Temperature Coefficient Reduction of AC-Bridge Circuit for Cryogenic Temperature Control System

Precise temperature control is crucial for the development of sensitive instruments, as temperature fluctuations will introduce many negative effects. In temperature control systems,
$1/{f}$
noise is dominant in the low-frequency range, which limits the temperature control precision. To suppress the
$1/{f}$
noise, AC bridges based on the modulation-demodulation method are commonly used. While the
$1/{f}$
noise is suppressed, other types of noise rise to domination, further limiting the precision of the temperature control system. The response of the AC-bridge readout circuit to temperature fluctuation is the most serious. This paper proposes a method for suppressing the response of the AC-bridge readout circuit to temperature fluctuations. Using this method, the temperature coefficient of the readout circuit is reduced by matching the temperature coefficients of the used electro-components according to their weights of impact. This method has been verified in the test of a precise temperature control system designed for a superconducting gravimeter. The temperature coefficient of the AC-bridge circuit was reduced by approximately 57.4 times compared with the unmatched AC-bridge circuit, and the temperature fluctuation in the vacuum chamber of the superconducting gravimeter was controlled within
$\pm 5~\mu \text{K}$
.