MAX2036
Ultrasound VGA Integrated
with CW Octal Mixer
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Detailed Description
The MAX2036 is an 8-channel VGA integrated with a
programmable octal quadrature mixer array designed
for ultrasound imaging and Doppler applications. The
device is optimized for efficient power consumption,
high dynamic range, and exceptionally low-noise
performance. The VGA path features differential inputs,
analog variable gain control, differential outputs for
direct ADC drive, and a selectable output voltage
clamp to avoid ADC overdrive. The integrated octal
quadrature mixer array includes serial-programmable
LO phase generators for CWD beamforming applica-
tions. The LO phase dividers can be programmed for 4,
8, or 16 quadrature phases. Lowpass filters are inte-
grated at the input paths of each CW mixer. The out-
puts for the mixers are summed into single I/Q
differential current outputs.
The MAX2036 also integrates an octal quadrature mixer
array and programmable LO phase generators for a
complete continuous wave (CW) Doppler beamforming
solution. The LO phase selection for each channel is
programmed using a digital serial interface and a sin-
gle high-frequency clock, or the LOs for each complex
mixer pair can be directly driven using separate 4 x LO
clocks. The serial interface is designed to allow multiple
devices to be easily daisy chained in order to minimize
program interface wiring. The LO phase dividers can
be programmed to allow 4, 8, or 16 quadrature phases.
The input path of each CW mixer consists of a selec-
table lowpass filter for optimal CWD noise performance.
The outputs of the mixers are summed into single I and
Q differential current outputs. The mixers and LO gen-
erators are designed to have exceptionally low noise
performance of -155dBc/Hz at 1kHz offset from a
1.25MHz carrier, measured with 900mV
P-P
differential
clutter signal.
Variable Gain Amplifier (VGA)
The MAX2036’s VGAs are optimized for high linearity,
high dynamic range, and low output-noise perfor-
mance, making this component ideal for ultrasound
imaging applications. The VGA paths also exhibit a
channel-to-channel crosstalk of -80dB at 10MHz and an
absolute gain error of less than ±0.5dB for minimal
channel-to-channel focusing error in an ultrasound sys-
tem. Each VGA path includes circuitry for adjusting
analog gain, an output buffer with differential output
ports (VGOUT_+, VGOUT_-) for driving ADCs, and dif-
ferential input ports (VGIN_+, VGIN_-), which are ideal
for directly interfacing to the MAX2034 quad LNA. See
the
High-Level Wave Mixer and Programmable Beam-
Former Functional Diagram
for details.
The VGA has an adjustable gain range from -10.5dB to
+39.5dB, achieving a total dynamic range of 50dB
(typ). The VGA gain can be adjusted using the differen-
tial gain-control inputs VG_CTL+ and VG_CTL-. Set the
differential gain-control input voltage at +2V for mini-
mum gain and -2V for maximum gain. The differential
analog control common-mode voltage is 3V (typ).
