JP2009290520A - Transimpedance amplifier, regulated transimpedance amplifier and optical receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transimpedance amplifier which deals with a wide dynamic range and also reduces input conversion noise in low input. <P>SOLUTION: A variable current source 201, a variable resistor 203 and a control circuit 205 therefor are applied to a transimpedance amplifier. A magnitude of an input current of the transimpedance is estimated from an output voltage, and a wide dynamic range enabled state is shifted to an input conversion noise reduction state. Thus, linearity of an output signal is maintained regardless of the quantity of an input current. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a transimpedance amplifier that converts a current signal output from a light receiving element into a voltage signal in an optical receiver.

  A transimpedance amplifier is an amplifier that converts current into voltage.

  In optical receivers that handle optical signals, signals in the optical receiver for each information processing device or for each channel due to differences in performance of light receiving and emitting elements, differences in signal transmission distance, differences in coupling efficiency of lenses that collect optical signals, etc. The current can vary greatly.

  Therefore, transimpedance amplifiers used in optical receivers have a wide dynamic range to convert current signals into voltage signals without waveform distortion when the input current is large, and errors occur when the input current is small. The input conversion noise is required to be small so as not to occur.

  In addition, the optical receiver is required to have a high bandwidth for large-capacity data transmission.

  FIG. 1 is a circuit diagram showing an example of a conventional transimpedance amplifier.

  In the conventional transimpedance amplifier, the transistor 102 whose gate is connected to a constant voltage source, the resistance element 103 whose both terminals are connected to the drain terminal and the power source of the transistor 102, the constant current source 101 connected to the source terminal of the transistor 102, The constant voltage source 104 is connected to the gate terminal of the transistor. An input signal is input from the input terminal 105, and an output signal is output from the output terminal 106.

  In this transimpedance amplifier, when a current signal is input to the input terminal, the current flowing through the resistance element 103 changes, and a voltage signal proportional to the product of the element value of the resistance element 103 and the amount of fluctuation of the current is output to the output terminal. Is output.

  This circuit configuration is a gate-grounded structure and has a low input impedance, which is suitable for increasing the bandwidth.

As a modification of the transimpedance amplifier, a technique described in Japanese Patent Laid-Open No. 11-205047 (Patent Document 1) can be given. In this patent document, by making the current value of the constant current source 101 variable, even if the input current increases, the current value of the variable current source increases following the input current. For this reason, a waveform can be output even at the time of a large input.
Japanese Patent Laid-Open No. 11-205047

  However, in order to realize a wide dynamic range with the conventional circuit, it is necessary to set the current value of the constant current source to be equal to or greater than the maximum input current. For this reason, it is difficult to reduce current-induced noise in the transistor.

  Further, it is necessary to operate the transistor by reducing the power supply voltage by miniaturizing the transistor. For this reason, in order to operate the transistor in the saturation region, the resistance value cannot be increased and the gain of the transimpedance amplifier cannot be increased. For this reason, the circuit noise at the subsequent stage greatly affects the input conversion noise.

  On the other hand, in order to reduce the input conversion noise, it is necessary to reduce the current value of the constant current source 101 and increase the element value of the resistance element 103, which makes it difficult to widen the dynamic range. For this reason, in the conventional circuit, even when the input current is different, it is difficult to convert the current signal to the voltage signal without waveform distortion and to reduce the input conversion noise.

  An object of the present invention is to provide a transimpedance amplifier that can cope with a wide dynamic range and can reduce input conversion noise at the time of low input.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  Of the inventions disclosed in the present application, the outline of typical ones will be briefly described as follows.

  A transimpedance amplifier according to a representative embodiment of the present invention includes a first transistor, a variable current source and an input terminal are connected to a source terminal of the first transistor, and a drain terminal of the first transistor is connected to the source terminal of the first transistor. A resistance element for determining the potential of the output terminal and the drain terminal is connected, and the resistance element is a variable resistance.

  The transimpedance amplifier may further include a control circuit, and the control circuit may control the variable current source and the variable resistance. This control circuit may be characterized in that it detects the output signal of the output terminal and controls the variable current source and the variable resistor.

  The variable current source of the transimpedance amplifier may be composed of two or more transistors.

  Furthermore, in the case of this transimpedance amplifier having a second transistor, the same variable current source and input terminal as the source terminal of the first transistor are connected to the source terminal of the second transistor, The gate terminal of the transistor may be controlled by a control circuit.

  A regulated transimpedance amplifier according to a representative embodiment of the present invention is composed of a variable current source, a transistor, and a resistance element, and a transimpedance adjustment circuit is connected to an input terminal, according to an output signal. The transimpedance adjustment circuit may adjust the current value of the variable current source.

  The use of these transimpedance amplifiers and regulated transimpedance amplifiers for optical receivers also falls within the scope of the present invention.

  The effects obtained by typical ones of the inventions disclosed in the present application will be briefly described as follows.

  With the transimpedance amplifier according to the representative embodiment of the present invention, when the input current is large, it is possible to convert the current signal to the voltage signal without waveform distortion by widening the dynamic range.

  Further, when the input voltage is small, the current-induced noise is reduced by reducing the current amount of the constant current source, and the influence of circuit noise in the subsequent stage is reduced by increasing the gain. As a result, the occurrence of errors due to noise can be suppressed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
The transimpedance amplifier according to the first embodiment of the present invention will be described. FIG. 2 is a circuit configuration diagram of the transimpedance amplifier according to the first embodiment of the present invention. FIG. 3 is a block diagram showing the configuration of the control circuit 205.

  The transimpedance amplifier includes a variable current source 201, a transistor 202, a variable resistor 203, a constant voltage source 204, a control circuit 205, and a memory 206. An input terminal 207 and an output terminal 208 are also included. Note that reference numerals 611, 612, and 613 in the figure are used in the description of FIG. 3 and will not be described here.

The variable current source 201 is a variable current source in which one terminal is connected to the source terminal of the transistor and the other is grounded. Current amount of the variable current source 201 is controlled by a control signal S _B. The specific configuration of the variable current source 201 can achieve the effects of the present invention by either a method of switching the number of parallel transistors or a method of adjusting the gate voltage of the transistor.

  The transistor 202 is an amplifier circuit in this circuit. The transistor 202 operates in the same manner as a field effect transistor or a bipolar transistor.

  The gate terminal of the transistor 202 is connected to a constant voltage source. The source terminal of the transistor 202 is connected to the variable current source 201. An input signal is input from the input terminal 207 to the connection point between the source terminal and the variable current source 201. The drain terminal of the transistor 202 is connected to the power supply Vcc via the variable resistor 203. A signal amplified by the transistor 202 is output from the connection point between the drain terminal of the transistor 202 and the variable resistor 203 to the output terminal 208.

  The variable resistor 203 is a variable resistor for determining the potential of the drain terminal of the transistor 202. A method for realizing the variable resistor 203 may be a method of switching the parallel number of resistance elements or a method of using a transistor as a load resistor and adjusting a gate voltage thereof.

  The constant voltage source 204 is a constant voltage source that determines the potential of the gate terminal of the transistor 202.

The control circuit 205 is a control circuit that detects the signal at the output terminal 208 and controls the variable current source 201 and the variable resistor 203. The control circuit 205 a control signal _{S B} to the variable current source 201, and outputs the control signal _{S R} to the variable resistor 203.

  The operation of the control circuit 205 will be described.

When the input current input from the input terminal 207 is large, the output current flowing through the output terminal 208 is proportionally increased. At this time, the control circuit 205 increases the current amount of the variable current source 201, and outputs a control signal S _B and the control signal S _R in order to reduce the resistance of the variable resistor 203.

On the other hand, when the input current inputted from the input terminal 207 is small, the output current 208 is also reduced proportionally. At this time, the control circuit 205 to reduce the current amount of the variable current source 201, and outputs a control signal S _B and the control signal S _R in order to increase the resistance value of the variable resistor 203.

  The control circuit 205 includes a peak hold circuit 608 including a transistor 601, a transistor 602, and a capacitor 603, a comparator 604, a reset circuit 605, a multiplier 606, and a multiplier 607 (see FIG. 3).

  Note that 611, 612, and 613 are indexes of connection with FIG. 2, and do not have any effect in terms of circuit. On the other hand, the reference voltage 610 is an input voltage serving as a threshold value of the comparator 604 and does not exist in FIG.

  The peak hold circuit 608 includes a transistor 601 having a switch function, a transistor 602, and a capacitor 603 for exhibiting a peak hold function. The ON / OFF operation of the transistor 601 is performed by the amplified signal (transimpedance) of the transistor 202. On the other hand, the ON / OFF operation of the transistor 602 is performed by the output signal of the reset circuit 605. When the switch of the transistor 601 is ON, electric charge is accumulated in the capacitor 603. On the other hand, when the transistor 602 is ON, the electric charge accumulated in the capacitor 603 is removed.

  The output voltage Vx input to the comparator 604 is determined by the electric charge accumulated in the capacitor 603. This output voltage Vx holds the maximum value of the output voltage at the output terminal 208.

  When the output of the transimpedance amplifier is input to the input terminal 613, it is input to the gate terminal of the transistor 601, and the transistor 601 operates as a switch. As a result, a charge proportional to the output of the transimpedance amplifier is accumulated in the capacitor 603. The charge accumulated in the capacitor 603 induces an output voltage Vx proportional to the output of the transimpedance amplifier at one end of the input of the comparator 604.

The comparator 604 compares the output voltage Vx of the peak hold circuit 608 with the reference voltage 610. When the output voltage Vx of the peak hold circuit 608 is larger than the reference voltage 610, the comparator 604 outputs a control signal. After the output signal of the comparator 604 is multiplied by the adjustment coefficient C _R and the adjustment period count C _B , the control circuit 205 outputs the control signal S _R and the control signal S _B to the variable resistor 203 and the variable current source 201. Further, the output signal of the comparator 604 is also output to the reset circuit 605.

  In response to the output signal of the comparator 604, the reset circuit 605 outputs a signal to the gate terminal of the transistor 602. Thereby, the electric charge accumulated in the capacitor 603 is removed.

  The reference voltage 610 is a voltage for comparison with the output voltage Vx of the transimpedance. In the present invention, a threshold value for detecting noise contained in the output signal is set. The reference voltage 610 determines this threshold value.

  The comparator 604 compares the reference voltage 610 with the output voltage Vx of the peak hold circuit 608. When the output voltage Vx of the peak hold circuit 608 exceeds a certain value, it corresponds to a wide dynamic range.

Memory 206 is a circuit for output adjustment factor for adjusting the variation in the individual control circuit 205 _{C R,} the adjustment period count _{C B} to the control circuit 205. By changing this setting, fine adjustment of the control circuit 205 of each optical receiver is performed.

  Next, the characteristics and applications of this circuit will be described.

  FIG. 4 is a graph showing the input / output characteristics of this transimpedance amplifier when the wide dynamic range is supported by increasing the current value of the variable current source 201 and decreasing the resistance value of the variable resistor 203. FIG. 5 is a graph showing the frequency characteristics of the input conversion noise of this transimpedance amplifier under the conditions of FIG. As can be seen from FIG. 4, in the input / output characteristics, the output voltage changes linearly with respect to the entire input range (0 mA to 0.9 mA), and a wide dynamic range is realized. . On the other hand, the input conversion noise is 2.0E-11 A / √Hz at least, which is relatively high.

  On the other hand, FIG. 6 is a graph showing the input / output characteristics of this transimpedance amplifier when the input conversion noise is reduced by decreasing the current value of the variable current source 201 and increasing the resistance value of the variable resistor 203. FIG. 7 shows the frequency characteristics of the input conversion noise of this transimpedance amplifier under the conditions of FIG. Compared with the case where this transimpedance amplifier is compatible with a wide dynamic range, the range of an effective range that can be converted from a current signal to a voltage signal without distortion is not wide (0 mA to 0.3 mA). On the other hand, input conversion noise is reduced in the entire frequency range.

  When using this transimpedance amplifier, it is assumed that a wide dynamic range is supported when the input current is large. Therefore, even if the input conversion noise becomes relatively large, there is no adverse effect such as the occurrence of an error in the transimpedance amplifier due to the noise.

  On the other hand, when the input conversion noise is reduced, a nonlinear interval (interval (b) in FIG. 6) occurs in the input / output characteristics. However, this is not a problem because it is not assumed to be used in the nonlinear interval. .

  Next, a specific operation of this circuit will be described.

  FIG. 8 shows the input / output characteristics of the transimpedance amplifier when the control circuit 205 is operated when the input conversion noise is reduced. On the other hand, FIG. 9 shows the input / output characteristics of the transimpedance amplifier when the control circuit 205 is operated when the wide dynamic range is supported.

  As can be seen by comparing FIG. 8 and FIG. 9, in FIG. 8, the period during which the output voltage rises in proportion to the input current is short (up to 3.0E-04A). On the other hand, in FIG. 9, this section extends to about 6.0E-04A. This switching means of the control circuit 205 according to the present invention will be described below.

  Here, the initial state is assumed to be when the input conversion noise in FIG. 8 is reduced.

  When the input current range input from the input terminal 207 (reflected in the voltage of the output terminal 208) is 0 mA to 0.5 mA in FIG. 9, the output voltage Vx of the peak hold circuit 608 (= the output voltage of the output terminal 208). The reference voltage 610 is set so that the maximum value becomes equal to or lower than the reference voltage 610.

  On the other hand, if it exceeds 0.5 mA, the output voltage Vx of the peak hold circuit 608 (= the maximum value of the output voltage of the output terminal 208) becomes the reference voltage 610 or more. At this time, the comparator 604 of the control circuit 205 issues a control signal, and the reset circuit 605 outputs a signal to the gate terminal of the transistor 602 so that the charge accumulated in the capacitor 603 is removed. By removing the charge of the capacitor 603, the output voltage Vx of the peak hold circuit 608 returns to the reference voltage 610 or lower.

Also with respect to the variable resistor 203 and the variable current source 201 through 611 and 612, the control signal _{S B} and the control signal _{S R} which is generated from the control signal of the comparator 604 is output. As a result, the variable resistor 203 and the variable current source 201 can shift to the characteristics corresponding to the wide dynamic range shown in FIG.

  When returning from the time corresponding to the wide dynamic range in FIG. 9 to the reduction of the input equivalent noise in FIG. 8, the variable current source 201 and the variable resistor 203 when the output amplitude of the output terminal 208 is smaller than the desired amplitude by a circuit (not shown). Switching the characteristics.

  With the above operation, it is possible to realize a transimpedance amplifier that converts a current signal into a voltage signal without distortion in the waveform in the input range.

(Second Embodiment)
FIG. 10 is a circuit configuration diagram of a transimpedance amplifier according to the second embodiment of the present invention. The second embodiment will be described using this.

  The transimpedance amplifier includes a variable current source including transistors 301 and 306, a gate-grounded transistor 302 and a transistor 307, resistance elements 303 and 308, a control circuit 309, and a memory 310. In addition, an input terminal 311 and an output terminal 312 are provided as input / output terminals.

  A variable current source including the transistor 301 and the transistor 306 corresponds to the variable current source 201 of the first embodiment. The transistor 306 is used as a circuit for adjusting the current amount of the variable current source. In this figure, two transistors are used in parallel, but the same effect can be obtained by paralleling three or more transistors.

  The resistance element 303 takes a fixed resistance value unlike the variable resistance 203 of the first embodiment. Instead, the transistor 307 and the resistance element 308 are arranged as a circuit for adjusting the transimpedance. Note that the same effect can be obtained even when a plurality of transistors 306 and resistor elements 308 are arranged in parallel as a circuit for switching the transimpedance.

  The control circuit 309 is a circuit that adjusts the current amount and transimpedance of the variable current source by controlling (ON / OFF) the gate terminals of the transistor 306 and the transistor 307 in accordance with the output voltage of the output terminal 312.

  In this embodiment, by switching ON / OFF of the transistor 306 and the transistor 307, it is possible to switch between wide dynamic range support and input conversion noise reduction support. As a result, the number of elements constituting the transimpedance amplifier can be reduced as compared with the first embodiment. In addition, since the influence of the non-linear operation of the transistor used for the variable resistance element can be suppressed, an output signal without waveform distortion can be obtained.

(Third embodiment)
FIG. 11 is a circuit configuration diagram of a transimpedance amplifier according to the third embodiment of the present invention. The third embodiment will be described using this.

  The transimpedance amplifier includes a variable current source 401, a transistor 402, a resistor element 403, a transistor 404, a resistor element 405, a transistor 406, a resistor element 407, a transistor 408, a resistor element 409, a transistor 410, a control circuit 411, and a memory 412. The The transimpedance amplifier has an input terminal 413 and an output terminal 414 as input / output terminals.

  The variable current source 401 has the same function as the variable current source 201 of the first embodiment.

  The transistor 402, the resistance element 403, the transistor 404, and the resistance element 405 constitute a regulated transimpedance amplifier.

  The transistor 406, the resistance element 407, the transistor 408, the resistance element 409, and the transistor 410 constitute a transimpedance adjustment circuit 420. The transimpedance adjustment circuit 420 switches the characteristics of the transimpedance amplifier by controlling ON / OFF of the transistor 410 by the control circuit 411.

  In this embodiment, by using a regulated transimpedance amplifier, the frequency band can be widened as compared with the transimpedance amplifier according to the first embodiment. As a result, the transimpedance amplifier according to the present embodiment is more suitable for large-capacity data transfer than the first embodiment.

(Fourth embodiment)
FIG. 12 shows an apparatus configuration to which an LSI equipped with the transimpedance amplifier of the present invention is applied. By providing a control signal monitor 901 capable of observing the output signal of the control circuit of the transimpedance amplifier of the present invention in real time on the device, it is possible to check the secular change and temperature fluctuation of the device, and to improve the reliability of the device. It becomes possible to improve.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiments. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say.

  The transimpedance amplifier according to the present invention is assumed to be used in an optical receiver, but is not necessarily limited thereto. There is room for application in fields where transimpedance amplifiers require linearity.

It is a circuit block diagram which shows an example of the conventional transimpedance amplifier. It is a circuit block diagram of the transimpedance amplifier in connection with 1st Embodiment. It is a block diagram which shows the structure of the control circuit in connection with 1st Embodiment. It is a graph showing the input-output characteristic of the transimpedance amplifier concerning 1st Embodiment at the time of a wide dynamic range correspondence. It is a graph showing the frequency characteristic of the input conversion noise of the transimpedance amplifier in connection with 1st Embodiment at the time of a wide dynamic range correspondence. It is a graph showing the input-output characteristic of the transimpedance amplifier concerning 1st Embodiment at the time of reducing input conversion noise. It is a graph showing the frequency characteristic of the input conversion noise of the transimpedance amplifier in connection with 1st Embodiment at the time of reducing input conversion noise. The input / output characteristics of the transimpedance amplifier when the control circuit operates when the input conversion noise is reduced are shown. The input / output characteristics of this transimpedance amplifier when the control circuit operates in response to a wide dynamic range are shown. It is a circuit block diagram of the transimpedance amplifier in connection with 2nd Embodiment. It is a circuit block diagram of the transimpedance amplifier in connection with 3rd Embodiment. 1 shows an apparatus configuration to which an LSI equipped with a transimpedance amplifier according to the present invention is applied.

Explanation of symbols

201 ... variable current source, 202 ... transistor, 203 ... variable resistor,
204 ... constant voltage source, 205 ... control circuit, 206 ... memory, 207 ... input terminal,
208: Output terminal, 301: Transistor, 302 ... Transistor,
303 ... Resistance element, 306 ... Transistor, 307 ... Transistor,
308... Resistance element, 309... Control circuit, 310.
401 ... Variable current source, 402 ... Transistor, 403 ... Resistance element,
404 ... transistor, 405 ... resistive element, 406 ... transistor,
407 ... resistive element, 408 ... transistor, 409 ... resistive element,
410 ... transistor, 411 ... control circuit, 412 ... memory,
420: Transimpedance adjustment circuit,
601 ... transistor, 602 ... transistor, 603 ... capacitor,
604 ... comparator, 605 ... reset circuit, 606 ... multiplier, 607 ... multiplier,
608: Peak hold circuit.

Claims (7)

A resistance element having a first transistor, a variable current source and an input terminal connected to the source terminal of the first transistor, and a potential of the output terminal and the drain terminal determined to the drain terminal of the first transistor; A transimpedance amplifier connected,
The transimpedance amplifier, wherein the resistance element is a variable resistance.   2. The transimpedance amplifier according to claim 1, further comprising a control circuit, wherein the control circuit controls the variable current source and the variable resistor.   3. The transimpedance amplifier according to claim 2, wherein the control circuit controls the variable current source and the variable resistor by detecting an output signal of the output terminal.   2. The transimpedance amplifier according to claim 1, wherein the variable current source includes two or more transistors. The transimpedance amplifier according to claim 1, further comprising a control circuit and a second transistor,
The same variable current source and input terminal as the source terminal of the first transistor are connected to the source terminal of the second transistor,
The transimpedance amplifier, wherein the gate terminal of the second transistor is controlled by the control circuit.   In a regulated transimpedance amplifier composed of a variable current source, a transistor, and a resistance element, a transimpedance adjustment circuit is connected to an input terminal, and a current value of the variable current source and a control circuit according to an output signal A regulated transimpedance amplifier characterized by adjusting the transimpedance adjustment circuit.   An optical receiver comprising the transimpedance amplifier according to any one of claims 1 to 5 or the regulated transimpedance amplifier according to claim 6.

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