Using a current-feedback op amp, you can generate high-frequency sine waves with larger amplitude than conventional op-amp-based designs. The circuit in Fig 1 uses four passive components, connecting one capacitor to the compensation node (another op amp that has this pin available is the OP660).
Oscillation requires that R2/R=C1/C2. The frequency of oscillation, in radians/sec, equals 1/[sqrt](R R1 C1 C2). Note that R2 and R1, respectively, independently adjust the oscillation amplitude and frequency.
The nonlinear internal mechanism associated with the output-stage saturation of the current-feedback amplifier ensures the existence of a stable limit cycle; this start-up is ensured for a value of R2, slightly lower than nominal value. If necessary, you can include additional amplitude limitation by using antiparallel zener diodes across C2.
For the values shown, the oscillation frequency is approximately 1 MHz, and you get a signal free of slew-rate distortion, even with amplitudes as high as 15V and THD of <1%. For more spectral purity, you can provide automatic amplitude control by substituting an FET as a voltage-controlled resistor (R2 is grounded). (DI#1711) EDN
To Vote For This Design, Circle No. 406
A handful of components configures a current-feedback op amp as a large-amplitude sine-wave oscillator with independent adjustment of amplitude (via R2) and frequency (via R1).
