what is differenece between ring-oscialltor and PLL?

what is differenece between ring-oscialltor and PLL?

ini my thought, It is not different.

please explain me in detail

thanks.

A pll includes pfd, charge pump,loop filter, divider and vco.

ring-oscillator is only a kind of vco.

The main difference between PLL and any oscillator in general is the negativr feedback action that the PLL performs,due to the jitter in any oscillator if it is running by it self this jitter accumulates by time causing unlimited phase error,while in PLL the jitter generated by the oscillator is sensed and and the oscillator freq. is adjusted to eliminate it such that it doesn't accumulate with time.

ring oscillator will simply generate frequencies for a control voltage.
there is no feedback or correction involved.
pll is nothing but ,it will compares the phaseerror with the reference frequency.,
and generates the vcntl to minimizing the error.
pll can be used for many applications other than frequency synthesis like recovery ckts,skew reduction circuits.

Added after 3 minutes:

hi
go through the doc.

A ring oscillator is just a kind of oscillator based on an odd number
of inversions and propagation delay around a loop. It can be very fast,
but is not very precice (frequncy depends heavyly on temperature, supply
voltage, etc). One application of ring oscillators is to determine inverter time delays as a means to evaluate the CMOS fabrication process

A phase locked loop is a system that (in its simplest form) includes some sort of
electronically variable oscillator and a phase detector that compares
that oscillator to an external signal. The output of the phase
comparator is linked to the oscillator in such a way that it drives
the oscillator into synchronism with the external signal.

A PLL has a VCO (voltage controlled oscillator) a phase detector (measure
the phase relation of two signals) and a loop filter. Often there are
additional dividers. A Pll can multiply clock signals, it can remove a delay from clock signals and it can clean up clock signals (remove jitter).