A 0.9pJ/Cycle 8ppm/°C DFLL-Based Wakeup Timer Enabled by a Time-Domain Trimming and An Embedded Temperature Sensing

31.2 A 0.9V 28MHz Dual-RC Frequency Reference with 5pJ/Cycle and ±200 ppm Inaccuracy from -40°C to 85°C

“…6 summarizes the performance of the proposed frequency reference and compares it to previous work. Its accuracy (2.56ppm/°C) represents a >3x improvement on [1,2] and is in line with the state-of-the-art [4]. Compared to [4,5], this work is 5x more energyefficient, and is also much smaller.…”

“…An external crystal oscillator is often used as the radio's reference clock, but its high cost and size are a bottleneck for miniaturized IoT sensor nodes. CMOS RC frequency references are promising alternatives due to their low-cost integration and high energy efficiency [1][2][3][4][5]. Conventional RC references, however, achieve only moderate accuracy (a few %) due to the large temperature coefficient (TC) of on-chip resistors [3].…”

“…Conventional RC references, however, achieve only moderate accuracy (a few %) due to the large temperature coefficient (TC) of on-chip resistors [3]. 1 st order TC compensation can be achieved by combining resistors with complementary TCs [1,2]. Although this is energy efficient (<6pJ/cycle), it only partially compensates for the resistors' high-order TCs, limiting the resulting accuracy to about ±500ppm.…”

A Millimeter-Scale Crystal-Less MICS Transceiver for Insertable Smart Pills

“…Therefore, the duty cycle ratio for up to two days of operation with a 1-mAh battery should be less than 0.64% (assuming T is low). To maximize the power efficiency, a stable on-chip 400 kHz real-time clock is adopted as the timer, whose T is less than ±20 ppm within the target temperature range (25-45°C) [13]. Such low T timer is critical to operate in the ultra-low duty-cycled (i.e., 0.01%) LP-LDC mode.…”

“…An on-chip 400 kHz real-time clock [13] is utilized to perform duty-cycling with high time accuracy, and it has a built-in temperature sensor with a resolution less than 1 °C. This temperature sensor together with a LUT is used to calibrate the DCO frequency.…”