Hi.
The following datasheet might be helpful.
http://www.analog.com/UploadedFiles/Data_Sheets/107897653AD9244_b.pdfAgilent 8644 is used as SG there.
But you have to insert LPF or BPF between SG and DUT for removing harmonics from SG.
Accuracy needed for evaluationg ADC with more than 10bit is very severe, it is beyond accuracy of SG itself.
So characteristics of LPF or BPF is more critical than SG.
You should order special fixed filter.
Variable filter or standard product fixed filter can't be consistent for more than 10bit ADC's evaluation.