JP3592262B2 - Preamplifier circuit, output control method therefor, and communication device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a preamplifier circuit and an output control method thereof, and more particularly to a transimpedance preamplifier circuit, an output control method thereof, and a communication device.
[0002]
[Prior art]
Conventionally, this kind of gain switching type preamplifier has a transimpedance type preamplifier circuit (hereinafter referred to as a preamplifier) which switches a gain by a gain switching signal 53 which is a signal for switching a feedback resistance when a large signal is input as shown in FIG. ), Which are disclosed, for example, in JP-A-09-008563. This preamplifier has a capacitor 7 for phase compensation used when the circuit gain is reduced, and when a data signal having a level lower than a predetermined threshold is input, the input gain switching signal 53 is set to a low level. When the data signal is fixed and a level higher than the threshold is input, the gain switching signal 53 is set to the high level. In the conventional circuit shown in FIG. 4, when the input level of the burst signal changes from low to high and the gain switching signal 53 becomes active, the capacitor 7 for phase compensation is charged.
[0003]
[Problems to be solved by the invention]
In the above-described conventional preamplifier, if the low-level preamplifier input signal 51 continues for a long time, the amount of discharge of the phase compensation capacitor 7 increases, and as shown in FIG. This has the problem of affecting the subsequent circuits.
[0004]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a preamplifier circuit capable of avoiding a circuit malfunction caused by discharge of a phase compensation capacitor in a preamplifier circuit, an output control method thereof, and a communication device.
[0005]
[Means for Solving the Problems]
A preamplifier circuit according to the present invention includes an inverting amplifier circuit for amplifying an input preamplifier input signal, a buffer circuit for buffering an output of the inverting amplifier circuit, and a first feedback circuit for switching a gain of the inverting amplifier circuit. And a second resistor, a capacitor for performing phase compensation of the inverting amplifier circuit, and a gain switching signal input to operate as a switch for switching gain and phase compensation, and operate as a switch for switching the inverting amplifier circuit via the second resistor. A first switch element provided between an input side and an output side of the buffer circuit, a second switch element provided between the input side of the inverting amplifier circuit and the capacitor, and the capacitor is constantly charged A third resistor provided in parallel with the second switch element. The third resistor is connected to the second switch element when the capacitor starts discharging. A third switch element which starts charging the capacitor. The switch element is a MOS transistor.
[0008]
A communication device according to the present invention includes an inverting amplifier circuit for amplifying an input preamplifier input signal, a buffer circuit for buffering an output of the inverting amplifier circuit, and first and second feedback circuits for switching a gain of the inverting amplifier circuit. 2, a capacitor for performing phase compensation of the inverting amplifier circuit, and a gain switching signal that is input to operate as a switch for switching gain and phase compensation and to operate as an input side of the inverting amplifier circuit via the second resistor. A first switch element provided between the first switch element and the output side of the buffer circuit, a second switch element provided between the input side of the inverting amplifier circuit and the capacitor, and parallel to the second switch element. And a third switch element that is connected and provided to start charging the capacitor when the capacitor starts discharging. It is. The switch element is a MOS transistor.
[0010]
An output control method in a preamplifier circuit according to the present invention includes a capacitor for phase compensation used when a circuit gain decreases, and is input when a data signal having a level lower than a predetermined threshold is input. A gain switching signal is fixed at a low level, and when a data signal having a level higher than the threshold value is input, in the output control method in a preamplifier circuit for setting the gain switching signal to a high level, A first switch element which operates as a switch for switching gain and phase compensation and is provided between an input side of an inverting amplifier circuit and an output side of a buffer circuit provided at an output side of the inverting amplifier circuit via a resistor. And by turning on a second switch element provided between the input side of the inverting amplifier circuit and the capacitor, When the capacitor lower the value of the feedback resistor begins to discharge, it is configured to initiate charging of the capacitor by means of a third switching element connected in parallel to said second switching element.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
[0012]
FIG. 1 shows a circuit diagram of a first embodiment of the present invention, which is used as a preamplifier of an optical receiver or the like. The preamplifier input signal 51 is connected to the inverting amplifier circuit 1, and the output of the inverting amplifier circuit 1 for amplifying the preamplifier input signal 51 is connected to the buffer circuit 2 for buffering the output of the inverting amplifier circuit 1. A feedback resistor 3 is connected between the input of the inverting amplifying circuit 1 and the output of the buffer circuit 2, and a metal operates similarly as a feedback resistor 4 and a switch between the input of the inverting amplifying circuit 1 and the output of the buffer circuit 2. An Oxide Semiconductor (MOS) transistor 5 is connected. A MOS transistor 6 operating as a switch and a phase compensation capacitor 7 are connected between the input and output of the inverting amplifier circuit 1. Further, a resistor 8 is connected in parallel with the MOS transistor 5. Gain switching signal 53 is input to MOS transistors 5 and 6. The constant of each part has the following relationship. The resistance of the feedback resistor 3 is sufficiently larger than the resistance of the feedback resistor 4, the resistance of the resistor 8 is sufficiently larger than the ON resistance of the MOS transistor 6, and the time constant of the resistor 8 and the capacitor 7 is the preamplifier cutoff frequency. Should be large.
[0013]
FIG. 2 is a waveform chart according to the first embodiment of the present invention. The operation will be described below with reference to FIGS.
[0014]
The basic operation of the present invention will be described with reference to the signal waveform of FIG. When data of a burst signal is input, when data of a level lower than a certain threshold is input, the gain switching signal 53 is fixed at a LOW level, and the gain of the circuit is set to a large state. . When an input at a level higher than the threshold value is input, the gain switching signal 53 goes high (HI).
[0015]
When the MOS transistor 5 and the MOS transistor 6 are turned on, the feedback resistor 4 is connected in parallel with the feedback resistor 3, so that the value of the feedback resistor decreases and the circuit gain decreases. As a result, the linearity is maintained without saturation of the preamplifier. In the circuit, a capacitor 7 for phase compensation used when the gain is reduced is connected. In this circuit, the capacitor 7 is always charged by the resistor 8. Therefore, at the time of gain switching, the preamplifier output signal 54 can operate normally as shown in FIG. However, the resistor 8 needs to have a value that does not affect the cutoff frequency of the preamplifier.
[0016]
Next, a second embodiment of the present invention will be described with reference to FIG. As in FIG. 1, the preamplifier input signal 51 is connected to the inverting amplifier circuit 1, and the buffer circuit 2 is connected to the output of the inverting amplifier circuit 1. A feedback resistor 3 is provided between the input of the inverting amplifier circuit 1 and the output of the buffer circuit 2, and a feedback resistor 4 and a MOS which operates as a switch between the input of the inverting amplifier circuit 1 and the output of the buffer circuit 2. The transistor 5 is connected. A capacitor 7 for phase compensation and a MOS transistor 6 and a MOS transistor 9 operating as switches are connected between the input and output of the inverting amplifier circuit 1. Gain switching signal 53 is input to the gates of MOS transistor 6 and MOS transistor 5. The MOS transistor 9 is connected to a reference voltage.
[0017]
When the voltage of the node 52 starts to decrease, that is, when the capacitor 7 starts discharging, the MOS transistor 9 gradually starts to enter the active region, so that the capacitor 7 starts charging. The resistance value of the feedback resistor 3 is sufficiently larger than the resistance value of the feedback resistor 4. The operation waveform is the same as that shown in FIG.
[0018]
Although the first and second embodiments show examples in which MOS transistors are used as the switch elements, other circuit elements having equivalent functions may be used.
[0019]
【The invention's effect】
As described above, according to the present invention, the capacitor for phase compensation is always charged, so that the input of the large-level signal (low preamplifier gain) after the long-time low-level signal input (high preamplifier gain) continues. At the time, since a phenomenon of drawing a large current into this capacitor due to discharge of the capacitor for phase compensation does not occur, it is possible to suppress noise generated in the output of the preamplifier when a large input signal is input.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a first embodiment of the present invention.
FIG. 2 is a waveform chart according to the first embodiment of the present invention.
FIG. 3 is a circuit diagram showing a second embodiment of the present invention.
FIG. 4 is a diagram illustrating an example of a conventional preamplifier circuit.
FIG. 5 is a waveform diagram in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Inverting amplifier circuit 2 Buffer circuits 3, 4, 8 Resistance 5, 6, 9 MOS transistor 7 Capacitor

Claims (4)

An inverting amplifier circuit for amplifying an input preamplifier input signal, a buffer circuit for buffering an output of the inverting amplifier circuit, first and second feedback resistors for switching a gain of the inverting amplifier circuit, A capacitor for compensating the phase of the amplifying circuit, and a gain switching signal that is input to operate as a switch for switching the gain and phase compensation, and the input side of the inverting amplifying circuit and the output side of the buffer circuit via the second resistor And a second switch element provided between the input side of the inverting amplifier circuit and the capacitor, and a second switch element provided in parallel with the second switch element for constantly charging the capacitor. A third resistor provided in connection therewith, wherein the third resistor starts charging the capacitor when the capacitor starts discharging. Preamplifier circuit which is a third switching element. 2. The preamplifier circuit according to claim 1, wherein said switch element is a MOS transistor. A communication device comprising the preamplifier circuit according to claim 1. A capacitor for phase compensation used when the circuit gain is reduced, and when a data signal having a level lower than a predetermined threshold is input, the input gain switching signal is fixed at a low level, and the threshold is fixed. In the output control method in the preamplifier circuit for setting the gain switching signal to a high level when a data signal having a higher level than the value is input, the gain switching signal is input and the gain and the phase compensation are switched. A first switch element provided between an input side of the inverting amplifier circuit and an output side of a buffer circuit provided at an output side of the inverting amplifier circuit via a resistor, and an input side of the inverting amplifier circuit and the capacitor. By turning on the second switch element provided therebetween, the value of the feedback resistor for the inverting amplifier circuit is reduced, and the capacitor starts discharging. When the output control method in the preamplifier circuit, characterized in that to start the charging of the second of said capacitor by means of a third switching element connected in parallel to the switching element.

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