To promote the adaptability of the practical Magnetocardiography (MCG) system working in unshielded environment, the SQUID readout electronics is required to improve its stability and the Electromagnetic Compatibility (EMC). It should be low-drift to the variation of cryogenic liquid level in long-time running, avoid Electromagnetic Interference (EMI) internally from the control circuit, be electrical isolated from host computer, and finally be compact to be embedded in the cryostat to implement external EMI shielding and filtering. Accordingly, we presented a low-drift and compact readout circuit design. It applies the differential amplifier in the Flux-Locked Loop (FLL) to reject the voltage drift, and avoids the internal EMI by using control circuit without Micro-Controller Unit (MCU). It simplifies the integration of multi-channel FLLs and the isolated accessing from host computer by using the Inter-Integrated Circuit (IIC) bus with fiber optic interface. In the experimental results, our MCU-free FLLs successfully suppressed the voltage drift, and exhibited the high consistency in reading of 9-channel gradiometers with noise level of about 6.5μΦ₀ /√Hz. Finally, we set up a 9-channel MCG system using our multi-channel SQUID readout electronics, and demonstrated the high quality 9-channel measurements of adult MCG signals in the unshielded environment.

为了提高在非屏蔽环境下工作的实用心磁图（MCG）系统的适应性，需要SQUID读出电子设备以提高其稳定性和电磁兼容性（EMC）。长期运行时应尽量降低低温液位的变化，避免内部从控制电路产生电磁干扰（EMI），与主机电气隔离，最后要紧凑地嵌入低温恒温器中以实现外部EMI屏蔽和滤波。因此，我们提出了一种低漂移且紧凑的读出电路设计。它在磁通锁定环路（FLL）中应用差分放大器来抑制电压漂移，并通过使用不带微控制器单元（MCU）的控制电路来避免内部EMI。通过使用带有光纤接口的集成电路间（IIC）总线，它简化了多通道FLL的集成以及与主机的隔离访问。在实验结果中，我们的不含MCU的FLL成功地抑制了电压漂移，并且在读取9通道梯度计时具有很高的一致性，噪声水平约为6.5μΦ₀ /√Hz。最后，我们使用多通道SQUID读出电子设备建立了9通道MCG系统，并演示了在非屏蔽环境中对成人MCG信号进行的高质量9通道测量。