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I came up with this linear regulator scheme wherein the value of constant current of a constant current sink is altered to control the series pass transistor and hence the output voltage.
With this setup, the regulator achieves a ripple rejection of 80dB and with a feed-forward capacitor of capacitance 100nF, a ripple rejection of 90dB is achieved (over here on EC).
Important: the 470ohm base resistor of the series pass transistor is critical. Without it, at low loads, the output won't be regulated.
You can find the LTspice simulation results here https://easyeda.com/prathikprashanth/high-ripple-rejection-linear-regulator
