EE 140 HW 7
Due Tuesday 3/13/01 at 5 pm in 497 Cory
Design a two stage op-amp with the following specs:
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open-loop low-frequency gain of at least 1,000
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open-loop low-frequency gain of at least 100 with a resistive load of 1k
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60 degree phase margin (fp2 >= 2*fu) with a capacitive
load of 20 pF
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+-2.5 V power supply, output swing to within 0.5V of either rail
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unity gain bandwidth of 100MHz
You may use 1 ideal current source in your design to set up bias voltages.
All other elements should be FETs and capacitors.
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Calculate Cc and gm, Id, and Vdsat
for the input pair and second stage input
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Calculate the corresponding W/L values for all transistors
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Calculate the parastic capacitances on each of the two high-impedance nodes,
and estimate their effect on your performance
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Carefully draw your complete circuit and label each device with your hand-calculated
values for gm, Id, and Vdsat (you don't
need gm for the bias transistors).
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Use spice (.op) to find the gm, Id, and Vdsat
values for all transistors at Vcm=0, 2, and -2 Volts, and label your plot
accordingly.
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Use spice to plot the DC input/output function and gain at Vcm =0, 2, and
-2 volts, with and without a 1k resistive load. Label your plot with
the gain spec, and your hand-calculated value.
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Use spice to plot the AC open-loop transfer function for the amplifier
with a 20pF capacitive load at Vcm=0, 2, and -2 V. Label the unity
gain frequency spec, and your hand calculated unity gain value. Label
the phase margin spec, and your hand calculated value.
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Use spice to plot the transient response of your amplifier to a 20MHz square
wave over one or two periods when it's wired up as a unity-gain buffer.
Try cutting your compensation capacitor in half and re-running the simulation.
How small can your compensation capacitor get before bad things happen?