Precision JFET op amp operates with 36V power
By Paul Rako, Technical Editor -- EDN, September 10, 2009
Analog Devices’ new ADA4627 JFET operational amplifier has 5-pA maximum bias current at 25°C and 500-pA maximum current at −40 to +85°C. The 19-MHz-bandwidth, A-grade part has less than 300-μV maximum offset voltage and 2 μV/°C maximum offset drift. The B-grade part has 200-μV of maximum offset and 1-μV/°C drift. The device achieves an 82V/μsec slew rate and has an open-loop gain of 120 dB. The output drives loads as low as 600Ω. Analog Devices built the device with the dielectrically isolated iPolar process technology, which enables 5.5- nV/=
voltage noise when operating on ±18V rails. Voltage noise at 10 Hz is 16.5 nV/=.
Because JFETs are buried devices, they are not subject to noise that surface defects create. The drawback is that diffusion or ion implantation rather than lithography controls JFET specs, complicating the manufacture of precision devices with low offset voltage. The combination of low noise, low bias current, and high precision makes the ADA4627 suitable for circuits that require accurate signal acquisition and fast settling in such applications as optical, communications, and high-speed data-acquisition systems; professional-audio and test equipment; and medical instrumentation. The device can also act as an output buffer in a DAC or as an amplifier for high-source-impedance sensors and photodiodes.
The ADA4627 comes in eight-pin SOIC packages and 3×3-mm, eight-pin LFCSPs. It operates over a temperature range of −40 to +125°C. The $6.75 (1000), A-grade part is inferior to the B-grade part, which cost $10.75 (1000).
