I'm looking for a low power clocking solution and it looks like crystals bottom out at 32 kHz. Are there any low power (nA) solutions (crystals/ceramic resonators/custom transistor oscillator circuitry) that operate on nanoAmps of power in the single digit kHz range or lower?
EDIT
I wanted to summarize the facts from the answers below as well as my own research:
- Crystals do not commercially exist lower than the standard 32 kHz flavor, due to size/resonance constraints of the quartz used internally (thanks to Olin Lathrop)
- For a 32 kHz clock solution in the 100s of nA range, this oscillator IC could be used (thanks to stevenvh)
- For lower frequencies (but not necessarily nA current consumption) many silicon oscillators, frequency synthesizers, PLLs, or real time clocks include internal clock divider circuitry and can be used to generate clocks as "slow" as 1 Hz.
So there is no solution which satisfies both of the constraints of sub-32 kHz & sub-\$\mu\$A operation, but individual solutions that will satisfy one or the other.
Best Answer
Some manufacturers refer to 100kHz ~ 1.8432MHz as "very low frequency". Below 100kHz you'll find only a few specific values like 77.5kHz for (DCF77 receivers) and of course the 32.768kHz watch crystal. You won't find standard crystals below 10kHz.
Nothing lost, by the way. They won't help you meeting your low power requirements, anyway. A crystal needs a certain power to maintain its oscillation, and if you look at the datasheets you'll often see drive levels in the order of 1mW.
The lowest power microcontroller application using a crystal I designed was an MSP430 running at 32.768kHz, and that used 3\$\mu\$A, a thousand times your requirements.
This oscillator still uses 300nA, that's 0.3\$\mu\$A.