OA-11 A Tutorial on Applying Op Amps to RF Applications

OA-11 A Tutorial on Applying Op Amps to RF Applications OA-11National SemiconductorA Tutorial on Applying Op OA-11September 1993Amps to RF ApplicationsWith operating frequencies exceeding 300MHz, National’s flat response with a -3dB bandwidth of 150MHz. To matchline of monolithic and hybrid current feedback operational this, a voltage feedback op amp would require 20*150MHz =amplifiers have become an attractive option for the RF (and 3GHz gain bandwidth product). Please refer to NationalIF) design engineer. Typical operational amplifier specifica- application note OA-13 for a description of the current feed-tions do not, however, include many of the common specifi- back op amp topology and transfer function.cations familiar to RF engineers. To help the designer exploit One of the big changes in going from a classical RF amplifierthe many advantages these amplifiers can offer, this appli- to using an op amp is the exceptional flexibility offered by thecation note will define the RF specifications of most interest op amps. The designer is now charged with setting up theto designers, detail what determines each of these particular proper operating conditions for the op amp, defining theperformance characteristics for National’s current feedback gain, and determining the I/O impedances with externalop amps, and, where possible, discuss performance optimi- components. Op amps allow the designer the option ofzation techniques. To apply op amps to RF ...