Analysis of Active Feedback and its Influence on UWB Low Noise Amplifier

Transcription

1 Volume 89 No 8, March 04 Analysis of Active Feedback and its Influence on UWB Low Noise Amplifier P.Keerthana PG Student Dept. of ECE SSN Collee of Enineerin, Chennai, India. J.Raja Professor Dept. of ECE Sairam Enineerin Collee, Chennai, India. V.Vaithianathan Assistant Professor Dept. of ECE SSN Collee of Enineerin, Chennai, India. R.Srinivasan Professor Dept. of IT SSN Collee of Enineerin, Chennai, India. ABSTRACT In this paper, various active feedback techniques for Ultra- Wide Band (UWB) CMOS Low Noise Amplifier (LNA) are proposed. First, an LNA consistin of Common Gate (CG) stae for input matchin, cascode with interstae current reuse as core stae and Common Drain (CD) stae for output matchin is presented. Three feedback techniques such as lobal feedback, local full feedback and local partial feedback techniques are employed in this LNA. The analysis is made for the different feedback networks consistin of resistive, common source, common ate and common drain. The proposed LNA is desined with 90 nm technoloy and its performance is analyzed with Ailent s ADS simulator. Amon the analyzed LNA s, CG partial active feedback and CD partial active feedback achieves power ain of 3.8 db and 3.75 and noise fiure of db and db respectively. General Terms Low Noise Amplifier, Noise Fiure, Linearity. Keywords Global feedback, Local full feedback, Local partial feedback.. INTRODUCTION UWB is an unlicensed wireless technoloy that coexists with other licensed wireless technoloies. FCC has allocated 7500 MHz bandwidth for UWB applications in the GHz. Low-enery and extremely short duration impulses are used over a wide spectrum of frequencies. The averae power spectral density limit is 4dBm/MHz or 75nW/MHz. Therefore UWB technoloy provides a promisin solution to the RF spectrum drouht by allowin new services to coexist with current radio systems with minimal or no interference []. This revolutionary technoloy is intended to provide an efficient use of scarce radio bandwidth while enablin both hih data rate short rane applications and low data rate loner-rane applications. With several advantaes and restrictions in UWB technoloies, many challenes exist in desinin receiver front end circuits. Low Noise Amplifier (LNA) is the first block in any receiver system. The main purpose of the LNA is to amplify the weak sinal without addin much noise of its own. Therefore the LNA desin has many challenes because of its need to achieve hih ain, low noise fiure (NF), ood input and output matchin, stability and better linearity. Accordin to Friis formula, the overall noise factor of the system is dominated by the first stae in the receiver system if the ain of the successive stae is made hih. Hence, the main desin consideration for the LNA is low NF. Several noise reduction techniques are discussed in the literature survey. The paper is arraned as follows. Section discusses about the existin noise reduction techniques. Section 3 discusses about the basic LNA taken for analysis. Section 4 discusses about noise cancellation principle in lobal feedback, local full feedback and local partial feedback. Section 5 deals with the results obtained from the simulations and finally the conclusions are provided in section 6.. LITERATURE SURVEY A feedforward noise reduction is discussed in [] and it addresses the problem of noise reduction with broadband impedance matchin. The feedforward path is desined such that it constructively adds the sinal but reduces the noise. A noise cancellin technique with current reuse confiuration is found in [3]. It consists of CS-CG with series resonated topoloy contributin less power and ood noise performance. The drawback is that it achieves only ain up to 5 db. In [4], Chin-Fu Li et al., proposed a sinal nulled feedback technique that consists of an additional loop with capacitance and a transistor such that it suppresses the noise but the drawback in this technique is the reduction of ain. In [5], the LNA is desined with CG input matchin and CD output matchin, cascade ain stae and shunt series peakin with interstae current reuse is proposed and the circuit offers moderate ain with low power. A folded LC cascaded topoloy with multiated transistor is found in [6] and it linearizes the output transconductance non-linearities and it achieves better linearity and ood noise fiure. In [7], noise reduction and linearity improvement techniques for differential LNA have been discussed. It uses cascade differential LNA and the inductor is connected at the ate of the cascode transistor and it uses a stratey called capacitive cross couplin to reduce noise and improve linearity. But the drawback is increased area and power consumption. In this paper in order to reduce noise, several noise reduction feedback techniques are proposed and their performances are analyzed. 9

2 Volume 89 No 8, March BASIC LNA The LNA circuit found in [5] consists of 3 staes as shown in fiure. The first stae is the Common Gate (CG) input stae which is used for input matchin for the entire UWB band of GHz. The second stae is the core stae consistin of cascode LNA with interstae current reuse. The interstae current reuse is used to increase the ain without increasin the power consumption. The shunt-series peakin in this stae enhances the bandwidth. The third stae is the Common Drain (CD) stae used for output matchin. This circuit is taken as the basic circuit and proposed feedback techniques are implemented in this circuit and the performances are analyzed. The CG input stae is devoid of miller capacitance. A very ood input matchin is achieved by the resister R and the inductor L. The inter stae current reuse network is formed by the inductors L 5, L 4 and C and it is used to bias the transistor M 3 and therefore it drives less power from the supply. At hih frequencies, a low impedance path is created throuh C as the impedance of L 3 becomes lare. This results in ain flatness. The shunt series peakin used may cause peakin of ain at certain frequencies leadin to less stability. This can be overcomed by the interstae peakin inductor. The common drain amplifier is used as a buffer to enable easy output matchin. The output impedance can be easily matched by adjustin the width of M 4, Fi : Basic LNA Fi : Analysis of basic LNA The schematic representation of the noise analysis of the basic LNA is shown in fiure.the noise fiure (NF) of the three staes are iven by the equations, and 3. The total noise factor is obtained by usin the Frii s formula and it is iven by the equation 0. The ain of the three staes is iven by the equations 3, 7 and 8 respectively. The total ain is iven by the equation 9. When the ain is increased, the net noise fiure will et reduced. RS NF ( ) Rs R m m Rs () f NF ( ) 3 Rs f m T 3 m RS () ( ) m4 NF 3 m4 r 04 R S ( ) m4 r 04 (3) m R (4) (( S 4 S 5) ) L m L SC S C s3 (5) (( 6 7) ) 3 SL R m SL S C s4 (6) (7) m4r 04 3 m4r 04 (8) 3 (9) NF tot NF NF A NF V A 3 V (0) where m, m, m3 and m4 are the transconductance of M, M, M 3 and M 4 respectively. R S is the source resistance, f T is the transition frequency, r 04 is the output resistance. 30

3 Volume 89 No 8, March PROPOSED ACTIVE FEEDBACK TOPOLOGIES AND FEEBACK NETWORKS A physical understandin of both intrinsic and extrinsic noise mechanisms in a Metal Oxide Semiconductor Field Effect Transistor (MOSFET) is necessary while desinin LNA [8]. The different sources of noise in LNA are channel thermal noise, ate induced noise, flicker noise, shot noise and substrate noise. In order to reduce the NF of the LNA, different feedback techniques are employed in this basic circuit. A Feedback amplifier is the one in which part of the output sinal is fed back to the input. There are four different feedback topoloies. They are shunt-shunt feedback, seriesshunt feedback, series-series feedback, shunt-series feedback. In this work, shunt-shunt feedback technique which is also called as transresistance is employed. The shunt-shunt feedback is employed in three ways. From the fiure, when the feedback is taken from the point B and iven to the point C, it is called as lobal feedback and its block diaram representation is shown in fiure 3 and 4. When the feedback is taken from the point A and iven to the point D, it is called as local full feedback and its block diaram representation is shown in fiure 5 and 6. When the feedback is taken from the point E and iven to the point D, it is called as local partial feedback and its block diaram representation is shown in fiure 7 and 8. The feedback network may be passive or active. The passive feedback network consists of resistor and the active feedback network consists of CG, CS and CD confiurations. The lobal feedback, local full and local partial feedback with the different feedback network as mentioned above are simulated and analyzed and the conceptual representation of how noise ets reduced are analyzed. The different feedback network and its feedback factor (β) are shown in the table. network causes a phase shift of 80 0, it will be a positive feedback otherwise the feedback will be neative feedback. Therefore, if the feedback network consists of CS network, it will be positive feedback and for the other feedback networks, the feedback will be neative. Fi 3: Analysis of lobal feedback with CS network Table. Feedback Network and its feedback factor (β) R CS CG CD Fi 4: Analysis of lobal feedback with CG/CD/R network Feedback network Feedback factor(β) R3 m5 R3 m ( ) 5 m 5 r 0 r 0 R3 4. Global Feedback In lobal feedback, the feedback is taken from the output stae and iven to the input stae. The feedback may be positive or neative. The input sinal is iven to the CG input stae and is amplified by the cascode stae in which CS in the cascode stae causes an 80 0 phase shift and the output stae does not cause any further phase shift. Hence if the feedback various staes of lobal feedback with CS network is shown in fiure 4. From the fiure 4, the input sinal is applied to the CG input stae. The CG confiuration has noise voltaes which are equal in manitude and opposite in phase at source and drain terminal. The CS stae will amplify this sinal causin a phase shift of 80 0 and also the noise from the CS stae will et added. As the phase of the noise sinal is arbitrary, if the noise voltae from CS stae is in phase with the noise from the previous staes, then the total noise will increase and if the noise voltae from CS stae is out of phase with the noise from the previous staes, then the total noise will decrease. Let us consider the worst case possibility that the noise voltaes are in phase so that the total noise voltae is increased. The amplified sinal with the increased noise is iven to the CG stae. As the noise voltaes at the source and drain terminal of CG stae are out of phase, the noise added at the input terminal of CG stae will et cancelled at the drain terminal of the CG stae. Thus, the total ain and noise fiure of the cascode stae is dominated by the CS stae. The sinal alon with the noise is then iven to the CD stae. The CD stae has ain less than unity and hence the sinal will not be amplified 3

4 Volume 89 No 8, March 04 and noise will et increased due to the internal noise of CD stae. A part of this output is iven as the feedback to the input stae. When the feedback network is resistive or CG or CD, the feedback is positive. The feedback sinal will et amplified and noise from the feedback network also ets added up. At the input stae, the feedback noise and the input noise are in phase and hence the noise will et added up. various staes of lobal feedback with CG/CD/resistive is shown in fiure 5. When the feedback is CS, the feedback will be neative. The feedback sinal will et amplified with a phase shift of 80 0 and noise from the feedback network also ets added up. At the input stae, the feedback noise and the input noise are out of phase and hence the noise will et reduced. The total noise factor will et reduced by factor of (+A v β) for CS feedback and it et increased by factor of (+A v β) for other feedback network as iven by the equation and respectively. NF tot NF () ( ) NF NF tot ( ) () 4. Local Feedback In local full feedback, the feedback is taken from the output of the CG stae and iven to the input of the CS stae. In local partial feedback, the feedback is taken from the output of the CS stae and iven to the input of the CS stae. various staes of local full feedback with CD/CG/R network is shown in fiure 5.The analysis of the sinal and the noise voltaes at the various staes without the feedback are same as the lobal feedback. As the feedback is taken at output of the CG stae and iven at the input of the CS stae, the feedback noise voltae will be out of phase with the noise voltae at the input of the CS stae and hence the noise ets reduced when the feedback network is CD/CG/R. various staes of local full feedback with CS network is shown in fiure 6. As the feedback network with CS causes a phase shift of 80 0, the feedback noise voltae will be in phase with the noise voltae at the input of the CS stae and hence the noise ets increased for the local full feedback with CS network. Fi 6: Analysis of local full feedback with CS network Fi 7: Analysis of local partial feedback with CG/CD/R network Fi 5: Analysis of local full feedback with CG/CD/R network Fi 8: Analysis of local partial feedback with CS network various staes of local partial feedback with CD/CG/R network is shown in fiure 7. As the total noise at the output of the CS stae consists of the noise contributed by the CG stae of the cascode stae, the noise at the output of the CS stae will be more when compared to the noise at the output of the CG stae. The feedback noise voltae will be out of phase with the noise voltae at the input of the CS stae and 3

5 Volume 89 No 8, March 04 hence the noise ets reduced for the local partial neative feedback. The noise cancelled will be more when compared to the local full feedback with CD/CG/R network. various staes of local partial feedback with CS network is shown in fiure 8. As the feedback network with CS causes a phase shift of 80 0, the feedback noise voltae will be in phase with the noise voltae at the input of the CS stae and hence the noise ets increased for the local partial feedback with CS network. The noise factor of the second stae will et reduced by factor of (+A v β) for CG/CD/R feedback and it et increased by factor of (+A v β) for CS feedback network as iven by the equation 3 and 4 respectively. NF NF (3) ( ) NF NF ( ) (4) 5. RESULTS AND DISCUSSION The simulation results of the proposed LNA are obtained usin Ailent s ADS simulator. Post layout simulations are also carried out. A 90 nm CMOS technoloy file is used for the simulation purposes. The results are elaborated in the followin sections and are summarized and shown in table. Alon with the proposed topoloies results, already existin topoloies such as sinal nulled feedback, feedforward and lobal resistive feedback concepts are taken and implemented in basic circuit and the results are compared. For the LNA to have better performance, power ain should be hih so that the noise added at the subsequent staes will have less effect. It can be inferred from the fiure 9 that full CS feedback has peak ain of 9. db due to positive feedback but it has poor noise performance. The local partial CD and CG feedback has peak ain of 3.75 and 3.8 db with reduction in ain of around.5 db from the base circuit due to neative feedback but it has ood noise performance. 5. Noise Fiure In the proposed techniques, the lobal feedback with CS network has less noise fiure of db when compared to the lobal feedback with CG network noise fiure of db as seen in fiure 0. It can be seen that partial CG feedback has NF in the rane db and partial CD feedback has NF in the rane db. All the other techniques except the feedback with CS network have NF in the rane db. Fi 0: Noise Fiure (NFmin) 5.3 Input matchin and Output matchin All the techniques has ood input matchin with input reflection coefficient < -7.5 db as seen from the fiure. From the fiure, the output reflection coefficient of all the topoloies except CS network and lobal CG network are less than < -7. db. 5. Power Gain (S) Fi : Input reflection coefficient Fi 9: Power Gain (S) 33

6 Volume 89 No 8, March 04 Fi : Output reflection coefficient 5.4 Stability factor k and Fi 4: Stability factor, Δ The stability of an amplifier is an important constraint while desinin an amplifier. The stability factor is determined from the S parameter. The Rollett s stability condition states that k should be reater than and should be less than.these topoloies are stable as k> and < as seen from the fiure 3 and Linearity (IIP3) From the fiure 5, all these topoloies have linear response as the sinal power is limited to only -4.3 dbm. Thus, by comparin the existin and the proposed topoloies, proposed partial CG and CD active feedback has better performance. Fi 3: Stability factor, k Table. Comparison results and analysis BW (GHz) S in db Nfmin in db S in db S in db IIP3 in dbm Proposed techniques Base circuit [5] <-8.6 < Global resistive feedback [3] <7.7 < Global sinal nulled feedback [4] <-9 < Feed forward [] <-0 < Local full resistive feedback <-9 <- -8 Local partial resistive feedback <-8 <-4-5 Local full CS feedback <-9.6 < Local partial CS feedback <-0 <-8 4 Local CG feedback <-0 <-5.9 Local partial CG feedback <-0 < Local full CD feedback <-8 <- -.5 Local partial CD feedback <-7.5 <-0 - Global CS feedback <-0 < Global CG feedback <-7.5 < Global CD feedback <-7.8 <

7 Volume 89 No 8, March 04 performance. CG partial active feedback ives noise factor of db and ain of around 3.8 db where as partial CD feedback ives the noise factor of db, ain of around 3.75 db. All the techniques has ood input matchin with input reflection coefficient < -7.5 db and the output reflection coefficient of all the topoloies except CS network and lobal CG feedback are less than < -7. db. From the analysis, it is found that proposed topoloies have ood stability and moderate linearity. Fi 5: Linearity, IIP3 Fi 6: Layout of partial CD feedback The Layout of the partial CD feedback is shown in fiure 6. Similarly the layouts for other confiurations are drawn and simulated. The area occupied is.344 x.3 mm. 6. CONCLUSION In the proposed topoloies, local feedback techniques such as CG and CD partial active feedback ive better noise 7. REFERENCES [] Stephen Wood and Roberto Aiello, Essentials of UWB, Cambride Univ. Press, 008. [] Chao-Shiun Wan, Chorn-Kuan Wan, A 90nm CMOS Low Noise Amplifier Usin Noise Neutralizin for GHz UWB System Proc. of 3 nd European Solid State Circuit Conf., pp. 5-54,006.. [3] Jianyun Hu, Yunlian Zhu, and Hui Wu, An Ultra-wide Band Resistive feedback Low noise amplifier with noise cancellation in 0.8µm Diital CMOS, IEEE Topical meetin on Silicon monolithic interated circuits in RF system, pp. 8-,008. [4] Chin-Fu Li et al., A Power-Efficient Noise Suppression Technique Usin Sinal-Nulled Feedback for Low Noise Wideband Amplifiers, IEEE Transactions on Circuits And Systems-II: Express Briefs, Vol. 59, No., pp. -5, 0. [5] Vaithianathan Venkatesan, Raja Janakiraman and Srinivasan Raj, A 90nm CMOS Low Noise Amplifier with Shunt Series Peakin for Ultra Wide Band Communication Systems, International Journal of Electrical Enineerin, Vol. 5, No. 4, pp , 0. [6] Yeo Myun Kim, Honul Han and Tae Wook Kim, A 0.6-V +4 dbm IIP3 LC Folded Cascode CMOS LNA With m Linearization, IEEE Transactions on Circuits and Systems ii: Express Briefs, Vol. 60, No. 3, pp. - 6, 03. [7] Xiaohua Fan, Hen Zhan and Edar Sánchez-Sinencio, A Noise Reduction and Linearity Improvement Technique for a Differential Cascode LNA, IEEE Journal of Solid-State Circuits, Vol. 43, No. 3,pp ,008. [8] Renuka P. Jindal, Compact Noise Models for MOSFETs, IEEE Transactions on Electron Devices, Vol. 53, No. 9, pp ,006. IJCA TM : 35