proj_3_09 - ECE 323 Project 3 Fall 2009 Write-up Due 11/3 1...

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ECE 323: Project 3, Fall 2009 Write-up Due: 11/3 1 University of Massachusetts Department of Electrical and Computer Engineering ECE 323 Electronics I Fall 2009 Project 2: Direct Coupling, Current Mirrors, and Active Loads Charlie was growing tired analyzing single transistor circuits, so he was interested when Dr. Designsalot told him that these simple circuits are often combined to form more complicated circuits. In amplifier designs, he said, a common challenge is to obtain high gain, high input impedance, and low output impedance all at the same time. Charlie tackled the problem with multiple transistors.
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ECE 323: Project 3, Fall 2009 Write-up Due: 11/3 2 1.0 Design Specifications Your designs will meet the same specifications that Charlie used: Parameter Value Transistors HCF4007 and 2n3904 Gain >40 Power Supply 9V Load Resistance 6k Ω Input Resistance >100k Ω Output Amplitude at THD<2.5% and 1kHz 4V pp Power Consumption <8mW Capacitors Only input and output For hand calculations use K n =0.75mA/V 2 , K p =0.75mA/V 2 , V TN =1.2, V TP =-1.2, and λ =0.03 for the transistors in the HCF4007. 2.0 Selecting a Topology Dr. Designsalot gave Charlie the specifications in section 1.0 to focus his design. Charlie knew how to design three single transistor amplifiers, i.e. Common Source, Common Gate, and Common Drain, but when he tried to meet these specifications with a single transistor he always fell short on at least one of the specifications. He decided to summarize what he knew about each topology (Sedra and Smith 318-320). Common Source Common Gate Common Drain R in R G 1/g m R G R out R D R D 1/g m A V -g m (R D ||R L ) g m (R D ||R L ) R L /(R L +1/g m ) Charlie needed to work with some real values, so he calculated g m at 1mA. What is 1/g m for I D =1mA? Since Charlie’s value for 1/g m was less than the required input resistance, Charlie decided he needed a common-source amplifier or common-drain amplifier at the input. At the output, he needed the low output impedance of a common-drain amplifier to drive a 6k Ω load. Charlie considered the two possible topologies: a common-source amplifier driving a common-drain amplifier and a common-drain amplifier driving another common-drain amplifier. He realized the common-source amplifier was needed to achieve the gain and decided on the topology in Fig. 1.
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ECE 323: Project 3, Fall 2009 Write-up Due: 11/3 3 Figure 1: Common-Source Amplifier followed by Common-Drain Amplifier Dr. Designsalot looked at Charlie’s topology and suggested a few changes. First, he reminded Charlie that an active load for the common-source stage would increase the gain. Then, he suggested that Charlie replace the common-drain MOSFET with a bipolar transistor. Dr. Designsalot explained that something called the body-effect complicates the behavior of many n-channel MOSFETs when the source is not connected to ground. Charlie will learn about this in ECE323, but for now it is easier to use a bipolar transistor.
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This note was uploaded on 10/27/2011 for the course ECE 323 taught by Professor Oliai during the Fall '07 term at UMass (Amherst).

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proj_3_09 - ECE 323 Project 3 Fall 2009 Write-up Due 11/3 1...

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