Front-End IC targets ultrasound imaging equipment.
Press Release Summary:
Combining active-input-termination LNA, VGA, anti-alias filter, and I/Q mixer continuous-wave Doppler beamformer in one monolithic device, Model MAX2078 supports input impedances of 50, 100, 200, and 1,000 W. Unit can achieve full receiver noise figure of 2.4 dB with 200 W input impedance termination, while consuming less than 65 mW per channel. Device boasts SNR of 140 dBc/Hz at 1 kHz from 5 MHz clutter signal, and 23 nV cascaded output-referred noise.
Original Press Release:
New Front-End Ultrasound IC Provides Breakthrough Levels of Performance for High-Channel-Count, Cart-Based and Portable Ultrasound Imaging Equipment
Low-power, high-performance, octal ultrasound front-end IC with programmable CWD
SUNNYVALE, CA-July 15, 2009-Maxim Integrated Products (NASDAQ: MXIM) introduces the MAX2078, the world's lowest power, octal, ultrasound front-end solution with integrated mixer-based CWD (continuous-wave Doppler) beamformer. The MAX2078 represents the latest generation of high-performance, low-power ultrasound cores from Maxim, and leverages the Company's industry-leading expertise in LNA, VGA, and CWD technology. It combines an active-input-termination LNA, VGA, anti-alias filter, and I/Q mixer CWD beamformer in one fully integrated, monolithic device. The MAX2078 targets high-channel-count, cart-based and portable ultrasound medical imaging applications where size and power are constrained and performance must be optimized. This front-end IC delivers the lowest noise and the highest dynamic range of any competing low-power, fully integrated ultrasound front-end. In addition, the MAX2078 utilizes Maxim's patented mixer-based CWD solution and is fully compliant with all known ultrasound beamforming patents.
Ultrasound Backgrounder
In ultrasound applications, enhanced image quality and sensitivity are often regarded as the key differentiators among competing systems. This is especially true in the highly competitive, small, cart-based and portable imaging segment where performance is often sacrificed to achieve the constrained size and power requirements. Image quality and sensitivity are directly affected by the ultrasound receiver's noise figure, dynamic range, and image resolution.
The receiver's noise figure determines the weakest signal levels (i.e., ultrasound echoes) that can be detected by the imaging system. An excellent noise figure improves the system's sensitivity to these weak signals, thus allowing it to image at deeper depths and detect weaker Doppler blood-flow signals.
Dynamic range is a measure of the system's ability to detect these important weak signals in the presence of large extraneous signals. An excellent dynamic range is particularly critical for second-harmonic imaging modalities, where strong signals at the fundamental imaging frequency can interfere with the weaker signals of interest at the second harmonic. Exceptional dynamic range is also necessary for all pulsed and continuous Doppler modalities, where large "clutter signals" from stationary reflectors can interfere with the weak Doppler signals of interest, sometimes located less than 1kHz away.
Finally, imaging resolution in a phased-array ultrasound receiver strongly correlates with the number of receive channels. The greater the number of channels supported, the larger the receive aperture that can be supported and the better the image resolution and quality. Large channel counts necessary to support larger apertures and improved image resolution put significant constraints on the cost, power, and size of small cart-based and portable ultrasound-system receiver front-end solutions.
Unprecedented Noise Performance and Dynamic Range Improve Overall Receiver Sensitivity and Image Quality
Optimal ultrasound receiver sensitivity is difficult to achieve, especially when terminating transducers into the relatively low-receiver-input impedances necessary for optimal time-domain pulse response and exceptional image quality. The MAX2078 is unique because it provides an ultra-low-noise, programmable, active-input-impedance LNA to optimize noise figure for a variety of common optimally matched transducer-termination-input impedances at a very low power. Consequently, the device can achieve an impressive full receiver noise figure of only 2.4dB with a 200W input impedance termination, while consuming less than 65mW per channel.
As stated above, dynamic range is also very important to preserve receiver sensitivity under all imaging conditions. As a result, some will argue that the MAX2078's most impressive advantage is its cascaded output-referred noise, rated at an incredibly low 23nV/ , a factor of 2x less noise than the closest competing chipset solution. Low output-referred noise is important, because a high level of output noise will overtake the noise floor of the subsequent ADC stage and degrade the broadband SNR of the receiver. This is why the VGA is often the limiting factor for the ultrasound receiver's overall dynamic range, and why improvements in ADC noise performance can many times be nullified. With high VGA output-referred noise the system is operating at a suboptimal level, since ADC input-referred noise levels are typically less than the output-referred noise of competing ultrasound receiver chipsets.
Of particular interest in pulsed Doppler imaging modes is the close-in, large-signal SNR performance of the imaging receiver lineup. Low-velocity Doppler signals can be within 1kHz or less of very large "clutter signals" or reflections from stationary tissue. The receiver's close-in, large-signal SNR performance is, therefore, a key performance specification that determines the receiver's ability to detect these weak, low-velocity blood-flow signals in the presence of large clutter signals. The MAX2078 has been specifically designed to detect these signals. The device boasts an impressive large-signal SNR of 140dBc/Hz at 1kHz from a 5MHz clutter signal. Many competitive devices even fail to list this important performance specification on their data sheets.
Excellent CWD Mixer Close-In, Large-Signal SNR and Linearity Enhance the Detection of Weak, Low-Velocity Blood-Flow Signals
During the MAX2078's CWD mode of operation, the LO phase dividers within the quadrature mixer array can be programmed to any one of 16 quadrature phases for optimal beamforming resolution. The MAX2078 provides the necessary close-in, large-signal dynamic range and noise performance to detect Doppler shifts ranging from 100kHz to less than 1kHz at optimal sensitivity.
The mixers and LO generators have exceptionally low close-in, large-signal SNR performance of -155dBc/Hz at 1kHz offset from a 200mVP-P, 1.25MHz input clutter signal. This exceptional SNR performance is critical for detecting weak, low-velocity CW Doppler blood-flow signals. The amount of clutter signal generated in CWD from stationary tissue, bone reflections, and transmit-to-receive crosstalk can be extreme. It is not uncommon for these unwanted signals to be as high as 200mVP-P at the receiver's input. With its excellent close-in SNR performance, the MAX2078 excels in measuring these difficult-to-detect blood-flow signals.
High Integration and Lower Power Allow Increased Channel Densities and Simpler Implementation
Ultrasound designs continually migrate toward greater imaging resolution and, therefore, larger channel counts. The MAX2078 enables higher channel counts in two fundamental ways.
First, by integrating eight channels within a single chip, Maxim's MAX2078 LNA/VGA/AAF/CWD solution uses very little board space. Virtually all of the necessary circuitry is on the chip.
Secondly, integration increases circuit functionality. Many ultrasound systems utilize multiple transducer types which support multiple imaging modes. Each transducer will have a unique output impedance. Similarly, multimode transducers have specific output impedances tailored for each mode of operation (e.g., 2D imaging vs. steerable CWD). To facilitate these wide ranges of output impedances, the MAX2078 integrates a unique switchable, input-impedance matching network. Impedances of 50, 100, 200, and 1000W are all supported on this single chip. The input impedance can be switched to optimize the performance of each mode of operation for the system.
The MAX2078 is available in a lead-free 64-TQFP package. A MAX2077*, with the same functionality and specifications as the MAX2078 but without the CWD beamformer, is available in both a pin-compatible lead-free 64-TQFP and a space-saving 56-TQFN package. Prices start at $47.50 for the MAX2078 and $34.30 for the MAX2077 (1000-up, FOB USA). For more information please visit: www.maxim-ic.com/Ultrasound-Front-End.
Maxim Integrated Products is a publicly traded company that designs, manufactures, and sells high-performance semiconductor products. The Company reported revenue in excess of $2 billion for fiscal 2008. Maxim was founded over 25 years ago with the mission to deliver innovative analog and mixed-signal engineering solutions that add value to its customers' products. To date, it has developed over 6000 products serving the industrial, communications, consumer, and computing markets. For more information, go to www.maxim-ic.com.
*Future product, which is currently sampling. Please contact factory for additional information.
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