Electronic Design

Low-Noise Differential Amplifiers Include 10-MHz Low-Pass Filter

The LT6600-10 combines a high-speed differential amplifier and a 10-MHz low-pass filter. Gain is programmed with two resistors for a gain range of −12 to 12 dB. It also provides the necessary level shifting to set the device's output common-mode voltage to accommodate the reference voltage requirements of analog-to-digital converters (ADCs).

By integrating the fully differential amplifier and the anti-aliasing filter into an SO-8 package, the LT6600-10 reduces board space and power requirements. Also, it removes much of the variability that would otherwise be a function of the board layout and the tuning requirements for a 0.5-dB ripple fourth-order low-pass filter. The part runs off of either single or dual supplies of 3, 5, and ±5 V.

The IC exhibits excellent noise performance. At unity gain, the measured in-band signal-to-noise ratio (SNR) is 82 dB with 3-V supply and 2-V p-p output. At higher gains, the input-referred noise decreases so the part can process smaller input differential signals without significantly degrading the output SNR.

As expected from a preamplifier to an ADC, the amp has low distortion to go along with the low noise. At 1 MHz, the LT6600-10 exhibits 88-dBc second-order and 90-dBc third-order distortion. At 5 MHz, the values are 74 dBc (second) and 82 dBc (third). Both sets of measurements are with a 2-V p-p signal into an 800-Ω load.

The LT6600-10 is fully specified for operation over the industrial and commercial temperature ranges. Prices start at $2.95 each in 1000-piece quantities.

Linear Technology Corp., (408) 432-1900; www.linear.com/prod/datasheet.html?datasheet=890.

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