JPS62150941A - Agc control circuit of optical receiver - Google Patents

Abstract

PURPOSE:To make the folded point of two control signal being outputs of an AGC control circuit with an optional input level by adopting a constitution that two differential amplifiers are switched by a diode and one differential amplifier keeps a constant output while the other is operated linearly. CONSTITUTION:When an input signal 21 is larger than the value E5 of a voltage source 29, a diode 28 is conducted, the differential amplifier 25 is operated linearly and the output of the differential amplifier 26 is zero. On the other hand, when the input signal 21 is smaller than the value E5 of the voltage source 29, the diode 28 is cut off, the output of the differential amplifier 25 is zero, while the differential amplifier 16 is operated linearly. Thus, the folded points of the 1st control signal 22 and the 2nd control signal 23 are always made coincident with each other and the folded point is matched to an optional input level by only adjusting the value E5 of the voltage source 29.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an AGC control circuit for an optical receiver used in optical communications and the like.

2. Description of the Related Art In a conventional optical receiver, as shown in FIG. On the other hand, the output level is detected by the level detection circuit 5 and the AG
The two types of A shown in FIGS. 4 and 5 are provided by the C control circuit 6.
When generating a GC control voltage and applying it to ADPI via the AGC amplifier 3 and DC/DC converter 7, respectively, to control the receiver gain with respect to the optical input level to have a downward-sloping characteristic, as shown in FIG. AG with the circuit configuration shown in
A C control circuit was used.

In Fig. 6, 11 is the AGC control circuit human input signal, 12 is A'
GC amplifier control signal, 13 is a DC/DC converter control signal, 14 and 15 are differential amplifiers, 16 and 17 are resistors, 18 and 19 are ideal diodes whose forward voltage is negligible or less, E1~ E4 indicates a voltage source.

Next, the operation of the above conventional example will be explained. In FIG. 6, when the control voltage 12 of the AGC amplifier attempts to become higher than the voltage source E2, the diode 18 becomes conductive and is limited to E2. Similarly, the control voltage 1 of the DC/DC converter
3 becomes lower than the voltage source E4, the diode 19
is conductive and electricity is 3 pages.

It is limited by pressure source E4. In an output voltage range other than the above, linear operation is performed and the characteristics shown in FIG. 3 can be realized. In this way, the input/output characteristics shown in FIG. 4 can also be realized in the conventional AGC control circuit.

Problems to be Solved by the Invention However, in the conventional AGC control circuit described above, when trying to set the bending points P and P shown in FIGS. 3(a) and 3(b) for a specific input level, the voltage source There was a problem in that each of E1 and E3 had to be delicately adjusted.

The present invention solves these conventional problems, and allows bending for any input level with one adjustment while keeping the bending points P and P' of the two control voltages always the same. The purpose of this invention is to provide an excellent AGC control circuit that can set the points.

Means for Solving the Problems In order to achieve the above object, the present invention provides a series connection of a resistor, a diode, and a voltage source at the output of an amplifier or the like into which a detection level is input, and connects each of the resistor and diode in series. The voltage at both ends is 1. input to the second differential amplifier, and from the output of each differential amplifier to the first . It is configured to extract the second control signal.

Therefore, according to the present invention, when the input level is lower than the voltage source, a potential difference is generated across the resistor, and when it is higher, a potential difference is generated across the diode, so by differentially amplifying these potential differences, , while the bending points P and P' always match with respect to the input level,
This has the advantage of being able to create two AGC control signals whose operating points can be set simply by adjusting one voltage source.

Embodiment FIG. 1 shows the configuration of an embodiment of the present invention. In the figure, 21 is an AGC control circuit input signal, 22 is a first control signal for controlling the AGC amplifier 3, 23 is a second control signal for controlling the DC/DC converter 7, and 24 to 26 are any of the following. is also a differential amplifier.

In series with the output of the differential amplifier 24 for sign inversion are resistors 5 and 7 27, a diode 28 with almost ideal characteristics, and a voltage source 29.
are connected in series between the ground, the differential amplifier (first differential amplifier) 25 detects the potential difference across the resistor 27, and the differential amplifier (second differential amplifier) 26 captures the potential difference between the terminals of the diode 28. They are connected to each amplify the potential difference.

Next, the operation of the above embodiment will be explained. In the above embodiment, when the input signal 21 of the AGC control circuit is larger than the value E5 of the voltage source 29, the diode 28 becomes conductive and the differential amplifier 25 operates linearly, but the output of the differential amplifier 26 becomes zero. On the other hand, when the input signal 21 of the input GC control circuit is smaller than the value E5 of the voltage source 29, the diode 28 is cut off and the differential amplifier 25 has an output of zero, but the differential amplifier 2
6 operates linearly. Therefore, the input/output characteristics shown in FIG. 5 can be realized.

(If a bias voltage is applied to each, it is equivalent to FIG. 3) According to the above embodiment, the bending points of the first control signal 22 and the second control signal 23 are always P and P'6 pages. match, just by adjusting the value E5 of the voltage source 29,
This has the effect that the bending points P and P' can be adjusted to any input level.

Effects of the Invention As is clear from the above embodiments, the present invention switches two differential amplifiers by switching diodes with almost ideal characteristics, and while one operates linearly, the other maintains a constant output value. With this configuration, the bending points of the two control signals output from the AGC control circuit can be made to match for any input level, making it unnecessary to set the bending points individually and making adjustments easier. It has the advantage of being simple.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an AGC control circuit of an optical receiver in an embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of the optical receiver, FIG. 3 is a characteristic diagram of the AGC control circuit, and FIG. 5 is a characteristic diagram of the same optical receiver, FIG. 5 is a characteristic diagram of FIG. 1, FIG. 6 is a circuit diagram of a conventional AGC control circuit, and FIG. 7 is a characteristic diagram of the same. 7 pages 21... Input signal, 22... First control signal, 23
... second control signal, 24-26 ... differential amplifier,
27...Resistor, 28...Diode, 29...
voltage source. Name of agent Patent attorney Toshio Nakao and 1 other person Figure 1 Figure 6 [Ueroni/Iwa,/'' Figure 7

Claims (1)

[Claims] The level of the optical receiver output is detected, the level is connected to one end of a series connection of a resistor, a diode, and a voltage source, and the other end is grounded, and the potential difference between the ends of the resistor and diode is measured through a differential amplifier. An AGC control circuit for an optical receiver, which obtains two sets of AGC control signals whose bending points coincide with each other with respect to the change in level.