determined by the first resistor R and the first capacitor C, =C□・R
It rises from zero point a in Figure 6 to VF (point a) by means of construction. The amount of light incident on optical element a is less than V7 <
In the state of Vt, the terminal voltage of the optical element rises to vF and it is in a cut-off state, but the amount of incident light is sufficient and V
In the state F, ZV, the optical element becomes conductive when the terminal voltage of the optical element rises from zero to V, and the operating point moves to point a9 in FIG. From this, it can be seen that as the value of V decreases depending on the amount of incident light, the optical element becomes conductive, and furthermore, the time from the cut-off state to the conductive state can be controlled.

Next, when the optical element becomes conductive, the first capacitor C0
The charge flows through the coil L to the optical element and is discharged.

Furthermore, since the optical element, the coil L, and the first capacitor C form a series resonant circuit 20, the moment the first capacitor C loses its charge, the optical element, the coil L, and the first capacitor C Current flows in the direction of □. This shows the current value in the opposite direction.

Next, consider the case where an optical pulse signal as shown in FIG. 7(A) is incident on the optical element. FIG. 7(A) is a diagram showing the temporal change in the amount of light incident on the optical element, and FIG.
) is a diagram showing temporal changes in terminal voltage of an optical element. In FIG. 7(A), time is plotted on the horizontal axis and light intensity is plotted on the vertical axis.
is the light intensity value that satisfies the condition that the turn voltage Vt of the optical element is - V, = V. If the light intensity value is smaller than P, the terminal voltage of the optical element is the time constant τ as described above. □
=R□・C0 increases.

The light amount value is P. When it reaches , the optical element becomes conductive, and
Due to the discharge of the first capacitor C□, the circuit is cut off again.

If we pay attention to the terminal voltage of the optical element, as is clear from FIG. It can be seen that the time interval up to
2) The terminal voltage of the optical element can be determined. Furthermore, by making the interval between the incident lights and the amount of change thereof sufficiently small compared to the time constant τ□=C□・R, the PFM modulated optical signal that inputs the integral amount of this terminal voltage to the D of the incident light can be , this optical element converts it into a voltage signal, which is then sent to the first capacitor C□
The signal is extracted from between both terminals of , is integrated by an integrating circuit z2, and is output as a PFM demodulated signal from an output terminal 16.

The second resistor R2 and second capacitor C2 shown in FIG. 1 constitute an integrating circuit 22 that integrates the terminal voltage of the optical element. The circuit conditions are that the time constant τ2=C2・R2 due to the second resistor R2 and the second capacitor C2 is t□<<1.2, and R□<<
The flexibility of R2 should be satisfied.

In addition, in the circuit shown in FIG. 1, the integrating circuit 22, which is composed of the second capacitor C2 and the second resistor R2, is connected to the first capacitor C0, but it may also be connected to the anode of the optical element. Perform the same operation as above.

The invention is not limited to the embodiments described above. For example, if the optical signal conversion element is an element that has S-shaped negative resistance characteristics and whose characteristics change depending on the amount of incident light,
Structures other than those described above can be used. moreover,
The series resonant circuit, the capacitor charging circuit, and the integrating circuit may also have other structures as long as they can be constructed only from passive elements.

(Effects of the Invention) As is clear from the above description, according to the present invention, an optical PFM signal demodulation circuit is constructed by combining an optical signal conversion element and a plurality of passive elements, and the following You can expect good results.

■ By simply combining an optical signal conversion element and multiple passive elements, an optical PFM signal demodulation circuit with light reception, amplification, pulse shaping, and low-frequency F wave functions can be configured, so PFM demodulation characteristics are comparable to conventional ones. In addition, the circuit configuration is much simpler than the conventional one, and therefore, the size can be reduced. Furthermore, since the number of parts used is significantly reduced, the manufacturing cost and reliability of the device are superior to the conventional case.

(2) Since the circuit of the present invention can be configured only with passive elements without using active elements, it consumes less power, and a small power supply or a small battery is sufficient, thus eliminating restrictions on installation location.

(2) Furthermore, since the circuit components other than the optical signal conversion element are passive elements, the circuit configuration is suitable for opto-electrical integrated circuit (OEIO).

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the optical PFM demodulation circuit of the present invention, Fig. 2 is a block diagram for explaining a conventional optical PFM demodulation circuit, and Fig. 3 is an optical signal used in the present invention. A cross-sectional view showing an example of the structure of a conversion element, Fig. 5 is a curve diagram showing voltage-current characteristics of the optical signal conversion element, and Fig. 5 explains the relationship between the turn voltage of the optical signal conversion element and the amount of incident light. Figure 6 is a curve diagram showing the voltage-current characteristics and load line for explaining the operating point of the optical signal conversion element of the present invention, Figure 7 (Additional and (B) shows the incident light intensity and It is a curve diagram showing each temporal change of the terminal voltage of the optical signal conversion element. 11... Optical fiber -6... Output terminal 20
...Series resonant circuit 21...Capacitor charging circuit 22...Integrator circuit D...Optical signal conversion element L...Coil C...First capacitor R...First resistor E. ···power supply
R2...Second resistor C2...Second capacitor Patent applicant Tatsuko Todoroki, Director of the Agency of Industrial Science and Technology, 418
Moonlight PFHAS No. I turtle tone ■ 1 shi) Figure 1 Conventional view PFM Cotton No. Demodundan Road Figure 2 Sian-! Natsume Senshi 0 Seikai Ichibu 1 Fig. 3 5 Kyo-type - Sex image resistance Fig. 4 (A) (B) Fig. 7 Person s ft - amount (1t w ') S' /// nm FIG.
*Ushi Figure 6

Claims (3)

[Claims] (1) Extract an output signal from a series resonant circuit including an optical signal conversion element having an S-shaped negative resistance characteristic that changes depending on the amount of incident light signal, a capacitor charging circuit, and a voltage signal generated in the series resonant circuit. 1. An optical PFM demodulation circuit characterized in that the series resonant circuit, the capacitor charging circuit, and the integrating circuit are constructed only from passive elements. (2) The series resonant circuit is configured by connecting an optical signal conversion element, a coil, and a first capacitor in series, and the capacitor charging circuit is configured by connecting a first resistor connected between both terminals of the first capacitor and a power source in series. The integrating circuit is configured by sequentially connecting a second resistor and a second capacitor between a connection point between the coil and the first capacitor and a connection point between the first capacitor and the power source. 2. The optical PFM signal demodulation circuit according to claim 1, wherein the output signal is extracted from a connection point between the second resistor and the second capacitor. (3) The series resonant circuit is configured by connecting an optical signal conversion element, a coil, and a first capacitor in series, and the capacitor charging circuit is configured by connecting a first resistor connected between both terminals of the first capacitor and a power source in series. The integrating circuit has a second resistor and a second capacitor connected in sequence between a connection point between the optical signal conversion element and the coil, and a connection point between the first capacitor and the power source. 2. The optical PFM signal demodulation circuit according to claim 1, wherein the optical PFM signal demodulation circuit is configured such that the output signal is extracted from a connection point with the second resistor and the second capacitor.