In addition to the systematic (binary-weighted) inductor array considered above, other arrangements for tuning series and shunt inductors, in the context of MEMS switch switching, have been advanced, as shown in Figures 4.5 to 4.7 . In Figure 4.5, MEMS switches S1, S2, ?, Sx are connected in parallel with inductors L1, L2, ?, Lx, which, in turn, are connected in series between nodes IN1 and OUT1. With all switches open, the total inductance between nodes IN1 and OUT1 equals the sum of all the series-connected inductors. When any of the switches is closed, however, the low impedance of the switch bypasses that of the inductor, in essence short-circuiting it, and the total inductance decreases by that of the shorted inductor.
For example, if all inductors have a common value L, then the total inductance between nodes IN1 and OUT1 may be set to be any multiple of L, from a minimum of L to a maximum of X times L (i.e., XL), where the minimum value is obtained by closing all switches but one, and the maximum value is obtained by opening all switches. If all switches are closed, a nearly zero inductance is obtained.
In Figure 4.6, MEMS switches S1, S2, ?, Sx are connected in series with inductors L1, L2, ?, Lx, which, in turn, are connected in parallel between nodes IN2 and OUT2. When all switches are closed, the reciprocal of the total inductance, between nodes IN2 and OUT2, equals the sum of the reciprocals of all the parallel-connected inductors. When any of the switches is open, however, the high impedance of the switch essentially disconnects the inductor in question.
For example, in a configuration of four inductors with a common value L, the total inductance will vary from a maximum of L, when all switches are open but one, to a minimum value of L/4, when all switches are closed. Clearly, by combining the series- and parallel-connected inductor arrays, an even more ample and fine-grained set of inductance values becomes available.