h23_mt - EE214 Winter 04/05 B. Murmann Handout #23 Page 1...

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EE214 Winter 04/05 Handout #23 B. Murmann Page 1 of 6 MIDTERM PROJECT (Due: Wednesday, November 24, 2004, noon PT) READ THIS ENTIRE HANDOUT THOROUGHLY! Part 1: Design Specifications and Deliverables Part 2: Spice Test Setup Part 3: Project Submission Procedure Your new job at ChipsForFree.com requires you to design of a high performance OTA for use in a pipelined A/D converter. After an exhaustive study of the business opportunity, your marketing department decides that the circuit shown in Figure 1 should meet the following specifications: Parameter Specification Static Gain Error < 0.25% Closed Loop -3dB Bandwidth 250MHz Phase Margin > 70 ° Power Dissipation Minimize C s + V sd - + V od - C s C f C f C L C L V id Figure 1 Given circuit parameters: Last modified 11/1/2004 1:30 PM
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EE214 Winter 04/05 Handout #23 B. Murmann Page 2 of 6 Parameter Value Technology EE214 0.35 µ m CMOS V DD 3V Input Common Mode Voltage 1.5V Output Common Mode Voltage 1.5V Differential Output Range* 4.2V Operating Temperature 27 ° C C L 100fF C s 200fF C f 100fF Compensation capacitors (if used) >100fF *Defined as the differential output swing at which the OTA’s Open Loop DC gain V od /V id has dropped by 30% relative to its quiescent point value. Additional design considerations and constraints Current mirror ratios cannot be larger than 20, and must be integer. Due to past failures at ChipsForFree.com, it is strictly forbidden to cancel nondominant poles via feedforward zeros. Your OTA must contain a suitable common mode feedback circuit. Since we want to focus on the design of the differential signal path in this project, you can simply use ideal common mode feedback, e.g. as used in homework 5. Your final circuit may use no more than one ideal floating current source. In case you decide to use cascodes in your design, you must generate all required bias voltages using MOS transistors. Note that before you could actually fabricate this design, several other aspects would need to be factored into the design process. E.g. noise performance, and also slewing, an effect that we’ll cover later in this class. To keep this project manage, we will ignore these additional difficulties. In addition, you don’t need to consider process and temperature variations. However, we still require that your circuit not be overly sensitive to either (i.e., no “marble balanced on the tip of a cone” behavior). We will be the final judges of whether such a condition exists. If you are unsure, please consult the teaching staff early on. Suggested design flow As you will find out, this problem has many more degrees of freedom than all of the homework assignments you have dealt with so far. Hence, we suggest that you tackle this design in two steps. First, generate a reasonable design that meets the performance requirements. E.g. pick reasonable L and g m /I D for all devices, calculate the required transconductance(s) that are needed to meet the specs, and determine all currents and
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h23_mt - EE214 Winter 04/05 B. Murmann Handout #23 Page 1...

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