JP5137141B2 - Transimpedance amplifier - Google Patents

Description

  The present invention relates to a transimpedance amplifier.

  With the progress of optical communication technology, the amount of data transmitted has increased dramatically, and there is a demand for an increase in capacity of the transmission apparatus. In order to realize this large capacity, it is required to increase the speed of the optical receiver.

FIG. 9 is a schematic diagram illustrating a configuration of an optical receiver that performs photoelectric conversion in general optical communication.
As shown in FIG. 9, an optical receiver generally includes a transimpedance amplifier (TIA) 100, a photodetector (PD) 103, and an input parasitic capacitance 104. The transimpedance amplifier 100 includes a negative feedback resistor R _F 101 and a first amplifier circuit 102.

The conventional optical receiver, the optical signal L _in received by the photodetector 103 converts the optical signal L _in the current signal I _in, further transimpedance amplifier 101 receives and amplifies the current signal I _in, subsequent Is converted into a voltage signal _Vout having a receivable amplitude. In order to increase the speed of data that can be received by the transimpedance amplifier 100, it is essential to widen the gain frequency characteristic.

  By the way, the factors that limit the band of the transimpedance amplifier 100 are first caused by the frequency characteristics of the input circuit due to the input parasitic capacitance 104 such as the photodetector 103 and the input impedance of the transimpedance amplifier 100, and secondly the transimpedance amplifier. Some are caused by the frequency characteristics of the constituent circuits constituting the circuit 100, and others are caused by the frequency characteristics of the output circuit of the transimpedance amplifier 100.

ここで、Ｒ_Fは負帰還抵抗、Ｃ_inはフォトディテクタ１０３等の入力寄生容量１０４、Ａ_oは増幅回路のオープンループ利得である。 First, band limitation resulting from the frequency characteristics of the input circuit, which is the first factor, will be described.
The impedance conversion gain Z _t of the transimpedance amplifier 100 is given by the following equation (1).

Here, R _F is a negative feedback resistor, C _in is an input parasitic capacitance 104 such as the photodetector 103, and A _o is an open loop gain of the amplifier circuit.

From the above equation (1), the 3 dB band f _3dB where Z _t becomes 1 / √2 is obtained as in the following equation (2).

Next, band limitation resulting from the frequency characteristics of the constituent circuits constituting the transimpedance amplifier 100, which is the second factor, will be described.
FIG. 10 is a schematic diagram showing the configuration of the transimpedance amplifier according to the first conventional example.
As shown in FIG. 10, the transimpedance amplifier 100 according to the first conventional example includes a common-source amplifier circuit (common-source amp.) Including a load resistor R _L 106, a transistor M ₁ 107, and a source resistor R _S 110. 105, a negative feedback resistor R _F 101, and a source follower circuit (Source follower) 106 including a transistor M ₂ 108 and a transistor M ₃ 109. In FIG. 10, I _in is a current signal, V _out is a voltage signal, VDD is a drain-side power supply, VSS is a source-side power supply, and V _CS is a constant source voltage.

As described above, the transimpedance amplifier 100 according to the first conventional example is mainly composed of the common-source amplifier circuit 105 and the source follower circuit 106, but is composed of the input parasitic capacitance C _in 104 and the feedback resistor R _F 101. Bandwidth is limited. In high-speed operation, the band limitation due to the input parasitic capacitance C _in 104 cannot be ignored, and it is difficult to improve the frequency characteristics. FIG. 11 shows an example of frequency characteristics in the transimpedance amplifier 100 according to the first conventional example shown in FIG.

Therefore, inductive peaking in which an inductor is inserted is conventionally used as means for improving the band of the transimpedance amplifier 100.
FIG. 12 is a schematic diagram showing a configuration of a transimpedance amplifier using inductive peaking according to a second conventional example.
As shown in FIG. 12, the transimpedance amplifier using inductive peaking according to the second conventional example is configured by connecting an inductor L _L 120 in series with a load resistor R _L 106. The transimpedance amplifier using inductive peaking according to the second conventional example has the same configuration as the transimpedance amplifier according to the first conventional example except for the configuration described above.

FIG. 13 is a schematic diagram showing the configuration of a transimpedance amplifier using inductive peaking according to a third conventional example.
As shown in FIG. 13, the transimpedance amplifier using inductive peaking according to the third conventional example has a first inductor L _L 120 connected in series to a load resistor R _L 106, and the output of the common source amplifier circuit. The second inductor L _S 130 is connected between the terminal and the input terminal of the source follower circuit. The transimpedance amplifier using inductive peaking according to the third conventional example has the same configuration as the transimpedance amplifier according to the first conventional example except for the configuration described above.

As shown in FIGS. 12 and 13, by connecting an inductor L _L 120 in series with the load resistor R _L 106, the load impedance at high frequency is compensated, and the band degradation due to the parasitic capacitance is compensated. As compared with the conventional transimpedance amplifier 100 according to the conventional example 1, the bandwidth can be improved by about twice.

  FIG. 14 is a diagram illustrating an example of frequency characteristics in the transimpedance amplifier using the transimpedance amplifier according to the first conventional example and the inductive peaking according to the second conventional example. In FIG. 14, the broken line shows an example of the frequency characteristic of the transimpedance amplifier according to the first conventional example, and the solid line shows an example of the frequency characteristic of the transimpedance amplifier using inductive peaking according to the second conventional example. Show.

  As shown in FIG. 14, the transimpedance amplifier using inductive peaking according to the second conventional example can achieve a bandwidth about twice that of the transimpedance amplifier according to the first conventional example by using inductive peaking. I understand that there is.

  However, the size of the inductor used for inductive peaking is extremely large compared to the size of the transistor, and there is a problem that the area of one inductor occupies about 50 times or more the area of the transistor. This problem is particularly noticeable in inductive peaking using two or more inductors. Here, FIG. 15 shows a schematic diagram showing a physical layout example of two conventional inductors. In FIG. 15, two spiral inductors 140 are connected to the core 141 of the transimpedance amplifier.

  In addition, since the size of transistors and resistors is extremely different compared to inductors, the length of wiring that connects the circuit portion composed of transistors and resistors and the inductor becomes longer, and parasitic capacitance, parasitic resistance, and parasitic inductors caused by the wiring become longer. The adverse effect of is also a problem.

  That is, the transimpedance amplifier according to the first conventional example composed of transistors and resistors and the transimpedance amplifier using the inductive peaking according to the second and third conventional examples have a problem that it is difficult to further increase the bandwidth. It was.

  Furthermore, since the element size of an inductor is extremely large compared to a transistor or a resistor, in particular, in a transimpedance amplifier using inductive peaking with a plurality of inductors, the element size of the inductor becomes large and the cost increases. was there.

JP 2004-274463 A

Chao-Yung Wang, 2 others, “An 18-mW Two-Stage CMOS Transimpedance Amplifier for 10 Gb / s Optical Application”, IEEE Asian Solid-State 11th March, 14th. 412-415

  As described above, the transimpedance amplifier according to the first conventional example and the transimpedance amplifier using the inductive peaking according to the second and third conventional examples have a problem that it is difficult to increase the bandwidth. Furthermore, the conventional transimpedance amplifier using inductive peaking with a plurality of inductors has a problem of increasing the chip size.

  In view of the above, an object of the present invention is to provide a transimpedance amplifier having a wide gain frequency characteristic and capable of high-speed operation and a small chip size.

The transimpedance amplifier according to the first invention for solving the above-described problem is
In a transimpedance amplifier that receives a current signal converted from an optical signal and outputs a voltage signal,
A grounded source amplifier circuit, a source follower circuit, a negative feedback resistor, and two inductors having inductive coupling,
The inductor is a first inductor constituting a load impedance of the common source amplifier circuit and a second inductor connected in series with the negative feedback resistor.

The transimpedance amplifier according to the second invention for solving the above-mentioned problems is
In a transimpedance amplifier that receives a current signal converted from an optical signal and outputs a voltage signal,
A grounded source amplifier circuit, a source follower circuit, a negative feedback resistor, and two inductors having inductive coupling,
The inductor is a first inductor that constitutes a load impedance of the common source amplifier circuit, and a second inductor that connects an output terminal of the common source amplifier circuit and an input terminal of the source follower circuit. And

A transimpedance amplifier according to a third invention for solving the above-described problems is the transimpedance amplifier according to the first invention or the second invention.
The first inductor and the second inductor are constituted by spiral inductors, and the first inductor and the second inductor are overlapped and inductively coupled.

  According to the present invention, it is possible to provide a transimpedance amplifier having a wide gain frequency characteristic and capable of high-speed operation and a small chip size.

It is the schematic diagram which showed the structure of the transimpedance amplifier which concerns on 1st Example of this invention. It is the schematic diagram which showed the physical layout example of two inductors. It is the schematic diagram which showed the structure of the transimpedance amplifier which concerns on the 2nd Example of this invention. It is the figure which showed the frequency characteristic of the impedance conversion gain in the transimpedance amplifier which concerns on 2nd Example of this invention. It is the schematic diagram which showed the other structure of the transimpedance amplifier based on the 2nd Example of this invention. It is the schematic diagram which showed the structure of the transimpedance amplifier which concerns on the 3rd Example of this invention. It is the schematic diagram which showed the other structure of the transimpedance amplifier based on the 3rd Example of this invention. It is the schematic diagram which showed the circuit which connected the inductor to the gate terminal of MOSFET. It is the schematic diagram which showed the structure of the optical receiver which performs the photoelectric conversion in general optical communication. It is the schematic diagram which showed the structure of the transimpedance amplifier which concerns on a 1st prior art example. It is the figure which showed the example of the frequency characteristic in the transimpedance amplifier which concerns on a 1st prior art example. It is the schematic diagram which showed the structure of the transimpedance amplifier using the inductive peaking which concerns on a 2nd prior art example. It is the schematic diagram which showed the structure of the transimpedance amplifier using the inductive peaking which concerns on a 3rd prior art example. It is the figure which showed the example of the frequency characteristic in the transimpedance amplifier using the transimpedance amplifier which concerns on a 1st prior art example, and the inductive peaking which concerns on the 2nd, 3rd prior art example. It is the schematic diagram which showed the physical layout example of the conventional two inductors.

  Hereinafter, embodiments for implementing a transimpedance amplifier according to the present invention will be described with reference to the drawings.

First, the operation principle of the transimpedance amplifier according to the present invention will be described.
The transimpedance amplifier according to the present invention is a transimpedance amplifier that receives a current signal converted from an optical signal and outputs a voltage signal. The transimpedance amplifier includes a source grounding circuit, a source follower circuit, and a negative feedback resistor. By providing two inductors having inductive coupling or two or more inductors, it is possible to widen the gain frequency characteristics.

  The transimpedance amplifier includes a first inductor that constitutes a load impedance of the source grounded circuit and a second inductor connected in series with a negative feedback resistor, and the first inductor and the second inductor are inductive. It was set as the structure provided with connectivity.

  A first inductor that constitutes a load impedance of the source grounded circuit; a second inductor that connects an output terminal of the source grounded circuit and an input terminal of the source follower circuit; and the first inductor and the second inductor. Is configured to have inductive coupling.

  Therefore, according to the transimpedance amplifier according to the present invention, the gain frequency characteristic can be widened by minimizing the increase in chip size by the two inductors having the inductive coupling property.

ここで、Ｒ_Fは負帰還抵抗、Ｃ_inはフォトディテクタ等の入力寄生容量、Ａ_oは増幅回路のオープンループ利得である。
上記式（３）より、トランスインピーダンスアンプのオープンループ利得Ａ_oを大きくすると、３ｄＢダウンの周波数帯域ｆ_3dBも大きくすることができることが分かる。 As described above, the optical receiver converts the optical signal input to the photodetector into a current signal in the photodetector, and then the transimpedance amplifier performs impedance conversion on the voltage signal. As described above, the band of the transimpedance amplifier is mainly limited by the frequency characteristic of the input circuit, and can be expressed as the following formula (3).

Here, R _F is a negative feedback resistor, C _in is an input parasitic capacitance such as a photodetector, and A _o is an open loop gain of the amplifier circuit.
From the formula (3), increasing the open loop gain A _o of the transimpedance amplifier, it can be seen that it is possible to increase also the frequency band f _3dB of 3dB down.

Further, the open loop gain A _o can be simply expressed as the following equation (4) by the transconductance g _{m of the} transistor and the load impedance Z _L.

トランジスタのトランスコンダクタンスｇ_mは周波数特性を持つため、高周波で劣化し帯域に制限がかかるが、上記式（５）のようにインダクタＬ_Lを追加することにより、インダクティブピーキングでは高周波でこの劣化を補うことが可能である。 Here, in the case of inductive peaking in which the load is configured by the resistor R _L and the inductor L _L , it can be expressed as the following formula (5).

Since the transconductance g _{m of the} transistor has a frequency characteristic, it deteriorates at a high frequency and limits the band. However, inductive peaking compensates for this deterioration at high frequency by adding an inductor L _L as shown in the above equation (5). It is possible.

  Furthermore, inductive peaking using a plurality of inductors, the inductive coupling of each inductor plays a role in assisting the operating current of each inductor, and each inductor is independent. A higher band improvement effect than peaking can be obtained.

磁気的に結合された２つの巻線の一方の電流Ｉ₁を変化させると、もう一方の巻線に誘導起電力が生じる。その大きさｅ₂は、下記式（７）のようになる。

Next, a description will be given of widening the bandwidth of a transimpedance amplifier using an inductor having inductive coupling.
The inductor is formed of a winding, and when the current flowing through the winding changes, the magnetic flux passing through the winding changes, and an induced electromotive force is generated in a direction that cancels the change of the magnetic flux by the magnetic flux. When L is a self-inductance and I is a current flowing through the inductor, the magnitude of the induced electromotive force e is expressed by the following formula (6).

When the current I ₁ of one of the two magnetically coupled windings is changed, an induced electromotive force is generated in the other winding. The magnitude e ₂ is expressed by the following formula (7).

ここで、ｋは結合係数、Ｌ₁は第１のインダクタの自己インダクタンス、Ｌ₂は第２のインダクタの自己インダクタンスである。そして、上述した誘導結合性を有するインダクタを用いることにより、以下に示すようにトランスインピーダンスアンプの周波数特性を改善できる。 Here, the mutual inductance M is expressed by the following formula (8).

Here, k is a coupling coefficient, L ₁ is the self-inductance of the first inductor, and L ₂ is the self-inductance of the second inductor. By using the inductor having the inductive coupling property described above, the frequency characteristics of the transimpedance amplifier can be improved as described below.

First, in the transimpedance amplifier, by using an inductor having inductive coupling for the load of the source grounded circuit, the open loop gain _Ao can be improved at a high frequency as shown below.

In a conventional transimpedance amplifier without an inductor having inductive coupling, the open loop gain A _o is given by the following equation (9) as described above.

上記式（１０）に示すように、インダクタＬ_LにｋＭが加算されるため高周波で開ループ利得Ａ_oは大きくなる。先に示したようにトランスインピーダンスアンプにおいて、開ループ利得Ａ_oが大きいと入力インピーダンスが低減さるため、トランスインピーダンスアンプの帯域向上効果が得られる。 On the other hand, in the transimpedance amplifier according to the present invention using the mutual inductance M, the open loop gain _Ao is expressed by the following equation (10).

As shown in the above equation (10), since kM is added to the inductor L _L , the open loop gain A _o increases at high frequencies. As described above, in the transimpedance amplifier, when the open loop gain _Ao is large, the input impedance is reduced, so that the band improvement effect of the transimpedance amplifier can be obtained.

ここで、αは周波数帯域を決める極である。一方、相互インダクタンスＭを用いた本発明に係るトランスインピーダンスアンプにおいては、Ｚ_tは、下記式（１２）のように表される。

すなわち、負帰還ループ部のインダクタＬ_fにｋＭが加算されるため、利得が低下する高周波で負帰還抵抗Ｒ_Fが大きくなり、トランスインピーダンスアンプの帯域向上効果が得られる。 Second, by using an inductor having inductive coupling for the negative feedback resistor R _F , it is possible to increase the bandwidth of the transimpedance amplifier as shown below.
The impedance conversion gain Z _t of the transimpedance amplifier in which the inductor is connected to the negative feedback loop is expressed by the following formula (11).

Here, α is a pole that determines the frequency band. On the other hand, in the transimpedance amplifier according to the present invention using the mutual inductance M, Z _t is expressed by the following formula (12).

That is, since kM is added to the inductor L _f in the negative feedback loop section, the negative feedback resistance R _F becomes large at a high frequency where the gain is reduced, and the effect of improving the band of the transimpedance amplifier can be obtained.

  Third, by using an inductor having inductive coupling property as the third inductor connecting the source grounded circuit and the source follower circuit, it is possible to widen the transimpedance band as shown below.

  In a transimpedance amplifier that receives a large input signal, a transistor having a large size is used in a source follower circuit in order to flow a large signal current. However, if the size is large, it is affected by band deterioration due to parasitic capacitance. By connecting a split inductor between the output terminal of the source ground circuit and the input terminal of the source follower circuit, it is possible to improve the band degradation due to the parasitic capacitance.

FIG. 8 is a schematic diagram showing a circuit in which an inductor is connected to the gate terminal of the MOSFET. 8A is a diagram showing the parasitic capacitance C _gs between the gate and the source of the transistor and the parasitic capacitance C _gd between the gate and the drain. FIG. 8B is an equivalent input resistance R _in of the transistor and the parasitic capacitance C _gd . an equivalent input capacitance C _in consisting of capacity is a diagram showing an equivalent circuit in which the inductor L _S is connected to the gate terminal of the transistor.

すなわち、トランジスタの寄生容量により高周波では、ソースフォロワ回路の入力インピーダンスが小さくなってしまい信号伝達帯域が劣化する。 Input impedance Z _in of the source follower circuit in a simple manner, is expressed by the following equation (13).

That is, the input impedance of the source follower circuit is reduced at high frequencies due to the parasitic capacitance of the transistor, and the signal transmission band is degraded.

すなわち、ソースフォロワ回路の入力インピーダンスＺ_inの高周波での劣化を改善することができ、トランスインピーダンスアンプの帯域向上効果が得られる。 On the other hand, the above equation (13) can be expressed as the following equation (14) by connecting an inductor in series with the input.

That is, it is possible to improve the deterioration in the high frequency input impedance Z _in of the source follower circuit, the bandwidth improvement of the transimpedance amplifier is obtained.

  Furthermore, since an inductor having inductive coupling can form a plurality of inductors within the area of one conventional inductor, the area can also be reduced to less than half that of a conventional transimpedance amplifier.

  Therefore, according to the transimpedance amplifier according to the present invention, the gain frequency characteristic which is limited by the performance of the transistor and cannot be improved by the conventional transimpedance amplifier can be greatly improved.

  Furthermore, even when a plurality of inductors are used, the chip area can be made substantially equal. Thereby, a transimpedance amplifier capable of high-speed operation at low cost can be provided.

The first embodiment of the transimpedance amplifier according to the present invention will be described below.
FIG. 1 is a schematic diagram showing the configuration of a transimpedance amplifier according to a first embodiment of the present invention. 1A is a circuit configuration diagram of the transimpedance amplifier according to the first embodiment of the present invention, and FIG. 1B is a configuration of the impedance element in the transimpedance amplifier according to the first embodiment of the present invention. FIG. 1C is a diagram showing an example, and FIG. 1C is a diagram showing a configuration example in which a plurality of inductors in the transimpedance amplifier according to the first embodiment of the present invention are inductively coupled.

As shown in FIG. 1 (a), a transimpedance amplifier according to the present embodiment, the source-grounded amplifier comprising a first impedance Z _L 10 and the first transistor M ₁ 13 and the source resistance R _S 16 Metropolitan as a load A negative feedback loop that connects the circuit 1, the source follower circuit 2 including the second transistor M ₂ 14 and the third transistor M ₃ 15, the input terminal of the common source amplifier circuit 1, and the output terminal of the source follower circuit 2. The second impedance Z _F 11 of negative feedback and the third impedance Z _S 12 connecting the output terminal of the common source amplifier circuit and the input terminal of the source follower circuit 2 are configured. In FIG. 1A, I _in is a current signal, V _out is a voltage signal, VDD is a drain side power source, VSS is a source side power source, and V _CS is a constant source voltage.

As shown in FIG. 1B, the first impedance Z _L 10, the second impedance Z _F 11, and the third impedance Z _S 12 are each composed of a resistor R17 and an inductor L18.

Furthermore, at least two inductors L among the inductors L constituting the first impedance Z _L 10, the second impedance Z _F 11, and the third impedance Z _S 12 are inductively coupled. FIG. 1C shows a configuration example when two inductors L are inductively coupled.

  FIG. 2 is a schematic diagram showing a physical layout example of two inductors. 2A is a diagram showing a physical layout example of two conventional inductors without inductive coupling, and FIG. 2B is a physical layout of two inductors with inductive coupling according to the present invention. It is the figure which showed the example. In FIG. 2B, the first inductor is indicated by a solid line and the second inductor is indicated by a broken line so that the determination can be easily performed.

  As shown in FIG. 2B, when two spiral inductors are wound and laid out, the current flowing through one inductor changes, so that the magnetic flux changes, and an induced electromotive force is generated in the other inductor. The high frequency characteristics of the transimpedance amplifier can be improved by the mutual inductance M caused by the induced electromotive force.

  Further, the size of the transistor used in the transimpedance amplifier is about several microns square, whereas the inductor is as large as several hundred microns square. Therefore, according to the present invention in which two spiral inductors are coupled, The area can be almost halved with respect to the configuration using the two inductors.

  The spiral inductor described above may be a meander inductor in which a transmission line is bent. In this case, an inductor having inductive coupling characteristics can be obtained by bringing the meander inductor close to each other.

  Moreover, although the example which used the field effect transistor (FET) was shown as a transistor which comprises the above-mentioned transimpedance amplifier, the same effect can be acquired even if it uses a bipolar transistor.

Hereinafter, a second embodiment of the transimpedance amplifier according to the present invention will be described.
FIG. 3 is a schematic diagram showing the configuration of a transimpedance amplifier according to the second embodiment of the present invention.

As shown in FIG. 3, the transimpedance amplifier according to this embodiment includes a common source amplifier circuit 1 including a load resistor R _L 21, a first transistor M ₁ 13, and a source resistor R _S 16, and a second transistor. In the transimpedance amplifier including the source follower circuit 2 including M ₂ 14 and the third transistor M ₃ 15, the first inductor L _L 20 is connected in series with the load resistor R _L 21 of the common source amplifier circuit 1. A second inductor L _F 22 is connected in series with the negative feedback resistor R _F 23 to a negative feedback loop connecting the input terminal of the source-grounded amplifier circuit 1 and the output terminal of the source follower circuit 2, and further, the first inductor L _L 20 and a second inductor L _F 22 are inductively coupled by a mutual inductance M. In FIG. 3, I _in is a current signal, V _out is a voltage signal, VDD is a drain side power supply, VSS is a source side power supply, and V _CS is a constant source voltage.

Here, an operation example of the transimpedance amplifier according to the present embodiment will be described.
FIG. 4 is a diagram showing frequency characteristics of impedance conversion gain in the transimpedance amplifier according to the second embodiment of the present invention. In FIG. 4, the solid line indicates the simulation result of the transimpedance amplifier according to the present embodiment, the broken line indicates the simulation result of the transimpedance amplifier according to the first conventional example shown in FIG. 10, and the alternate long and short dash line in FIG. The simulation result of the transimpedance amplifier using the inductive peaking according to the second conventional example shown in FIG. The analysis data is obtained by simulation using a circuit simulator “HSPICE” of Synopsys.

  From FIG. 4, according to the transimpedance amplifier according to the present embodiment, the transimpedance amplifier according to the first conventional example is approximately twice as large as the transimpedance amplifier using the inductive peaking according to the second conventional example. It can be seen that a 1.5 times wider bandwidth characteristic is obtained.

As described above, in the transimpedance amplifier according to the present embodiment, the load resistor R _L 21 and the first inductor L _L 20 are connected in series to the load of the first stage of the transimpedance amplifier, and the negative feedback resistor R is connected to the negative feedback loop. _A second inductor L _F 22 is connected in series with _F 23, and the first inductor L _L 20 and the second inductor L _F 22 are inductively coupled.

With the configuration of the transimpedance amplifier according to the present embodiment, when a signal current is input to the transimpedance amplifier, a current flows through the second inductor L _F 22, so that the first inductor L that is inductively coupled according to the current flows. _An induced electromotive force is generated in L20, and the impedance becomes equivalently high at high frequencies.

On the other hand, when a current flows through the first inductor L _L 20, an induced electromotive force is generated in the second inductor L _F 22 inductively coupled in accordance with the current, and the negative feedback resistor R _F 23 is equivalent in high frequency. growing. Therefore, according to the configuration of the transimpedance amplifier according to the present embodiment, the frequency characteristics can be improved by these synergistic effects.

  In particular, in the configuration of the transimpedance amplifier according to the present embodiment, an inductor is used for each of the load impedance portion and the negative feedback impedance portion, which are factors that determine the characteristic gain band characteristics in the transimpedance amplifier, and inductive coupling is performed between these two inductors. This is the first effective configuration for a transimpedance amplifier.

Note that the connection order between the load resistor R _L 21 and the drain-side power source VDD of the first inductor L _L 20 and the drain terminal of the first transistor M ₁ 13 in this embodiment shown in FIG. As shown in FIG. 5, the order may be reversed, or the connection order of the negative feedback resistor R _F 23 and the second inductor L _F 22 may be reversed.

The third embodiment of the transimpedance amplifier according to the present invention will be described below.
FIG. 6 is a schematic diagram showing the configuration of a transimpedance amplifier according to the third embodiment of the present invention.

As shown in FIG. 6, the transimpedance amplifier according to this embodiment includes a common source amplifier circuit 1 including a load resistor R _L 21, a first transistor M ₁ 13, and a source resistor R _S 16, and a second transistor. In a transimpedance amplifier composed of a source follower circuit 2 composed of M ₂ 14 and a third transistor M ₃ 15, a first inductor L _L 20 is connected in series to a load resistance R _L 21 of the common source amplifier circuit 1, A negative feedback resistor R _F 23 is connected to the negative feedback loop connecting the input terminal of the ground amplifier circuit 1 and the output terminal of the source follower circuit 2, and the second terminal is connected between the output terminal of the source ground amplifier circuit 1 and the input terminal of the source follower circuit 2. 3 of inductor L _S 30 is connected, furthermore, to the first inductor _L L 20 third inductor L _S 30 is inductively coupled It is configured Ri. In FIG. 6, VDD indicates a drain side power source, VSS indicates a source side power source, and V _CS indicates a constant source voltage.

As described above, in the transimpedance amplifier according to this embodiment, the load resistance R _L 21 and the first inductor L _L 20 are connected in series to the load impedance of the source grounded amplifier circuit 1 in the first stage of the transimpedance amplifier, and the source grounded. A third inductor L _S 30 that connects the output terminal of the amplifier circuit 1 and the input terminal of the subsequent source follower circuit 2 is inductively coupled.

With the configuration of the transimpedance amplifier according to the present embodiment, when a signal current is input to the transimpedance amplifier circuit, a current flows through the third inductor L _S 30, and the first inductor L _L 20 that is inductively coupled according to this flows. Inductive electromotive force is generated at the high frequency and becomes equivalently high impedance at high frequencies.

On the other hand, when a current flows through the first inductor L _L 20, an induced electromotive force is generated in the third inductor L _S 30 inductively coupled in accordance with this, and the band degradation due to the parasitic capacitance of the transistor at a high frequency by the inductively coupled inductor. Can be compensated. Therefore, according to the configuration of the transimpedance amplifier according to the present embodiment, the frequency characteristics can be improved by these synergistic effects.

The connection order between the load resistor R _L 21 and the drain-side power source VDD of the first inductor L _L 20 and the drain terminal of the first transistor M ₁ 13 in this embodiment shown in FIG. The reverse is also possible as shown in.

  As described above, according to the transimpedance amplifier according to the present invention, in the transimpedance amplifier that converts an optical signal by photoelectric conversion to obtain a photoelectric current, and converts and amplifies the photoelectric current into a voltage signal, gain frequency characteristics are obtained. Can be widened. That is, a transimpedance capable of high-speed operation can be provided.

  In particular, due to the effect of the mutual inductance M, the same effect can be obtained without increasing the value of each inductor, so that the band can be improved without increasing the chip size. Furthermore, according to the present invention, when the conventional wideband technology using a plurality of chip inductors is used, the chip size can be made almost the same while the chip size is increased, which is effective in reducing the cost and increasing the operation speed. is there.

  INDUSTRIAL APPLICABILITY The present invention can be used, for example, in a transimpedance amplifier that performs signal equalization in an optical receiver circuit that performs photoelectric conversion of an optical transmission system, and in particular, a transimpedance amplifier having a wide-band gain frequency characteristic that can be operated at high speed. Can be used.

  Specifically, optical receiver ICs used in various optical transmission systems such as optical backbone transmission systems, optical access systems, and optical interconnections, high-speed optical receiver modules using the same, optical receiver transceivers, etc. Can be used.

1 Source-grounded amplifier circuit 2 Source follower circuit 10 First impedance Z _L
11 Second impedance Z _F
12 Third impedance Z _S
13 First transistor M ₁
14 Second transistor M ₂
15 Third transistor M ₃
16 Source resistance R _S
17 Resistance R
18 Inductor L
20 First inductor L _L
21 Load resistance R _L
22 Second inductor L _F
23 Negative feedback resistance R _F
30 Third inductor L _S

Claims (3)

In a transimpedance amplifier that receives a current signal converted from an optical signal and outputs a voltage signal,
A grounded source amplifier circuit, a source follower circuit, a negative feedback resistor, and two inductors having inductive coupling,
The transimpedance amplifier, wherein the inductor is a first inductor constituting a load impedance of the common source amplifier circuit and a second inductor connected in series with the negative feedback resistor. In a transimpedance amplifier that receives a current signal converted from an optical signal and outputs a voltage signal,
A grounded source amplifier circuit, a source follower circuit, a negative feedback resistor, and two inductors having inductive coupling,
The inductor is a first inductor that constitutes a load impedance of the common source amplifier circuit, and a second inductor that connects an output terminal of the common source amplifier circuit and an input terminal of the source follower circuit. Transimpedance amplifier. The second inductor and the first inductor constituted by spiral inductors, claim, characterized in that to inductive coupling by overlapping the first inductor and the second inductor 1 or claim 2 Transimpedance amplifier described in 1.

Images