JPH0397302A - Amplifier - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

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

[Conventional technology]

Conventionally, in optical communication, an optical signal is received by a photodiode 1 as shown in FIG. The signal voltage ■ is obtained from. Here, the minus Out sign attached to the voltage amplification degree means that the polarities of the input signal and the output signal are reversed. The amplifier 2 is a so-called transimpedance type in which the feedback resistor Rr is externally attached or integrated.
986 OQE86-68p. 51-p. 56), which is equivalent to the circuit shown in FIG.

In the circuit of FIG. 6, an inverter stage consisting of FETs Q and Q2 and a level shift/buffer stage consisting of FETs Q and Q4 are driven by the same power supply vDD. FETQ. Q is a constant current load with the gate and source 24 short-circuited. The level shifting diodes D 1 and D 2 have the function of determining a predetermined bias point. According to the circuit having such a configuration, an input voltage signal can be amplified at an amplification degree (1 A) and an inverted output signal V can be obtained.

[Problem to be solved by the invention]

However, with the amplifying device as described above, when an excessive input reaches the photodiode 1, the amplifying device becomes saturated and becomes unsuitable for practical use. In other words, the dynamic range of the input optical power is approximately 25 dB at most due to saturation, and accurate signal reception is possible by 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 receiver. The problem was that I couldn't get it.

Specifically, an NRZ signal consisting of repeating rOJ and rlJ of 300 Mbps as shown in FIG. 7 as shown in FIG. 7 is input to the circuit shown in FIG. 6 at an input photocurrent of 0. When applying at 1 mA (cas e 1) and input photocurrent 1 mA
(case 2), the output terminal 3 to the 8th
The output signal shown in the figure is obtained. In other words, the 8th
As is clear from the figure, in case 1, there is no significant distortion in the output signal, but in case 2, the output signal is greatly distorted, making it almost impossible to reproduce the human input signal.

In order to analyze the above phenomenon in detail, each FETQ in Fig.
Figure 9(a) shows the results of monitoring the voltage between the drain and source of Q4 and the voltage between the gate and source of FETQ and Q3. (b), and shown in FIGS. 10(a) and (b). In these figures, the symbol Q1
-Q4 indicate curves corresponding to each of the FETs Q1 to Q4 in FIG. From these figures, when the human photocurrent PD exceeds a predetermined value and the output voltage value V exceeds the predetermined value, the drain-source voltage increases in the FET constituting the amplifier 2. may fall into the FET's non-saturation region (less than 1v in this example), or the gate-source voltage may exceed the FET's threshold voltage (pinch-off voltage, -1v 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 with small distortion even when a large input photocurrent arrives, and when used for optical communication, it is possible to improve the saturation characteristics at the time of excessive input. 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]

An amplifier device according to the present invention includes a transimpedance amplifier, a gate circuit that is provided in a shunt channel that shunts the input current of the amplifier, and that opens and closes the shunt channel, and an integrating circuit that integrates the output signal of the amplifier. , a gate control means that creates a control signal for opening the gate circuit in response to the input signal of the transimpedance amplifier becoming larger than a predetermined value based on the output of the integrating circuit, and applies the control signal to the gate circuit. It is characterized by being prepared.

[Effect]

Since the amplifier device according to the present invention is configured as described above, when an excessive input signal arrives at the transimpedance type amplifier, the DC level of this output signal decreases, so that the result of integrating this output signal also decreases. Its level decreases. When this level becomes smaller than a predetermined value, the gate circuit can be opened, and a part of the human power current of the transimpedance type amplifier flows to the shunt path, thereby avoiding an excessive human power state.

〔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 4 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 a configuration diagram according to an embodiment of the present invention.

In this embodiment, the drain is connected to the input terminal of the transimpedance amplifier 2, and a constant voltage V is applied to the gate.

is connected to FETQ5, which is a gate circuit given.

On the other hand, a gate control means 100 including an integrating circuit 101 is connected to the output terminal of the amplifier 2. Since the integrating circuit 101 integrates the output signal of the amplifier 2, the input photocurrent ' PD
When V increases, the output voltage V of the amplifier 2 decreases, and the output DC voltage of the integrating circuit out 101 also decreases. The output of this integrating circuit 101 is guided to a buffer circuit 102. The buffer circuit 102 is a circuit that has an impedance conversion function or a level shift function in addition to impedance conversion. Therefore, a low-impedance DC signal appears at the output of the buffer circuit 102, which decreases as the optical signal incident on the photodiode 1 increases, and this DC signal
Given to the source of ETQ5.

On the other hand, a constant voltage V is applied to the gate of FETQ5. is given, the gate-source voltage increases as the optical signal incident on the photodiode 1 increases. Therefore, by selecting the threshold voltage of FET Q5 to an appropriate value, when the average power of the light incident on photodiode 1 exceeds a predetermined value, the FET
Q5 becomes conductive, and a shunt path is formed through which a part of the human power photocurrent PD is shunted. As a result, when an excessive input occurs to the amplifier 2, the shunt path (FET
) input photocurrent 'P to the buffer circuit 102 via Q5
A portion of D flows, and the degree of saturation of the amplifier 2 can be suppressed.

FIG. 2 shows an embodiment corresponding to FIG. 6 that can be implemented as an IC.

In this embodiment, a series circuit consisting of a resistor R and a capacitor CI is connected between the drain of FET Q4, which is the output terminal of the transimpedance amplifier, and the ground, and the integral is calculated from the connection point between the resistor R and the capacitor CI. We are getting the resulting signal.

A signal resulting from the integration is applied to FETQ6, and a control signal is obtained from the source of FETQ6 to the source of FETQ5. Here, FETQ SFETQ76 constitutes the buffer circuit 102. That is, FETQ6 is a source follower whose drain is supplied with +vDD, and a current flows from FETQ7 whose gate and source are short-circuited to a certain constant current load, thereby sending out a low impedance control signal.

In the above circuit, the threshold voltage of FETQ -Q7 is set to -IV, and each FET
The gate width of T is 150μm, 75μm, 150μm in order.
, 150 μm. 200μm, 15μm. It was set to 20 μm. Further, the resistance value of the feedback resistor Rr is 2 kΩ, the value of the resistor R is 10 kΩ, and the capacitance of the capacitor C1 is 1 pF.

In a circuit with such a configuration, 300M as shown in Fig.
bps rOJ. An NRZ signal consisting of rlJ repetitions was added. Here, when the human photocurrent was a large input of 1 mA, an output signal indicated by V in FIG. 3 could be obtained from the output terminal 3. In addition, vcoNT in the same figure is a buffer circuit 10.
2 shows the potential at point P in FIG. 2, which is the output potential of No. 2. From this figure, it can be seen that for a while after the arrival of an excessive input, the output potential V CONT of the buffer circuit 102 gradually decreases and FET Q5 transitions to a conductive state, thereby correcting the pulse width distortion of the output waveform. You can observe the situation. Note that the time until the output signal (2) becomes stable is determined by the time constant of the integrating circuit 101out.

Next, add 300Mb to the circuit with the above configuration as shown in Figure 7.
An NRZ signal consisting of repeated ps "0" and "1" was added. Here again, when the input photocurrent is 0.1 mA, c
asel, and case 2 is when it is 1 mA. As a result, an output signal as shown in FIG. 4 could be obtained from the output terminal 3. In other words, when the amplifier 2 is not saturated (case 1), it is possible to obtain an output signal without significantly distorting the input signal, as in the conventional case, and in the case where the amplifier 2 is saturated, it is impossible to reproduce the input signal. Even in the case (case 2), this embodiment was able to obtain an output without substantially distorting the 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 input current of a transimpedance amplifier becomes larger than a predetermined value, an integrating circuit is used to generate an average value that is larger than the predetermined value. The gate circuit is accordingly opened to form a shunt path for the input current. For this reason, excessive human power current no longer flows into the feedback resistor of the transimpedance type amplifier, which works to prevent the output voltage from dropping, weakening the saturation of the amplifier and increasing the input photocurrent. It is possible to obtain an output signal with less distortion even if 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 output on the transmitting side and the magnitude of attenuation between transmitter and receiver, without using any other structure. can.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an amplifier device according to one embodiment of the present invention, FIG. 2 is a circuit diagram of an amplifier device according to another embodiment constructed using FETs, and FIGS. 3 and 4 are 2 shows the output signal of the device, FIGS. 5 and 6 are block diagrams of conventional amplification devices, FIG. 7 shows an example of the input optical signal, and FIG. 8 shows the conventional amplification device of FIG. FIG. 9 is a diagram showing the change in the drain-source voltage of the FET in the conventional example shown in FIG. 6, and FIG. 10 is a diagram showing the gate-source voltage in the conventional example shown in FIG. 6. It is a diagram. 1...Photodiode, 2...Amplifier, 3...
Output terminal, 100... Gate control means, 101...
Integrating circuit, 102...Buffer circuit, Rr...Feedback resistor, Q-Q...FET, Dl-D2...
Diode for level shift 17.

Claims (1)

[Scope of Claims] A transimpedance type amplifier; a gate circuit provided in a shunt channel that shunts an input current of the transimpedance type amplifier to open and close the shunt flow path; and a gate circuit that integrates an output signal of the transimpedance type amplifier. The gate circuit includes an integrator circuit, and generates a control signal to open the gate circuit when the input signal of the transimpedance amplifier becomes larger than a predetermined value based on the output of the integrator circuit. 1. An amplification device characterized by comprising: gate control means for applying a signal to a gate.