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NOTE: Passive high impedance probes are not suitable for high fidelity measurements above 100 MHz. The non- negligible (5-10 pF) tip capacitance loads the signal causing distortion and/or ringing when combined with the ground lead inductance. 3.3. Data Acquisition The table below summarizes the characteristics discussed in the sections that follow: Model Max. Sampling Rate Max. CONVER TERS PER CHANNEL/ CHANNELS Default Memory points/ channel Maximum Optional Memory/ channel Maximum Segments TTI Reso- lution Timebase Accuracy External Clock Max./ Min. Thresh. DP105 500 MS/s 1 / 1 128K 2M 4000 80 ps 50 ppm ± 2 V DP106 500 MS/s 1 / 1 128K 2M 4000 80 ps 50 ppm ± 2 V DP110 1 GS/s 1 / 1 128K 8M 8000 80 ps 50 ppm ± 2 V DP111 1 GS/s 1 / 1 128K 2M 4000 5 ps 2 ppm ± 3 V DP210 2 GS/s 1 / 1 256K 16M 8000 5 ps 2 ppm ± 3 V DP211 2 GS/s 1 / 1* 256K 16M 8000 5 ps 2 ppm ± 3 V DP212 2 GS/s 1 / 1 256K 16M 8000 5 ps 2 ppm ± 3 V DP214 2 GS/s 1 / 1 256K 16M 8000 5 ps 2 ppm ± 2 V DP235 1 GS/s 2 / 2 128K 2M 4000 5 ps 2 ppm ± 2 V DP240 2 GS/s 2 / 2 128K 8M 8000 5 ps 2 ppm ± 2 V DP1400 2 GS/s 2 / 2 128K NA 1000 ~13ps 2 ppm AC 0 V DC110 1 GS/s 1 /1 128K 8M 8000 5 ps 50 ppm ± 2 V DC135 1 GS/s 2 /2 128K 2M 4000 5 ps 2 ppm ± 2 V DC140 2 GS/s 2 / 2 128K 8M 8000 5 ps 2 ppm ± 2 V DC211 4 GS/s 1 / 1 512K 32M 8000 5 ps 2 ppm ± 2 V DC211A 4 GS/s 1 / 1 128K 8M 8000 5 ps 2 ppm ± 2 V DC240 2 GS/s 1 / 2 256K 16M 8000 5 ps 2 ppm ± 3 V DC241 4 GS/s 2 / 2 256K 16M 8000 5 ps 2 ppm ± 2 V DC241A 4 GS/s 2 / 2 128K 8M 8000 5 ps 2 ppm ± 2 V DC265 500 MS/s 1 / 4 128K 2M 4000 5 ps 2 ppm ± 2 V DC270 1 GS/s 1 / 4 128K 8M 8000 5 ps 2 ppm ± 2 V DC271 4 GS/s 4 / 4 128K 8M 8000 5 ps 2 ppm ± 2 V DC271A 4 GS/s 4 / 4 128K 8M 8000 5 ps 2 ppm ± 2 V DC271AR 2 GS/s 2 / 2 128K 8M 8000 5 ps 2 ppm ± 2 V The * indicates a Dual Input module where there is one channel which can digitize the signal on one of the two BNC inputs 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, 4, 5 sequence (i.e. 1 MS/s, 2 MS/s, 2.5 MS/s, 4 MS/s, 5 MS/s, 10 MS/s, … 1 GS/s, 2GS/s, 4 GS/s). The maximum sampling rate shown above sometimes 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 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. For example, the model DC110 or DP110 with 2 Mpoints of memory can record a signal over a 2 ms period with a sampling rate of 1 GS/s (1 ns per point). The fast sampling rate ensures that all high frequency signal components, up to the full 250 MHz bandwidth of the digitizer, are accurately recorded. If the memory were reduced to just 20 Kpoints then the sampling rate would need to be reduced to just 10 MS/s (20,000/2 ms) to record the same 2 ms period. All frequencies above 5 MHz would then be incorrectly digitized and important signal characteristics may be distorted or even completely missed. 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. 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. The Single Acquisition mode is the normal operation of most digitizer products. In this mode an acquisition consists of a waveform recorded with a single trigger. The user selects the sampling rate and acquisition memory size and sets the number of segments to 1 (default value). The Sequence Acquisition mode allows the capture and storage of consecutive “single” waveforms. Sequence Acquisition mode is useful as it can optimize the digitizer’s sampling rate and memory requirements for applications where only portions of the signal being analyzed are important. The mode is extremely useful in almost all impulse- response type applications (RADAR, SO...

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