Very Low Noise, Differential Amplifier and 20MHz Lowpass Filter

The LT6600-20 combines a fully differential amplifier with a 4th order 20MHz lowpass filter approximating a Chebyshev frequency response. Most differential amplifiers require many precision external components to tailor gain and bandwidth. In contrast, with the LT6600-20, two external resistors program differential gain, and the filter’s 20MHz cutoff frequency and passband ripple are internally set. The LT6600-20 also provides the necessary level shifting to set its output common mode voltage to accommodate the reference voltage requirements of A/Ds.

Using a proprietary internal architecture, the LT6600-20 integrates an antialiasing filter and a differential amplifier/ driver without compromising distortion or low noise performance. At unity gain the measured in band signal-to-noise ratio is an impressive 76dB. At higher gains the input referred noise decreases so the part can process smaller input differential signals without significantly degrading the output signal-to-noise ratio.

The LT6600-20 also features low voltage operation. The differential design provides outstanding performance for a 2VP-P signal level while the part operates with a single 3V supply.

The LT6600-20 is packaged in an SO-8 and is pin compatible with stand alone differential amplifiers.

Applications

* High Speed ADC Antialiasing and DAC Smoothing in Networking or Cellular Base Station Applications

* High Speed Test and Measurement Equipment

* Medical Imaging

* Drop-in Replacement for Differential Amplifiers

* Programmable Differential Gain via Two External Resistors

* Adjustable Output Common Mode Voltage

* Operates and Specified with 3V, 5V, ±5V Supplies

* 0.5dB Ripple 4th Order Lowpass Filter with 20MHz Cutoff

* 76dB S/N with 3V Supply and 2VP-P Output

* Low Distortion, 2VP-P, 800Ω Load

* 2.5MHz: 83dBc 2nd, 88dBc 3rd

* 20MHz: 63dBc 2nd, 64dBc 3rd

* Fully Differential Inputs and Outputs

* SO-8 Package

* Compatible with Popular Differential Amplifier Pinouts