Fixed-gain differential amplifiers balance noise and linearity

Three precision fixed-gain differential amplifiers have been announced by Analog Devices. The LTC6363-0.5, LTC6363-1 and LTC6363-2 amplifiers are fixed-gain variants of the company’s LTC6363 amplifier.

The trio is available in fixed gains of 0.5, 1.0 and 2.0V/V which provide flexibility when scaling inputs to the full range of ADCs, adds Analog Devices.

Precision resistors integrated in LTC6363-0.5, LTC6363-1 and LTC6363-2 have been designed for overall system performance, balancing noise and linearity, and using laser trimmed factory calibration to achieve a level of precision which is difficult and costly to achieve discretely.  Initial gain accuracy is 45 parts per million, maximum and varies by only 0.5 parts per million/degreeC maximum over temperature.  Common mode rejection ratio, which is typically limited by discrete resistor matching, is an outstanding 94dB minimum, equivalent to a 0.002 per cent resistor matching.

One of the challenges when driving high performance SAR ADCs is finding an appropriate driver that consumes comparable power while maintaining the noise and linearity performance of the ADC, explains Maziar Tavakoli, design manager, Linear Products and Solutions at Analog Devices. “For example, the LTC2378-20 20-bit SAR ADC consumes 21mW at 1Msps,” he says, adding that the LTC6363 family’s noise and linearity have negligible impact on ADC performance while consuming just 19mW, comparable to the ADC’s power consumption.  The LTC6363-0.5, LTC6363-1 and LTC6363-2 can achieve the same ADC driving performance with added precision courtesy of the precision integrated resistors. Distortion is as low as 118dB SFDR at 2kHz, 18VP-P.

The entire LTC6363 family operates with supply voltages from 2.8V (±1.4V) to 11V (±5.5V) while drawing 1.75mA typical supply current. The devices are specified for operation over a temperature range from –40 to +125 degree C.

The LTC6363 fixed-gain series are available in a 3.0 x 5.0mm plastic MSOP8 package. The LTC6363 (without resistors) is also offered in the 2.0 x 3.0mm DFN package.

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