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2.4.2 Zero Suppression

One of Ndigo 5G’s key features is on-board zero suppression to reduce PCIe bus load. Only data

that passes speciﬁcations predeﬁned by the user is transmitted. This guide refers to transmitted

wave form data as “packets”. A packet contains the wave form data and a timestamp giving

the absolute time (i.e. the time since start of data acquisition) of the packet’s last sample.

Figure 2.10 shows a simple example: Data is written to the PC only if values exceed a speciﬁed

threshold. Expanding on that, Ndigo 5G’s zero suppression can be used to realize much more

complex scenarios.

timestamp

Retrigger

Precursor Postcursor

Figure 2.10: Simple zero suppression: Only data with values above a threshold are written to

the PC.

2.4.3 Trigger Blocks

Ndigo5G-10 and Ndigo5G-8 record analog wave forms using zero suppression. Whenever a

relevant waveform is detected, data is written to an internal FIFO memory. Each ADC channel

has one trigger block determining whether data is written to the FIFO. The parameters are set

in Structure ndigo trigger block(See chapter 3.4.3 on page 34).

Each trigger block consists of two independent units that check the incoming raw data stream

for trigger conditions (Fig. 2.10 on page 10). Users can specify a threshold and can choose

whether triggering is used whenever incoming data is below or above the threshold (level trig-

gering) or only if data exceeds the threshold (edge triggering).

A gate length can be set to extend the trigger window by multiples of 3.2ns. Furthermore, if

users choose precursor values > 0, the trigger unit will start writing data to the FIFO precursor·

3.2ns before the trigger event.

When using edge triggering, all packets have the same length (Figure 2.11 on page 11):

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