Implementing ultra-high-value floating tunable CMOS resistors

Introduction: Integrated high-value resistors (HVR) are key elements in many applications. Compact HVRs can be applied for biasing purposes or for implementing very-low-frequency filters [1, 2]. In addition to achieving high resistance, usually it is necessary to have good tuning capability of the resistor value, thus the controllability of the HVR is another important design issue. In this Letter, a compact HVR is introduced that utilises only PMOS transistors operating in the subthreshold regime. The resistance is adjustable in a very wide range. This property makes this technique very suitable for ultra-low-power reconfigurable applications. A test chip has been fabricated in conventional 0.18 mm CMOS technology and characterised to verify this concept. The proposed HVR has been applied to implement a low-frequency MOSFET-C filter with a wide tuning range and a constant dynamic range (DR).