- Reference: A 120nW 18.5kHz RC Oscillator with Comparator Offset Cancellation for ±0.25% Temperature Stability
- ISSCC 2013
- Frequency: 18.5kHz
- Process: 65nm CMOS 1V
- Power: 120nA
- Temperature Coefficient: ±0.25% for -40°C ~ 90°C
- Area: 0.032mm2
最大的创新点，V1和V2交替充电；基准和Ramp信号在比较器的输入端交换了，从而实现一次充IR+Vos, 一次充IR-Vos，实现了 offset cancellation；这样可以不顾及offset，取激进的尺寸，提高比较器的速度；而且chop消除了1/f噪声，提高了 long-term stability。
对于比较器的 tdelay，放松 offset 的要求有了优化空间，同时用 PTAT 偏置实现较恒定的速度；开关的漏电和导通阻抗会都会影响 TC，但是这对尺寸的要求却是矛盾的，导致S1/S2稍微需要取折中选择；R=5MΩ，C1=C2=5pF，I=30nA，这里使用较大的C和较小的I，减小电压摆幅（V=I×T/C）以减少漏电。
功耗分配：The current sources charging R and C consume 30nA each, the comparator 40nA, current mirrors 10nA and the Schmitt triggers and buffers consume 10nA. The current reference, shared with the rest of the system, works from a system supply voltage of 1.5V-3.3V and consumes 25nA. It generates the 10nA PTAT current reference required for the oscillator.