Design and Analysis of Spiral Inductors by Genemala Haobijam & Roy Paily Palathinkal

Author:Genemala Haobijam & Roy Paily Palathinkal
Language: eng
Format: epub
Publisher: Springer India, New Delhi

Spiral inductors consume a lot of die area in RF circuitry as compared to the area required by active devices. To minimize the cost, the performance can be carefully traded off with the area ( ). These tradeoffs can also be explored from Figs. 2.15 and 2.16. Inductors with larger number of turns have smaller area but quality factor is lower because of smaller inner diameter. The magnetic fields of the adjacent outer turns will pass through some of the innermost turns, inducing eddy current loops which result in non-uniform current in the innermost turns thereby increasing the effective resistance and hence lowering the quality factor. This eddy current effect can be minimized by increasing the inner diameter and realized with the same inductance of 2–3 turns, but the area will also increase. However, it does not improve quality factor due to the increase in the series resistance as the total length increases with increase in area. For a fixed turn the spiral area also increases with the increase in width. Spiral structure may be selected considering both the quality factor and area. For a 5 % reduction in the quality factor, area can be saved by 39 % as compared to the optimum structure with the combination W = 9 m, N = 6 and = 199 m that results Q = 6.7. Similarly for a 10 % reduction in the quality factor, area can be saved by 49 % as compared to the optimum structure with the combination W = 8m, N = 7 and = 181 m which results Q = 6.4.

In the literature, spiral inductor optimization techniques are presented for different process parameters at different operating frequencies. Hence, it would be difficult to compare the results closely. For a fair comparison we have repeated the proposed optimization method using the process parameters employed in [14–16]. The spacing was fixed at 2 m since the turn-to-turn spacing in the published results was 2 m. The comparison of the proposed method with other optimization techniques [14–16] for inductance values close to 6 nH is given in Table 2.4. Enumeration method always results in a global optimum solution as compared to numerical algorithms that may sometimes lead to non-convergence and local optimum solutions.Table 2.4Performance comparison of optimization techniques

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