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

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Table 33. Performances Comparison Filter [VI.1] Filter 1 Filter 2 Units Linearization tech. DSD* DSD* MGTR - Tuning range 50 - 300 45 - 385 45 - 450 MHz Q factor 6 3.5 3.7 - Gain 6 10 6 dB NF 20 18 16.3 dB IIP3 2 to 6 -4 to 2 8 to 10 dBm Power consumption 7.6 16.5 30 mW Supply 1.2 2.5 2.5 V CMOS Technology 130 65 65 nm From the Gm-C filters design, it comes out that the main limitation of the performance is the gyrator. Indeed, the RF signal undergoes strong distortion and degradation when flowing through the active inductor. It has also been assessed the ability of the Gm-C filter to be used at higher frequencies. However, linearity is strongly degraded as soon as frequency increases. This is due to the use of smaller capacitances in the capacitors banks ensuring the frequency tuning. Indeed, the switch capacitances non-linearity of the switches becomes non negligible compared to the classically capacitances. Furthermore, a selectivity of 4 in UHF only rejects adjacent channels by 1dB or less. A higher Q is demanded but enhancing the quality factor would result in higher NF. Rauch filters To overcome Gm-C limitations due to the signal flowing through the gyrator, operational amplifier (OA) based filters are investigated. The purpose is to take advantage of both a high loop gain and a filter response introduced by to the RC network. Hence, we are aiming at designing a highly linear filter while not compromising noise at the same time. However, RC filters are more selective at high gain. Among the structures found in the literature, the positive feedback Rauch topology presents the highest selectivity for a given gain. It also presents limited sensitivity to passive components, making it a more robust solution. It has been chosen to limit the filter gain to 10dB, which corresponds to a quality factor of 3 when optimizing the dimensioning of the Rauch filter. Indeed, if the gain on the RF filter stage is too high, this would result in very high noise constraints on the LNA. - 174 -
The positive feedback Rauch filter is unstable under a certain condition. An innovative solution has been proposed to stabilize the filter, based on a non-inverting operational amplifier, which prevents from fulfilling this instability condition. Specifications on the operational amplifier have then been set to obtain the best performances and choose the technology. The choice of the technology turns to 0.25µm BiCMOS instead of 65nm CMOS due to the higher OA voltage gain. Stability margins have then been taken to ensure the robustness of the circuit. It has then be realized on a test-chip and measured in a laboratory. Measurements show a perfect agreement with the post-layout simulations. As specified, a quality factor of 3 is obtained for 10dB gain. As summarized in Table 34, NF is 15dB whereas IIP3 is higher than 9dB up to 240MHz. IIP3 is 19dBm at 45MHz, which demonstrates the highly linear characteristic of the filter. The tuning range is limited to 240MHz due to the drop of the gain of the OA which strongly degrades the linearity performances of the filter. Moreover, a Q of 3 at higher frequencies would reject by less than 1dB the adjacent channels. Table 34. Sum-up of the Rauch filter performances Rauch Filter Units f0 Tuning Range 45 - 240 MHz Q-factor 3 - Filter Gain at f0 10 dB NF 15 dB In-band IIP3 19 to 9 dBm Max. Input Power -5.5 dBm Supply 3.3 V Consumption 155 mW Technology BiCMOS 0.25µm - - 175 -
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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
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Using this structure and considerin
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The dimensioning of the transistors
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III.3.c Gm-cells with MGTR III.3.c.
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Furthermore, the high sensitivity t
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Figure 136. Filter in-band IIP3 ver
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III.4 Comparison of the filters III
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III.5 Conclusion Once the Gm-C seco
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IV. Rauch Filtering IV.1 Sallen-Key
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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 and 160: IV.4.c Performances Sum-up The filt
Page 161 and 162: Table 30. Frequency Limitations of
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: RF selectivity challenges In this t
Page 181 and 182: It is worth highlighting that FOM1
Page 183 and 184: étudiée. Il s’avère que la lin
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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
Page 211 and 212: C.5 References C.5.a Gyrator-C filt
Page 213 and 214: [C.23] J. De Lima and C. Dualibe,
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Page 217 and 218: this gives: I I I md d1 d 2 = I I =
Page 219 and 220: D.2 MOS Degenerated Common-Source C
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Page 223 and 224: 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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