A +/- 0.5% Precision On-Chip Frequency Reference With Programmable Switch Array for Crystal-Less Applications

An on-chip frequency reference is designed for low-power, low-cost, and fully integrated system-on-chip designs. In this relaxation oscillator, pseudodifferential architecture is used to eliminate frequency variation caused by bias current, and interleaving capacitors are implemented to extend its discharge time. A low-leakage programmable switch array (PSA) trimming method is proposed to calibrate the first- and second-order temperature coefficients (TCs) of the composite resistor. The oscillator was fabricated in a 0.35-mu m 2P4M CMOS process with an area of 0.162 mm(2). The oscillator operates at 130 kHz, and measurement results show that it achieves a frequency variation of less than +/- 0.5% over a temperature range of -20 degrees C-100 degrees C and less than +/- 0.4% over a supply voltage range of 1-3 V