High-Resistance Resistor Consisting of a Subthreshold CMOS Differential Pair

We propose a CMOS circuit that can be used as an equivalent to resistors. This circuit uses a simple differential pair with diode-connected MOSFETs and operates as a high-resistance resistor when driven in the subthreshold region of MOSFETs. Its resistance can be controlled in a range of 1-1000 M Omega by adjusting a tail current for the differential pair. The results of device fabrication with a 0.35-mu m 2P-4M CMOS process technology is described. The resistance was 13 M Omega for a tail current of 10 nA and 135 M Omega for 1 nA. The chip area was 105 mu m x 110 mu m. Our resistor circuit is useful to construct many high-resistance resistors in a small chip area