conversion of LC oscillator to RC oscillator

how can we replace L with R or C in an oscillator so that it doesnot affect the frequency range?

There are two basic methods:
1.) In a passive reference topology you simply can replace a (grounded) L by an active circuit (actively simulated inductance),
2.) You can replace the role of the inductance (NOT the inductance as a part) using one of the various active RC topologies.
For this purpose, the transfer function is necessary.

Of course, in both cases it is possible to keep the frequency characteristics.

can you please post any circuit reg option2 that u have mentioned about replacing with an RC topology?

LC has higher Q than RC so is more stable.

Ceramic resonator has even higher Q

Yes - as long as you speak about PASSIVE circuits. However, for ACTIVE RC circuits you can realize Q values as large as you want.

@Inder7: Show me the LC oscillator you have in mind - and I can you give an equivalent RC oscillator.

what is the passive equivalent circuit of basic LR circuit i.e L can be replaced by any passive component such that the frequency remains same.

The RL high-pass can be replaced by a RC high-pass with same cut-off frequency, but only under specific conditions for the source and load impedance. As long as the external impedances are unknown, there's no solution.

A condition that can be easily solved is ZS = 0, ZL = infinity.

[QUOTE=LvW] Yes - as long as you speak about PASSIVE circuits. However, for ACTIVE RC circuits you can realize Q values as large as you want.

Not quite

The LC equivalent circuit of a passive crystal or ceramic resonator is still far higher Q and stability than any Active RC Filter (Q~10,000 for AT xtal, Q>100k for SC Xtal). This is not easily achievable in RC active filters.