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

ADCLPF DSP

Trigger/Clock

Interface(Bus, USB,

LAN)

RFInput

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

ADCLPF FIFO DSP

Trigger/Clock

InterfaceUSB, LAN,Bus, etc

RFInput

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

ADCLPF

DSP

Trigger/Clock

Interface(Bus, USB,

LAN)

RFInput

Counter

SRAM

Multiplexer

Data

Address

Multiplexer

Address

Data

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

ADC

LPF

DSP

Trigger/Clock

Interface(Bus, USB,

LAN)

RFInput

Counter

SRAM B

Multiplexer

Data

SRAM A

Multiplexer

Multiplexer Multiplexer

Data Data

Address Address

Address

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

ADC

LPF

DSP

Trigger/Clock

Interface(Bus, USB,

LAN)

RFInput

Counter

Dual PortSRAM

DataB

AddB

DataA

AddA

Address

Data

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

ADC14100-USB Block Diagram

Decimator256K x 18

FIFO

ADSP 21262Floating Point

DSP

100 MHz80 MHz

ExtClock

USB 2.0RFInput

ADC14 Bits

100MSPS

RS232

ADC14100-USB Front Panel

ADC14100-USB Rear Panel

ADC14100-USB Features

• 14 Bit 100 MSPS ADC

• Analog Devices ADSP-21262 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