High-Precision Digital-to-Analog Tunable Capacitors With Improved Quality Factor Using a Parallel Digital Actuator Array

Abstract

We present a micromechanical digital-to-analog (DA) tunable capacitor using a parallel digital actuator array, which is capable of accomplishing high-precision tuning and quality factor improvement. The present DA tunable capacitor uses a parallel interconnection of digital actuators and thus achieves a low-resistive structure for wireless communications. Based on the criteria for the capacitance range (0.348-1.932 pF) and the actuation voltage (25 V), the present parallel DA tunable capacitor is estimated to have a quality factor that is 2.0 times higher than the previous serial-parallel DA tunable capacitor. In the experimental study, the parallel DA tunable capacitor changed the total capacitances from 2.268 to 3.973 pF (0.5 GHz), 2.384 to 4.197 pF (1.0 GHz), and 2.773 to 4.826 pF (2.5 GHz), thus achieving tuning ranges of 75.2%, 76.1%, and 74.0%, respectively. The capacitance precisions were measured to be 6.16 +/- 4.24 fF (0.5 GHz), 7.42 +/- 5.48 fF (1.0 GHz), and 9.56 +/- 5.63 fF (2.5 GHz), which were 10 times higher than the precisions (> 100 fF) compared to the conventional analog tunable capacitors. The parallel DA tunable capacitor showed total resistances of 2.97 +/- 0.29 Omega (0.5 GHz), 3.01 +/- 0.42 Omega (1.0 GHz), and 4.32 +/- 0.66 Omega (2.5 GHz), resulting in quality factors measuring 33.7 +/- 7.8 (0.5 GHz), 18.5 +/- 4.9 (1.0 GHz), and 4.3 +/- 1.4 (2.5 GHz) for large capacitance values (2.268-4.826 pF). We experimentally verified the high-precision tuning capability of the present parallel DA tunable capacitor with improved quality factor.