A delta-sigma true RMS-to-DC converter using an indirect-charge-transfer filter

An indirect charge transfer (IDCT) technique is applied to a delta-sigma (/spl Delta//spl Sigma/) true RMS-to-DC converter. This technique makes the converter gain depend only on the capacitors' ratio. It reduces the gain drift and the absolute gain error. The RMS-to-DC converter is fabricated in a 0.8 /spl mu/m double-poly double-metal (DPDM) CMOS process. Measured results show that, with no trimming and calibration required, this converter achieves an absolute error /spl plusmn/0.8% of reading, even with input RMS levels up to 800 mV.