Datasheet

Ultrasound-Specific IMD3 Specification
Unlike typical communications applications, the two
input tones are not equal in magnitude for the ultra-
sound-specific IMD3 two-tone specification. In this
measurement, f
1
represents reflections from tissue and
f
2
represents reflections from blood. The latter reflec-
tions are typically 25dB lower in magnitude, and hence
the measurement is defined with one input tone 25dB
lower than the other. The IMD3 product of interest
(f
1
- (f
2
- f
1
)) presents itself as an undesired Doppler
error signal in ultrasound applications (see Figure 6).
PCB Layout
The pin configuration of the MAX2078 is optimized to
facilitate a very compact physical layout of the device
and its associated discrete components. A typical
application for this device might incorporate several
devices in close proximity to handle multiple channels
of signal processing.
The exposed pad (EP) of the MAX2078’s TQFN-EP
package provides a low thermal-resistance path to the
die. It is important that the PCB on which the MAX2078
is mounted be designed to conduct heat from the EP.
In addition, provide the EP with a low-inductance path
to electrical ground. The EP MUST be soldered to a
ground plane on the PCB, either directly or through an
array of plated via holes.
MAX2078
Octal-Channel Ultrasound Front-End
with CW Doppler Mixers
______________________________________________________________________________________ 23
-25dB
ULTRASOUND
IMD3
f
1
- (f
2
- f
1
)f
2
+ (f
2
- f
1
)f
1
f
2
Figure 6. Ultrasound IMD3 Measurement Technique