High Speed Data Acquisition Architectures Some Basic Architectures
High Speed Data Acquisition Architectures
Some Basic Architectures • • • Non-Buffered (streaming) FIFO Buffered Multiplexed RAM “Ping Pong” Multiplexed RAM Dual Port RAM
Streaming Interface Block Diagram
Advantages / Disadvantages of Streaming • Advantages – Simple, low cost – If only a small sample block is required, internal DSP RAM can be used for buffering – Processing takes place in real time • Disadvantages – Limited sampling speed
FIFO Buffered Block Diagram
Advantages / Disadvantages of FIFO Buffered • Advantages – Simple – Allows initial samples to be processed while subsequent samples are collected – Moderate cost, low to moderate density – Fast: 100 MHz clock rates readily available • Disadvantages – Sequential access, unneeded samples must be unloaded – Calculations cannot be done “in place”
Multiplexed RAM Block Diagram
Advantages / Disadvantages of Multiplexed RAM • Advantages – Low cost – High density – Random access – Calculations can be done in place • Disadvantages – More complex than FIFO, requires multiplexers, counters, etc – RAM only available after all data has been collected. Processing of first samples cannot proceed in parallel with subsequent data collection – RAM access time may require that ADC data be demultiplexed into multiple data streams
“Ping Pong” Multiplexed RAM Block Diagram
Advantages / Disadvantages of “Ping Pong” Multiplexed RAM • Advantages – High density – Random access – One data buffer is always available to DSP/Host, so next data set is collected while first data set is processed – Calculations can be done in place • Disadvantages – Complex, requires dual RAM banks, several multiplexers, counters, etc – RAM access time may require that ADC data be demultiplexed into multiple data streams
Dual Port RAM Block Diagram
Advantages / Disadvantages of Dual Port RAM • Advantages – Simple – Random access – First data point is available for processing immediately – Calculations can be done in place • Disadvantages – Low density, high cost – RAM access time may require that ADC data be demultiplexed into multiple data streams
Interfaces • • USB 2. 0 10/100 LAN Gigabit LAN Parallel Bus (PXI, CPCI, VME, VXI, etc)
USB 2. 0 • Advantages – Simple hardware – 480 Mbps – Widely available on desktops and laptops • Disadvantages – Can require substantial software overhead – Sharing bus with over devices limits bandwidth – Must be in close proximity to computer
10/100 LAN • Advantages – Widely available on desktops and laptops – Operates over long distances • Disadvantages – Typically requires coprocessor – Can require substantial software overhead – Sharing bus with other devices limits bandwidth
Gigabit LAN • Advantages – 1000 Mbps – Operates over long distances • Disadvantages – Typically requires embedded SBC with operating system support – Can require substantial software overhead – Sharing bus with other devices limits bandwidth
Parallel Bus • Advantages – – Fastest possible data transfer DSP may not be required for some applications Can use off the shelf SBC as controller/host processor Host processor/OS could support other interfaces (e. g. Gigabit LAN) • Disadvantages – Expensive (requires SBC) – Size, power consumption
ADC 14100 -USB Block Diagram
ADC 14100 -USB Front Panel
ADC 14100 -USB Rear Panel
ADC 14100 -USB Features • • 14 Bit 100 MSPS ADC Analog Devices ADSP-21262 DSP 256 K x 18, 100 MHz FIFO memory USB 2. 0 Interface RS 232 Interface Hardware decimator for lower sample rates at full analog bandwidth 3 software selectable clock sources: – Internal 100 MHz oscillator – Internal 80 MHz oscillator – External clock
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