The natural choice for generating a pulse of variable frequency and duty cycle is a good bench-top pulse generator. If you don't have a generator or must build one into your system, however, you can ...
One does not expect to generate a sine wave with –100dBc distortion using a 5V low power op amp. All the same, a bandpass filter using the LTC6258 can combine with an easy-to-use low power oscillator ...