阅读说明：本技术 放大器 (Amplifier with a high-frequency amplifier ) 是由 苏米特·巴戈 于 2018-10-30 设计创作，主要内容包括：一种放大器(500),其包含：放大元件(M<Sub>1</Sub>),其具有跨第一端子和第三端子的电压输入以及第二端子与所述第三端子之间的电压控制电流路径；以及三线变压器,其具有初级绕组(L<Sub>p</Sub>)、次级绕组(L<Sub>s</Sub>)和第三绕组(L<Sub>T</Sub>)；其中所述初级绕组(L<Sub>p</Sub>)连接到所述第三端子,所述次级绕组(L<Sub>s</Sub>)连接到所述第一端子并且所述第三绕组(L<Sub>T</Sub>)连接到所述第二端子；其中所述初级绕组(L<Sub>p</Sub>)和所述次级绕组(L<Sub>s</Sub>)以反相关系相互耦合；其中所述初级绕组(L<Sub>p</Sub>)和所述第三绕组(L<Sub>T</Sub>)以非反相关系相互耦合；其中所述次级绕组(L<Sub>s</Sub>)和所述第三绕组(L<Sub>T</Sub>)以反相关系相互耦合；并且其中所述第三绕组(L<Sub>T</Sub>)在放大器输出与所述第二端子之间。(An amplifier (500), comprising: amplifying element (M) 1 ) Having a voltage input across a first terminal and a third terminal and a voltage controlled current path between a second terminal and the third terminal, and a three-wire transformer having a primary winding (L) p ) A secondary winding (L) s ) And a third winding (L) T ) Wherein the primary winding (L) p ) Connected to the third terminal, the secondary winding (L) s ) Connected to the first terminal and the third windingGroup (L) T ) Connected to the second terminal, wherein the primary winding (L) p ) And the secondary winding (L) s ) Are coupled to each other in an anti-correlation system, wherein the primary windings (L) p ) And the third winding (L) T ) Are coupled to each other in a non-anti-correlation system, wherein the secondary windings (L) s ) And the third winding (L) T ) Are coupled to each other in an anti-correlation system, and wherein the third winding (L) T ) Between the amplifier output and said second terminal.)

1. An amplifier, comprising:

an amplifying element having a voltage input across a first terminal and a third terminal and a voltage controlled current path between a second terminal and the third terminal; and

a three-wire transformer having a primary winding, a secondary winding, and a third winding;

wherein the primary winding is connected to the third terminal, the secondary winding is connected to the first terminal and the third winding is connected to the second terminal;

wherein the primary winding and the secondary winding are coupled to each other in an anti-correlation system;

wherein the primary winding and the third winding are coupled to each other in a non-anti-correlation system;

wherein the secondary winding and the third winding are coupled to each other in an anti-correlation system; and is

Wherein the third winding is between an amplifier output and the second terminal.

2. The amplifier of claim 1, wherein the effective turns ratio of each pair of windings is selected such that the real part of the amplifier input impedance is positive and the real part of the amplifier output impedance is positive.

3. The amplifier according to claim 1 or 2, wherein the effective turns ratio of each pair of windings is selected such that the phase difference between the first terminal and the third terminal is in the range of 120-240 degrees.

4. An amplifier as claimed in claim 1, 2 or 3, wherein the effective turns ratio of each pair of windings is selected such that the phase difference between the first and third terminals is in the range of 150 and 210 degrees.

5. The amplifier of any preceding claim, wherein the primary winding, the secondary winding and the third winding are all concentric, and wherein the primary winding separates the secondary winding from the third winding.

6. An amplifier as claimed in any preceding claim, wherein the primary winding is intertwined with the secondary or third winding.

7. The amplifier of claim 6, wherein the other of the secondary winding and the third winding is concentric with the intertwined windings.

8. The amplifier of any preceding claim, wherein the three-wire transformer is a stacked transformer formed in two metal layers, wherein the primary winding is stacked with one of the secondary winding and the third winding, and the primary winding is formed in the same layer and concentric with the other of the secondary winding and the third winding.

9. An amplifier as claimed in any preceding claim, wherein the secondary winding is shaped to have near zero mutual coupling with the third winding.

10. An amplifier as claimed in any preceding claim, wherein the amplifying element is a transistor.

11. The amplifier according to claim 10, wherein the transistor is a FET, preferably a MOSFET.

12. The amplifier of claim 11, wherein the FETs are arranged in a common gate configuration.

13. The amplifier of claim 12, wherein the primary winding is connected to a source of the FET, the secondary winding is connected to a gate of the FET, and the third winding is connected to a drain of the FET.

14. A method of amplifying a signal with an amplifying element comprising a voltage input across a first terminal and a third terminal, and comprising a voltage controlled current path between a second terminal and the third terminal, the method comprising:

applying the signal to a third terminal of the amplifying element;

sensing a voltage at the third terminal with a primary winding of a three-wire transformer;

coupling at least a portion of the sensed voltage from the third terminal in anti-phase to the first terminal of the amplifying element via a secondary winding of the three-wire transformer;

sensing a current at the second terminal with a third winding of a three-wire transformer;

coupling at least a portion of the sensed current from the second terminal to the third terminal of the amplifying element non-anti-phase via a third winding of the three-wire transformer; and is

Outputting the amplified signal from an output node positioned such that the third winding is between the output node and a second terminal.

Technical Field

The present invention relates to amplifiers, in particular to low noise amplifiers (L NA), and more particularly to low noise amplifiers that employ reactive components as part of an impedance and/or noise matching and gain boosting mechanism.

Background

However, as well as providing gain, it is also important that the L NA has a well-defined input impedance so that it matches the antenna power for maximum power transfer between the two blocks in the RF front-end.

A basic Common Gate (CG) L NA is shown in fig. 2 the basic amplifying element of amplifier 200 is transistor M₁From a DC current source I_DCBiased to a saturated state. Active gain is simply provided by transistor M₁Transconductance g of_mProviding, which is defined as the ratio of the output current to the input voltage (i)_out/v_in). As shown in FIG. 2, M₁Is AC grounded and maintained at a constant DC voltage, while the input signal RF_iIs applied to the source and thus changes the gate-source voltage, thereby generating a drain-source current. Output signal RF_oTaken from the drain. For a CG stage, the output current is approximately equal to the input current (i.e., intrinsic current gain is). Thus, the input impedance of a CG stage is defined as:

in order to set the input impedance to a certain value for impedance matching, it is necessaryIs to be mixed with₁The intrinsic transconductance is chosen to have a specific value, thus also determining the gain (g) of the amplifier_mAnd a load impedance Z_LThe product of (d). This limits the gain of the amplifier. For example, to obtain an input impedance of 50 Ω (typical impedance of an RF antenna), M₁It is necessary to have a transconductance of 20 milliamps per volt (mA/V).

Modification of the CG-L NA of fig. 2 uses a transformer to boost the transconductance g of the CG stage_mAnd thereby boost the gain of the amplifier, this modification is shown in fig. 3, except that a secondary winding L is provided_pAnd a secondary winding L_sThe amplifier 300 has the same basic arrangement as in fig. 2 except for the inverse transformer 310, primary winding L_pIs connected to the transistor M₁And secondary winding L_sConnected to the gate in an anti-correlation such that primary winding L_pSenses the input voltage, and secondary winding L_sAn inverted and proportional voltage is applied to the gate. Therefore, when the input voltage decreases, the gate voltage increases, and when the input voltage increases, the gate voltage decreases. Thus, the gate-source voltage is passively amplified by transformer 300, which in turn is coupled to M₁The intrinsic transconductance of (a) combine to result in a larger overall transconductance. The overall gain depends on the characteristics of the transformer 300, in particular its turns ratio n and its coupling coefficient k. For an ideal transformer, the coupling coefficient is 1, but in practice is always less than 1, usually 0.7-0.9 (moderate to strong mutual coupling). The input impedance of this amplifier 300 is defined as:

the transconductance of this amplifier 300 is increased by a factor of (1+ nk). However, from the point of view of impedance matching, in order to match a particular impedance, for example a 50 Ω antenna, it is still necessary to couple the transistor M₁Is specifically set at a particular level. Comparing amplifier 200 of FIG. 2 with amplifier 300 of FIG. 3, g_mThe enhanced amplifier 300 may use a smaller transistor M with a lower transconductance₁And/or power may be saved at lower DC currents. However, electricityThe circuit 300 is still constrained by the input impedance so that the signal gain is not improved overall. For example, for an ideal transformer 310 (where n is 1 and k is 1), M must be matched to an input impedance of 50 Ω₁Intrinsic transconductance g of_mFrom 20mA/V to 10 mA/V. The increased passive gain from transformer 310 must be provided by transistor M₁The reduced transconductance of (a) exactly cancels out.

Another amplifier 400 is shown in FIG. 4. in this circuit, amplifier 400 uses a current source having a primary winding L in a positive (current) feedback arrangement_pAnd a secondary winding L_sTransformer 410 primary winding L of transformer 410_pIs connected to the transistor M₁And secondary winding L_sConnected to source primary winding L_pThe current at the output (drain) is sensed and applied (non-inverted) at the input (source) in parallel with the input signal, increasing the pass transistor M₁And thus increases the overall current gain of the amplifier 400. The input impedance of this amplifier 400 is defined as:

where k is the coupling coefficient, n is the turns ratio, and k/n is the effective turns ratio of the transformer. Although the overall current gain of the amplifier 400 is greatly improved (much higher current gain can be obtained for a given input voltage), the circuit 400 still has limitations when viewed from an impedance matching perspective. This time, the factor (1-k/n) in the above equation means that for a given g_mThe input impedance increases. To compensate for this, and thus achieve impedance matching, transistor M must be added₁The intrinsic transconductance of (a). For example, for a transformer where n is 1 and k is 0.9, M must be matched to an input impedance of 50 Ω₁Intrinsic transconductance g of_mSet at 200 mA/V. Thus, while amplifier 400 results in higher current gain (10), the increased transconductance requires higher power consumption for impedance matching, which is far from ideal, particularly in portable and/or battery operated applicationsIn the application of electrical devices.

Disclosure of Invention

According to the present invention, there is provided an amplifier comprising:

an amplifying element having a voltage input across a first terminal and a third terminal and a voltage controlled current path between a second terminal and the third terminal; and

a three-wire transformer having a primary winding, a secondary winding, and a third winding;

wherein the primary winding is connected to the third terminal, the secondary winding is connected to the first terminal and the third winding is connected to the second terminal;

wherein the primary winding and the secondary winding are coupled to each other in an anti-correlation system;

wherein the primary winding and the third winding are coupled to each other in a non-anti-correlation system;

wherein the secondary winding and the third winding are coupled to each other in an anti-correlation system; and is

Wherein the third winding is between the amplifier output and the second terminal.

The three-wire transformer arrangement provides more than one gain mechanism by which the overall transconductance/gain of the circuit is increased. First, the voltage feed forward arrangement provided by the primary and secondary windings increases the gain by sensing the voltage at the amplifier input on the third terminal and applying its inverse to the voltage input at the first terminal. This increases the voltage across the first and third terminals, which in turn controls the magnitude of the current through the voltage controlled current path, thereby increasing the transconductance of the amplifying element. At the same time, the positive current feedback provided by the mutual coupling of the third winding and the primary winding causes a second gain mechanism, which increases the current through the voltage controlled current path, thus also providing an increased current gain of the amplifier.

The third gain mechanism is also in operation due to the mutual coupling of the third winding and the secondary winding. The voltage sensed by the third winding is coupled to the voltage input on the first terminal in a positive feedback arrangement. It should be noted, however, that this third gain mechanism is only desirable if it can be kept at a sufficiently low levelIn (1). If the mutual coupling between the secondary winding and the third winding is too high, there is a risk of instability and circuit oscillation. However, at a sufficiently low level, this third gain mechanism is beneficial, providing additional overall gain. More specifically, to ensure stability when the gain of the amplifier is greater than or equal to 1 (over a frequency range from dc to the transit frequency), the effective turns ratio (i.e., n) of each pair of windings₁/k₁、n₂/k₂And n₃/k₃) Should be chosen such that the real part of the input impedance is positive and the real part of the output impedance is positive. This may be achieved by selecting the effective turns ratio of each pair of windings such that the phase difference between the first and third terminals (gate and source in the case of a single transistor) is in the range of 120-.

In some embodiments, the three-wire transformer may be arranged such that the mutual coupling between the secondary winding and the third winding is lower than the mutual coupling between the primary winding and the secondary winding and/or lower than the mutual coupling between the primary winding and the third winding. By keeping the secondary-third phase mutual coupling lower than the mutual coupling of the other windings, the amplifier is more likely to be stable (although n cannot be guaranteed)_i、k_iAll selected stabilities of). The coupling coefficients of the various windings may be adjusted by the transformer design, for example by adjusting the relative sizes and/or positioning of the windings.

Thus, the amplifier provides excellent overall gain. However, an additional and significant benefit of this arrangement is that the input impedance of the circuit can be adjusted for impedance matching without adversely affecting the gain or imposing undesirable constraints on the intrinsic transconductance of the amplifying element. The input impedance of the amplifier is defined as:

wherein:

n_P,Sis the turns ratio of the primary winding to the secondary winding;

n_T,Sis the turns ratio of the third winding to the secondary winding;

n_T,Pis the turns ratio of the third winding to the primary winding;

k_P,Sis the mutual coupling coefficient of the primary winding and the secondary winding;

k_T,Sis the mutual coupling coefficient of the third winding and the secondary winding;

k_T,Pis the mutual coupling coefficient of the third winding and the primary winding;

g_mis the intrinsic transconductance of the amplifying element.

In the above equation, it can be seen that there is a factor introduced by the transformer that depends on the three mutual couplings. Advantageously, this factor is the product of two terms. First term (1+ n)_P,Sk_P,S+n_T,Sk_T,S) Is always greater than 1, and the second term (1-k)_T,P/n_T,P) Always less than 1 (although it should be noted that this second term remains positive, which would always be the case, for example, if n is greater than or equal to 1). Thus, by careful selection of the turns ratio and coupling coefficient, the input impedance can be matched to a particular value, while still having excellent gain and without having to use an amplifying element with a particularly large transconductance and therefore power consumption.

In some preferred embodiments, the primary winding is mutually coupled with each of the secondary winding and the third winding, and the secondary winding and the third winding are not substantially coupled with each other. This arrangement is preferred in case the secondary-tertiary coupling is completely unnecessary and should be minimized or completely eliminated. However, as noted above, in many applications, some secondary-tertiary couplings may be tolerated and even beneficial. As discussed above, although the stability of the amplifier cannot be guaranteed, in many embodiments a reduced mutual coupling coefficient between the secondary winding and the third winding is a good indicator. Thus, in some preferred embodiments, the mutual coupling coefficient between the secondary winding and the third winding is smaller than the mutual coupling coefficient between the primary winding and the secondary winding and/or smaller than the mutual coupling coefficient between the primary winding and the third winding. More preferably, the mutual coupling coefficient between the secondary winding and the third winding is less than two thirds, preferably less than one half, more preferably less than one third, of the mutual coupling coefficient between the primary winding and the secondary winding and/or the mutual coupling coefficient between the primary winding and the third winding.

Perfect coupling between the primary winding and each of the secondary and third windings is generally not achievable, especially in on-chip transformers where the size and shape of the windings are constrained by the manufacturing process, but strong coupling may be obtained, e.g., a coupling coefficient of about 0.8-0.9 is possible in some embodiments. The magnitude of the mutual coupling coefficient between the secondary and third windings that may be used with the stabilizing amplifier will depend on the particular circuit arrangement, but in some particularly preferred embodiments the mutual coupling coefficient between the secondary and third windings is less than 0.4, preferably less than 0.3, more preferably less than 0.2, still more preferably less than 0.1.

The three windings of the three-wire transformer may be arranged in any of a number of different configurations. For example, the windings may be concentric, intertwined or stacked or any combination of these. For on-chip transformers, the windings are formed in thick (or ultra-thick) metal layers, and in such an arrangement, the windings may all be in a single layer, two stacked layers, or even three stacked layers. In some particularly preferred embodiments, the primary winding, the secondary winding and the third winding are all concentric, and the primary winding separates the secondary winding from the third winding. By placing the primary winding between the secondary winding and the third winding, there will be a stronger coupling between the primary winding and the secondary winding and between the primary winding and the third winding than between the secondary winding and the third winding, since the secondary winding and the third winding have the largest separation.

In other embodiments, the primary winding may be intertwined with the secondary winding or the tertiary winding. The other of the secondary winding and the third winding may be concentric with the intertwined windings.

In other embodiments, the three-wire transformer may be formed in two metal layers with the primary winding in a different layer than one of the secondary and third windings, and the primary winding formed in the same layer and concentric with the other of the secondary and third windings.

As discussed above, in some cases it may be desirable to reduce the mutual coupling of the secondary winding and the third winding to the greatest possible extent, if possible, to virtually zero. This can be achieved by appropriate shaping of the windings. Thus, in some preferred embodiments, the secondary winding is shaped to have near zero mutual coupling with the third winding. This of course depends on the relative shapes of both the secondary and tertiary windings. Mutual coupling close to zero can be considered relatively when compared to mutual coupling of other winding pairs (e.g. less than one fifth of them). However, for example, in some embodiments, a near-zero mutual coupling may be employed to represent a mutual coupling of less than 0.1, preferably less than 0.05, such as where other winding pairs have a mutual coupling of about 0.5-0.7. One configuration for decoupling is where one winding is a loop winding and the other is a figure-of-eight winding, such that coupling along one half of "eight" cancels coupling along the other half of "eight". The third winding may be arranged to be coupled to both windings. This arrangement is beneficial in a differential amplifier embodiment (when driven symmetrically, the impedance on both ports of each winding is the same).

Although it should be understood that the following does not limit the invention, in some preferred embodiments the amplifying element has an intrinsic transconductance between 10 and 100mA/V, preferably between 20 and 50 mA/V. With the architecture described herein, the amplifier can achieve high gain while maintaining the intrinsic transconductance of the amplifying element within these more normal and optimal ranges, while also achieving impedance matching.

The amplifying element is preferably a transistor, although it will be appreciated that the principles discussed above may be applied to any amplifying device. For example, the amplifying element may be a plurality of transistors or other components connected together to form an amplifying circuit. However, in some preferred embodiments, a single transistor is used as the amplifying element. The circuit described herein is particularly advantageous for providing a simple amplifier with high gain and impedance matching in a simple circuit having a single transistor as the main amplifying element. The transistor may be any type of transistor, for example a Bipolar Junction Transistor (BJT), but more conveniently the transistor may be a FET, preferably a MOSFET.

The FETs are preferably arranged in a common gate configuration. It will be appreciated that in a BJT arrangement, this is equivalent to a common base configuration.

In a particularly preferred embodiment in which the amplifying element is a FET, the primary winding is connected to the source of the FET, the secondary winding is connected to the gate of the FET, and the tertiary winding is connected to the drain of the FET.

According to another aspect, the present invention provides a method of amplifying a signal using an amplifying element comprising a voltage input across a first terminal and a third terminal, and comprising a voltage controlled current path between a second terminal and a third terminal, the method comprising:

applying a signal to a third terminal of the amplifying element;

sensing a voltage at the third terminal with a primary winding of a three-wire transformer;

coupling at least a portion of the sensed voltage from the third terminal in anti-phase to the first terminal of the amplifying element via a secondary winding of a three-wire transformer;

sensing a current at the second terminal with a third winding of the three-wire transformer;

coupling at least a portion of the sensed current from a second terminal to a third terminal of an amplifying element via a third winding of a three-wire transformer without inverting; and is

The amplified signal is output from an output node positioned such that the third winding is between the output node and the second terminal.

It should be understood that all of the preferred and optional features discussed above may be applied to the method of operation accordingly.

Drawings

Certain preferred embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:

FIG. 1 illustrates a basic block diagram of a direct RF sampling receiver front-end suitable for wideband signal processing;

FIG. 2 shows a basic common gate low noise amplifier (L NA);

fig. 3 shows a modified common gate L NA that uses a transformer to enhance the transconductance of the amplifier through a voltage feed forward arrangement;

fig. 4 shows another common gate L NA that uses a transformer to boost current gain through reactive positive current feedback;

FIG. 5 illustrates an amplifier according to an embodiment of the invention;

fig. 6a and 6b show examples of transformer layouts; and is

Fig. 7 illustrates some characteristics of the amplifier of fig. 5.

Detailed Description

Fig. 1 depicts a typical direct RF sampling receiver front end 100 for a wideband receiver operating in, for example, the 6 to 8.5GHz band. The antenna 101 receives the RF signal and passes it to a high pass filter 102 which rejects signals below about 6GHz (and may have a high rejection notch at about 5.1 to 5.8GHz, although it will be appreciated that these numbers are provided purely by way of example). The output of the high pass filter 102 is fed to the input of a low noise amplifier 103, which low noise amplifier 103 provides gain for the signal of interest over an operating band of 6 to 8.5 GHz. The output of the low noise amplifier 103 is then fed to an analog to digital converter (ADC)104 which ultimately digitizes the RF signal.

Fig. 2-4 have been described above, but these figures briefly show the basic common gate L NA circuit (fig. 2), the modified common gate L NA with transformer voltage feed-forward gain boost (fig. 3), and the modified common gate L NA with transformer current feedback gain boost (fig. 4).

Fig. 5 shows an embodiment of a low noise amplifier 500 having a three-wire transformer 510, the three-wire transformer 510 being formed by a primary winding L_PSecondary winding L_SAnd a third winding L_TAnd (4) forming. The windings of the three-wire transformer 510 are connected to an amplifierComponent M₁In the present embodiment, the amplifying element M₁Is a Field Effect Transistor (FET). Amplifying element M₁Functions as a voltage-controlled current source, whereby a voltage (gate-source voltage) applied between the first terminal and the third terminal controls a current flowing between the second terminal (drain) and the third terminal (source).

Transistor M₁The RF input signal is applied to the source (third terminal) such that it causes a change in the gate-to-source voltage_PTo the third terminal, i.e. in parallel with the RF input, and to ground (e.g. in the case of a differential amplifier this may be an analog ground or it may be a virtual ground).

Secondary winding L_SConnected in series with the DC bias voltage and with the primary winding L_PFirst terminal (gate) with an inverse phase relationship, primary winding L_PAnd a secondary winding L_SForm a voltage feed forward circuit, thereby forming the primary winding L_PSensing input RF_iAnd applying it in reverse phase to M₁Thus, when the input signal at the source falls, primary winding L_PAnd a secondary winding L_SThe feed forward of (a) causes the gate voltage to increase in proportion to the input signal, and when the input signal at the source rises, the primary winding L_PAnd a secondary winding L_SThe feed forward of (a) causes the gate voltage to decrease in proportion to the input signal, thus increasing the gate-source voltage and thereby increasing the overall transconductance (i.e., g) of the amplifier 500_mEnhancement).

Third winding L_TTo communicate with primary winding L_PConnected in non-inverting relationship to the second terminal (drain) and, therefore, primary winding L_PAnd a third winding L_TForming a positive current feedback loop, thereby forming a third winding L_TCurrent sensed at the drain on is fed back to the primary winding L on the source_PThereby amplifying the pass transistor M₁Current of the current path (i.e., drain-source current is amplified)。

Output RF of amplifier 500_oTaken from amplifying element M₁To the other side of the third winding. Output RF_oMay be taken directly from third winding L_TI.e., from terminal P6. The ideal load for current output is 0 omega. In the embodiment of fig. 5, a current buffer M is provided₂To couple the load on the drain side (e.g., inductor L)₁) And low impedance seen at the source (i.e., M)₂1/g of_m) And (5) separating. In other embodiments, a current choke (i.e., high impedance for RF) arrangement (for DC biasing) such as shown in fig. 4 may be used.

Third winding L_TAnd a secondary winding L_SAre also coupled to each other and they are in an inverse relationship. The pair of M₁The gate of (a) provides further positive feedback, which is acceptable (or even beneficial) if it is kept within the boundary conditions. If the magnitude of this tertiary-secondary feedback is too large, the circuit will oscillate and become unstable, and care needs to be taken to avoid this.

As discussed above, the input impedance of the amplifier 500 is defined as:

thus, by controlling (i.e., properly designing) the turns ratio and mutual coupling coefficient of the three transformer windings, the input impedance can be controlled so that it matches other circuit elements, such as an RF antenna, to maximize power transfer to the amplifier. The circuit provides an improvement over the amplifiers of fig. 3 and 4 since impedance matching can be achieved by appropriate design of the transformer windings, rather than by requiring an amplifier with a specific intrinsic transconductance or limiting gain. Amplifier 500 can achieve impedance matching and high gain without requiring an amplifier with high transconductance and corresponding high power consumption.

Avoid the secondary winding L_SAnd a third winding L_TAre coupled to each other and fed back to cause one of oscillation and instabilityThe method is to reduce the coupling coefficient of the two windings by transformer design. An example of a suitable transformer design that may be used with amplifier 500 of fig. 5 is shown in fig. 6.

Fig. 6 shows a three-wire transformer 600 formed in two separate (stacked) metal layers of a die. The primary, secondary and tertiary windings are all formed as concentric windings (i.e., although the layers are stacked, no winding is stacked directly on top of another layer). The primary and secondary windings are formed in one metal layer and the third winding is formed in a second metal layer. The primary windings P1-P2 are intermediate windings (in terms of radius), with the secondary windings P3-P4 formed around the intermediate windings (with a larger radius) and the tertiary windings P5-P6 formed inside the intermediate windings (with a smaller radius).

Fig. 6a shows an isometric view of the transformer 600 arrangement, while fig. 6b shows a plan view showing concentric coils.

The connections to the three windings P1-P6 are also labeled in fig. 5 to show how the three-wire transformer 600 of fig. 6 is used to construct the circuit of fig. 5.

An example of a transformer design in a 55nm CMOS process is as follows:

with 2.3mA I_DCBiasing a transistor to provide intrinsic

L_P＝0.85nH，L_S0.65nH and L_T＝0.9nH

n_P,S＝0.87，n_T,S0.85 and n_T,P＝0.95

k_P,S＝0.6，k_T,S0.33 and k_T,P＝0.5

From these numbers, the gain and the input impedance Z_iCan be calculated as:

using the same design except with k_T,S0 (i.e. with the third-secondary coupling coefficient reduced to zero):

thus, in both cases, the input impedance is well matched to the 50 Ω antenna and the amplifier has a high gain.

FIG. 7 shows the forward reflection coefficient (return loss) S of an embodiment of the amplifier 500 of FIG. 5 in 55nm CMOS₁₁And forward transmission coefficient S₂₁. Coefficient of forward reflection S₁₁It is shown that the amplifier can be considered impedance matched (below-10 dB) over a wide frequency range from about 6.5GHz to 11 GHz. This is an excellent wideband response suitable for Ultra Wideband (UWB) applications. Forward transmission coefficient S₂₁An excellent signal response is shown, peaking in excess of 30db at about 7.3GHz the peak response of the amplifier can be tuned in frequency by appropriate selection of the load inductance and capacitance (actual or parasitic), forming a parallel L C resonant circuit therein the Q factor of the L C resonant circuit determines the frequency selectivity (bandwidth) of L NA.

It will be appreciated that variations and modifications can be made to the above described circuit without departing from the scope of the appended claims.