A 1.66-nW/kHz, 32.7-kHz, 99.5ppm/°C fully integrated current-mode RC oscillator for real-time clock applications with PVT stability

An Area‐Efficient Resistor‐less On‐Chip Frequency Reference for Ultra‐Low Power Real‐Time Clock Application

“…Figure shows a simplified schematic of the conventional ROSC . The ROSC consists of a BCG , integrator (INTEG), voltage to current converter (VCC), current mode comparator with latch circuit (CMC), and output logic circuit.…”

“…), it needs a large resistor R for ultra‐low power operation and occupies a large area of the silicon chip. Although a charge‐recycle‐integrator (CRI) in the conventional ROSC is used to save the resistor area in the BCG, it still needs a large resistor (e.g., 30 MΩ) . Therefore, a low‐power and resistor‐less ROSC is strongly required.…”

“…However, because they are bulky (∼1 mm 3 ) [7] and require relatively high power (several hundreds of nW), they are not suitable as an RTC for IoT devices [1]. Fully on-chip solutions have been reported [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. These circuits are based on a ring or relaxation oscillator (ROSC) and can generate a stable frequency with low power and moderate accuracy against process, voltage, and temperature (PVT) variations.…”

“…Note that all the simulations were performed using SPICE BSIM4 v4.5 model and 65-nm CMOS process parameters. Figure 1 shows a simplified schematic of the conventional ROSC [27]. The ROSC consists of a BCG [29], integrator (INTEG), voltage to current converter (VCC), current mode comparator with latch circuit (CMC), and output logic circuit.…”

“…In order to show the effectiveness of our ROSC, we also perform SPICE simulations considering temperature variation. The proposed ROSC is based on our conventional current‐mode ROSC and is modified to be an area‐efficient circuit configuration without resistors. The proposed ROSC uses a temperature‐compensated bias current generator (BCG), proportional to absolute temperature (PTAT) voltage source, and shunt regulator to compensate for the temperature dependence of the frequency.…”