Acqiris U5309A User Manual page 24

2.4 Real-time averaging (AVG option)
The NSA basenoise must be equal or smaller than NSA threshold.
Self trigger mode
See Trigger output (page 51).
Apart from the trigger sources described in the section Trigger (page 12) (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,
st
switching between the ADC cores to acquire the 1 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 —Similar SNR improvement is expected on a U5309A starting from minimum SNR.
Figure 2.5 - Example of signal to noise ratio vs Number of averagers for U5303A.
24 U5309A User's Manual