I was thinking of how this chip could be used considering that the output is square wave and hence full of harmonics. Wondering if I could do with only a single generator ( vs using two, the second at an offset frequency. . If the test signal was amplitude modulated at a very low frequency say one khz and if the  If the signal at the "in" port of the mixed with a copy of the un-modulated original signal one could get to use a low pass filter to detect this the carrier would appear as DC in the output while the LF ( I khz ) could be measured for finding the response?  just thinking. i need to work out the details but was wondering what your response would be. AM of the exciting signal would be easy to arrange?