ELE 704 Analog CMOS Integrated Circuits
Laboratory Two - Single-Stage Amplifiers
Professor Fei Yuan
September 2011
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Pre-Laboratory
Single-stage amplifiers, such as common-source (CS), common-gate (CG),
and common-drain (CD) (source follower), are the basic building blocks of
complex analog systems. In this laboratory, you are required to carry out a
detail analysis of characteristics of common-source, common-gate, commondrain, and cascode common-source amplifiers.
1. Complete the schematic of common-source, common-gate, and commondrain configurations. The load of the amplifier should be a current
source implemented using a MOSFET transistor biased in the saturation. The biasing voltage of the load MOSFET transistor is an ideal
voltage source.
2. Choose the size of each transistors properly. To obtain appropriate DC
biasing conditions, the width of PMOS transistors should be made approximately twice that of NMOS transistors. Do not use the minimum
width (default) as they will make the circuits more sensitive to process
variation (mismatch effects). Use large width, for example, 10-100µm,
will also give you a larger gm , subsequently a larger voltage gain.
3. Show the small-signal equivalent circuit of the three single-stage amplifiers. The finite resistance of the load transistor should be considered.
Derive the expressions of the voltage gain Av , input impedance Rin and
output impedance Rout of the three amplifiers at low frequencies.
4. Find the frequency of the poles of all amplifiers at the input and output
terminals with Cgs and Cgd considered. All other parasitic capacitances
are neglected. Using Miller’s theorem to simplify your analysis.
5. Tabulate your results for all three configurations.
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Laboratory Work
For each common-source, common-gate, common-drain, and cascode commonsource configuration,
1. Create the corresponding schematic view and symbol view. Choose
components from cmosp18 | nfet | spectre, the substrate of the NMOS
transistors should be connected to the ground. If you are using PMOS
as the active load, the n-well of the PMOS transistors should be connected to VDD .
2. Create a testfixture.(You may use one text fixture cell for all three
configurations).
3. Apply appropriate biasing voltages. Perform DC analysis to find out
DC operating points of each transistor: VGS , VDS and ID . Record
the DC operation points. Using pinch-off condition to verify that all
transistors are biased in the saturation. Calculate the value of the AC
parameters of gm and Av at low frequencies.
4. Perform DC analysis by sweeping the amplitude of the input DC source
and record the output. Plot the output voltage as a function of the
amplitude of the input DC voltage. This plot will show the dynamic
range of the amplifiers. Record the maximum input voltage at which a
clear distortion of the output voltage is observed.
5. Perform an AC analysis and determine Rin . Note that no load should
be connected to the output of the amplifier in this case. In a similar
manner, measure Rout . Note that both Rin and Rout are small-signal
parameters and their values depend upon the dc biasing conditions.
6. Perform an AC analysis to find the bandwidth. Open the Analog Artist
Window. Chose Results | Direct Plot | AC dB20. Then click on the
output, a -3 dB Plot will appear, use the markers to measure the -3 dB
frequency. Plot the phase response.
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7. Perform transient analysis to find out the average slew rate, i.e. the
rise time of the amplifiers to a step voltage input.
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Post-Laboratory Report
The followings must be included in your Post-laboratory Report.
1. The schematic of amplifiers studied in the Laboratory Work with an
appropriate border. Your name and student ID must be shown in the
border area. The dimensions of all transistors and the value of other
circuit components must be clearly shown in the schematics.
2. The schematic of the test fixture with an appropriate border.
3. A table documenting the exact dimension of all transistors used in your
design.
4. Tabulate the DC biasing conditions of all transistors.
5. Simulated frequency response, both magnitude and phase, of the output voltage. Clearly show the bandwidth of the amplifier and the phase
at the bandwidth frequency.
6. Tabulate the results of Av , Rin , Rout and f−3dB at low frequencies for
three configurations.
7. Using both the Pre-Laboratory Report and the results from the Laboratory Work to qualitatively and quantitatively compare the three
basic configurations in terms of their advantages and disadvantages.
Comments on your findings.
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