2.4 Real-time averaging (AVG option)
22
U5303A User's Manual
The NSA basenoise must be equal or smaller than NSA threshold.
The U5303A uses an ADC with 12-bit of vertical resolution. To improve the baseline stability, the
U5303A averager firmware provides a baseline stabilization processing which is optimum with 13-
bit of vertical resolution. Therefore, the averager firmware provides raw data for each single
accumulation in 13-bit format. If the baseline stabilization is not enabled, the output is raw data
output and is still in 13-bit format. As the NSA is performed after the baseline stabilization, the NSA
Threshold and NSA Base Noise are defined in ADC counts and can set up from 0 to 8191 ADC
counts. See
Self trigger mode
See
Apart from the trigger sources described in the section
(internal and external
triggering), another trigger mode called Self-Trigger enables minimum synchronous (pattern) noise.
Acqiris’s ADC cards use several interleaved ADC cores. In applications where multiple waveforms
are accumulated, the synchronicity between ADCs sequence and trigger results in a synchronous
noise which often becomes the dominant factor.For successive measurements, or averaging,
switching between the ADC cores to acquire the 1
st
sample of a data record avoids accumulation of
synchronous noise.
Self trigger
In self-trigger mode an autonomous trigger signal is generated internally in the ADC card and output
through the front panel I/O3 connector. This trigger signal consists of programmable periodic pulses
that are synchronous to the sample clock.
The self-trigger mode serves two purposes:
– Reducing trigger jitter by synchronizing the input signal to the sample clock
– Minimizing the synchronous noise, which consistently improve SNR through averaging of
successive measurements.
To use the Self-Trigger mode, the
Trigger ActiveSource
must be set to
SelfTrigger
.
Figure below shows the signal to noise ratio using an external trigger at a frequency multiple of the
sampling frequency (worst case) and the Self-Trigger at any frequency (best case), on a U5303A ADC
card.
