Differential Amplifier Enhances ADC Performance April 2005 Issue Published Date: April 04, 2005
Designed to drive high-speed ADCs, the THS4509 differential amplifier is rated for a small-signal (<1 Vp-p) bandwidth of 1.9 GHz and a slew rate of 6,600 V/μs. Input referred noise voltage is 2.0 nV/√Hz, and second- and third-order harmonic distortion at 70 MHz are specified at –80 dBc and –87 dBc respectively (2 Vp-p into a 200Ω load). Settling time is 2 ns with a 2V output step. When driving a 14-bit high-speed ADC at 125 Msamples/s, single-tone spurious-free dynamic range is 81 dBc and signal-to-noise ratio is 70.1 dBFS. The amplifier is fabricated in BiCom-III, a SiGe process that integrates complementary NPN and PNP transistors enabling analog and mixed-signal circuitry that permits high-speed performance without requiring complex compensation circuits or drawing large currents. The chip’s architecture decouples the gain, output common-mode voltage and output impedance matching from one another, allowing them to be set independently. In a 16-pin QFN, price is $3.75 each/1,000. TEXAS INSTRUMENTS INC., Dallas TX. (800) 477-8924.
