Electronic Design

Fast ADC Sips Power, Simplifies Design-In

For portable applications as diverse as medical imaging units, professional video cameras, batterypowered software-defined radios, and industrial test and measurement designs, the 14-bit, 125-Msample/s LTC2261 analogto- digital converter (ADC) from Linear Technology dissipates 127 mW—less than one-third the power of alternative chips. The company acknowledges that much of the power savings arises from running the LTC2261 at 1.8 V (see the figure). But Linear also points out that its engineers achieved that low-voltage operation without sacrificing ac performance. This ADC offers signal-to-noise ratio (SNR) performance of 73.4 dB and spurious free dynamic range (SFDR) of 85 dB at baseband. Ultra-low jitter of 0.17 psRMS enables the undersampling of IF frequencies with excellent noise performance.

Other helpful features include a data randomizer that simplifies life for designers routing digital outputs on circuit boards. With high-speed ADCs, it’s often hard to avoid digital noise coupling back and distorting the analog reading. When that happens, interference from digital feedback is visible as unwanted tones in the ADC output spectrum. By randomizing the digital output, the LTC2261 reduces the amplitude of these unwanted tones by spreading this energy into the noise floor. This can reduce the digital feedback effect by 10 to 15 dB.

The LTC2261’s digital outputs can be set to full-rate CMOS, double-data-rate (DDR) CMOS, or DDR low-voltage differential signaling (LVDS). DDR outputs reduce the number of data lines needed by half. A separate output power supply allows the CMOS output swing to range from 1.2 to 1.8 V. There’s also a clock duty cycle stabilizer circuit to facilitate non-50% clock duty cycles, programmable digital output timing, programmable LVDS output current, and optional LVDS output termination. These features combine to make the data transmission between the ADC and the microcontroller more flexible.

Still, the main focus of the LTC2261 and its sister parts is the marriage of low power at lithium-cell voltages with high performance, lowering the power budget for high-speed data acquisition and making it possible to “cut the cord” and migrate products into the portable world. Supporting that is the device’s 6- by 6-mm quad flat no-lead (QFN) packaging. The LTC2261 family parts that comprises six pin-compatible members, offering 14-bit resolution at 125, 105, and 80 Msamples/s and 12-bit resolution at 125, 105, and 80 Msamples/s. Pricing starts at $9.50 each.

DON TUITE

LINEAR TECHNOLOGY
www.linear.com

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