Bob Pease in his notes:
on page 4 looks at few low frequency oscilators. The goal is to have lowest current draw. His best result with CD4007 was 22uA, and best overall was low power comparator which gave him
1.4uA.I tried classic circuit from AOE (p. 426 figure 7.2) using
74HC04. I used 20M resistor as R1, 10M as R2, 1nF as C1 and 20pF speedup capacitor C2. With 1.5V supply current draw is 70nA frequency 21Hz, circuit works at least down to 1V. At 2V current is below 1uA but grow quickly with raising voltage to 9.6uA at 3V. Without speedup capacitor current draw is much higher, for example at 1.5V it grow to 1.2uA.Some remarks:
- Pease works at 6V. Working directly at 6V it seems hard do better than he did. OTOH low-speed level shifter is probably doable at cost of 200nA
- current seem to go down with increased resistors. 20M is largest resistor that I have (and largest that I seen at resonable price)
- my measurement includes extra buffer gate but with no load. Adding mulitmetr in frequency mode (via a capacitor) increased current draw by about 30nA.
BTW: I measured static current for those HC chips and got 0.1nA with difference form 0 within measurent error. So one can hope for some really low power circuits.