AD9042
Rev. B | Page 21 of 24
RECEIVE CHAIN FOR DIGITAL AND ANALOG BEAM FORMING MEDICAL ULTRASOUND USING
THE AD9042
The AD9042 is an excellent digitizer for digital and analog beam-
forming medical ultrasound systems. The price/performance ratio
of the AD9042 allows ultrasound designers the luxury of using
state-of-the-art ADCs without jeopardizing their cost budgets.
ADC performance is critical for image quality. The high dynamic
range and excellent noise performance of the AD9042 enable
higher image quality medical ultrasound systems.
Figure 45 shows the AD9042 used in one channel of the receive
chain of a medical ultrasound system. The AD604 receives its
input directly from the transducer or from an external preamp
connected to the transducer. The AD604 contains two separate
stages. The first stage is a preamp with a fixed gain (14 dB to
20 dB) selected by a fixed resistor. The second stage is a variable
gain amplifier with the gain set by the AD7226 DAC. The gain
is increased over time to compensate for the attenuation of
signal level in the body.
AD9042
AD604
AD8041
G
–14dB TO +34dB
PRE-AMP
+14dB TO +20dB
TRANSDUCER/
PRE-AMP
INPUT
LPF
AD7226
00554-063
Figure 45. Using the AD9042 in Ultrasound Applications
Following the AD604, a low-pass filter is used to minimize the
amount of noise presented to the ADC. The AD8041 is used to
buffer the filter from the AD9042 input. This function may not
be required depending on the filter configuration and PCB
partitioning. The digital outputs of the AD9042 are then presented
to the digital system for processing.
