Linear – Low-noise fully-differential 1.6GHz buffer drives 50ohm load

The latest from Linear Technology is the LTC6417, a fully-differential buffer amplifier with only 1.5nV/vHz output-referred noise. The LTC6417 is capable of driving a differential 50ohm load and is optimized for driving 14- and 16-bit pipeline ADCs. It can be DC- or AC-coupled at its inputs, and achieves excellent distortion performance for signals up to and beyond 600MHz. At 140MHz, OIP3 is 46dBm, and HD3 is -69dBc with 2.4VP-P output swing into a 50ohm load.

In addition to its high performance specification, the LTC6417 includes several features designed to simplify interfacing with ADCs. The LTC6417 is configured internally as a unity gain buffer. Because its input impedance is 18.5kohm, additional gain can be achieved by applying a 1:4 or 1:8 transformer at the inputs. Its low impedance output helps manage the capacitive charge injection common to pipeline ADCs. Fast output clamps can be programmed with a single pin to prevent ADC over-range conditions. An over-range pin signals when the clamps limit the output voltage. An output common mode pin makes it easy to match the LTC6417 output swing to the input range of the ADC.

The LTC6417 operates from a single 5V supply. A PWRADJ pin enables the designer to trade off power consumption for HD3 performance. This feature dynamically lowers supply current from 123mA to 74mA, and a shutdown mode further reduces current consumption to 24mA. The LTC6417 is available in a 3mm x 4mm 20-lead QFN package with an easy to use flow-through pin-out. It is fully specified for 0C to 70C and -40C to 105C (case temperature) operation ranges, says the company.