A Thermal-Diffusivity-Based Frequency Reference in Standard CMOS With an Absolute Inaccuracy of $pm $0.1% From $-$55 $^{circ}$C to 125 $^{circ}$C

摘要

An on-chip frequency reference exploiting the well-defined thermal-diffusivity (TD) of IC-grade silicon has been realized in a standard 0.7 $mu{hbox{m}}$ CMOS process. A frequency-locked loop (FLL) locks the frequency of a digitally controlled oscillator (DCO) to the process-insensitive phase shift of an electrothermal filter (ETF). The ETF's phase shift is determined by its geometry and by the thermal diffusivity of bulk silicon ($D$ ). The temperature dependence of $D$ is compensated for with the help of die-temperature information obtained by an on-chip band-gap temperature sensor. The resulting TD frequency reference has a nominal output frequency of 1.6 MHz and dissipates 7.8 mW from a 5 V supply. Measurements on 16 devices show that it has an absolute inaccuracy of $pm $0.1% ($sigma= pm $0.05%) over the military temperature range ($-$55 $^{circ}{hbox{C}}$ to 125 $^{circ}{hbox{C}}$), with a worst case temperature coefficient of $pm hbox{11.2~ppm}/^{circ}{hbox{C}}$.