JP2009077142A - Low-noise amplifying circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-noise amplifying circuit using an MOSFET which can satisfy an input matching characteristic and a low noise characteristic. <P>SOLUTION: A low-noise amplifying circuit has an input terminal connected to a signal source, an amplifying unit amplifying an input signal of the input terminal, and a terminal circuit having input impedance provided between the input terminal and the amplifying unit and matching with the impedance of a signal source. The terminal circuit has a grounded-gate transistor in which a load impedance circuit is connected to a drain and the input terminal is connected to a source, and the source and the drain of the grounded-gate are connected to the input of the amplifying unit through first and second capacity elements. When thermal noise is generated in the grounded-gate transistor, a voltage variation is generated in the source, and a voltage variation obtained by multiplying a gain of the grounded-gate transistor by the source voltage variation is generated in the drain in a reverse phase. Therefore, by connecting the voltage variation of the source and the voltage variation of the reverse phase of the drain to the amplifying unit with the first and the second capacity elements, an influence of the thermal noise of the grounded-gate transistor can be controlled or removed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a low noise amplifying circuit, and more particularly to a low noise amplifying circuit comprising a MOSFET and having reduced thermal noise.

  Along with the miniaturization and power saving of portable wireless devices, it is desired that the low noise amplifier circuit (LNA) provided in the input unit of the wireless receiver is constituted by a MOSFET instead of a conventional bipolar transistor. However, since the MOSFET itself generates thermal noise, it is necessary to suppress this thermal noise.

  Low noise amplifier circuits are required to have input matching characteristics and low noise characteristics. Since the low-noise amplifier circuit is provided at the input section of the wireless receiver, input from the antenna is achieved by matching the input impedance of the low-noise amplifier circuit with the impedance of the coaxial cable or filter provided on the input side of the low-noise amplifier circuit. Can be input efficiently without reflection. Further, by reducing the noise, a finer input signal can be received without being buried in noise.

The low noise amplifier circuit is described in, for example, the following Patent Documents 1, 2, 3, and Non-Patent Document 1.
JP-A-11-31931 JP 2005-64747 A JP 2002-271147 A F.Bruccoleri, B.Nauta et al., “Wide-Band CMOS Low-Noise Amplifier Exploiting Thermal Noise Canceling,” IEEE Journal of Solid-State Circuits, Vol. 39, pp.275-282, Feb. 2004

  In order to realize low noise characteristics, it is necessary to reduce the input conversion noise of the MOSFET. In particular, the MOSFET itself has become a noise source due to the recent trend toward shorter channels due to higher integration. It has been found that the input conversion noise of the MOSFET can be reduced by increasing the mutual conductance gm of the MOSFET.

  However, it is difficult to increase both the mutual conductance gm and the input matching characteristics. For example, in the case of a grounded gate amplifier circuit, if the input impedance Zin = 1 / gm is made equal to the signal source impedance Rs on the input side, good input matching characteristics can be realized in a wide band. However, as described above, in order to reduce the thermal noise of the MOSFET, there is a restriction that the mutual inductance gm is made as large as possible, and it is not easy to achieve both the input matching characteristics.

  Furthermore, in the case of a grounded source amplifier circuit, the input is connected to the gate of the MOSFET, so the input impedance is capacitive (open terminal with infinite impedance), and a termination circuit with good input matching characteristics in a wide band is gated. Must be provided at the input stage. However, if this termination circuit is composed of a resistor or a MOSFET, the thermal noise is added and the noise index (NF) of the amplifier circuit becomes much larger than 1. In other words, it is difficult to reduce the noise even if a configuration in which the common source amplifier circuit and the termination circuit are combined and a good input matching characteristic is obtained.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a low noise amplifier circuit using a MOSFET that can satisfy an input matching characteristic and a low noise characteristic.

  Another object of the present invention is to provide a low noise amplifier circuit having a termination circuit having low noise characteristics and input matching characteristics.

  In order to achieve the above object, according to a first aspect of the present invention, a low noise amplifier circuit includes an input terminal connected to a signal source, an amplification unit that amplifies an input signal of the input terminal, and an input terminal. And a termination circuit having an input impedance that matches the impedance of the signal source. This termination circuit has a grounded-gate transistor having a drain connected to a load impedance circuit and a source connected to the input terminal, and the source and drain of the grounded-gate transistor are connected to the first and second capacitive elements, respectively. Coupled to the input of the amplification unit. When thermal noise occurs in the grounded-gate transistor, voltage variation occurs in the source, and voltage variation in the drain that is obtained by multiplying the source voltage variation by the gain of the grounded-gate transistor occurs in reverse phase. Therefore, the influence of the thermal noise of the grounded-gate transistor can be suppressed or eliminated by coupling the voltage fluctuation of the source and the voltage fluctuation of the reverse phase of the drain to the amplification unit by the first and second capacitive elements.

  According to the present invention, it is possible to obtain a low noise amplifier circuit using a MOSFET that can satisfy the input matching characteristic and the low noise characteristic. Further, it is possible to provide a low noise amplifier circuit having a termination circuit having low noise characteristics and input matching characteristics.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments, but extends to the matters described in the claims and equivalents thereof.

A miniaturized MOSFET generated by a recent CMOS process has a short channel and itself becomes a noise source. The input conversion noise ν _n of the MOSFET is as shown in the following equation (1). Here, k _B is the Boltzmann constant, T is the temperature, γ is the noise coefficient of the MOSFET, and gm is the mutual conductance of the MOSFET.

上記（１）式によれば，相互コンダクタンスｇｍをできるだけ大きくすることで，入力換算雑音を低減することができる。

According to the above equation (1), the input conversion noise can be reduced by increasing the mutual conductance gm as much as possible.

By the way, when the low-noise amplifier circuit is composed of a grounded-gate transistor, an input signal is input to the source of the grounded-gate transistor, and an amplified signal is output from the drain. In this case, the input impedance Zin of the common-gate transistor is Zin = 1 / gm. Therefore, if this input impedance Zin is made equal to the signal source impedance R _s , good input matching characteristics can be realized in a wide band. However, as described above, in order to reduce the thermal noise of the MOSFET, it is necessary to increase the mutual conductance gm as much as possible, and it is difficult to achieve both thermal noise reduction and input matching characteristics.

On the other hand, when the low noise amplifier circuit is composed of a common source transistor, an input signal is input to the gate of the common source transistor, and an amplified signal is output from the drain. Also in this case, if the mutual conductance gm is made as large as possible, the thermal noise of the MOSFET can be reduced. However, since the gate is a capacitive terminal formed of a gate oxide film, in order to perform impedance matching with the signal source impedance R _s , it is necessary to provide a termination circuit having good input matching characteristics in a wide band at the input terminal.

FIG. 1 is a diagram illustrating an example of a common source amplifier circuit. FIG. 1 shows a low noise amplifier circuit LNA in which a signal source V _s having a signal source impedance R _s is connected to an input terminal IN, amplifies an input signal of the input terminal IN, and outputs the amplified signal from the output terminal OUT. . The low noise amplifier circuit LNA is provided between a source grounded transistor Q1 having a source connected to the ground Vss, a drain connected to the load impedance _RL , and an input signal input to the gate, and the input terminal IN and the gate. constituted by the termination circuit TC consisting resistive element R _M.

A minute input signal received by an antenna (not shown) is input to the input terminal IN via a coaxial cable or a filter. Impedance of the coaxial cable and the filter corresponds to the signal source impedance R _s. Then, if the resistance value _{R M} of the resistive element _{R M} of the termination circuit TC is equal to the signal source impedance _{R s (R M = R S} ), good input matching characteristics can be obtained, the input signal is at the gate of the transistor Q1 There is no reflection.

However, the noise index NF of this circuit includes the noise 4k _B TR _S of the signal source impedance R _s , the noise 4k _B TR _M of the resistance element RM of the termination circuit, and the source ground as shown in the following formula (2). It is obtained by dividing the sum of the noise 4k _B Tγ / gm of the transistor Q1 by the noise 4k _B TR _S of the signal source impedance R _s .

上記（２）式では，インピーダンス整合の条件Ｒ_Ｍ＝Ｒ_Ｓに基づいて簡略化されている。

In the above equation (2), the impedance matching condition R _M = R _S is simplified.

  According to equation (2), it can be seen that the noise index NF exceeds 2 no matter how large the mutual conductance gm is. The noise index is obtained by normalizing the entire noise with the noise of the signal source, and is in an ideal state where NF = 1 when no noise other than the noise of the signal source is generated. In other words, the expression (2) means that noise equal to or higher than the noise of the signal source is generated in the low noise amplifier circuit LNA.

  FIG. 2 is a diagram illustrating another example of the common-source amplifier circuit. In this example, the termination circuit TC is composed of a MOSFET Q2 having a common gate. The rest is the same as FIG. The grounded transistor Q2 of the termination circuit TC has a constant voltage V2 applied to the gate, a drain connected to the power supply Vdd, and a source connected to the input terminal IN. The source node n2 is connected to the gate of the common source transistor Q1 via the capacitive element C0.

The input impedance viewed from the source terminal of the common-gate transistor Q2 is 1 / gmM (gmm is the mutual conductance of Q2). Therefore, in order to obtain the input matching characteristics, be equal to the input impedance 1 / GMM source impedance _{R s} and the transistor Q2 is required _{(R s = 1 / gmM)} .

However, noise index NF of this circuit, as shown in the following equation (3), the noise 4k _B TR _S of the signal source impedance _{R s,} and noise 4k _B Tγ / gmM gate-grounded transistor Q2 termination circuit, It is obtained by dividing the sum of the noise 4 k _B Tγ / gm of the common source transistor Q1 by the noise 4 k _B TR _S of the signal source impedance R _s .

上記（３）式では，インピーダンス整合の条件Ｒ_ｓ＝１／ｇｍＭに基づいて簡略化されている。（３）式によれば，相互コンダクタンスｇｍをどんなに大きくしても，雑音指標ＮＦは１＋γを上回ってしまうことがわかる。しかも，古い世代の微細化されていないＭＯＳＦＥＴの場合はＭＯＳＦＥＴの雑音係数γは２／３程度であったが，近年の微細化されたＭＯＳＦＥＴでは雑音係数γは２〜３と高くなっている。よって，上記の雑音指標ＮＦの相互コンダクタンスｇｍを大きくしても３〜４を上回ることになる。

The expression (3) is simplified based on the impedance matching condition R _s = 1 / gmM. According to equation (3), it can be seen that no matter how large the mutual conductance gm is, the noise index NF exceeds 1 + γ. In addition, in the case of an old generation unminiaturized MOSFET, the noise coefficient γ of the MOSFET is about 2/3, but in recent miniaturized MOSFETs, the noise coefficient γ is as high as 2-3. Therefore, even if the mutual conductance gm of the noise index NF is increased, it exceeds 3-4.

  As described above, it is difficult to reduce noise in the amplifier circuits of FIGS. 1 and 2 even if good input matching characteristics are obtained.

FIG. 3 is a diagram showing a basic configuration of the low noise amplifier circuit according to the present embodiment. Low noise amplifier circuit LNA of FIG. 3, the signal source V _s having a signal source impedance R _s to the input terminal IN is connected. An inductance element Li is connected to the input terminal IN. Further, the low noise amplifier circuit LNA has a source grounded transistor Q1 whose source is grounded, whose drain is connected to the power supply Vdd via the load impedance _{RL, and} whose gate is inputted with the input signal of the input terminal IN. This constitutes a common source amplifier circuit. Furthermore, the termination circuit TC which is provided between the gate input terminal IN and the transistor Q1 has a source n2 is connected to the input terminal IN, the drain n3 is connected to the power supply Vdd through a load impedance circuit R _M, the gate Has a common gate transistor Q3 connected to a constant voltage V3. That is, by connecting the load impedance circuit _{R M} to the gate grounding transistors Q3, constitute grounded-gate amplifier circuit voltage gain _A M ₌ R M · _gmM. The termination circuit TC includes first and second capacitive elements C1 and C2 that couple the source terminal n2 and the drain terminal n3 of the transistor Q3 to the output terminal n4 of the termination circuit. The common source transistor Q1 and the common gate transistor Q3 are N-channel MOSFETs. However, these can also be constituted by P-channel MOSFETs.

FIG. 4 is a diagram showing a functional configuration of the low-noise amplifier circuit of FIG. The low noise amplifier circuit LNA in FIG. 4 has the same configuration as in FIG. That is, the signal source 10 is connected to the matching amplifier stage 12 comprising a gate grounding transistors Q3, is set equal to the input impedance of the matching amplifier stage 12 is a signal source impedance R _s. In this case, noise generated from the common-gate transistor Q3 of the matching amplification stage 12 causes a voltage fluctuation at the source terminal n2. However, due to the amplification function of the common-gate transistor Q3, a negative-phase voltage fluctuation obtained by multiplying the voltage fluctuation by the voltage gain of the transistor Q3 occurs at the drain terminal n3. Therefore, if the source terminal n2 and the drain terminal n3 are coupled to the node n4 by the coupling circuit 14 composed of the first and second capacitive elements C1 and C2, the voltage fluctuation of the source terminal n2 caused by the thermal noise of the transistor Q3 can be reduced. , It is possible to cancel out the voltage fluctuation in the reverse phase of the drain terminal n3. For the common source transistor Q1, the thermal noise caused by the transistor Q1 can be reduced by increasing the mutual conductance gm as much as possible. As a result, the noise index NF of the low noise amplifier circuit LNA can be as close to 1 as possible.

Note that a negative phase voltage fluctuation obtained by multiplying the voltage fluctuation of the source terminal n2 by a gain occurs at the drain terminal n3 of the common-gate transistor Q3, so that the capacitance ratio C1: between the first and second capacitive elements C1, C2 of the coupling circuit. By making C2 as close as possible to the voltage gain A _M : 1, the thermal noise caused by the transistor Q3 can be removed. However, since the voltage gain A is affected by process variations, it is not always easy to accurately generate C1: C2 = A _M : 1, but thermal noise can be reduced by setting at least C1> C2. become.

The above principle will be described in detail as follows. First, the impedance of the capacitor C1, C2 in the frequency band of the received signal is greater than the source impedance R _s. In this case, the input impedance Zin of the termination circuit TC is Zin = 1 / GMM, consisting in order to obtain good input matching characteristic is Zin = _{R S,} assuming that satisfy gmM = 1 / _{R S} . Therefore, the voltage gain _{A M} of the gate grounded _circuit, since it is A M = GMM · _{R M,} becomes _{A M = R M / R S} .

Therefore, it is assumed that the thermal noise of the transistors Q3, noise current i _n occurs toward the source end from the drain end. The noise voltage is generated by a noise current i _n to the source terminal n3 and the drain terminal n2.

Since signal source impedance R _s and the transistor Q3 to the source terminal n3 and (impedance 1 / GMM) are connected in parallel, the noise voltage generated at the source terminal n3 is the parallel resistance to noise current i _n resistor The value is multiplied by (4). In the equation (4), the arrangement is based on gmM = 1 / _RS .

一方，ドレイン端子ｎ２には，ソース側と同じノイズ電流−ｉ_ｎが発生すると共に，トランジスタＱ３の増幅作用により，（４）式のソース端子のノイズ電圧Ｒ_Ｓ・ｉ_ｎ／２に相互コンダクタンスｇｍＭを乗じた電流Ｒ_Ｓ・ｉ_ｎ・ｇｍＭ／２が発生する。ノイズ電流−ｉ_ｎではドレイン端子ｎ３に負のノイズ電圧が発生し，電流Ｒ_Ｓ・ｉ_ｎ・ｇｍＭ／２ではドレイン端子ｎ３に正のノイズ電圧が発生する。その結果，ドレイン端子ｎ２でのノイズ電圧は，前述の２つの電流に負荷インピーダンスＲ_Ｍを乗じて（５）式の通りになる。（５）式では，ｇｍＭ＝１／Ｒ_Ｓに基づいて整理されている。

On the other hand, the drain terminal n2 is with the same noise current -i _n and the source side is generated by the amplifying action of the transistor Q3, (4) expression of a noise voltage _R S · _i n / 2 transconductance gmM source terminal the current _{R S · i n · gmM /} 2 is generated by multiplying. Negative noise voltage is generated on the drain terminal n3 in noise current -i _n, positive noise voltage is generated in the current _{R S · i n · gmM /} 2 in drain terminal n3. As a result, the noise voltage at the drain terminal n2 will as multiplied by the load impedance R _M into two currents described previously (5). In the formula (5), it is arranged based on gmM = 1 / _RS .

つまり，（５）式のドレインノイズ電圧は，（４）式のソースノイズ電圧の電圧ゲイン倍になっていて，逆相である。したがって，このドレインに生じるノイズ電圧を利用することで，ソースに生じるノイズ電圧を抑制または望ましくは相殺して除去することができる。すなわち，ソース端子ｎ２とドレイン端子ｎ３とを容量素子Ｃ１，Ｃ２を介して結合することで，終端回路ＴＣの出力端子ｎ４でのゲート接地トランジスタＱ３に起因するノイズ電圧は，（６）式のとおりである。（６）式のノイズ電圧は，（４）（５）式のノイズ電圧が容量比Ｃ１：Ｃ２に基づいて結合されている。

That is, the drain noise voltage of the equation (5) is a voltage gain times the source noise voltage of the equation (4), and is in reverse phase. Therefore, by using the noise voltage generated at the drain, the noise voltage generated at the source can be suppressed or desirably canceled and canceled. That is, by coupling the source terminal n2 and the drain terminal n3 via the capacitive elements C1 and C2, the noise voltage caused by the common-gate transistor Q3 at the output terminal n4 of the termination circuit TC is expressed by the following equation (6). It is. The noise voltage of equation (6) is combined with the noise voltage of equations (4) and (5) based on the capacitance ratio C1: C2.

この（６）式の出力端子ｎ４でのノイズ電圧を０にするためには，（７）式が満たされる必要がある。その結果，（８）式のとおり，容量比Ｃ１／Ｃ２はトランジスタＱ３の電圧ゲインＡ_Ｍと等しくなる。

In order to reduce the noise voltage at the output terminal n4 of the equation (6) to 0, the equation (7) needs to be satisfied. As a result, (8) as, capacitive ratio C1 / C2 is equal to the voltage gain _{A M} of the transistor Q3.

以上の通り，図３の終端回路ＴＣのゲート接地増幅回路と結合容量Ｃ１，Ｃ２とにより，終端回路内のトランジスタＱ３に起因するノイズ電圧を抑制または望ましくは除去することができる。

As described above, the noise voltage caused by the transistor Q3 in the termination circuit can be suppressed or desirably removed by the common-gate amplifier circuit and the coupling capacitors C1 and C2 of the termination circuit TC in FIG.

Here, the voltage gain from the input terminal IN to the output terminal n4 of the termination circuit TC will be described. When the signal amplitude at the input terminal IN and Vin, the signal amplitude at drain terminal n3 of the gate grounded circuit Q3 becomes the voltage gain _{A M} = _gmM · _R M multiplied by the _A M · Vin to the input signal amplitude Vin. Therefore, since the signal amplitude A _M · Vin of the input signal amplitude Vin and the drain terminal n3 is coupled by capacitor C1, C2, the signal amplitude at the output terminal n4 becomes as (9).

この（９）式から終端回路ＴＣの入力ＩＮから出力ｎ４までの電圧ゲインは，（１０）式の通りになる。そして，前述の（８）式のトランジスタＱ３に起因するノイズが終端回路の出力端子ｎ４に現れない条件の場合は，（１０）式の電圧ゲインは，（１１）式のとおりになる。

From this equation (9), the voltage gain from the input IN to the output n4 of the termination circuit TC is as shown in equation (10). Then, under the condition that the noise caused by the transistor Q3 in the above-described equation (8) does not appear at the output terminal n4 of the termination circuit, the voltage gain in the equation (10) is as in the equation (11).

（１１）式でゲート接地トランジスタＱ３の電圧ゲインＡ_ＭをＡ_Ｍ＞１にすれば，（１１）式の電圧ゲインは１以上にすることができ，さらに，電圧ゲインＡ_Ｍを大きくすれば（１１）式の電圧ゲインは２に近づくことになる。よって，結合容量Ｃ１，Ｃ２を設けたとしても，終端回路ＴＣによる入力信号振幅Ｖinが減衰することはない。本実施の形態では，終端回路ＴＣを利用することで，入力信号を減衰することなく終端回路内のゲート接地トランジスタＱ３に起因するノイズを抑制または除去することができる。

(11) If equation voltage gain _{A M} of the gate-grounded transistor Q3 to _A M> 1, the expression (11) the voltage gain can be 1 or more, further, by increasing the voltage gain _{A M} ( The voltage gain in the equation (11) approaches 2. Therefore, even if the coupling capacitors C1 and C2 are provided, the input signal amplitude Vin by the termination circuit TC is not attenuated. In the present embodiment, by using the termination circuit TC, it is possible to suppress or eliminate noise caused by the common gate transistor Q3 in the termination circuit without attenuating the input signal.

  FIG. 5 is a diagram showing a specific circuit configuration of the low noise amplifier circuit according to the present embodiment. In this circuit configuration, the termination circuit TC is provided with a grounded gate transistor Q4 in addition to the grounded gate transistor Q3 so as to be in cascode connection. The drain terminal n5 of the transistor Q4 is coupled to the output terminal n4 through the capacitive element C2. Fixed potentials V3 and V4 are connected to the gates of the transistors Q3 and Q4, respectively.

  In general, in the case of an amplifier circuit using a grounded-gate transistor Q3 and a load impedance RM in the termination circuit TC of FIG. 3, ideally, the drain voltage with respect to the drain-source voltage VD is drained with respect to the gate voltage Vg in the saturation region. The current ID is constant. However, in an actual device, the drain current ID has a positive slope with respect to the drain-source voltage VD. Therefore, when the drain-source voltage VD changes due to the transistor amplification operation, the drain current ID also changes, and the effective voltage gain of the amplifier circuit is suppressed. Even if the mutual inductance gmM is increased, the effective voltage gain is about 10 dB. But it ’s pretty bad.

  Therefore, by adding the common-gate transistor Q4, the potential of the drain terminal n3 of the transistor Q3 can be maintained from the fixed voltage V4 to a potential lower than the threshold voltage of the transistor Q4, and the drain voltage VD of the transistor Q3 can be made constant. . As a result, the effective voltage gain can be set to a large value corresponding to the mutual conductance gmM, for example, 30 to 40 dB.

Therefore, by the cascode connection, may be able to increase the voltage gain A _M of the aforementioned (11), to increase the voltage gain according to the termination circuit TC.

In the circuit example of FIG. 5, the common source transistor Q1 is also cascode-connected. That is, the transistor Q1b having a fixed potential V1b applied to the gate is provided between the drain terminal of the source-grounded transistor Q1a and the load impedance _RL . As a result, for the same reason as the common gate transistors Q3 and Q4, the drain voltage of the common source transistor Q1a is kept constant, and the effective voltage gain of the common source transistor Q1 can be increased. A bias circuit composed of a resistor R1a and a low voltage V1a is connected to the gate of the common source transistor Q1a.

FIG. 6 is a diagram showing a modified example of the low-noise amplifier circuit in the present embodiment. In this example, it is provided two P-channel MOSFET Q5, Q6 of the cascode connected in parallel to the load resistor _{R M} of the termination circuit TC. Fixed potentials V5 and V6 are applied to the gates of the transistors Q5 and Q6. That is, the transistors Q5 and Q6 are cascode-connected constant current sources. 5, when the power supply voltage Vdd is not sufficiently high, only the load resistance R _M can not supply sufficient bias current. In contrast, in the case of FIG. 6, since there is provided a constant-current source transistors Q5, Q6 in parallel with the load resistor R _M, it is possible to supply voltage Vdd to provide the required bias current even be sufficiently high .

FIG. 7 is a diagram showing another modified example of the low-noise amplifier circuit according to the present embodiment. In this example, it is provided a capacitor C3 between the load resistor R _M and the power supply Vdd of the termination circuit TC. Thereby, the bias current is supplied only from the constant current source of the transistor Q5, Q6, not supplied from the load resistor R _M. Therefore, a constant bias current source can be obtained. However, the load resistor R _M is for high frequency signal acting as a load impedance.

  FIG. 8 is a diagram showing another modified example of the low-noise amplifier circuit according to the present embodiment. The circuit of FIG. 8 is an example in which the N-channel MOSFETs Q1a, Q1b, Q3, and Q4 of FIG. 5 are realized by P-channel MOSFETs. Termination circuit TC includes a cascade-connected gate grounded transistor formed of P-channel transistors Q3 and Q4, and coupling capacitors C1 and C2. Further, source-grounded amplification P-channel transistors Q1a and Q1b are also cascade-connected.

  Note that the load impedance circuit of the termination circuit TC of the circuit of FIG. 8 can be modified as shown in FIGS. In that case, the transistors Q5 and Q6 for supplying the bias current source are both N-channel transistors.

  The above embodiment is summarized as follows.

(Supplementary note 1) An input terminal connected to a signal source, an amplification unit that amplifies an input signal of the input terminal, and an input impedance that is provided between the input terminal and the amplification unit and matches the impedance of the signal source In a low noise amplifier circuit having a termination circuit having
The termination circuit includes a grounded-gate transistor having a drain connected to a load impedance circuit and a source connected to the input terminal, and the first and second capacitive elements coupling the source and drain to the input of the amplification unit, respectively. A low noise amplifier circuit.

(Appendix 2) In Appendix 1,
A low-noise amplifier circuit, wherein the first capacitor element of the coupling circuit has a larger capacitance than the second capacitor element.

(Appendix 3) In Appendix 1,
The low-noise amplifier circuit, wherein the first capacitive element and the second capacitive element of the coupling circuit have a capacitance ratio of voltage gain to 1 of the common-gate transistor.

(Appendix 4) In Appendix 1,
The grounded gate transistor includes first and second grounded gate transistors that are cascode-connected, and the drain of the first grounded gate transistor and the source of the second grounded gate transistor are connected to each other. The input terminal is connected to the source of the common-gate transistor, the load impedance circuit is connected to the drain of the second common-gate transistor, and the source of the first common-gate transistor and the second common-gate transistor are connected to each other. A low noise amplifier circuit, characterized in that a drain is coupled to an input of the amplification unit via the first and second capacitive elements.

(Appendix 5) In Appendix 1,
The load impedance circuit is a circuit in which a resistance element and a gate-grounded load transistor are connected in parallel.

(Appendix 6) In Appendix 5,
The load transistor of the load impedance circuit includes cascode-connected third and fourth gate-grounded transistors.

(Appendix 7) In Appendix 5,
The low-noise amplifier circuit, wherein the resistance element of the load impedance circuit is connected to a power source via a third capacitance element.

(Appendix 8) In Appendix 1,
The amplifying unit includes a common source transistor, and a low noise amplifying circuit.

(Appendix 9) In Appendix 1,
2. The low noise amplifier circuit according to claim 1, wherein the grounded gate transistor and the grounded source transistor are either an N-channel MOSFET or a P-channel MOSFET.

It is a figure which shows an example of a common source amplifier circuit. It is a figure which shows another example of a source grounding amplifier circuit. It is a figure which shows the basic composition of the low noise amplifier circuit in this Embodiment. It is a figure which shows the function structure of the low noise amplifier circuit of FIG. It is a figure which shows the specific circuit structure of the low noise amplifier circuit in this Embodiment. It is a figure which shows the modification of the low noise amplifier circuit in this Embodiment. It is a figure which shows another modification of the low noise amplifier circuit in this Embodiment. It is a figure which shows another modification of the low noise amplifier circuit in this Embodiment.

Explanation of symbols

LNA: Low noise amplifier circuit Q1: Common source transistor RL: Load impedance Q3: Common gate transistor RM: Load impedance circuit Vs: Signal source Rs: Signal source impedance

Claims (5)

An input terminal connected to a signal source, an amplification unit that amplifies the input signal of the input terminal, and a termination circuit that is provided between the input terminal and the amplification unit and has an input impedance that matches the impedance of the signal source In a low noise amplifier circuit having
The termination circuit includes a grounded-gate transistor having a drain connected to a load impedance circuit and a source connected to the input terminal, and the first and second capacitive elements coupling the source and drain to the input of the amplification unit, respectively. A low noise amplifier circuit. In claim 1,
A low-noise amplifier circuit, wherein the first capacitor element of the coupling circuit has a larger capacitance than the second capacitor element. In claim 1,
The low-noise amplifier circuit, wherein the first capacitive element and the second capacitive element of the coupling circuit have a capacitance ratio of voltage gain to 1 of the common-gate transistor. In claim 1,
The grounded gate transistor includes first and second grounded gate transistors that are cascode-connected, and the drain of the first grounded gate transistor and the source of the second grounded gate transistor are connected to each other. The input terminal is connected to the source of the common-gate transistor, the load impedance circuit is connected to the drain of the second common-gate transistor, and the source of the first common-gate transistor and the second common-gate transistor are connected to each other. A low noise amplifier circuit, characterized in that a drain is coupled to an input of the amplification unit via the first and second capacitive elements. In claim 1,
The amplifying unit includes a common source transistor, and a low noise amplifying circuit.

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