1) Design an NMOS-input telescopic cascode amplifier with a 100fF load
capacitance. Use Vdsat=0.2 for all devices, and W/L = 10 for NMOS
(except the current source) and W/L=20 for PMOS.
Assume a +-2.5V supply. Design all of the bias circuitry using only 1 ideal current source. Assume that the amplifier will be used in unity gain feedback with signals near zero volts.
2) Design an NMOS-input folded cascode amplifier with the same Vdsats and W/Ls on the input stage as in 1C. Draw the input/output swing plot in 2D for this amplifer and the amplifier from part 1C. Compare the input/output swing, unity gain frequency, low frequency gain, and power consumption of both amplifiers. Which do you like better?
- Using L=1um for all devices except the PMOS mirror (M4A and B, not the PMOS cascode devices), and L=5um for the PMOS mirror devices M4AB, calculate the low frequency gain, pole frequency, and unity gain frequency, and the pole frequency for the nmos cascode and the doublet for the PMOS mirror. Draw the magnitude *and* phase plots, and compare to SPICE. In this case, the mirror doublet should be at a lower frequency then the cascode pole.
- Using L=1um for all devices except the NMOS cascode (M2AB), and L=5um for M2AB do the same calculations, plot, and SPICE comparison. In this case, the cascode pole should be at a lower frequency than the mirror doublet.
- Using L=1um for all devices, do the same calculations, plot, and SPICE comparison.
- Which of these opamps is stable in unity gain feedback? For those that are stable, what is the phase margin?