A MIM-cap free digitally tunable NMOS capacitor

A novel approach of digitally tunable capacitors using only NMOS transistors of a Bulk-CMOS process is presented. Instead of using MIM-capacitors, stacked transistors are used to tune the capacitance value and have an additional low loss through mode. Using the 0.13 μm Bulk CMOS triple well process from Infineon Technologies, the device features a tuning range of 0.2 to 3.0 pF with a maximum Q of 90 at 900 MHz. The through mode shows an insertion loss of only 0.2 dB at 900 MHz. Including the MIPI control interface, voltage regulator and charge-pump, the Chip size is only 1100 μm × 900 μm. Current consumption is about 110 μA at 3.5V operation. The design is cost effective, as no MIM capacitances are required.