  The Simons Array (SA) project is a ground-based Cosmic Microwave Background
(CMB) polarization experiment. The SA observes the sky using three telescopes,
and POLARBEAR-2A (PB-2A) is the receiver system on the first telescope. For the
ground-based experiment, atmospheric fluctuation is the primary noise source
that could cause polarization leakage. In the PB-2A receiver system, a
continuously rotating half-wave plate (HWP) is used to mitigate the
polarization leakage. However, due to the rapid modulation of the polarization
signal, the uncertainty in the time constant of the detector results in an
uncertainty in the polarization angle. For PB-2A, the time constant of each
bolometer needs to be calibrated at the sub-millisecond level to avoid
introducing bias to the polarization signal. We have developed a new calibrator
system that can be used to calibrate the time constants of the detectors. In
this study, we present the design of the calibration system and the preliminary
results of the time constant calibration for PB-2A.
