A 0.5-V sigma-delta modulator implemented in a 0.15-mum FD-SOI process with low V_TH of 0.1V using analog T-switch (AT-switch) scheme to suppress subthreshold-leakage problems is presented. The scheme is compared with the conventional circuit, which are also fabricated in the same chip. The measurement result demonstrates that the sigma-delta modulator based on AT-switch realizes 6-bit resolution through reducing nonlinear leakage effects while the conventional circuit can achieve 4-bit resolution