Date: 07/08/2009

Integrated octal ultrasound VGAs with on-chip CWD beamformers

Maxim has introduced the MAX2036/MAX2038 integrated, SiGe variable-gain amplifiers (VGAs) with on-board continuous-wave Doppler (CWD) beamformers for ultrasound-imaging applications.

The MAX2036/MAX2038 combine the linearity and noise performance of the previously introduced MAX2035/MAX2037 VGAs with an on-chip, octal quadrature mixer array and programmable LO phase generators. During normal operation, the MAX2036/ MAX2038 are configured either the VGA path is enabled while the mixer array is powered down (VGA mode), or the quadrature mixer array is enabled while the VGA path is powered down (CW mode). When in CW mode, the LO phase dividers can be programmed to allow 4, 8, or 16 quadrature phases for optimal beamforming resolution.

MAX2036/MAX2038 detects Doppler shifts ranging from 100kHz to less than 1kHz, and the mixers and LO generators are designed for low thermal and jitter noise performance of -155dBc/Hz at 1kHz offset from a 900mVP-P, 1.25MHz carrier signal. This noise performance is critical for detecting weak, low-velocity, Doppler-shift blood-flow signals.

In ultrasound systems, these low-velocity Doppler-shift signals are difficult to detect due to exceptional strong blocking signals referred as clutter. Since Doppler measurements must be in the presence of a continuous-wave transmit signal, the amount of clutter signal generated from stationary tissue and bone reflections, and transmit-to-receive crosstalk in the transducer, can be 200mVP-P at the receiver's input. These clutter signals degrades the receiver's ability to detect weak, low-velocity Doppler signals (i.e., those which are closest in frequency to the CW carrier signal). Because the MAX2036/MAX2038 have such close-in noise performance, they excel in making these difficult-to-detect, velocity blood-flow measurements.

The MAX2036/MAX2038 VGA mode with MAX2034 quad LNA yields low, cascaded output-referred noise of 20nV/—2x less noise than the chipset solution. Another key feature is VGA supports either 10-bit or 12-bit ADCs. The MAX2036 supports 10-bit ADCs, for greater variable-gain range performance and the MAX2038 supports 12-bit ADCs, for applications where superior dynamic range performance to capitalize on the ADC's inherent resolution.

Package: lead-free, 100-pin TQFP package.
Price: Starts at $39.98 for 1k pieces
For more details visit www.maxim-ic.com/ultrasoundinfo.