ADA4896-2 AD [Analog Devices], ADA4896-2 Datasheet - Page 23

• Manufacturer Part Number: ADA4896-2
• Description: 1 nV/?Hz, Low Power, Rail-to-Rail Output Amplifiers
• Manufacturer: AD [Analog Devices]

MEDICAL ULTRASOUND APPLICATIONS
Overview of the Ultrasound System
Medical ultrasound systems are among the most sophisticated
signal processing systems in widespread use today. By transmit-
ting acoustic energy into the body and receiving and processing
the returning reflections, ultrasound systems can generate
images of internal organs and structures, map blood flow
and tissue motion, and provide highly accurate blood velocity
information. Figure 53 shows a simplified block diagram of an
ultrasound system.
The ultrasound system consists of two main operations, the
time gain control (TGC) operation and the continuous wave
(CW) Doppler operation. The
components of these two operations into a single IC. It contains
eight channels of a variable gain amplifier (VGA) with a low
noise preamplifier (LNA), an antialiasing filter (AAF), an
analog-to-digital converter (ADC), and an I/Q demodulator
with programmable phase rotation. For detailed information
about how to use the
the
ADA4896-2/ADA4897-1
The
in the ultrasound application after the I/Q demodulators of
the AD9279. Doppler signals can be typically between 100 Hz
to 100 kHz.The low noise floor, high dynamic range of the
ADA4896-2/ADA4897-1
processing weak Doppler signals.
AD9279
ADA4896-2/ADA4897-1
TRANSDUCER
data sheet.
ARRAY
AD9279
makes them an excellent choice for
in the Ultrasound System
DEMUX
MUX/
are used in the CW Doppler path
in the ultrasound system, refer to
HV
AD9279
integrates the essential
Figure 53. Simplified Ultrasound System Block Diagram
SWITCHES
T/R
BEAMFORMER
Rev. 0 | Page 23 of 28
CW (ANALOG)
ADA4896-2/
ADA4897-1
AD9279
LNA
OUTPUT
AUDIO
Tx BEAMFORMER
VGA
The rail-to-rail output feature and the high output current drive
of the
for the I-to-V converter, summer, and as a ADC driver.
Figure 54 shows an interconnection block diagram of all eight
channels of the AD9279. Two stages of
are used. The first stage does an I-to-V conversion and filters
the high frequency content that results from the demodulation
process. The second stage of
sum the output currents of multiple AD9279, to provide gain,
and to drive the AD7982, an 18-bit SAR ADC.
The output-referred noise of the CW signal path depends on
the LNA gain and the selection of the first stage summing
amplifier and the value of R
referred noise, it is important to know the active low-pass
filter (LPF) values R
Typical filter values for all eight channels of a single
are 100 Ω for R
values implement a 100 kHz single-pole LPF.
The gain of the I-to-V converter can be increased by increasing
the filter resistor, R
decrease the filter capacitor, C
limiting the magnitude of the gain is the output swing and drive
capability of the op amp selected for the I-to-V converter, in
this example, the ADA4896-2/ADA4897-1. Because any
amplifier has limited drive capability, there is a finite number of
channels that can be summed.
ADA4896-2/ADA4897-1
AAF
PROCESSING
SPECTRAL
DOPPLER
MODE
ADC
A
, 500 Ω for R
FILT
A
, R
. To keep the corner frequency the same,
FILT
PROCESSING
IMAGE AND
(B MODE)
MOTION
, and C
ADA4896-2/ADA4897-1
CENTRAL CONTROL
FILT
ADA4896-2
FILT
BEAMFORMER
Rx BEAMFORMER
(B AND F MODES)
FILT
. To determine the output
make them a suitable candidate
, and 2.0 nF for C
, by the same factor. The factor
DISPLAY
FILT
, as shown as Figure 54.
DOPPLER (PW)
ADA4896-2
PROCESSING
(F MODE)
amplifiers is used to
COLOR
FILT
amplifiers
AD9279
; these