3 ms·

At the boundary between analog and digital, you typically need to provide an anti-aliasing filter. If you are measuring a differential signal with a large high

At the boundary between analog and digital, you typically need to provide an anti-aliasing filter. If you are measuring a differential signal with a large high-frequency common-mode component, then it also makes sense to perform the subtraction in analog. Otherwise the inevitable small phase shift between the sampling of the two channels in your ADC will end up coupling the common-mode signal into your difference.

dragontamer 10y ago
While what you say is true, its incredibly amazing how good ADCs are in the modern era. 3 Gigasamples / second: http://www.ti.com/lit/ds/symlink/adc07d1520.pdf http://www.ti.com/lit/ds/symlink/adc07d1520.pdf The fastest OpAmp I can find is this 18GHz GBP: http://www.ti.com/lit/ds/symlink/ths4303.pdf http://www.ti.com/lit/ds/symlink/ths4303.pdf At 3 GHz, the OpAmp would only offer a gain of 6 which isn't really enough for much accuracy. Granted, the OpAmp is like $5 and the ADC is hundreds of dollars (and the ADC is only 7-bit accurate)... but the digital world has gotten scary fast and scary good. That's why Oscilloscopes, even GHz-Oscilloscopes are being made with digital technology today. Hell, this crazy product raises eyebrows: http://www.digikey.com/product-detail/en/analog-devices-inc/HMCAD5831LP9BE/1127-3475-ND/5170112 http://www.digikey.com/product-detail/en/analog-devices-inc/... 26Giga-samples (Nyquist of 13). I mean, 3-bits sucks, but holy crap is that fast. A 26GHz ADC would be able to perform digital-filter analysis on 2.4GHz Bluetooth and Wifi without any aliasing what-so-ever.
- brandmeyer 10y ago
  Like anything, its a cost tradeoff. DSP can be much cheaper than active analog for many frequency ranges. You can certainly oversample your way to a cheaper antialiasing filter in many applications. But you can't ever eliminate it entirely.

dragontamer 10y ago

While what you say is true, its incredibly amazing how good ADCs are in the modern era. 3 Gigasamples / second: http://www.ti.com/lit/ds/symlink/adc07d1520.pdf http://www.ti.com/lit/ds/symlink/adc07d1520.pdf The fastest OpAmp I can find is this 18GHz GBP: http://www.ti.com/lit/ds/symlink/ths4303.pdf http://www.ti.com/lit/ds/symlink/ths4303.pdf At 3 GHz, the OpAmp would only offer a gain of 6 which isn't really enough for much accuracy. Granted, the OpAmp is like $5 and the ADC is hundreds of dollars (and the ADC is only 7-bit accurate)... but the digital world has gotten scary fast and scary good. That's why Oscilloscopes, even GHz-Oscilloscopes are being made with digital technology today. Hell, this crazy product raises eyebrows: http://www.digikey.com/product-detail/en/analog-devices-inc/HMCAD5831LP9BE/1127-3475-ND/5170112 http://www.digikey.com/product-detail/en/analog-devices-inc/... 26Giga-samples (Nyquist of 13). I mean, 3-bits sucks, but holy crap is that fast. A 26GHz ADC would be able to perform digital-filter analysis on 2.4GHz Bluetooth and Wifi without any aliasing what-so-ever.

brandmeyer 10y ago
Like anything, its a cost tradeoff. DSP can be much cheaper than active analog for many frequency ranges. You can certainly oversample your way to a cheaper antialiasing filter in many applications. But you can't ever eliminate it entirely.