Datasheet

AD9272
Rev. C | Page 21 of 44
THEORY OF OPERATION
ULTRASOUND
The primary application for the AD9272 is medical ultrasound.
Figure 36 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, using
the lowest power at the lowest possible noise is of chief importance.
Most modern machines use digital beam forming. In this
technique, the signal is converted to digital format immediately
following the TGC amplifier, and then beam forming is
accomplished digitally.
The ADC resolution of 12 bits with up to 80 MSPS sampling
satisfies the requirements of both general-purpose and high-
end systems.
Power conservation and low cost are two of the most important
factors in low-end and portable ultrasound machines, and the
AD9272 is designed to meet these criteria.
For additional information regarding ultrasound systems, refer
to “How Ultrasound System Considerations Influence Front-End
Component Choice,Analog Dialogue, Volume 36, Number 1,
May–July 2002, and “The AD9271—A Revolutionary Solution
for Portable Ultrasound,” Analog Dialogue, Volume 41, Number 3,
July 2007.
BEAM-FORMER
CENTRAL CONTROL
Rx BEAM FORMER
(B AND F MODES)
COLOR
DOPPLER (PW)
PROCESSING
(F MODE)
IMAGE AND
MOTION
PROCESSING
(B MODE)
SPECTRAL
DOPPLER
PROCESSING
MODE
DISPLAY
AUDIO
OUTPUT
Tx BEAM FORMER
CW (ANALOG)
BEAM FORMER
TRANSDUCER
ARRAY
128, 256, ...
ELEMENTS
BIDIRECTIONAL
CABLE
HV
MUX/
DEMUX
T/R
SWITCHES
Tx H
V
AMPs
MULTICHANNELS
AD9272
AAF
VGALNA
ADC
CW
07029-077
Figure 36. Simplified Ultrasound System Block Diagram