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Unformatted text preview: ECE 327: Electronic Devices and Circuits Laboratory I Notes for Lab 4 (Oscillators Lab) 1. Introduce operational amplifiers • “Operational” and (historical) analog computers – Simulation of dynamical systems — think “ Simulink ” – Wider range of applications now – Simple integrators are still very influential * Switched-capacitor integrators make IC state variable filters cheap (“SC filters”) – High-speed current-feedback (CFB) varieties available • Differential amplifier with very high gain (i.e., gain near ∞ or ∞ /s ) • Despite having same symbol, operational amplifiers are NOT comparators ! – Comparators are faster (more like a switch ) and can have special switching features • Example: non-inverting unity gain buffer (i.e., negative feedback and A/ (1 + A )) – Extension: “Superdiode” (i.e., “ideal” diode) – Op. amp. as integrator (i.e., from A to A/s ) — input stage current driven into output capacitor • Real operational amplifiers (OAs) – PSRR (ripple rejection) * As in FET lab, power supply noise artifacts in output – Clipping near supply rails * Many OAs are not “rail-to-rail” (e.g., LM741 ) and may not even be symmetric * Oscillators depend on hard clipping * PSRR issues (solution discussed below) – Input leakage/bias current * Varies with input implementation · Tens of nanoamps bias with BJT-based (e.g., LM741 ) · Tens of picoamps leakage with BiJFET (e.g.,Tens of picoamps leakage with BiJFET (e....
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This note was uploaded on 08/05/2011 for the course ECE 209 taught by Professor Staff during the Fall '08 term at Ohio State.
- Fall '08