Standard Amplifiers with DeltaSigma ADC & 100kHz LPF

We have measured the Slew rate / rise time on DEWE-43, STGM v3 and HD amplifiers:


Settings in  DEWESoft:

Sample rate = 200kS/s (max)

Measurement range = 10V

Low Pass filters = OFF


Measured with 5000V/us pulse as a reference.


Typical Slew rate of all of the above amplifiers is 1V/us.


Typical measured result for rise time was 2 samples (t=5us @ 200kS/s) for the change from 0V to 10V so SR = 10V/(2*5us) = 1V/us.

Inline image 1


This is typical result for all three amplifiers. Analog circuits before ADC may have different slaw rates but this can not be seen by user, user sees only sampled results as are above.


High Speed Amplifiers with SAR ADC & LPF Off

Slew rate / rise time on Sirius HS LVv2 amplifier:


Settings in DEWESoft:
Sample rate = 1000kS/s (max)
Measurement range = 10V
Low Pass filters = OFF

Measured with 5000V/us pulse as a reference.

Typical Slew rate of Sirius HS LV amplifier is 10V/us.



Bandwidth

Standard

Standard SIRIUS amplifiers have integrated anti aliasing 100kHz Low Pass Filter. However, ADC has bandwidth normalized to sample rate from 0.5 (100Hz to 100kHz) to 0.38*SR (100kHz to 204.8kHz).

Maximum analog bandwidth, ADC & 100kHz LPF = 70-72kHz.

High Speed

LP Filter disabled

HS-ACCHS-CHGHS-HVHS-LVHS-STG
500kHz500kHz
200kHz for CHG
2MHz
1.2MHz @ 50V
700kHz @ 20V
1MHz
800kHz @ <0.2V
1MHz
800kHz @ <0.2V


HS SIRIUS amplifiers have integrated anti aliasing anti aliasing filter at 100 kHz (5th order, Bessel) which can be turned OFF for maximum BW specified in table above.


Rule of Thumb

When signal Rise Time (RT) is measured with 10% to 90% method this rule of thumb is plausible:

BW = 0.35 / RT


Example for Standard SIRIUS: 2 samples (t=5us @ 200kS/s) 

BW = 0.35 / 5us = 70kHz (Really good result)


Example for HS SIRIUS: less than 1 sample (t=<1us @ 1MS/s) 

BW = 0.35 / <1us = >350kHz (Rule is confirmed but is not accurate in full)


NOTE: To measure analog BW in full it should be measured BEFORE ADC on analog side or use FRF method. Rule of Thumb does not give whole information of analog BW because it does not take into account possibility of aliasing the frequencies.


Based on:

https://www.edn.com/rule-of-thumb-1-bandwidth-of-a-signal-from-its-rise-time/ 

https://www.signalintegrityjournal.com/blogs/12-fundamentals/post/853-back-to-basics-bandwidth-and-rise-time