Unit of Output data of pwelch

Since I wasn't able to take a lecture on Signal Processing, this question might be too silly I guess..

I have a EEG signal (in mV) for 15 secs.

What I want to do is analyze the signal with pwelch function to get PSD estimate for a signal.

I've got the data but I'm wondering what is the unit of the y-axis of the plot(pwelch(sig)).

I want to plot a graph with [x-axis : Frequency(Hz)][y-axis : Power(mV^2/Hz)].

Y-axis unit of the figure with this data(in mV) and (if the unit is not mV^2/Hz) how to convert y-axis unit to mV^2/Hz would be really grateful!

Answer 1

[Walter Roberson]

http://www.mathworks.com/help/signal/ref/pwelch.html#outputarg_pxx

"PSD estimate, returned as a real-valued, nonnegative column vector or matrix. Each column of pxx is the PSD estimate of the corresponding column of x. The units of the PSD estimate are in squared magnitude units of the time series data per unit frequency. For example, if the input data is in volts, the PSD estimate is in units of squared volts per unit frequency. For a time series in volts, if you assume a resistance of 1 Ω and specify the sampling frequency in hertz, the PSD estimate is in watts per hertz."

So if your input is mV and you specify Hz then the output would be in mV^2/Hz