Op. Amps Applications The Inverting Configuration SJTU Zhou Lingling 2 The Noninverting Configuration SJTU Zhou Lingling 3 The Voltage follower (a) The unity-gain buffer or follower amplifier. (b) Its equivalent circuit model. SJTU Zhou Lingling 4 The Weighted Summer SJTU Zhou Lingling 5 The Weighted Summer Ra Rc Ra Rc Rc Rc vo v1 ( )( ) v2 ( )( ) v3 ( ) v4 ( ) R1 Rb R2 Rb R3 R4 SJTU Zhou Lingling 6 A Single Op-Amp Difference Amplifier Application of superposition Inverting configuration R2 vo1 vI 1 R1 SJTU Zhou Lingling 7 A Single Op-Amp Difference Amplifier Application of superposition. Noninverting configuration. R2 R4 vo 2 (1 )( )vI 2 R1 R4 R3 SJTU Zhou Lingling 8 Integrators The inverting configuration with general impedances in the feedback and the feed-in paths. SJTU Zhou Lingling 9 The Inverting Integrators The Miller or inverting integrator. SJTU Zhou Lingling 10 Frequency Response of the integrator SJTU Zhou Lingling 11 The op-amp Differentiator SJTU Zhou Lingling 12 The op-amp Differentiator Frequency response of a differentiator with a time-constant CR. SJTU Zhou Lingling 13 Bistable Circuit • • • The output signal only has two states: positive saturation(L+) and negative saturation(L-). The circuit can remain in either state indefinitely and move to the other state only when appropriate triggered. A positive feedback loop capable of bistable operation. SJTU Zhou Lingling 14 Bistable Circuit The bistable circuit (positive feedback loop) The negative input terminal of the op amp connected to an input signal vI. R1 v vo vo R1 R2 SJTU Zhou Lingling 15 Bistable Circuit The transfer characteristic of the circuit in (a) for increasing vI. Positive saturation L+ and negative saturation L- VTH L SJTU Zhou Lingling 16 Bistable Circuit The transfer characteristic for decreasing vI. VTL L SJTU Zhou Lingling 17 Bistable Circuit The complete transfer characteristics. SJTU Zhou Lingling 18 A Bistable Circuit with Noninverting Transfer Characteristics R2 R1 v v I vo R1 R2 R1 R2 SJTU Zhou Lingling 19 A Bistable Circuit with Noninverting Transfer Characteristics The transfer characteristic is noninverting. VTH L( R1 R2) VTL L( R1 R2) SJTU Zhou Lingling 20 Application of Bistable Circuit as a Comparator • • • • • Comparator is an analog-circuit building block used in a variety applications. To detect the level of an input signal relative to a preset threshold value. To design A/D converter. Include single threshold value and two threshold values. Hysteresis comparator can reject the interference. SJTU Zhou Lingling 21 Application of Bistable Circuit as a Comparator Block diagram representation and transfer characteristic for a comparator having a reference, or threshold, voltage VR. Comparator characteristic with hysteresis. SJTU Zhou Lingling 22 Application of Bistable Circuit as a Comparator Illustrating the use of hysteresis in the comparator characteristics as a means of rejecting interference. SJTU Zhou Lingling 23 Making the Output Level More Precise For this circuit L+ = VZ1 + VD and L– = –(VZ2 + VD), where VD is the forward diode drop. SJTU Zhou Lingling 24 Making the Output Level More Precise For this circuit L+ = VZ + VD1 + VD2 and L– = –(VZ + VD3 + VD4). SJTU Zhou Lingling 25 Generation of Square Waveforms Connecting a bistable multivibrator with inverting transfer characteristics in a feedback loop with an RC circuit results in a square-wave generator. SJTU Zhou Lingling 26 Generation of Square Waveforms The circuit obtained when the bistable multivibrator is implemented with the positive feedback loop circuit. SJTU Zhou Lingling 27 Waveforms at various nodes of the circuit in (b). This circuit is called an astable multivibrator. Time period T = T1+T2 1 ( L L ) T1 RC ln 1 1 (L L ) T2 RC ln 1 1 T 2RC ln 1 SJTU Zhou Lingling 28 Generation of Triangle Waveforms SJTU Zhou Lingling 29 Generation of Triangle Waveforms SJTU Zhou Lingling 30