# Differences

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 — courses:ee3703_2017:invchar [2017/01/10 09:36] (current) Line 1: Line 1: + ====== Inverter characteristics ====== + ===== Goals ===== + * You'll be using inverters in a CD4069 CMOS inverter chip as transconductors(VCCS). In this experiment you'll measure the large and small signal characteristics of this transconductor. In all experiments,​ remember to disable the unused inverters. Do all steps for V<​sub>​dd​=6V for the inverter unless otherwise specified. Choose the supply voltages ​ V<​sub>​cc​ and  V<​sub>​ee​ of the opamp appropriately. + * Determine the large signal I<​sub>​out​ versus V<​sub>​in ​ + * Determine the large signal V<​sub>​out​ versus V<​sub>​in​ + * Determine the small signal parameters of the transconductor + + ===== References ===== + * View the [[http://​www.ee.iitm.ac.in/​~nagendra/​EC330/​200801/​lectures/​ec330-intro/​ec330-intro.swf|lecture]] + ===== Experiments ===== + + {{invchar1.png?​400}} + + * Determine I<​sub>​out​ versus V<​sub>​in​ of the transconductor using the circuit above. Vary the input voltage from 0 to Vcc. You can use a separate power supply for generating the variable bias voltages or a resistive voltage divider(say,​ a chain of 16 identical resistors from Vcc to ground). What is the self bias voltage V<​sub>​M​ of the inverter? Estimate the transconductance at V<​sub>​M​. ** Choose the supply voltages for the opamp appropriately so that it doesn'​t saturate **. + + {{invchar2.png?​200}} + + * Determine V<​sub>​out​ versus V<​sub>​in​ of the transconductor(with an open circuit load as shown above). Take more points in the high gain region for accurate determination of gain. + + {{invchar3.png?​300}} + + * Bias an inverter at V<​sub>​M​ by shorting its input and output as shown above. What is the small signal resistance looking into this circuit? Measure it by forming a voltage divider with one arm being the small signal resistance as shown in the circuit above. Are the values consistent with the earlier measurements?​ Repeat this measurement for V<​sub>​dd​=5V and V<​sub>​dd​=9V. These will be useful for future experiments. + + ===== Exercises ===== + + * From the above measurements,​ estimate the small signal output resistance Rout of the transconductor,​ and threshold voltages and current factors of nMOS and pMOS transistors. + + * You'll need the measured parameter values for subsequent experiments(g<​sub>​m,​inv,​ r<​sub>​out,​inv,​ V<​sub>​Tp,​ V<​sub>​Tn,​ μ<​sub>​p​C<​sub>​ox​W<​sub>​p/​L<​sub>​p,​ μ<​sub>​n​C<​sub>​ox​W<​sub>​n/​L<​sub>​n​). So keep a record of them. + + ===== Applications ===== + + * Transconductors are building blocks of practically all analog ICs albeit with numerous other topologies besides the CMOS inverter. Regardless of the topology, you'll need to do similar simulations/​measurements as the ones here to ascertain their parameters. ​