I was given this transfer function and instructed to use a Sallen-key cascaded with a 1st order filter to achieve it.
$$H(s)=\frac{628^3}{(s+628)(s^2+628s+628^2)}$$
The first order transfer function is
$$H(s)=\frac{628}{s+628}$$
So if I choose \$c=10\mu F\$, then \$R=159\Omega\$.
That leave the Sallen-key transfer function to be
$$H(s)=\frac{628^2}{(s^2+628s+628^2)}=\frac{\frac{A}{R^2C^2}}{s^2+\frac{2}{RC}s+\frac{1}{R^2C^2}}$$
So \$A\$ must be equal to \$1\$ and \$\frac{1}{R^2C^2}=628^2\$. The same values for R and C as the first order filter work here.
The problem is that middle term, \$628s=\frac{2}{RC}\$. This contradicts the other values. It works fine if this was a typo and that term was meant to be \$\frac{1}{2}\$ that value. Did I make a mistake here? I've wasted hours deriving and rederiving the transfer function for the filter to no avail.