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“Op-Amp” Operational Amplifier Op-Amp name derives from early usage of these elements in performing mathematical operations in analog computers. • Non Inverting Amplifier • Inverting Amplifier • Adder – (and Subtractor using an Inverter) • Differential Amplifier • Integrator • Differentiator Three Ways to Examine Op-Amp Behavior • Consider as an Ideal Op-Amp Component • Consider as a Feedback Model and Examine Behavior • Perform Conventional Circuit Analysis VE = VIN+ - VIN- VIN- VIN+ VOUT = a * VE Ideal Op-Amp Model VE = VIN+ - VIN- VOUT = a * VE Behavior of Feedback Model Behavior of Feedback Model of Non Inverting Amplifier Behavior of Feedback Model Behavior of Feedback Model Behavior of Feedback Model Behavior of Feedback Model Summary Circuit Analysis Approach Circuit Analysis Approach “Op-Amp” Operational Amplifier Op-Amp name derives from early usage of these elements in performing mathematical operations in analog computers. • Non Inverting Amplifier • Inverting Amplifier • Adder – (and Subtractor using an Inverter) • Differential Amplifier • Integrator • Differentiator Differential Amplifier Circuit Analysis a (V+ - V-) Differential Amplifier Circuit Analysis a (V+ - V-) Differential Amplifier Circuit Analysis a (V+ - V-) Differential Amplifier Circuit Analysis a (V+ - V-) Differential Amplifier Circuit Analysis a (V+ - V-) ZF / ZG Common Mode Rejection Ratio v1 v1 v2 vi1 vi2 Original Inputs vid / 2 vicm vid / 2 v2 Model of inputs with commonmode and differential-mode components Common Mode Rejection Ratio CMRR A CMRR Acm where A is the differential mode gain and Acm is the common mode gain A CMRRdB 20 log dB Acm Ideally: CMRR Typically: 60 dB CMRR 120 dB Assumes R2 = R4 and R1 = R3 Differential Amplifier Circuit Analysis with Component Imbalance Differential Amplifier Circuit Analysis with Component Imbalance Differential Amplifier Circuit Analysis with Component Imbalance Differential Amplifier Circuit Analysis with Component Imbalance Differential Amplifier Circuit Analysis with Component Imbalance The Maximum Power Transfer Theorem simply states, the maximum amount of power will be dissipated by a load resistance when that load resistance is equal to the Thevenin/Norton resistance of the network supplying the power. To create the Thevenin Equivalent Circuit we need: 1. Value of the Thevenin Voltage Source 2. Value of the Thevenin Resistance Input and Output Impedances of Noninverting Op-amp Configuration - Rai Rd vd ii vi The unity gain buffer input impedance is much higher than the op-amp input impedance Rd. The amplifier output impedance is much smaller than the op-amp output impedance Ro. + Ro + - Avd vo io Rao RL CL Rai Rd ( A 1) Rd A Rao Ro /( A 1) Ro / A Instrumentation Amplifier v1 R3 R4 R2 vout R1 R2 vref v2 vout - vref R3 R4 R 1 2 2 v2 - v1 R3 R1 R4 G vout - vref v2 - v1 R4 R2 1 2 R3 R1 Instrumentation Amplifier Example Burr-Brown INA118 Parameters: R1 RG vout Vo R2 25k vref Ref Gain: G Vo - Ref 50k 1 VIN - VINRG If RG 49.9, G 1 50,000 1,003 49.9 R3 R4 60k v2 VIN v1 VIN- Instrumentation Amp (cont.) A feedback network may also be included with the instrumentation amplifier. v1 R2 vdiff = v2 - v1 R4 R3 vout 2R1 R2 v2 R3 R4 R Vout s Gs Vdiff s s 1 RC C