FROM EDN EUROPE: Low-noise op amp targets 16- and 18-bit designs

Analog Devices is not (quite) tagging its AD8099 amplifier as "the only op amp you'll ever need," but it does claim new low levels of noise and distortion for a high-speed amplifier and ease of use that means that the part should be able to occupy multiple sockets and reduce your inventory of multiple device types. The company specifies noise at 0.95 nV/ or 2.6 pA/ as a current figure, and it specifies distortion at –100 dBc at 1 MHz or –90 dBc at 10 MHz for both second and third harmonics. The amplifier is rated to 500 MHz; capacitive compensation allows you to make it stable at gains from 2 to 10 with little bandwidth change and get a slew rate of more than 500V/µsec and a gain of 2; you reach the peak specification of 1400V/µsec at a gain of 10. Quiescent current is 15 mA from a supply of 5 to 12V.

Analog Devices officials say that its developers designed the part to optimise the parameters—primarily noise and distortion—that you cannot trim out in practice. However, offset, for example, is still less than 1 mV. The new device uses an architecture that the company does not yet fully disclose but describes as "common-mode linearised." With a design having high output impedance, you can multiplex the amplifier into an ADC input.

You can source the device in a conventional SO8 package with standard pinout, but you do not get the full noise and distortion specification. To achieve that spec, the company had to shift to a chip-scale package and a new pinout. The "traditional" pinout routes input connections close to the supply pins, which has a negative effect on second harmonic distortion due to mutual inductance coupling. The LFCSP still has eight pins—four on a side; but (counterclockwise, from above) they are now Pin 1, disable; 2, feedback; 3, negative input; 4, positive input; 5, supply negative; 6, compensation; 7, output; and 8, supply positive. The chip output is directly connected to Pin 7, but this output is also internally connected to Pin 2, allowing you to make feedback connections on one side of the package with minimum trace inductance. The result is that the device is stable at gains of 2 or more in the new package but only at 4 or more in the conventional SO-8. The new package will be the company's preferred format for future high-performance products.

Overall, the company says that you should be able to use the 8099 in a range of circuit locations on a board, perhaps replacing several types because you can obtain its noise, distortion, bandwidth, and slew-rate performance with minimal trimming and simple external compensation; price is less than $2 (1000).

Analog Devices, +44 1 932 266000, www.analog.com.