A novel topology for grounded-to-floating resistor conversion in CMOS technology

A new circuit topology to convert grounded resistors to an equivalent floating resistor is presented and discussed. The value of the resulting floating resistor equals the sum of the two grounded resistors. The new topology can be used to convert either passive, active grounded resistors or active grounded conductances. The new topology is used in the design of a current controlled very high value floating resistor in the range of GΩ. This was achieved by utilising the output conductance of two matched transistors operating in the subthreshold region and biased using a 500 nA current. The practicality of the new topology is demonstrated through the design of a very low frequency bandpass filter for artificial insect vision and pacemaker applications. Simulations results using Level 49 model parameters in HSPICE show an introduced total harmonic distortion of less than 0.25% for a 1 V_pp input signal in a 3.3 V 0.25 μm CMOS technology. Statistical modelling of the new topology is also presented and discussed.