III. Gm-C Filtering - Epublications - Université de Limoges

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IV.5 Frequency Limitations As said, the Rauch filter has originally been designed to be tunable between 45 and 240MHz. The use of this filter at higher operating frequencies results in using the OA with a reduced voltage gain. Indeed, due to its finite GBW, the gain of the OA decreases with frequency [IV.7]. since Furthermore, a lower OA gain leads to a higher K and so to a Q-factor enhancement ( Z 0 + Z f ) − ( Z + Z ) A( jω) K( jω ) = . (V.31) A( jω) Z 0 Indeed, the fixed capacitor decrease to 6pF in the capacitors banks so that the central frequency increases as well leads to a Q factor of 6 at 450MHz, and to a gain of 15dB. Q is enhanced due to a lower OA gain. Moreover, due to this smaller voltage gain, the input RF signal is more subject to distortions from the OA. This is why IIP3 strongly decreases as frequency increases. At 450MHz, in this configuration, IIP3 falls down to -3dBm. One possibility to counter the change in the value of K is to implement a tunable capacitor Cf (or C0) in order to keep K constant. This partially fights the drop of the OA gain and gives the results described in Table 30 where 5dBm IIP3 (for 10dB gain) are obtained at 450MHz for a 3.5 Q factor value. Last point preventing us from using the Rauch structure at higher frequencies is the trade-off selectivity versus filter gain. As explained in introduction, a more demanding selectivity is required in UHF in order to reject adjacent channels in a sufficient way. This is only possible increasing the gain of the filter. However, this solution would require amplifying less on the front-end LNA and it would result in challenging noise constraints on this LNA as well [IV.3]. 0 - 156 - f
Table 30. Frequency Limitations of the Rauch Filter Frequency Band Rauch BiCMOS 0.25µm Rauch 65nm CMOS 40 - 240 MHz 240 - 470 MHz 470 - 750 MHz 750 - 1000 MHz MEASURES SIMULATIONS G=10dB Q=3 G=10dB, Q=3 IIP3=9 to 19dBm IIP3=3 to 2 dBm NF=15 to 16,5dB NF=17,5dB 155mW @70MHz SIMULATIONS linearity falls down in frequency due to OA frequency limitation G=10dB Q=3,5 NF=15dB IIP3 down to 5dBm @ 450MHz if switches on C0 G=10dB Q=3,5 OpAmp limits linearity N+6 selectivity too low - 157 - OpAmp limits linearity N+6 selectivity too low
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UNIVERSITE DE LIMOGES ECOLE DOCTORA
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Acknowledgments En préambule à ce
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Summary ACKNOWLEDGMENTS ...........
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V. A PERSPECTIVE FOR FUTURE DEVELOP
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French Introduction Les signaux TV
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I. Introduction to TV tuners and to
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I.1.b.ii Digital modulations In dig
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makes the covering of a large terri
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I.1.c.iii Terrestrial spectrum Firs
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I.1.e Broadband Reception Systems F
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I.2.b TV Tuner High Performance Spe
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I.2.b.ii High linearity Although co
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I.3 RF Filter Specifications I.3.a
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27. This leads to the downconversio
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These adjacent channel rejection re
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Above 870MHz, there are no more ter
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Newest silicon tuners generations,
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I.6 References [I.1] B. Razavi, RF
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II. Challenges of RF Selectivity Fo
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Figure 39. H3 and N+5 rejections of
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Figure 43. Second order Low-pass Fi
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Figure 46 illustrates the transfer
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H HPF s ( s) = s 1 + ω This corres
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Topologies comparison for a same Q-
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Figure 56. Low-pass to Notch Transf
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II.2 Passive LC Second Order Bandpa
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A possible solution is to split the
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II.2.c Second Order Bandpass Filter
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Figure 69. Band Switching Figure 70
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Another paper [II.7] provides a FOM
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A parallel self resonating circuit
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This gives the following values for
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Vb - 63 - M1 M2 Zin Figure 76. Anot
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when given, reported noise figures
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In all publications dedicated to Gm
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II.4.c Second Order Bandpass Filter
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Figure 87. Biquad Schematic The Gm-
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Vin Rm - 73 - C Vout Figure 89. Der
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Figure 93 depicts the RF performanc
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A second advantage of advanced BiCM
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II.7 Conclusion As a conclusion, th
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[II.13] C. Andriesei, L. Goras, and
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III.I Theoretical Study III. Gm-C F
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g V m3 in III.1.b Linearity Conside
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Assuming an ideal input transconduc
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Figure 102. Linearity of the filter
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Furthermore, a Gm-C circuit is not
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In terms of noise, the Flicker nois
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Table 7 summarizes the specificatio
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Idiff (A) levels reached with this
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III.2.e Unbalanced Differential Pai
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Hence, the combination of the expon
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Technique Current Increase Source D
Page 109 and 110: Using this structure and considerin
Page 111 and 112: The dimensioning of the transistors
Page 113 and 114: III.3.c Gm-cells with MGTR III.3.c.
Page 115 and 116: Furthermore, the high sensitivity t
Page 117 and 118: Figure 136. Filter in-band IIP3 ver
Page 119 and 120: III.4 Comparison of the filters III
Page 121 and 122: III.5 Conclusion Once the Gm-C seco
Page 123 and 124: IV. Rauch Filtering IV.1 Sallen-Key
Page 125 and 126: Thus, an equation linking Q and Gai
Page 127 and 128: IV.1.c.ii Proposed positive feedbac
Page 129 and 130: For both Rauch and Sallen-Key filte
Page 131 and 132: The high sensitivity to passive com
Page 133 and 134: Furthermore, it should also be take
Page 135 and 136: IV.2.b Innovative Implementation of
Page 137 and 138: esulting gain K, constituted of the
Page 139 and 140: Table 25. Sum-up of the OA specific
Page 141 and 142: Figure 153. OA voltage gain versus
Page 143 and 144: Filtering in the mirror, by means o
Page 145 and 146: However, this feedback makes the fi
Page 147 and 148: Figure 160. OA Gain and phase versu
Page 149 and 150: IV.3.c Implemented Filter and Test
Page 151 and 152: Figure 165 depicts the layout of th
Page 153 and 154: Figure 169. PVT variations of the f
Page 155 and 156: IV.4 Rauch Filter Performances: Mea
Page 157 and 158: Figure 178. IIP3 versus input power
Page 159: IV.4.c Performances Sum-up The filt
Page 163 and 164: IV.7 References [IV.1] Y. Tsividis
Page 165 and 166: V. A Perspective for Future Develop
Page 167 and 168: V.2 4-path Filter Simulations V.2.a
Page 169 and 170: The frequency tunability is ensured
Page 171 and 172: V.3 State-of-the-Art V.3.a 4-path F
Page 173 and 174: V.4 Conclusion In this chapter, it
Page 175 and 176: IEEE International, 2009, pp. 222-2
Page 177 and 178: RF selectivity challenges In this t
Page 179 and 180: The positive feedback Rauch filter
Page 181 and 182: It is worth highlighting that FOM1
Page 183 and 184: étudiée. Il s’avère que la lin
Page 185 and 186: It is worth noticing that S0 only d
Page 187 and 188: A.3 Signal-to-Noise Ratio These dif
Page 189 and 190: A.5 Friis’ Formula In case of mul
Page 191 and 192: A.7 References [A.1] Friis, H.T., N
Page 193 and 194: To estimate the influence of the di
Page 195 and 196: Now, let’s have a look to the cub
Page 197 and 198: Figure 200. Third order intercept p
Page 199 and 200: B.2 RF Filter Linearity Measurement
Page 201 and 202: B.2.c IIP2 measurement To measure t
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Page 205 and 206: C.1 Gyrator-C filtering year Ref. f
Page 207 and 208: C.2 Gm-C Filtering year Ref. f0 (MH
Page 209 and 210: year C.3 Rm-C filtering Ref. f0 (MH
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C.5 References C.5.a Gyrator-C filt
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[C.23] J. De Lima and C. Dualibe,
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this gives: I I I md d1 d 2 = I I =
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D.2 MOS Degenerated Common-Source C
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⎛ I s ⎞ Vout = Vin + U T ln ⎜
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Computing, this leads to: V out + v
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FIGURE 54. H3 AND N+5 REJECTIONS AC
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FIGURE 168. PVT VARIATIONS OF THE F
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