Consider the circuit shown in the figure.
The CMOS digital logic circuit has infinite input impedance. Assume the opamp is ideal. A 1.8 V Zener diode with a minimum Zener current of $2 \mathrm{~mA}$ is used. The corresponding maximum value of resistance $\mathrm{Rz}$ is $\mathrm{k} \Omega$. (rounded off to one decimal place).