Berkeley ELENG 247A - Lecture Notes (29 pages)

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Lecture Notes



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Lecture Notes

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Pages:
29
School:
University of California, Berkeley
Course:
Eleng 247a - Introduction to Microelectromechanical Systems (MEM...
Introduction to Microelectromechanical Systems (MEM... Documents

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EE247 Lecture 7 Summary last lecture Automatic on chip filter tuning continued from last lecture Continuous tuning Reference integrator locked to a reference frequency DC tuning of resistive timing element Periodic digitally assisted tuning Systems where filter is followed by ADC DSP existing hardware can be used to periodically update filter freq response Continuous time filters Bandpass filters Example Gm C BP filter using simple diff pair Linearity noise issues Various Gm C Filter implementations Comparison of continuous time filter topologies EECS 247 Lecture 7 Filters 2005 H K Page 1 Summary last lecture Continuous time filters Opamp MOSFET C filters Opamp MOSFET RC filters Gm C filters Frequency tuning for continuous time filters Trimming via fuses Automatic on chip filter tuning Continuous tuning Utilizing VCF built with replica integrators Use of VCO built with replica integrators EECS 247 Lecture 7 Filters 2005 H K Page 2 Master Slave Frequency Tuning Reference Integrator Locked to Reference Frequency Replica of main filter Gm C Vin I Gm Vref Gm C Vref Vout Vtune Replica of main filter integrator e g Gm C building block used Utilizes the fact that a DC voltage source connected to the input of the Gm cell generates a constant current proportional to the transconductance and the voltage reference I Gm Vref EECS 247 Lecture 7 Filters 2005 H K Page 3 Reference Integrator Locked to Reference Frequency Consider the following sequence Integrating capacitor is fully discharged t 0 At t 0 the integrator input is connected to the output of the Gm cell then Vin I Gm Vref Gm Vout Vref C1 Vtune VC1 T t 0 EECS 247 Lecture 7 Filters VC1 Gm Vref T C1 time 2005 H K Page 4 Reference Integrator Locked to Reference Frequency Since at the end if the period T VC1 G m Vref T I Gm Vref Vin C1 Gm Vout Vref C If VC1 is forced to be equal to Vref then Vtune VC1 C T N Gm fclk VC1 G m Vref T T C1 time t 0 How do we manage to force VC1 Vref Use feedback EECS 247 Lecture 7 Filters 2005 H



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