I'd like to get a better understanding of the noise and distortion properties of the ADG4612 part. This is a 4:1 analog MUX rated at a bandwidth of 193 MHz, but the data sheet treats it as an audio part, with the THD+N characterized with an AP audio analyzer. The published THD+N specs are relatively poor, on the order of 1% or -20 dBc.
However, when I measured the part's HD2 and HD3 performance on your eval board at various frequencies from 100 kHz-20 MHz, I'm seeing much better HD2 numbers in the -60 dB to -70 dB range as long as I keep the level around 0 dBm. The odd-order distortion appears to be negligible, as does additive noise.
So the question is, what's up with this part's THD+N specs? These were measured at very high signal levels (3V peak) into 110 ohms according to the data sheet so that might account for the harmonic performance. But I'm looking at using it as an RF part in a 50-ohm system, and it seems to be a good performer from what I can tell. I'm a little nervous at the lack of RF distortion measurements on the data sheet, so I'd like some confirmation that I'm not missing anything before I use it to drive a 14-bit RF ADC. Is there some reason why it wasn't characterized as an RF part?