Transcript High Speed Data Acquisition Architectures

High Speed Data Acquisition
Architectures
Some Basic Architectures
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Non-Buffered (streaming)
FIFO Buffered
Multiplexed RAM
“Ping Pong” Multiplexed RAM
Dual Port RAM
Streaming Interface Block
Diagram
RF
Input
LPF
Trigger/
Clock
ADC
DSP
Interface
(Bus, USB,
LAN)
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
RF
Input
LPF
Trigger/
Clock
ADC
FIFO
DSP
Interface
USB, LAN,
Bus, etc
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
Multiplexer
RF
Input
LPF
Data
ADC
Data
SRAM
DSP
Address
Trigger/
Clock
Counter
Multiplexer
Address
Interface
(Bus, USB,
LAN)
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
Data
RF
Input
LPF
ADC
Multiplexer
Multiplexer
Data
Data
SRAM A
SRAM B
Address
Address
Multiplexer
Multiplexer
DSP
Address
Trigger/
Clock
Counter
Interface
(Bus, USB,
LAN)
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
RF
Input
Data
A
LPF
Data
B
Address
ADC
Dual Port
SRAM
Trigger/
Clock
Counter
Add
A
Add
B
DSP
Data
Interface
(Bus, USB,
LAN)
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
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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
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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
RS232
RF
Input
ADC
14 Bits
100MSPS
100 MHz
80 MHz
Ext
Clock
Decimator
256K x 18
FIFO
USB 2.0
ADSP 21262
Floating Point
DSP
ADC14100-USB Front Panel
ADC14100-USB Rear Panel
ADC14100-USB Features
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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