JPH04905A - Optical receiver - Google Patents

Abstract

PURPOSE:To keep sensitivity and jitter constant by applying a characteristic, which corrects a change in the gain of an amplifier caused by the fluctuation of a power supply voltage, to a filter circuit for removing noise by exerting photoelectric conversion and amplification onto received optical signals. CONSTITUTION:Onto the optical signals received by a light receiving element 1, pre-amplification 2 and main amplification 3 is exerted through a filter circuit 4, and when the output is larger than the threshold value of a comparator 5, a signal is outputted, The filter circuit 4 composes an RC filter of a resistor RDS and a capacitor C of an MOSFET Q1. The gate of the FET Q1 is connected through a resistor R1 to a high voltage Vcc, grounded by a Zener diode D and biased to a fixed voltage at all times. The source of the FET Q1 is grounded by a parallel circuit composed of a resistor R3 and the capacitor C while being impressed with a voltage interlocked with the high voltage Vcc by the resistors R2 and R3. A resistor RDS of the FET Q1 is controlled by a VGS of the FET Q1. Thus, even when the power supply voltage is fluctuated and the gain of the amplifier is changed, the sensitivity and jitter is kept constant.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to optical receivers. More specifically, the present invention relates to a circuit configuration of an optical receiver that converts an optical signal into an electrical signal.

2. Description of the Related Art FIGS. 2 and 3 are block diagrams of typical conventional optical receivers, respectively. The optical receiver shown in FIG. 2 includes a preamplifier 2 that amplifies received signals received by a photodetector 1 such as a photodiode and converted into electrical signals, and a main amplifier 3 connected in series to the preamplifier 2. A comparator 5 is connected in series to the main amplifier 3 and outputs a signal to an output terminal 6 when a voltage higher than the reference voltage is input. The optical receiver shown in FIG. 3 is provided with a filter circuit 4 between the front stage amplifier 2 and the main amplifier 3 of the optical receiver shown in FIG. The filter circuit 4 is provided to remove high frequency noise, and is composed of, for example, a passive filter circuit such as an RC filter.

Problems to be Solved by the Invention In the above-mentioned conventional optical receiver, when the power supply voltage fluctuates during use, the frequency characteristics of the amplifier change, causing fluctuations in reception sensitivity and jitter characteristics. SUMMARY OF THE INVENTION An object of the present invention is to provide an optical receiver that solves the problems of the prior art described above and in which the frequency characteristics of the amplifier do not change even if the power supply voltage changes.

Means for Solving the Problems According to the present invention, a power source, a light receiving element that receives an optical signal and converts it into an electrical signal, an amplifier that amplifies the electrical signal, and removes noise from the electrical signal amplified by the amplifier. The optical receiver is characterized in that the filter circuit is provided with a characteristic of correcting a change in the gain of the amplifier with respect to fluctuations in the power supply voltage. provided.

The main feature of the optical receiver of the present invention is that the filter circuit has a characteristic of canceling out the change in gain due to fluctuations in the power supply voltage of the amplifier.

For example, in the optical receiver of the present invention, if an amplifier is used that has a characteristic that the band becomes wider as the power supply voltage increases, the filter circuit is given a characteristic that the band becomes narrower as the power supply voltage increases. It is preferable. When an amplifier with such characteristics is combined with a filter circuit, the characteristics of the filter circuit cancel out the characteristics of the amplifier, so
This is effective in suppressing the deterioration of reception sensitivity of the optical receiver and the increase in jitter.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the following disclosure is merely an example of the present invention and does not limit the technical scope of the present invention in any way.

Embodiment FIG. 1 shows a block diagram of an optical receiver of the present invention. 1st
The optical receiver shown in the figure has the same configuration as the conventional optical receiver shown in FIG. 3, except that the configuration of the filter circuit 4 is different. Therefore, the explanation will focus on the configuration of the filter circuit 4.

The filter circuit 4 of the optical receiver of the present invention shown in FIG.
R using the drain-source resistance Rvs of depletion type n-channel MO3FETQ and capacitor
It is a C filter. FETQ has a drain connected to the output terminal of the preamplifier 2 and a source connected to the main amplifier 3.
Connected to the 0 input terminal. Further, the gate of FETQ is connected to the high voltage side Vcc via a resistor R1.

The gate of FETQ is further grounded via Zener diode D. The source of FETQI is resistor R
3 to the high voltage side Vcc, and is also connected to the resistor R
3 and a capacitor C in parallel circuit. In this way, high frequency cutoff RC
The filter is basically configured.

The drain-source resistance RDS of FETQ is
It can be controlled as shown in FIG. 4 by the gate-source voltage VGs of Q. In the filter circuit of the optical receiver of the present invention, FETQ is used.

The source of is biased by resistor division so as to be linked to the power supply voltage. Further, the gate of FETQ is always biased at a constant level by a Zener diode D even if the power supply voltage changes. Therefore, in the filter circuit of the optical receiver of the present invention, when the power supply voltage rises, only the source potential rises and V (, 5 becomes smaller, so that
The drain-source resistance RDS of the FET increases.

Therefore, in the optical receiver of the present invention, the filter circuit 4 has a characteristic that the band becomes narrower as the power supply voltage increases. This characteristic functions in the direction of suppressing this when the preamplifier has a frequency characteristic in which the band becomes wider due to an increase in the power supply voltage. Therefore, in the optical receiver of the present invention, even if the power supply voltage fluctuates, the reception sensitivity and jitter of the receiver are kept constant.

Effects of the Invention As described above, the optical receiver of the present invention maintains its sensitivity and jitter constant even if the power supply voltage fluctuates during use.

Therefore, it is effective in the field of optical communications, especially when used in optical receivers that require small size and high performance.

[Main reference number]

1... Light receiving element, 2...Pre-stage amplifier, 3... Main amplifier, 4...filter circuit, 5... Comparator Patent applicant: Sumitomo Electric Industries, Ltd.

Claims (1)

[Claims] An optical receiver comprising a power source, a light receiving element that receives an optical signal and converts it into an electrical signal, an amplifier that amplifies the electrical signal, and a filter circuit that removes noise from the electrical signal amplified by the amplifier, An optical receiver characterized in that the filter circuit is provided with a characteristic that corrects a change in the gain of the amplifier with respect to a variation in the power supply voltage.