accumulator in pll

Can Delta-Sigma replace Accumulator in Fraction-N PLL?

IF Delta-Sigma can replace accumulator in Fraction-N PLL, how to difine input, output of sigma-delta and swallow counter input?

It can.
The Delta-Sigma input is swallow out.
The swallow input is Delta-Sigma 1 bit out.

The accummulator in the Fractional-N represent the "sigma", it is already delta-sigma.?

No, it is not.
The accummulator is only represent the "sigma" in the Fractional-N PLL application.

The delta-sigma function can be a time * pulse density cost function.
It is also M-bit * time => N bit * time density transfer function.
The time is times in in Fraction-N PLL application.
So, The 1 bit output is index divisor.

Can you explain clearly?
Many papers saidthat the The Delta-Sigma input is fractional code,and it can't be the swallow out.