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: 100MHz 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 /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

ADC14100-USB Block Diagram

ADC14100-USB Front Panel

ADC14100-USB Rear Panel

ADC14100-USB Features 14 Bit 100 MSPS ADC Analog Devices ADSP DSP 256K x 18, 100 MHz FIFO memory USB 2.0 Interface RS232 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