JPH0360208A - Optical pre-amplifier - Google Patents

Abstract

PURPOSE:To prevent the frequency characteristic of a pre-amplifier from being deteriorated by raising the maximum light receiving level of an optical receiver by connecting a non-linear resistor whose resistance value becomes smaller when a current flows such as a diode, etc., in parallel to the feedback resistor of the pre-amplifier. CONSTITUTION:The maximum light receiving level of the optical receiver is raised by providing the non-linear resistor 1 whose resistance value becomes smaller when the current flows in parallel with the feedback resistor Rf of the pre-amplifier. A Schottky diode, for example, is used for the non-linear resistor 1. Since the resistance value of the non-linear resistor 1 becomes smaller when light input Pin to an optical receiving element is large, transfer impedance becomes smaller, and the voltage of a point (a) does not becomes below a definite value, and the pre-amplifier operates normally. Thus, the frequency characteristic of the pre-amplifier is never deteriorated, and the deterioration of waveform can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a circuit configuration of a preamplifier in an optical receiver.

[Conventional technology]

As described in Japanese Patent Publication No. 59-29013, the conventional device has a configuration in which a nonlinear resistor whose impedance decreases as the photocurrent of the light receiving element increases is connected in front of the preamplifier.

[Problem to be solved by the invention]

The above conventional technology does not take into consideration the deterioration of frequency characteristics due to a decrease in the amount of feedback of the preamplifier when the nonlinear resistance becomes small, and there is a problem that the frequency characteristics of the preamplifier deteriorate due to an increase in photocurrent. - The present invention aims to increase the maximum light reception level of an optical receiver by preventing the saturation of the preamplifier without deteriorating the frequency characteristics even when the photocurrent increases.

[Means to solve the problem]

In order to achieve the above object, a nonlinear resistor, such as a diode, whose resistance value decreases when current flows, is connected in parallel to the feedback resistor of the preamplifier.

[Effect]

The nonlinear resistor connected in parallel to the feedback resistor of the preamplifier has a large resistance value when the photocurrent is small, and has no effect on the feedback resistor. However, when the photocurrent is large, the resistance value of the nonlinear resistor becomes small, the feedback resistance of the preamplifier becomes small, and the gain of the preamplifier decreases. This reduces the gain of the preamplifier when the photocurrent is large. Furthermore, since the amount of feedback becomes large, there is no deterioration of frequency characteristics and no deterioration of waveforms.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. In this embodiment, a Schottky diode is used as the nonlinear resistor. When the light input Pin to the light receiving element is small,
The photocurrent rp is also small, the nonlinear resistance is reverse biased, and the resistance value is very large.

Transimpedance is determined by Rf.

On the other hand, when the optical input Pin to the light receiving element is large, the resistance value of the nonlinear resistor becomes low, so the transimpedance becomes small to Rf//R, and the voltage at point a is a constant value (approximately O
, SV). Therefore, TR2 does not turn off and operates normally.

Also, the frequency characteristics of the preamplifier at this time are Rf//R
It gets better because 1 gets smaller. Circuit simulation values of this example are shown in FIGS. 2 to 4.

QUT Figure 2 shows the transimpedance ZT=I,
This is the frequency characteristic of It can be seen that the case with R1 is better than the case without it. Naturally, the ZT value is also low. Figure 4 shows when the photocurrent shown in Figure 3 is input (
This is a waveform response of approximately -10 dBm (optical power). R1
It can be seen that in the case of presence, the deterioration of DUTY is smaller than in the case of absence.

FIG. 5 shows an embodiment in which a general silicon diode, which is not a Schottky type, is used as R1.

FIG. 6 shows an example using another circuit.

〔Effect of the invention〕

According to the present invention, it is possible to reduce waveform deterioration when the optical input is large using a simple circuit, and therefore it is possible to expand the dynamic range of an optical receiver (particularly for digital use). Furthermore, conventionally, when the optical input is strong, an optical attenuator has been used in the receiver, but according to the present invention, the optical attenuator is not required, making it possible to realize an economical resystem.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the invention. FIG. 2 shows a circuit in which the transimpedance frequency characteristic circuit of the embodiment of FIG. 1 is a different embodiment. 1... Nonlinear resistance (diode), 2... Light receiving element, Rf... Feedback resistor. First stage I...-Park resistance, (evening) 2--Receiver bus 0. Retire timing (1δ- Hanawa 2) (Re-wood - 1") ? ・Additional material now 〆f-, Return to Japan resistance

Claims (1)

[Claims] 1. In an optical receiver consisting of a photodiode or avalanche photodiode and a transimpedance type negative feedback preamplifier, a nonlinear resistor whose resistance value decreases as the current increases in parallel to the feedback resistor of the preamplifier. An optical preamplifier characterized in that the maximum light reception level of an optical receiver is increased by providing the optical preamplifier.