Low-noise 1.6-GHz differential buffer drives 50-? load

Linear Technology has announced the LTC6417, a fully differential buffer amplifier with only 1.5nV/?Hz output-referred noise. The LTC6417 is capable of driving a differential 50-? 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 600 MHz. At 140 MHz, OIP3 is 46 dBm, and HD3 is -69 dBc with 2.4 V p-p output swing into a 50-? load. In addition to its outstanding performance specifications, the LTC6417 includes several features that simplify interfacing with ADCs. The LTC6417 is configured internally as a unity gain buffer. Because its input impedance is 18.5 kOhm, circuits can take additional gain 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 5 V supply. A PWRADJ pin enables the designer to trade off power consumption for HD3 performance. This feature dynamically lowers supply current from 123 mA to 74 mA, and a shutdown mode further reduces current consumption to 24 mA. The LTC6417 is available in a 3 mm x 4 mm 20-lead QFN package with an easy to use flow-through pinout. The differential buffer is fully specified for 0 to 70 °C and -40 to 105 °C (case temperature) operation ranges. Pricing starts at $3.89 (1,000). Summary of Features: LTC6417

• 1.6 GHz -3 dB small-signal bandwidth
• Low distortion driving 50-? load, 2.4 V p-p output
  • -100 dBc HD2 and -69 dBc HD3 at 140 MHz
  • -80 dBc IM3 and 46 dBm OIP3 at 140 MHz
  • -100 dBc HD2 and -66 dBc HD3 at 380 MHz
  • -68 dBc IM3 and 39 dBm OIP3 at 380 MHz
• 1.5 nV/?Hz output noise
• 4.3 pA/?Hz input current noise
• Programmable high-speed, fast-recovery output clamping
• 4.28 V p-p maximum output swing
• DC-coupled signal path
• Operates on single 4.75 to 5.25 V supply
• Power: 615 mW on 5 V, can be reduced to 370 mW; shutdown mode 120 mW
• 3 mm x 4 mm 20-lead QFN package