Start with the waveform you need to measure
A useful digitizer specification starts with the signal: its frequency content, voltage range, source impedance and whether the baseline matters. A high sample rate alone cannot compensate for an unsuitable analog input. For pulses, consider rise time and the waveform detail required, rather than only the pulse repetition rate.
Sample rate and analog bandwidth describe different limits
Sample rate is the number of samples acquired per second. Analog input bandwidth describes the frequency response of the signal path before conversion. Compare the bandwidth listed for the exact model; it is not universally one-half of the sample rate.
For ordinary baseband acquisition, choose a sampling strategy and anti-alias filtering appropriate to the highest signal frequency you need to retain. Bandpass sampling requires a separate review of the signal spectrum and alias locations. A high-bandwidth AC-coupled input should not be treated as a drop-in replacement for a DC-coupled input.
Resolution is not the same as measurement accuracy
ADC bit depth describes the number of nominal quantization levels. Noise, distortion, input range and the analog front end also affect usable signal detail. Compare actual performance information for the intended signal frequency and range; do not assume that every 16-bit configuration has the same effective resolution.
Compare an actual pair of configurations
The AD816x-500M14 and AD816x-500M16 both list 500 MS/s sampling. Their published input bandwidths differ: DC–250 MHz and DC–220 MHz, respectively. The choice therefore involves both ADC resolution and analog input response, not bit depth alone.
AD816x-500M14 specifications · AD816x-500M16 specifications
A practical selection checklist
- Match input range and impedance to the source.
- Decide whether DC coupling is required.
- Check sample rate and bandwidth separately.
- Confirm active channels, trigger and clock requirements.
- Check record length, memory and sustained transfer for the host system.
Compare digitizers and data acquisition cards or prepare a model-specific selection request.