Agilent Technologies DC152 - Manual (Page 30)

3.3. Data Acquisition
The table below summarizes the characteristics discussed in the sections that follow:
Model
Agilent # Max.
Sampling
Rate Max.
CONVERTERS
PER CHANNEL/
CHANNELS Default Memory
points/ channel
Maximum
Optional
Memory
points/ channel
Maximum
Segments
DC122
U1062A
4 GS/s 1 / 1 512K -- 1K
DC152
U1062A
4 GS/s 2 / 2 256K -- 1K
DC222
U1065A
8 GS/s 1 / 1 1024K 1G 125K
DC252
U1065A
8 GS/s 2 / 2 512K 512M 125K
DC282
U1065A
8 GS/s 4 / 4 256K 256M 125K
3.3.1. Sampling Rate
All Acqiris digitizers contain an analog-to-digital conversion (ADC) system that can sample waveforms, in a real
time sampling mode, at rates from the maximum allowed rate down to 100 S/s (10 ms per point). The sampling rate
can be programmed and is selectable in a 1, 2, 2.5, 5 sequence (i.e. 1 MS/s, 2 MS/s, 2.5 MS/s, 5 MS/s, 10 MS/s, … 1
GS/s, 2GS/s, 4 GS/s, 8 GS/s). The maximum sampling rate shown above exploits the possibility of combining
channels.
3.3.2. Acquisition Memory
Data from the ADC is stored in on-board acquisition memory. The amount of memory in use for acquisition can be
programmed and is selectable from 1 point to the full amount of acquisition memory available.
For technical reasons, a certain acquisition memory “overhead” is required for each waveform, reducing the available
memory by a small amount. In order to simplify programming, an interface function recommends the best sampling
rate and the maximum possible number of data points, taking into account the available memory, the requested time
window, the number of segments (in Sequence mode), as well as the required memory overhead.
To ensure maximum sampling rate and high timing resolution, we strongly recommend the use of long acquisition
memories whenever possible.
Optional Memory is available on most models. It allows the maximum number of segments to be increased
significantly. However, this memory is divided into 2K sample pages and a segment must start at the beginning of
the page. Additional memory is used for segment time stamps. These constraints must be kept in mind when trying to
understand how the driver limits the number of points as the number of segments changes. Furthermore, multi-
segment event readout must read entire pages for each ADC. This can introduce significant overhead for small
segments and/or when channels are combined.
3.3.3. Single and Sequence Acquisition Modes
Digitizers acquire waveforms in association with triggers. Each waveform is made of a series of measured voltage
values (sample points) that are made by the ADC at a uniform clock rate. The digitizer can also measure and store
the arrival time of each trigger using the information from the on board Trigger Time Interpolator (TTI). Readout of
the individual trigger time stamps makes it possible to determine the time from one trigger to any other trigger. Time
differences up to 213 days can be measured. The TTI resolution sets the resolution of the trigger time stamps (see
section 3.3.5 TIMING). To maximize sampling rates and utilize memory as efficiently as possible, the digitizers
include both Single and Sequential storage modes. For both of these modes the data of all of the active channels is
acquired synchronously; all of the ADC’s are acquiring data at the same time, to within a small fraction of the
maximum sampling rate.
User Manual: Family of 10-bit Digitizers Page 30 of 55