Hi Zhenhua, There are a few ways that you could implement this. 1. You could use an audio DAC with a higher sample rate - for example you could use the PCM5100A with a sample rate of 200kHz. 2. You could use one of our MDACs such as the DAC8811 . MDACs offer fast settling time, but will need to be buffered externally if you are going to drive any kind of load with the output. You could use a low voltage reference, but I would not recommend it. I think you should use a higher reference, then attenuate the output to the 100mV range with an external opamp. Finally how you could measure the RMS voltage is not a simple questions. If you know that the input signal is a sinewave, and will always be a sinewave, then you can use an ADC with a fast sample rate. If you are expecting 100kHz to be the high frequency you will measure, then you would want an ADC that will be able to measure the Vpeak value of the sinewave no matter the phase of the signal, think >500ksps. Then all you need to do is measure the peak value of the input wave. Vrms= Vpeak/sqrt(2) for a sign wave. If you are trying to measure the RMS value of a arbitrary wave form, then you will need to implement some kind of TRUERMS measurement method, and that a bit out of scope of this forum questions. Thanks! Paul
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