Datasheet
Low-Noise Amplifier (LNA)
The MAX2078’s LNA is optimized for excellent dynamic
range and linearity performance characteristics, making it
ideal for ultrasound imaging applications. When the LNA
is placed in low-gain mode, the input resistance (R
IN
),
being a function of the gain A (R
IN
= R
F
/(1 + A)), increas-
es by a factor of approximately 2. Consequently, the
switches that control the feedback resistance (R
F
) have to
be changed. For instance, the 100Ω mode in high gain
becomes the 200Ω mode in low gain (see Table 2).
Variable-Gain Amplifier (VGA)
The MAX2078’s VGAs are optimized for high linearity,
high dynamic range, and low output-noise performance,
all of which are critical parameters for ultrasound imaging
applications. Each VGA path includes circuitry for adjust-
ing analog gain, as well as an output buffer with differen-
tial output ports (OUT_+, OUT_-) for driving ADCs. See
the
High-Level CW Mixer and Programmable Beamformer
Functional Diagram
for details.
The VGA gain can be adjusted through the differential
gain control input VG+ and VG-. Set the differential gain
control input voltage at -3V for minimum gain and +3V for
maximum gain. The differential analog control common-
mode voltage is 1.65V (typ).
Overload Recovery
The device is also optimized for quick overload recovery
for operation under the large input signal conditions that
are typically found in ultrasound input buffer imaging
applications. See the
Typical Operating Characteristics
for an illustration of the rapid recovery time from a trans-
mit-related overload.
Octal Continuous-Wave (CW) Mixer
The MAX2078 CW mixers are designed using an active
double-balanced topology. The mixers achieve high
dynamic range and high linearity performance, with
exceptionally low thermal and jitter noise, ideal for ultra-
sound CWD signal reception. The octal quadrature
mixer array provides noise performance of 154dBc/Hz
at 1kHz offset from a 1.25MHz, 200mV
P-P
input clutter
signal and a two-tone third-order ultrasound-specific
intermodulation product of -48.5dBc (typ). See the
Ultrasound-Specific IMD3 Specification
section.
The octal array exhibits quadrature and in-phase differ-
ential current outputs (CQ+, CQ-, CI+, CI-) to produce
the total CWD beamformed signal. The maximum differ-
ential current output is typically 3mA
P-P
and the mixer-
output compliance voltage ranges from 4.5V to 12V.
MAX2078
Octal-Channel Ultrasound Front-End
with CW Doppler Mixers
______________________________________________________________________________________ 17
High-Level CW Mixer and Programmable Beamformer Functional Diagram
CHANNEL 1
I/Q PHASE
DIVIDER
SELECTOR
CHANNEL 2
I/Q PHASE
DIVIDER
SELECTOR
5 5
5-BIT
SR
5-BIT
SR
DIN
CS
CLK
DOUT
CLP PD
LO+
LO-
CW_QOUT
CW_IOUT
CW_IN1
CW_IN3
CW_IN2
CW_IN5
CW_IN4
CW_IN7
CW_IN6
CW_IN8
IQ IQ
CHANNEL 3
I/Q PHASE
DIVIDER
SELECTOR
5
5-BIT
SR
IQ
CHANNEL 4
I/Q PHASE
DIVIDER
SELECTOR
5
5-BIT
SR
IQ
CHANNEL 5
I/Q PHASE
DIVIDER
SELECTOR
5
5-BIT
SR
IQ
CHANNEL 6
I/Q PHASE
DIVIDER
SELECTOR
5
5-BIT
SR
IQ
CHANNEL 7
I/Q PHASE
DIVIDER
SELECTOR
5
5-BIT
SR
IQ
CHANNEL 8
I/Q PHASE
DIVIDER
SELECTOR
5
5-BIT
SR
IQ
MAX2078