JPH0354909A - Amplifier device - Google Patents

Abstract

PURPOSE:To reduce the saturation degree of a transformer impedance type amplifier and to obtain an output signal having no distortion from a large input light current by using a gate means as a by-pass route when the potential difference between the input and output of the amplifier is more than a prescribed value to prevent an output voltage from being dropped. CONSTITUTION:An enhancement type FET Q5 to be a gate means having a gate is connected in parallel with a feedback resistor Rf. The source of the FET Q5 is connected to the output terminal 3 of the amplifier 2 and its drain and gate are connected to the input terminal of the amplifier 2. When an input light current iPD is increased and current flowing into the resistor Rf is increased, the potential difference between the input and output of the amplifier 2 is increased. When the value exceeds a threshold voltage, current starts to flow between the drain and source and the by-pass route is formed. Consequently, the saturation of the amplifier 2 can be suppressed without advancing the drop of the output voltage VOUT to a prescribed value or less.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an amplifier device used as a preamplifier for optical communications.

[Conventional technology]

Conventionally, in optical communication, as shown in Fig. 4, a photodiode l receives an optical signal, and the resulting signal is guided to an amplifier 2 with an amplification factor (1 A), where it is amplified and output from an output terminal 3 to a signal voltage. I got V out. The amplifier 2 is a so-called transimpedance type amplifier in which a feedback resistor Rr is externally attached or integrated.
For example, the Institute of Electronics, Information and Communication Engineers Technical Report (1986 OQE
86-68 p. 51-p. 56), which is equivalent to the circuit shown in FIG.

In the circuit shown in FIG. 5, an inverter stage consisting of FETs Q, Q, and a level shift/buffer stage consisting of FETs Q, Q4 are driven by the same power supply DD. FETQ, Q are gates. It is a constant current load with short circuit between source 24 and source. The level shifting diodes D1 and D2 have the function of determining a predetermined bias point. According to a circuit having such a structure, an input signal can be amplified by an amplification factor (A) and an inverted output signal V can be obtained.

Out [Problem to be Solved by the Invention] However, according to the above-described amplifier device, when an excessive input is applied to the photodiode 1, the amplifier device becomes saturated and becomes unsuitable for practical use. In other words, the dynamic range is approximately 25 dB at most due to saturation, making it impossible to receive signals accurately while absorbing changes in various external conditions, such as the magnitude of the output on the transmitting side and the magnitude of attenuation between the transmitter and the receiver. There was a point.

Specifically, an NRZ signal consisting of repeating rOJ and rlJ of 300 Mbps as shown in FIG. 6 as shown in FIG. 6 is applied to the circuit shown in FIG. When added at lmA (cas e 1) and human photocurrent 1mA
(case 2), from the output terminal 3 to the 7th
The output signal shown in the figure is obtained.

In other words, as is clear from FIG. 7, there is no significant distortion in the output signal in Case 2, but the output signal in Case 2 is so distorted that it is almost impossible to reproduce the human input signal.

In order to analyze the above phenomenon in detail, each FETQ in Fig.
The results of monitoring the drain-source voltage of FET-04 and the gate-source voltage of FETQ and Q3 are shown in Figures 8(a) and (b), and Figures 9(a) and (b). ). In these figures, the symbol Q
-Q is 14 for each FET Q -Q4 in Figure 5.
t shows the corresponding curve. From these figures, when the input photocurrent lPD exceeds a predetermined value and accordingly the output voltage value V exceeds a predetermined value, the drain-source voltage in the FET constituting the amplifier 2out becomes FE.
This is because some cases may fall into the non-saturation region of T (less than IV in this example), or the gate-source voltage may become close to the FET threshold voltage (pinch-off voltage, -IV in this example). , it can be seen that the output signal of the amplifier is greatly distorted.

Therefore, the present invention improves the saturation characteristics at the time of excessive input, makes it possible to obtain an output signal without distortion even when a large human-powered photocurrent arrives, and when used for communication, the magnitude of the output on the transmitting side It is an object of the present invention to provide an amplifying device that can absorb changes in various external conditions, such as the magnitude of attenuation between transmitting and receiving, without using an optical attenuator or the like.

[Means to solve the problem]

The amplifier device according to the present invention has a transimpedance amplifier gate means connected to a feedback resistor, the gate means is connected in parallel to the feedback resistor, has a gate, and has an input gate of the transimpedance amplifier. The present invention is characterized in that the gate is controlled based on the potential difference between the outputs.

[Effect]

j! according to the present invention! ! Since the 7-width device is configured as described above, when excessive human power arrives at the transimpedance type amplifier, the potential difference between the human outputs of this i-span amplifier becomes large, so the gate is controlled based on this. is possible,
Since the gate means is connected in parallel to the feedback resistor, the gate means serves as a bypass route, so that the output voltage does not fall below a predetermined voltage, and the degree of saturation of the amplifier device can be reduced.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An amplifier device according to an embodiment of the present invention will be described below with reference to FIGS. 1 to 3 of the accompanying drawings.

In addition, in the description of the drawings, the same elements are given the same reference numerals, and redundant description will be omitted.

FIG. 1 shows the configuration of an amplifier device according to an embodiment of the present invention. In this embodiment, an enhancement type FET Q5 having a gate is connected in parallel to the feedback resistor Rr. The source of the FET Q5 is connected to the output terminal 3, and the drain and gate are connected to the input terminal of the amplifier 2.

In an amplifier with such a configuration, the input photocurrent iPD
As the current flowing through the feedback resistor R increases, the difference in voltage between the input and output of the amplifier 2 increases.

On the other hand, the gate-source voltage of the enhancement type FET Q5 connected in parallel to the feedback resistor Rr is equal to the above potential difference. Therefore, the human photocurrent 'P
When D is increased by 1 and the voltage between the human outputs of the amplifier 2 (voltage between the gate and source of FET Q5) exceeds the threshold voltage, a current begins to flow between the drain and source. Therefore, FETQ5 functions as a bypass route for feedback resistor Rr. As a result, the output voltage V does not decrease below a predetermined level, and the degree of saturation of the 1-segment divider 2 can be suppressed.

FIG. 2 shows an embodiment that corresponds to the conventional example shown in FIG. 5 and can be implemented as an IC.

In this example, FETQ -Q4 is a day 1 compression type, the threshold voltage is set to -TV, and the gate width of each FET is set to 150
μm, 75 μm, 150 μm, and 150 μm. Further, FETQ5 was an enhancement type, had a threshold voltage of +0.2V, and a gate width of 20 μm. Further, the resistance value of the feedback resistor R' is 2KΩ.

In a circuit with such a configuration, 30 as shown in FIG.
An NRZ signal consisting of rOJ, rlJ repetitions of 0 Mbps was applied. Here again, the human photocurrent is 0.1
When it is mA, it is called ease, and when it is 1mA, it is called case.
Set it to 2. As a result, an output signal as shown in FIG. 3 could be obtained from the output terminal 3. That is, when the Dosso width transducer 2 is not saturated (case 1), an output signal can be obtained without heavily distorting the input signal as in the conventional case, and in the case where the input signal is not saturated in the conventional case Even in the case where reproduction becomes impossible (case 2), in this example, an output could be obtained without greatly distorting the human input signal. In other words, it was possible to significantly correct the conventional pulse width distortion of the output waveform at saturation. When this amplifier device is used, since it has a wide dynamic range, it is possible to absorb fluctuations in the magnitude of optical communication signals without using other components such as an optical attenuator.

〔Effect of the invention〕

As described above in detail, according to the present invention, when the potential difference between the human outputs of the transimpedance amplifier exceeds a predetermined value, the gate is controlled and the gate means becomes a bypass route to prevent the output voltage from decreasing. Since the saturation of the amplifier is weakened, it is possible to obtain an output signal without distortion even when a large manual photocurrent arrives. Therefore, when the device of the present invention is used for optical communication, it is possible to absorb changes in various external conditions, such as the magnitude of the output on the transmitting side and the magnitude of the attenuation between the transmitter and the receiver, without using any other configuration. .

[Brief explanation of drawings]

FIG. 1 is a block diagram of an amplifier according to an embodiment of the present invention, FIG. 2 is a circuit diagram of an amplifier according to another embodiment configured using FETs, and FIG. 3 is a circuit diagram of an amplifier according to another embodiment of the invention. Figures 4 and 5 are diagrams showing output signals, and Figures 4 and 5 are configuration diagrams of conventional amplifier devices.
Figure 7 shows an example of an input optical signal, Figure 7 shows an output signal according to the conventional example shown in Figure 5, and Figure 8 shows changes in the drain-source voltage of the FET in the conventional example shown in Figure 5. figure,
FIG. 9 is a diagram showing the gate-source voltage in the conventional example shown in FIG. 1...Photodiode, 2...Amplifier, 3...
Output terminal, Q...gate means, R,...feedback resistor, 5Q-Q5...FET, DI-D2...diode for level shift 1.

Claims (1)

[Scope of Claims] A transimpedance type amplifier connected to a feedback resistor; and a gate connected in parallel to the feedback resistor, the gate being connected to the feedback resistor based on the potential difference between the inputs of the transimpedance type amplifier. An amplifying device characterized by comprising: gate means for performing control.