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 — courses:ec330_2013:invchar [2013/01/17 02:47] (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>​cc​=6V unless otherwise specified + * 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 + + {{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​. ​ + + {{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>​cc​=5V and V<​sub>​cc​=9V. These will be useful for future experiments. + + * 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,​ μ<​sub>​n​C<​sub>​ox​). 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. ​