JPS584274Y2 - Fiber optic digital link receiver circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical fiber digital link receiver circuit that compensates for threshold level variations.

The circuit configuration of the optical fiber digital link reception system is shown in Figure 1, which includes one light receiving element such as a photodiode,
It consists of a resistor R1, an amplifier A, a comparator C1, and a reference power source Es, receives the signal light transmitted through the fiber with a light-receiving element, converts it into one electrical signal with the resistor R, and amplifies this with the amplifier A. Thereafter, a comparator C compares it with a reference voltage and shapes the waveform.

This receiving circuit has a light receiving element, amplifier A, and comparator C that are directly connected to each other so that direct current can be transmitted, and is therefore susceptible to power supply fluctuations and temperature fluctuations.

For example, when the power supply voltage fluctuates, the output voltage Vou of amplifier A
Since the DC level of t changes and, on the other hand, the voltage of the reference power source Es is constant, the discrimination level of the comparator C fluctuates, which is unfavorable in terms of characteristics.

For example, in the present circuit 1, this appears as a variation in the minimum reception level.

The same applies if there is a temperature fluctuation. The present invention is an attempt to improve these points by using extremely simple means, and its feature is that an optical fiber digital link receiving circuit is used as a light receiving element.

a two-output type amplifier that generates two outputs that change by one in the positive and negative directions in response to the output of the element, and a comparator to which the two outputs of the amplifier are applied to the positive input terminal and one resistor element. , the positive and negative input terminals of the comparator are connected to one end and the other end, and a potentiometer is connected to the intermediate sliding terminal to which a reference voltage is applied.

This will be explained in detail below with reference to Examples.

FIG. 2 shows an embodiment of the present invention, in which D, R, and C are a light receiving element, a resistor, and a comparator, as in FIG.

In the present invention, the amplifier A has two outputs +Vout, -Vou that change by one direction, positive or negative, depending on the input signal.
Using a two-output amplifier Aa that produces t, one output +
Vout is connected to the positive input terminal of the comparator C through the resistor R1, and the other output -Vout is connected to the negative input terminal of the comparator C through the negative input terminal -IN+ through the resistor R2. The terminal +IN -IN# is further connected to one end and the other end of the potentiometer VR, and a reference voltage Vc is applied to the middle sliding terminal of the potentiometer.

If you go through this circuit, the outputs of amplifier Aa +Vout and -
The DC level of Vout is the same, and the amount of variation in the DC level due to power supply voltage fluctuation is also the same and the direction of change is also the same, so from the perspective of comparator C, this power supply voltage The fluctuation in the DC level due to the fluctuation 1 is canceled out, and thus the influence of the power supply voltage fluctuation can be eliminated.

If the voltages applied to the positive and negative input terminals +IN and -IN* of the comparator C are Vinl and Vin2, these can be expressed by the following equation.

Here, vRl and VR2 are the resistances on the R2 side and R2 side of the potentiometer VR.

Regarding the DC level, ■ Vout = Q Vo
u t, and let this be V, then the differential voltage applied to the comparator C, l (V is JV = Vjn - Vin2 ■ That is, resistor R19R2, potentiometer dividing resistor VR
, , VR2), and by selecting one of them, the difference voltage between the output voltage V of the amplifier Aa and the reference voltage Vc is input to the comparator Ct, as in FIG.

Therefore, it is possible to identify the received voltage using the reference voltage Vc and perform waveform shaping.

Identification Rehe/L/ Gi Kot'l's resistances R1, R2,
It can be adjusted simply by adjusting vRl and VR2.

Note that the resistance R1°R2 is usually set so that R1=R2.

Temperature fluctuations and fluctuations in discrimination level are shown in Figure 3 or 4.
Compensation can be achieved using the circuit 1 shown in the figure.

In these figures, R2Aa and C are 1 as in Figure 1.
These are a light receiving element, a resistor, an amplifier, and a comparator, and R1 and R2 are resistors, VR is a potentiometer, and VC is a reference voltage.

In this circuit, in the case of Fig. 3, a semiconductor diode D1 is inserted in series with the resistor R2i, and temperature compensation is performed using the temperature characteristics of this diode.In the example of Fig. 4, a thermistor is inserted in place of the resistor R2. Element R with temperature characteristics combined with resistance
Temperature compensation is performed using TH.

As explained in detail above, this invention (according to this invention) uses a two-output type amplifier and combines it with a resistor network, which is a simple method to reduce fluctuations in the power supply voltage and, therefore, in the identification level. It is possible to easily incorporate temperature sensitive elements such as diodes and thermistors for temperature compensation, and an excellent receiving circuit for optical fiber digital links can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a conventional receiving circuit diagram, and FIGS. 2 to 4 are circuit diagrams showing embodiments of the receiving circuit of the present invention. D... Light receiving element, Vc... Reference voltage,
R, R,. R2...Resistance, VR...Potentiometer A. Aa...Amplifier, Dl...Diode, C...Comparator, RTH...Temperature characteristic element, R8...Reference voltage.

Claims (3)

[Scope of utility model registration request] (1) A light-receiving element and the output of the element in positive and negative directions 1
A two-output amplifier that produces two outputs that change, a comparator to which the two outputs of the amplifier are applied to positive and negative input terminals via a resistor element, and one positive and negative input terminal of the comparator. 1. An optical fiber digital link receiving circuit comprising a potentiometer having one end connected to the other end and having a reference voltage applied to an intermediate sliding terminal. (2) The resistance element connected in series with one terminal that produces an output that changes by one in the negative direction of the two-output width divider is composed of a pure resistance and a diode with temperature characteristics in series with it. An optical fiber digital link receiving circuit according to claim (1) of the utility model registration. (3) The two-output width divider is characterized in that the resistance element connected in series with one terminal that produces an output that changes by one in the negative direction is a thermistor. An optical fiber digital link receiving circuit according to claim (1) of the utility model registration.