AD9271 Analog Devices, AD9271 Datasheet - Page 20

• Manufacturer Part Number: AD9271
• Description: Octal LNA/VGA/AAF/ADC and Crosspoint Switch
• Manufacturer: Analog Devices

Specifications of AD9271

• Resolution (bits): 12bit
• # Chan: 8
• Sample Rate: 50MSPS
• Interface: LVDS,Ser
• Analog Input Type: SE-Uni
• Ain Range: 0.25 V p-p,0.32 V p-p,0.4 V p-p
• Adc Architecture: Pipelined
• Pkg Type: QFP

AD9271
THEORY OF OPERATION
ULTRASOUND
The primary application for the AD9271 is medical ultrasound.
Figure 39 shows a simplified block diagram of an ultrasound
system. A critical function of an ultrasound system is the time
gain control (TGC) compensation for physiological signal
attenuation. Because the attenuation of ultrasound signals is
exponential with respect to distance (time), a linear-in-dB VGA
is the optimal solution.
Key requirements in an ultrasound signal chain are very low
noise, active input termination, fast overload recovery, low
power, and differential drive to an ADC. Because ultrasound
machines use beam-forming techniques requiring large binary-
weighted numbers (for example, 32 to 512) of channels, the
lowest power at the lowest possible noise is of key importance.
Most modern machines use digital beam forming. In this
technique, the signal is converted to digital format immediately
TRANSDUCER
128, 256, ETC.,
ELEMENTS
ARRAY
BIDIRECTIONAL
CABLE
DEMUX
MUX/
HV
Tx HV
AMPs
SWITCHES
Figure 39. Simplified Ultrasound System Block Diagram
T/R
Rev. B | Page 20 of 60
LNA
BEAM FORMER
CW
CW (ANALOG)
Tx BEAM FORMER
OUTPUT
AUDIO
VGA
following the TGC amplifier, and then beam forming is
accomplished digitally.
The ADC resolution of 12 bits with up to 50 MSPS sampling
satisfies the requirements of both general-purpose and high-
end systems.
Power consumption and low cost are of primary importance in
low-end and portable ultrasound machines, and the AD9271 is
designed for these criteria.
For additional information regarding ultrasound systems, refer
to
Component
May–July 2002, and “The AD9271—A Revolutionary Solution
for Portable Ultrasound,” Analog Dialogue, Volume 41, Number 7,
July 2007.
“How Ultrasound System Considerations Influence Front-End
AD9271
AAF
PROCESSING
SPECTRAL
Choice, ” Analog Dialogue, Volume 36, Number 3,
DOPPLER
ADC
MODE
CENTRAL CONTROL
PROCESSING
MULTICHANNELS
IMAGE AND
(B MODE)
BEAM FORMER
Rx BEAM FORMER
MOTION
(B AND F MODES)
DISPLAY
DOPPLER (PW)
PROCESSING
(F MODE)
COLOR