JPS6028422B2 - Optical receiving system control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Field of Application of the Invention The present invention relates to an optical receiving amplifier for optical communication using an APD as a light receiver, and particularly relates to an optimal control method that always maximizes the reception S/N.

■ Conventional technology Aura soanche Photo Diode (APD)
In an optical receiving system using a light receiver as a light receiver, there is an APD multiplication gain that maximizes the photoelectric conversion S/N.

This shows that when the photoelectric conversion S/N is defined, the optical reception power can be minimized with the optimal multiplication gain. Incidentally, the optical reception power varies significantly depending on changes in loss over time of the light source and transmission path, manufacturing deviations, and the length of the transmission distance.

It is desirable to always ensure optimization of the receiving system even in the presence of such large fluctuations in optical reception power. In particular, in the case of analog transmission, a high S/N ratio is required, so this optimal control is an indispensable technique. However, at present, there have been no reports on a method or device that provides this optimal control solution. (3' Purpose of the Invention The purpose of the present invention is to provide an optimal control method for obtaining a high S/N in an optical receiving system using an APD as a light receiver.

{4} General description of the invention In order to achieve the above object, the present invention simultaneously controls the gain of the APD and the subsequent amplifier, but in this case, the functional form of the amplifier is adjusted to the APD multiplication gain and the This is determined using a certain relationship with the optical reception power.

Note that the gain control of the amplifier may be performed using either the input voltage or the output voltage of the amplifier, but the functional forms are different. (2) Examples Hereinafter, the present invention will be explained in detail with reference to examples.

The S/N of an optical receiving system using an APD as a light receiver is expressed as.

Here, M is the APD multiplication gain, R is the photoelectric conversion system, P is the optical reception power, e is the electronic charge, x is the excess noise factor of the APD, kT is the thermal energy, B is the reception band strength, and F' is the amplifier. The thermal noise power of , Req is the equivalent thermal noise resistance. '1} From the equation, the optimum multiplication gain Mopt that maximizes the S/N is given by the following equation. Mopt Ni AP, -Blade Px
......■ However, A: (Yoimo special;) Soup increases or decreases.

The relationship between S/N and optical reception power at this time is S/N Hiro P12
10x......[4I] Figure 1 shows the relationship between S/N and optical reception power when the gain is optimized. The peak value of S/N increases as the optical reception power increases, and the peak point is Move to the side with higher received power. This shows that it is necessary to optimize the spare gain in order to maintain a high S/N even if the optical reception power changes. FIG. 2 shows an embodiment of the present invention.

In the figure, 1 is an optical input terminal, 2 is a front end circuit including an APD, 3 is an amplifier, 4 is an output terminal, and 5 is an APD bias voltage control circuit. To briefly explain the operation of this system, an optical signal inputted from a terminal 1 is photoelectrically converted and internally amplified by an APD, then amplified by an amplifier 3, and outputted to a terminal 4. When the optical reception power changes, this terminal voltage also changes, but a part of the change is amplified by the control circuit 5, and the change is suppressed by controlling the bias voltage of the APD and the gain of the amplifier. For example, when the optical reception power increases, the voltage at Satoko 4 increases, but this increase is canceled out through the control circuit 5 to reduce the APD multiplication gain and amplifier gain. The change in voltage can be extremely small. Now, in the system shown in Figure 2, the fluctuation of the gain gain when the optical reception power changes is the output voltage vo, the control voltage va of the APD bias voltage, and the gain gain M
and the control function of the amplifier gain G, respectively, v.

dV. (P,,G,M),vaniva(v.)}M=M
(va), G=G(v.).・・・．・・・． ...[5} If it is defined, it can be expressed as.

From this, the amplifier gain control function can be found by replacing aG/avo→dG/dvo.
That is, next, the functional form of the amplifier gain is determined so as to satisfy the optimum control condition expressed by equation (2).

The output voltage and control voltage are v.

=GMP, RReq ・・・・・・・・・
[8'va=Gdvo (Gd: feedback system gain).・・・．
...Represented by ■.

Also, the multiplication gain is approximated by the following equation. However, V is the power supply voltage, VB is the APD breakdown voltage, and n is a constant.

{2) {8) From the formula [9}, find the differential term necessary for the formula (7), substitute it, and rearrange it to get the functional form of the amplifier gain. .....(11)
V.

-Since it will be City G City, from now on is given by

Therefore, by defining the functional form in this way, it is possible to perform optimal control that always maximizes the S/N even if the optical reception power changes. FIG. 3 shows another embodiment of the present invention, in which the amplifier gain is controlled by the amplifier input, and the optimum control solution for this method can be found in the same manner as the method shown in FIG.

That is, the functional form of the amplifier gain of this system may be defined by where v is the amplifier input voltage and C is a constant.

Usually, the gain of the amplifier is controlled linearly with the control signal, and the lead configuration is easy.

Therefore, in order to embody the methods shown in FIGS. 2 and 3, it is better to create a control function using a function control circuit and use the signal to control the amplifier gain. FIG. 4 and FIG. 5 show an example of another embodiment of the present invention. FIG. 4 is a modification of FIG. 2, in which the function control circuit 51 includes a constant section 52, a variable section 53, a section 54 that adds the outputs of the constant section 52, a section 55 that adds up the outputs, and a section 55 that adds the ground calculation (- logic). It can be configured more easily.

Also, Figure 5 is a modified version of Figure 3 (13)
According to the formula, the function control circuit 61 can be similarly constructed by a section 62 that is inversely proportional to the input, a section 63 that varies depending on the best and the best, and a section that adds their outputs. '6} Summary As described above, in the present invention, the multiplication gain of the APD and the gain of the amplifier are set simultaneously, but at this time, the control function of the amplifier gain is determined so as to satisfy the relationship between the multiplication gain and the optical reception power (Equation 2'). The feature is that it attempts to secure a high S/N by doing so.

Therefore, according to the present invention, even if the optical reception power changes, the S/N
Since optimization is performed so that the value is always maximized, this method is particularly effective in the case of analog digital transmission, and enables stable high-quality transmission of images and the like.

[Brief explanation of drawings]

Figure 1 is a diagram showing the correlation between optical reception power and S/N in the optimal state of an optical receiving system using an APD as a receiver, and Figures 2, 3, 4, and 5 are 1 is a block connection diagram showing an embodiment of the invention. FIG. Multi-Z drawing multi-Z drawing multi-Z drawing multi-Z drawing multi-Z drawing

Claims (1)

[Scope of Claims] 1. An optical receiving system consisting of a Front End circuit that uses an APD as a light receiver, a variable gain amplifier that uses the output of the circuit as an input, a fixed amplifier that uses the output of the amplifier as an input, and a function control circuit. The fixed amplifier output causes the A
The multiplication gain of the PD is controlled, and at the same time, the gain G of the amplifier is set to Gα=K_1v_0β by the output of the function control circuit.
+K_2 (However, v_0: amplifier output, α, β, K_1, K_
2: A control method for an optical receiving system, characterized in that the output of the amplifier is controlled to be constant.