Analogue, Mixed Signal, LSI


FET input amplifiers designed for high performance

10 September 2002 Analogue, Mixed Signal, LSI

When it came to using FET-input amplifiers, it used to be that the inexpensive ones did not have the necessary performance and the ones that did were just too expensive. But according to Analog Devices, all that has changed with the release of a new class of FET input amplifiers called FastFETs.

FastFETs are high performance amplifiers that combine the desirable specs of FET input amps with those of ADI's proprietary XFCB wafer fabrication process, resulting in FET input amps that are claimed to have outstanding all around specs: precision DC specs, pA bias currents, low offsets, low drift and low noise - and at speeds not previously achieved in FET amps.

Well balanced spec combination

The company's AD8033/AD8034 FastFETs offer a well-balanced combination of specifications: wide supply voltage range, low input bias current and noise, low distortion, low offset voltage, high common load rejection, and single supply rail-to-rail output at a very low cost. In addition, both products come in very small packaging (SC70, SOT23-8) for use on very space-constrained boards.

The AD8034 is a dual voltage feedback amplifier with FET inputs and a single version, the AD8033, will be available soon. The AD8034 is a lower priced version of the AD8065 with similarly high performance while consuming only 3,3 mA supply current maximum per amplifier. With 80 MHz bandwidth, slew rate of 80 V/µs, and low DC errors of 2 mV max Vos and 11 nV/rt Hz noise, the manufacturer says the AD8034 offers significant performance improvements over other low cost FET amplifiers. A wide operating supply voltage range of 5 to 24 V with rail-to-rail output adds to their general usefulness. The AD8034 is available in a very small SOIC 8 and SOT23-8.

Typical applications are for: instrumentation, filters, level shifting, buffering, photodiode pre-amplifiers.

High performance FastFETs

The AD8065/AD8066 FastFETs are the highest performance amplifiers of ADI's FastFETs family products, representing a new performance level for JFET input op amps. The AD8065 is noteworthy for its very low noise (7 nV/rt Hz and 0,6 fA/rt Hz) and very low distortion (88 dB SFDR @ 1 MHz and single supply rail-to-rail operation). The devices have a bandwidth of 145 MHz with a slew rate of 180 V/µs.

The AD8065 also has superior DC performance with an input bias current of 1 pA typical, a Vos of 1,5 mV max, and a drift of less than 1 µV/°C. The differential gain and phase errors are 0,02% and 0,02ø, with 0,1 dB flatness out to 7 MHz, making the parts ideal for video applications. The AD8065 consumes 6,5 mA supply current. It is a single voltage-feedback amplifier with FET inputs, with a dual version, AD8066. In addition, the AD8065 comes in very small packaging (SOIC 8 and SOT23-5) for use on even the most space-constrained boards.

Precision JFET amplifier

In addition to raising JFET amplifier speed barriers, ADI has also applied FastFETs technology to precision amplifiers. The AD8610 and AD8620 FastFETs amplifiers set a new performance standard with the lowest offset and drift of any JFET amplifier coupled with outstanding speed. AD8610 is simple to use, offering DC precision usually seen only in much slower bipolar amplifiers, low noise, and superior dynamic performance. It is ideally suited for precision photodiode amplifiers, signal and reference buffers, integrators, high speed instrumentation, and high performance filters including PLL filters.

Here key specs are: 100 µV max offset voltage; 1 µV/°C max TcVos; 6 nV/rt. Hz noise; 10 pA max bias current; 50 V/µs slew rate; 500 ns settling to 0,01% for 10 V step.

The AD8610 (single) is available in the tiny MSOP 8 and narrow SOIC 8 surface mount packages. The AD8620 (dual) is available in the narrow SOIC 8 package.

For more information contact Parsec, 012 349 2282.





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