Ultra-High-Resistance Pseudo-Resistors With Small Variations in a Wide Symmetrical Input Voltage Swing

• Published in: IEEE transactions on circuits and systems. II, Express briefs Vol. 70; no. 8; pp. 2794 - 2798
• Main Authors: Karami Horestani, Fatemeh, Rosa, Jose M. de la
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.08.2023; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Amplifiers; Analog circuits; Circuit design; Cutoff frequency; Electric potential; Harmonic distortion; High resistance; Immune system; low-power biomedical systems; low-voltage; MOST-based resistors; RC circuits; Resistance; Resistors; System-on-chip; Transistors; Voltage
• ISSN: 1549-7747; 1558-3791; 1558-3791
• DOI: 10.1109/TCSII.2023.3258880

This brief presents a new strategy and circuit configuration composed of serially-connected PMOS devices operating in the subthreshold region for implementing ultra-high-value resistors required in very low-frequency active-RC filters and bio-amplifiers . Depending on the application, signal bandwidth for instance in bio-amplifiers may vary from a few mHz up to a maximum of 10 kHz. Three different resistor structures are proposed to achieve ultra-high resistance. While ranging in the order of several <inline-formula> <tex-math notation="LaTeX">\text{T}\Omega </tex-math></inline-formula>, the proposed ultra-high-resistance pseudo-resistors occupy a small on-chip silicon area, which is one of the main issues in the design of analog front-end circuits in ultra-low power implantable biomedical microsystems. In addition, these ultra-high-value resistors lead to the use of a small capacitance to create a very small cut-off frequency. Therefore, the large area to implement capacitances is also considerably reduced. The proposed resistor structures have very small variations about 7% and 12% in a wide input voltage range (−0.5 V~+0.5 V), thus significantly improving the total harmonic distortion of bio-amplifiers and the analog front-end of the system. Simulation results of different circuits designed in a 180nm CMOS technology, are shown to demonstrate the advantages of the proposed ultra-high-resistance pseudo-resistors.