ANALYSIS OF FIRST-ORDER FEEDBACK LOOP WITH LOCK-IN AMPLIFIER

A dc-SQUID (Superconducting QUantum Interference Device) is usually op erated in a first order feedback loop with a lock-in amplifier and thi s configuartion is called 'lock-in flux locked loop''. The system resp onse of this configuration was studied, The effect of the phase differ ence between the modulator and demodulator of the lock-in amplifier wa s quantitatively examined, The system is stable as long as the phase d ifference does not exceed pi/2. The system response is given as a func tion of the phase difference. Transfer gains from two input sites to t he output were calculated. Analyzes were verified to be correct by exp eriment.