JFET op amps suit use in professional-audio applications
Paul Rako -- EDN, June 10, 2010
Texas Instruments' Burr-Brown Division recently released the single OPA1641, dual OPA1642, and quad OPA1644 operational amplifiers, which feature a JFET input stage. The parts operate with ±2.25 to ±18V power supplies, and output distortion is 0.00005% at 1 kHz. The devices feature a ±20-pA maximum bias current at 25°C and a 70-pA typical bias current at 85°C. The 11-MHz-bandwidth IC has less than 3.5-mV maximum offset voltage. It consumes 1.8 mA quiescent current per channel and achieves a 20V/μsec slew rate. The amp is unity-gain stable and has an open-loop gain of 105 dB. The rail-to-rail output has a 2-kΩ load. The amplifiers have 5.1-nV/√Hz voltage noise at 1 kHz and 8 nV/√Hz at 10 Hz.
Because JFETs are buried devices, they are not subject to noise that surface defects create. These amplifiers' JFETs also feature a flicker-noise corner of less than 20 Hz, making them ideal for professional-audio applications. The low bias-current inputs also suit them for use with signals having high source impedance.
The single-channel OPA1641 is available in an SO-8 package for 95 cents (1000). The two-channel OPA1642 is available in an SO-8 or an MSOP-8 package for $1.45, and the four-channel OPA1644 is available in an SO-14 or a TSSOP-14 package for $1.95.
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