EEL6935-F10-HLec04-opamps-2spp

# EEL6935-F10-HLec04-opamps-2spp - Lecture 4 Opamp Review...

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1 Lecture 4: Opamp Review Effect of finite open-loop gain, A Frequency dependence of open-loop gain Frequency dependence of closed-loop gain Output voltage and current saturation Output slew rate Offset voltage Input bias and offset current Non-zero output resistance Assume NON-ideal op amp. Inverting Amplifier (Finite A 0 ) 2 1 0 2 1 1 1 1 R R A R R V V in out For finite open loop gain A0, the error term indicates the larger the closed-loop gain, the less accurate the circuit becomes.

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2 Noninverting Amplifier (Finite A 0 ) 2 1 0 2 1 1 1 1 1 R R A R R V V in out Opamp speed limitation Due to internal capacitances, the gain of op amps begins to roll off.
3 Unity Gain Bandwidth ω b =internal pole of opamp Bandwidth and closed loop gain (Finite A 0 ) Product of gain and bandwidth ω t =A 0 ω b ω 3db =closed loop opamp 3dB bandwidth

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4 Gain Bandwidth Product Having a loop around the op amp (inverting, noninverting, etc) helps to increase its bandwidth. However, it also decreases the low frequency gain. ~(1+R 2 /R 1 ) Slew Rate of Op Amp In the linear region, when the input doubles, the output and the output slope also double. However, when the input is large, the op amp slews so the output slope is fixed by a constant current source charging a capacitor. This further limits the speed of the op amp. For large input, the internal circuitry of the op amp reduces to a constant current source charging a capacitor. The slope of the output ramp is called he “slew rate” As it can be seen, the settling speed is faster without slew rate (as determined by the closed-loop time constant).
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EEL6935-F10-HLec04-opamps-2spp - Lecture 4 Opamp Review...

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