A measurement device such as a DMM may include four basic units—an analog
circuit path, an analog to digital converter (ADC), a digital filter, and an RMS
computation unit. The four basic units may be operable to multiplex or to process
one or more of the plurality of channels at the same time. The analog circuit path
may include the necessary circuitry for the plurality of channels to couple to
one or more analog signals. The analog circuit path may couple to the ADC. The
ADC may be operable to receive the one or more analog signals from the analog circuit
path and convert it to one or more digital signals. The ADC may include a cascaded
ADC, which may include a first ADC and a second ADC. The first and the second ADC
and may be able to convert analog data to digital data during a cycle. In one embodiment,
the first ADC may generate a conversion result and an error signal. The second
ADC may be operable to receive the error signal, digitize the error signal, and
process the error signal, thus performing noise cancellation. A summation operation
may combine the data from the first ADC and the processed data from the second
ADC. The cascaded ADC may consist of a continuous-time 1-bit sigma-delta modulator
followed by a SAR ADC. Digital output from sigma-delta modulator may be weighted
and summed with the output of the SAR ADC in an FPGA.