Ultra-low noise limiting amplifier. Designed for stabilizing the amplitude of the RF voltages used in ion traps.

The circuit uses a low-noise digital circuit to convert an input "clock" to a square-wave with very stable amplitude. After band-pass filtering, we recover a sinusoid with stable amplitude.

The output RF power is fixed at around 10dBm depending on frequency. The optional DAC Board provides very fine digital tuning (1dB with 16-bit resolution). If a larger dynamic range is required, a step attenuator after the squareatron is recommended.

Measurements using an R&S phase/amplitude noise meter demonstrate:

• No added phase noise compared with a top-of-the-range R&S synth
• AM noise limited by the measurement device at almost all offset frequencies (100k correlations). Broadband noise approximately at the -197dBc/Hz thermal noise floor!

Measurements with power detector show very low long-term drift. Temperature coefficient of output voltage amplitude is roughly -500ppm/C (exaxt number TBC).

Locking barrel connector is Switchcraft 760K.

Enclosure has been designed for mounting squareatron and DAC board: https://github.com/OregonIons/Squareatron_Box

Design files (schematics, PCB layouts, BOMs) can be found at Squareatron-5000/releases.