CURRENT REUSE ACTIVE INDUCTOR BASED WIDEBAND LNA

Transcription

1 Current Reue Active Inductor baed Wideband LNA CURRENT REUSE ACTIE INDUCTOR BASED WIDEBAND LNA DIPALI DASH, MARINA E J, J MANJULA M-Tech LSI Deign, Dept. of ECE, SRM Univerity, Chennai, India Eail: dipali.dah@gail.co, erujohn009@gail.co, janjula_75@rediffail.co Abtract Thi paper preent the deign of an active inductor baed wideband LNA uing current reue topology,which i deigned and iulated in 0.8u CMOS technology. The low noie aplifier i conidered to be the key block in an RF receiver. It play a critical role in deterining the noie figure of a receiver. The ain function of an LNA i to provide ufficient gain to reduce the noie of ubequent tage while adding a little noie a poible. To achieve a good ipedance atching over a deire bandwidth (0.05GHz to.5ghz) active inductor i ipleented baed on gyrator tructure and it noie i iproved by eploying a feed-forward path (FFP). The iulation how a axiu power gain of 7.3dB, iniu noie figure (NF) of 0.87dB with a 3db bandwidth of.0ghz over GHz range. The total power conuption i 6.38W with.8 power upply. Keyword- Low Noie Aplifier (LNA),Active Inductor, Noie Figure (NF),Current reue technique. I. INTRODUCTION The coon objective in deign of a low noie aplifier(lna) are to provide high gain, to achieve a iniu noie figure (NF) a poible, to iniize the nonlinearitie and finally to have good input and output ipedance atching a thi will enure axiu power tranfer and optiized gain and noie perforance. In radio receiver, the LNA, a the firt input block, i to be atched with the antenna characteritic ipedance (generally 50 Ω)[].For thi purpoe a atching network i needed to enure optiu noie perforance a well a tability and alo power atching between the antenna and LNA[3]. Shunt feedback aplifier ugget yet a olution for achieving the required atching at the input port. However, thi ethod uffer fro a relatively high NF due to the theral noie of hunt reitor[4]. The inductive ource degenerated cacode LNA topology can provide excellent ipedance atching and noie figure[5].traditional LNA deign[] i their heavy reliance on large paive inductor to achieve variou perforance requireent. Where a paive inductor take up the ajority of the chip area and on the other hand ha liited quality factor(q). Active inductor have been advocated for a long tie a area efficient replaceent for paive inductor. The inductance value of the active inductor can be eaily changed either in a continuou anner or in dicrete tep, which provide flexibility in the tuning of atching circuit. Higher accuracy, eaier layout floor-planning, all area, and abence of agnetic coupling are other advantage of active inductor copared to their paive counterpart[].several active inductor topologie[6],[7],[8] have been deigned and dicued, ot of which utilize a capacitor- gyrator(c-g) tructure to duplicate the required inductive propertie. However, due to poor noie and linearity perforance of active inductor, their application are liited in RF receiver. In recent year input atching circuit i ipleented by a low noie, good linearity active inductor[],which i fully on chip and occupie a all die area, but tend to uffer fro larger power diipation to achieve high center frequency. In thi paper, a inductive ource degenerated cacode LNA topology i preented for which input atching circuit i ipleented uing an active inductor. In addition to that current reue technique i adopted to achieve low power conuption. The propoed circuit i deigned and iulated uing TSMC 0.8- µ CMOS Technology. Thi paper i organized a follow. In ection II, a low noie tunable Active inductor i preented. In ection III Cacode Low Noie Aplifier and all ignal analyi of that LNA i preented. It alo decribe the deign of Cacode LNA uing Active Inductor and current reue topology.in ection I eaureent reult are reported and finally, ection provide concluion. II. ACTIE INDUCTOR The gyrator-c tructure i a well known circuit topology to ynthei active inductor. It conit of two back to back connected tran-conductor, one that ha a negative tranconductance, another that ha a poitive tranconductance and an external hunt capacitor c[9]. The input ipedance of the circuit i inductive and can be written a, C Zin G G The conventional circuit realization of the gyrator concept (G and G )[0] i hown in Fig..(b), for which the input ipedance i inductive with

2 potentially high quality factor(q) and high elfreonant frequency(f r ). The paraitic capacitance and the input/output reitance of the tranconductance aplifier degrade the quality factor and reduce the elf-reonant frequency of the active inductor. Uing the hybrid- all ignal odel for the tranitor and auing ideal current ource, the coponent of the equivalent circuit of Fig..(c) can be calculated a[0], Fig.. Active inductor. (a) General tructure. (b) Typical ipleentation. (c)equivalent RLC odel. C L a g g C C Cgd Cgd 3 Cdb3 b RS, RP r03 g g r c 0 Current Reue Active Inductor baed Wideband LNA i n, in 4kT g 3 d g L The active inductor can be placed at the input of LNA to provide ipedance atching at the input. The active inductor reonate with the aplifier input capacitance C in, at the reonant frequency and leave the equivalent reitance of the active inductor a the input ipedance. The typical value of capacitance and the tranitor output reitance, i often larger than the antenna characteritic ipedance. Alo, being connected to the input node, the atching inductor ha to be low noie for a low noie figure of the overall LNA. Therefore, to deign a low noie active inductor with reduced equivalent reitance, a hown in Fig..[] the following change i applied to the conventional gyrator-baed active inductor circuit. For low-noie perforance, it ue the odified differential pair with the FFP to realize the tranconductance G. The current irror (M 5 and M 6 ) i ued to cancel the effect of the coon ode noie generator uch a that of the tail current ource. III. DESIGN OF LNA The general topology of an LNA can be broken down into three tage: an input atching network, the aplifier core, and the output atching network [3]. In fig 3., the LNA and the atching network are characterized by the S-paraeter. There are four S- paraeter, S, S, S, and S, where S i the input ipedance, S i the revere traniion factor, S i the forward gain, and S i the output ipedance. Where M and are aued to be identical, C i the total capacitance een at the gate ofm 3 ;C, C gd, and C db are the tranitor capacitor, g and r o are the tranitor tranconductance and output reitance, repectively. The flicker noie i neglected at high frequencie and the channel theral noie i aued to be i d 4kT g where i the channel exce noie factor. In order to iprove the noie perforance of the differential tage, a feed-forward path (FFP) i added to the baic differential pair coniting of tranitor and, a hown in Fig.[]. Fig 3. Generalized LNA topology To addre thee challenge in the deign of a wideband LNA, everal topologie and circuit technique have been propoed. In thi paper the inductive ource degenerated cacode LNA topology, hown in Fig.3., ha deontrated the potential for excellent ipedance atching, noie figure, and power diipation a well a decreae the Miller effect copared to other topology[]. Fig.. Low noie active inductor

3 Current Reue Active Inductor baed Wideband LNA Fig.3.3 Serie RLC Circuit with Lg and L Fig3.(a)Cacode LNA, (b)sall-ignal equivalent cheatic The deign and analyi of the aplifier in all apect, uch a input atch, gain and noie, are dicued a follow. Part a: Fro thi odel, in iin j Lg j L iin I j L a jc 0 3. i0 g giin 3. b jc Subtitute 3.(b) in 3.(a). gl in iin j Lg L 3. c jc C Input ipedance, in gl Zin j Lg L 3. iin jc C For atching L g + L are cancelled out by C. So at frequency of interet 0 Lg L C 0 0 L L C g 3.3 gl ource reitance, R C In the deign, L i choen uch that Real(Z in ) = ωtl = 50 Ω. L g i choen according to (3.).o that iaginary (Z in ) = 0 at ω 0. NOTE: ) L i typically all and ay be realized by the bond wire for ource. ) L g can be ipleented by piral/external inductor. Part b:for erie RLC Circuit[] L 0L Q, and. C Qin R C RC Quality factor of circuit (fig 3.3) can be calculated a follow, 0 Lg L 0 Lg L Qin 3.5 gl R R T L C Qin 3.6 gl 0 R C C gl for atch load, R 3.7 C Q in R C 0 Gain: 3.8 = Q in in (3.9) Tranitor tranconductance i given by, I out g g 3.0 G I g out Q in g in in g 3. out ga in in G R L 3. Fro (3.) it i clear that, the gain i proportional to RL which can be ade large: a few hundred to over a thouand Oh and alo tranconductance of aplifier. Noie Figure: For calculation of the noie factor of the LNA, only the claical channel noie of M and the theral noie of RL are conidered a indicated in Fig The noie contribution of M and other paraitic noie ource are ignored. The derivation wa baed on the quai tatic approxiation and the influence of the cacode pole, the Miller-effect and other paraitic are neglected. Noie figure i given a ratio of total noie power at the output to total noie power at the output due to input ource. For thi calculation channel noie i ignored[]. 3

4 n0, R n0, d n0, d F 3.3 n0, R n0, R Noie contribution of tranitor i defined a, i R n0, d n, d L where i 4kT g f 3.4 n, d Fro above expreion (3.4) it i cleared that noie figure decreae with quare of Q-factor, where a Q- value depend upon L g +L, L i uually all. So Q- value ainly depend on L g. But a L g can be ipleented by piral/external inductor it will occupy larger area. So in order to reduce area the propoed active inductor [8] can be placed at the input of LNA. It alo provide noie reduction a well a good ipedance atching at the input. Current Reue Active Inductor baed Wideband LNA Figure 3.5[4] illutrate the LNA with a current reue topology. For the low power conuption requireent, the two-tage aplifier i folded into a ingle tage. It ean that it i cacode for DC and cacade for RF ignal. The two cacading coon ource aplifier hare the ae upply current to reduce power conuption. Hence,with the ae gain perforance, thi circuit only conue about half the power of the two-tage aplifier. C coupling i a coupling capacitor, L i an RF choke and C pa i a capacitor providing AC ground. In thi topology, the Miller effect i ore eriou than in a cacade aplifier, ince the firt coon ource aplifier ha a large voltage gain. Thi effect can be reduced by inerting an inductor before the gate of the econd tage. The input ipedance of the LNA i atched to 50Ω ince the band pa filter (BPF) required in ot conventional receiver architecture i in a 50 Ω yte. The ource degeneration ethod for input atching i eployed. A. PROPOSED LNA Thi fig3.4 how the propoed LNA which i applicable for noie reduction. For ot broadband aplifier there i a evere trade-off between inputipedance atch and NF becaue for iniu NF, high input ipedance Zin of the aplifier i required wherea for axiu power tranfer, Zin need to be atched with 50oh a it entioned. Becaue of thi trade off, ot of the CMOS WB LNA how NF above 3dBwhen atched to 50oh. The cacoded tage provide a reaonably low (about 3dB) noie figure a derived previouly. If the body effect i abent then the width of the cacoding tranitor M, hould be choen three tie le than that of the input tranitor M. Fig.3.5 CMOS LNA with a current-reue topology Fig.3.4 Propoed Cacode LNA with Active Inductor Fig.3.6 Propoed Cacode LNA with Current reue B. LNA uing CURRENT REUSE TOPOLOGY 4

5 Figure.3.6 how the LNA with active inductor uing current reue topology.the Active inductor with ource degeneration ethod i eployed for input ipedance atching. I. SIMULATION RESULT In thi ection, the iulation reult of Active inductor baed wideband LNA uing current reue topology which i deigned in TSMC 0.8µ CMOS proce i preented. Current Reue Active Inductor baed Wideband LNA Fig 4.3 S Fig4..Input Ipedance of Active Inductor Fig 4. how the input ipedance of Active Inductor which i inductive in nature fro 0MHz to.5ghz. The eaureent reult are decribed in Fig.4.- Fig.4.5.The gain hown in Fig. 4. ha peak value 7.3dB at 0.3GHz.In Figure4., the input atching ha S low than -0dB and the output atching ha S lower than -4 db. The revere iolation S i aintained well below -40 db throughout the frequency of 0.05GHz to.5ghz, which i hown in Figure 4.4. Fig.4.4 S Fig.4.5 S The noie figure depicted in Fig.4.5 ha iniu value of 0.87dB at 0.58GHz,noie voltage of 3.75n /Hz and it aintained well below 3.5dB over the range of frequency below.5ghz. Fig 4. Gain of LNA (S ) 5

6 Current Reue Active Inductor baed Wideband LNA the propoed work with other publihed work i uarized in TABLE II. Fig.4.6 Noie figure of LNA Fig.4.7Noie oltage of LNA Linearity refer to ability of aplifier to produce ignal that are accurate copie of input. Linearity can be iprove by exploiting a noie or ditortion cancellation technique. Although there are any way to evaluate the linearity of the LNA, to eaure the third-order intercept point (IP3) i the ot coonly ued ethod. The IIP3 i obtained graphically by plotting the output power veru the input power both on logarithic cale. A in Fig.4.8 the input third-order intercept point ( IIP 3 ) can attain -0.4dB. TABLE I. Coparion of reult Paraeter Propoed LNA Propoed LNA uing Current reue S (db) <- <-0 S (db) <-46.3 <-3 S Gain(dB) S (db) <-9.3 <-4.3 Noie figure(db) Noie oltage(n /Hz) IIP 3 (db) DD ().8.8 DC Power(W) TABLE II. Coparion of the propoed circuit with the exiting work Paraeter Ref [] Ref [8] Ref[4] Thi work Technology 0.8µ 0.3µ 0.8µ 0.8µ Freq(GHz) GainS(dB) Noie figure IIP3 (db) - _ DD () Power(W) CONCLUSION In thi paper, a current reue active inductor baed wideband LNA ha been preented. The circuit i deigned with TSMC 0.8µ CMOS technology. The wideband LNA exhibit axiu gain of 7.3dB, iniu noie figure of 0.87dB over the frequency range of GHz with a 3db bandwidth of.0ghz while conuing a DC power of 6.3W fro.8 upply. Thu by uing the current reue technique, the propoed paper achieve an optiu power and iniu noie figure copared to other exiting work. [] MohenMoezzi, Meber, IEEE, and M. Sharif Bakhtiar Wideband LNA Uing Active Inductor With Multiple Feed-Forward Noie Reduction Path : IEEE Tranaction On Microwave Theory and Technique, OL. 60, NO. 4, APRIL Fig.4.8 IIP3 Analyi 0.(Bae Paper) TABLE I uarize and copare the perforance [] B. Razavi, "Deign Conideration for with Active inductor baed LNA uing Current reue Direct-Converion Receiver,"IEEE Tranaction on and without current reue topology. Coparion of 6 REFERENCES

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