A double relaxation oscillation SQUID (DROS) provides a large flux-to-voltage transfer coefficient, and a room-temperature preamplifier can detect the DROS output directly. When the DROS is connected to a preamplifier consisting of several bipolar transistors, SSM2210s or MAT02s, the operation of DROS can be disturbed because the input-bias current of the preamplifier can flow through the DROS and exceed the critical current of the reference junction in the DROS. In order to know how the DROS acts when an input-bias current goes through the reference junction of DROS, we made a current controller to regulate the input-bias current of the preamplifier. The controller regulates an input-bias current of 0-12.5 μA with a resolution of 3 nA, which can cover preamplifiers made up of 10 pairs of SSM2210s in parallel. We have determined the input-bias current range for stable operation of the DROS when using Flux-Locked-Loop electronics with a preamplifier consisting of 4 SSM2210s. The higher the critical current of the reference junction in DROS is, the wider the operation input-bias range is. If the DROS has a low critical-current of the reference junction below 3 μA, however, a fixed input bias for reducing the input-bias current of the preamplifier may disturb the operation of the DROS. When the output of the DROS is detected by a preamplifier with an input-bias current controller, the noise of the DROS attains the same level of 10 fT/√Hz at 1 Hz and 5 fT/√Hz at 100 Hz, as long as the preamplifier has an input-bias current within the operation range, ever though it flows through the reference junction of the DROS.
|Number of pages
|Journal of the Korean Physical Society
|Published - May 1 2006
All Science Journal Classification (ASJC) codes
- General Physics and Astronomy