1/f Noise Reduction with Noise Modulation in Time-Division Multiplexing (TDM)

We present a novel noise modulation technique using SQUID gain switching for Time Division Multiplexing (TDM) readout systems that reduces 1/f noise by a factor of 3.5 while preserving the architectural simplicity that makes TDM a widely used technique for Transition Edge Sensor (TES) arrays. In contrast to frequency division multiplexing or microwave multiplexing, where signal modulation inherently provides immunity to low-frequency noise, conventional TDM systems can be susceptible to 1/f noise from downstream electronics as the TES signals remain in the low-frequency band. In our approach, the operating point of the SQUID amplifier alternates between positive and negative gain slopes at the frame frequency, combined with synchronized digital inversion of the error signals prior to flux-locked loop integration. This modulation scheme shifts the readout noise, including the 1/f components of low noise amplifiers, analog-to-digital converters and room temperature electronics, into the frame frequency range where it can be separated from the DC-TES signal by decimation filtering. Laboratory validation using an 8 column × 32 row TDM platform designed for Athena X-IFU applications shows a reduction in 1/f noise from 73 pA/√Hz@1 Hz (9.3 µΦ0/√Hz) to 21 pA/√Hz@1 Hz (2.7 µΦ0/√Hz) in channels with no TES connected, with the additional benefits of a 14-fold reduction in SQUID bias sensitivity through dynamic resistance matching and a 6.5-fold reduction in temperature-induced baseline drift. The technique avoids the disadvantage of doubling white noise, which occurs with conventional noise subtraction methods, and at the same time achieves a comparable suppression of 1/f noise. Implementation requires only minor firmware modifications to existing TDM systems, making it easily implementable for far-infrared bolometric and X-ray spectroscopy applications.