Noise in current mirror
how do we obtain the equation of output noise current = (16/3)KT*gm in the same document 


The thermal noise in the drain current in a MOSFET is given by:
$$\overline{\frac{i_{nd}^2}{\Delta f}} = 4kT\gamma g_{d0}$$
For transistor in saturation region \$\gamma = \frac{2}{3}\$  and \$g_{d0} \approx g_m\$, thus noise current (PSD) in each of the transistor of the current mirror is given by \$\frac{8}{3}kTg_{m}\$. Since the current in M1 (in the document you are referring) is mirrored at the output, noise current will similarly get mirrored. Since the two noise sources are uncorrelated their PSD (variances) will add giving a total noise current of  \$\frac{16}{3}kTg_{m}\$ at the output.


  why there is a factor of (1+gmREF*Rb)2 in the denominator


The input impedance of the \$M_{REF}\$ seen from its drain/gate is \$\frac{1}{g_{mREF}}\$. The voltage at the capacitor will be given by a simple voltage divider equation:
$$V_{C} = \frac{\frac{1}{sC}}{R_B + \frac{1}{g_mREF} + \frac{1}{sC}} = \frac{g_{mREF}}{s(1+g_{mREF}R_B)C_B + g_{mREF}}$$
Thus noise sources from reference current and \$R_B\$ will be filtered by the above transfer function and then will be amplified by \$g_{m1}\$ before getting to the output. The noise from the transistor \$M1\$, though, appears directly at the capacitor output and will not be filtered by this transfer function. Again all the noise sources are uncorrelated so we add the PSD's.