Agilent Technologies DC122 User Manual download pdf (Page 15)

User Manual: Agilent Acqiris 10-bit Digitizers Page 15 of 27

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

Samples/ channel

Maximum

Optional Memory

Samples/ channel

Maximum

Segments

DC122

U1062A

-001

4 GS/s 1 / 1 512K 512M 125K

DC152

U1062A

-002

4 GS/s 2 / 2 256K 256M 125K

DC222

U1065A

-001

8 GS/s 1 / 1 1024K 1G 125K

DC252

U1065A

-002

8 GS/s 2 / 2 512K 512M 125K

DC282

U1065A

-004

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 10 MS/s (100 ns per point). The sampling rate

can be programmed and is selectable in a 1, 2, 2.5, 5 sequence (i.e. 10 MS/s, 20 MS/s, 25 MS/s, 50 MS/s, 100 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. It should also be understood that the maximum theoretical transfer

rate from the external memory to the cPCI bus is limited to 215 MS/s. For a 64-bit 66 MHz cPCI bus this leads to a

real maximum transfer rate of ~400 MB/s in the 16-bit data mode and ~200 MB/s in the 8-bit data mode.

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

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