JPS62202635A - Optical reception circuit - Google Patents

Abstract

PURPOSE:To attain the miniaturization at low cost by providing a current switch controlling the bias current of a preamplifier converting a current signal into a voltage signal so as to apply DC coupling between the preamplifier and an equalizing amplifier thereby reducing the number of components. CONSTITUTION:An input current signal is inputted from an input terminal 10 and converted into a voltage signal by a preamplifier 1 comprising transistors (TRs) Q1, Q2, a collector resistors 101, 102, an emitter resistor 104 and a feedback resistor 103 and inputted to the equalizing amplifier 4, to which a reference voltage 31 is also inputted and its output is supplied as a prescribed amplitude signal from terminals 41, 42. An offset of the output signal is detected by an offset detector 5 to activate a current switch 7 via the amplifier 6. The switch 7 adjusts the bias current of the collector resistor of the output TR Q2 of the preamplifier 1 to compensate the offset.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a receiving circuit for source and reverse signals, and particularly to an optical receiving circuit that requires a wide dynamic range.

[Conventional technology]

Generally, in optical receiving circuits, AC coupling is used between the preamplifier and the equalizing amplifier 2°, but DC coupling is desirable for cost reduction, and therefore the Institute of Electronics and Communication Engineers Technical Research Report ASS
s-175, pages 69 to 46, “400
In the paper entitled "Prototype of Mb/s Integrated Submarine Optical Repeater", the power supply voltage was raised and DC coupling was used. In order to achieve DC coupling between the preamplifiers, it was necessary to reduce the gain of the preamplifier to suppress output level fluctuations, or to increase the power supply voltage to ensure the offset control range. It is not suitable for cases where an increase in noise due to a decrease in gain is a problem or when driving at a low voltage.

An object of the present invention is to provide an optical receiver circuit that enables direct current coupling without sacrificing circuit characteristics and is small, low cost, and highly reliable. The above object is achieved by first increasing the output level by outputting the preamplifier output from the collector of the output transistor, and then controlling the output level by applying a bias current to the collector resistor.

[Effect]

The output level of a preamplifier output from the collector side is determined by the product of the collector current and collector resistance of the output transistor. Therefore, the DC voltage is at a higher level than when using the vine follower type, and since the output impedance is high, the output level can be easily controlled by the current bias current in the collector resistance. A wide offset control range can be obtained with the power supply voltage.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

The input current signal is inputted from the input terminal 10, amplified by the transistor Q1 and the collector resistor 102, further subjected to negative feedback by the transistor Q2, the emitter resistor 104, and the feedback resistor 103, and outputted from the collector resistor 101. In this way, it is converted into a heavy pressure signal by the preamplifier 1 and output from the preamplifier output 11, and this output 1
1 and the reference voltage 61 from the reference voltage source 6 are input and amplified by the equalizing amplifier 4 and output to signal output terminals 41 and 4.
2 outputs a signal with a constant amplitude. Here, if the input signal amplitude to the input terminal 10 fluctuates or an offset occurs in the outputs 41 and 42 due to variations in the elements of the equalizing amplifier 4, the input 11 of the equalizing amplifier 4 becomes The dynamic range of the signal input cannot be increased unless the level is changed to compensate for the offset.

Therefore, the output offset is detected by the offset detector 5 which detects the peak value or average value of the output signal, and the offset component is amplified by the differential error amplifier 6 which amplifies the offset component. The output level of the output resistor 101 is controlled by adjusting the amount of current generated by the output resistor 101, thereby applying negative feedback to compensate for the offset1.In this way, the bias current of the collector resistor of the output transistor pQ2 is adjusted. As a result, the output DC potential is high and the control range can be widened. Therefore, even if the output level of the preamplifier 1 fluctuates greatly (and even if the driving pressure is low), the direct current coupling with the equalizing amplifier 4 will be avoided.

Further, an embodiment that takes advantage of the features of the present invention will be described with reference to FIG.

FIG. 2 shows that a duplex device amplifier 2 having the same circuit configuration as the preamplifier 1 is used in place of the reference voltage source 6 in FIG. Since the amount of current is differentially controlled, the amount of adjustment can be halved. Therefore, the allowable output fluctuation range is twice that of Fig. 1, and the difference in the amount of current flowing through terminals 71 and 72 is proportional to the amount of signal input current, so resistor '81.82 and comparator 8 are provided. In this case, by detecting the potential difference between terminals 71 and 72, input level detection can be performed with a simple circuit that does not require a capacitor. Therefore, the circuit becomes stable against fluctuations in external conditions such as power supply noise and temperature fluctuations.

〔Effect of the invention〕

According to the present invention, an input device can be used in an optical receiving circuit.

Since it is possible to widen the offset control range without reducing the inamitsu range or preamplifier gain or increasing the RASS degree pressure of the circuit, the preamplifier and equalizing amplifier can be DC coupled, and especially When integrated, it has the effect of reducing the number of parts and reducing costs due to miniaturization.

[Brief explanation of drawings]

1 and 2 are circuit diagrams of two embodiments of the optical receiving circuit according to the present invention, 1... preamplifier, 2... dummy preamplifier, 6... reference voltage source. , 4... Equalization amplifier, 5... Offset detector, 6... Error amplifier,
7...Current switch, 8...Comparator. □1, -1

Claims (1)

[Claims] (1) A preamplifier that converts a current signal into a voltage signal, a reference voltage source, a differential equalizing amplifier whose inputs are the output of the preamplifier and the output of the reference voltage source, and the output of the equalizing amplifier. an offset detector that detects the equalization amplifier offset from the offset detector; an error amplifier that amplifies the output of the offset detector; and a current switch that controls the amount of bias current of the preamplifier using the output of the error amplifier. Features an optical receiver circuit.