TLV320ADC6120: Audio ADC: missing power consumption & digital filter issues

Hey Christian,

Thank you for your feedback and interest in our parts! I'm glad to hear the ADS127L01 is serving you well!

For the TLV320ADC6120 the parts are available to sample, but this is not a fully released device yet so there was still some remaining characterization to be done to update some of the TBD specs. We are planning to fully release the device by the end of the next month and an updated version of the datasheet should be available shortly. In addition to this, at the time of release we will have an app note that details the power consumption in various operating modes and sample rates, similar to what we have for the TLV320ADC6140.

On the decimation filter side, this really boils down to the design tradeoffs in making a more complex filter vs. things like package size, cost, and power consumption. Generally for audio applications we have found that the 70-80dB of stopband rejection is sufficient for a few reasons:

1) These systems are generally bandwidth limited in multiple other ways. These devices are only intended to be paired with microphones that might extend up into the ultrasonic range and the out of band noise that these microphones might pick up/generate would be very low level such that 70-80dB is enough to bring this noise well below the measurable level. Any playback path is also going to have similar levels of stopband rejection.

2) The front end PGA of our device has a bandwidth of ~80kHZ, so any frequencies higher than this are going to be inherently filtered by the PGA prior to reaching the decimation filters. 

3) These are highly integrated devices so there generally aren't a lot of ways that this higher frequency noise would be able to couple into the signal path. It essentially boils down to noise on the supply (for which these devices have a typical PSRR of ~100dB) and noise on the input. If there is the potential for large amounts of high frequency noise to couple in to the input then an anti-aliasing filter can always be used.

4) You could potentially have some ground interference issues, but generally this can be avoided with proper ground plane management and by following the layout guidelines.

All of this is really to say that we have found that for most consumer audio applications these devices were designed for, 70-80dB stopband rejection is sufficient to not pass significant amounts of higher frequency noise that might degrade performance, and as long as this noise isn't mixing with something else it would be well outside of the audible bandwidth anyways. We do recognize that some people like to use these devices outside of traditional audio applications and we try to make them as flexible as possible to support that, but they are still designed with the audio market in mind first.

We always appreciate the feedback though and I say all of this not to be confrontational but just to explain some of our reasoning behind these decisions. If you have an application that has suffered from this limitation though I would be curious to hear about it as we are always looking to improve our next generation of devices!

Best,

Zak