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Problem Set 5
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ECE 453 Homework Assignment 5
Topic: Op Amp Design Active current Mirrors
Consider the following amplifier:
Vdd
VoutC
M4
M3
M1 M2
M5 M6
M7M8
Vb3
Vb2
Vb1
M9M10
M11M12
CL
AVin+ Vin
-
This is a single stage amplifier with differential inputs, a single output and high gain. In otherwords, an op-amp.
1. Find the differential gain and output swing of this op-amp
2. How many poles does the differential response contain? Where are they? What is thebandwidth given by the output pole? Sketch magnitude and phase Bode plots.
3. Estimate common mode gain and frequency response. Sketch magnitude and phase plots.
4. Explain what the op-amp is doing and how it works. Answer the floowing in your description.
• Why are there two transistors stacked at node “A” (M3 and M4) rather than 1? Whyis/isn’t this a good idea.
• What does the connection at node “C” do?
• How would you size M5 and M6 and what do they do?
• What do M1 and M2 do?
5. Redraw the amplifier with NFET inputs. Is the gain the same? Why or why not?
6. Design a bias network to set Vb1, Vb2, and Vb3
1