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| SEC. 18-1 INTRODUCTION TO
OP AMPS A typical op amp has a noninverting input, an inverting input, and a singleended output. An ideal op amp has infinite open-loop voltage gain, infinite input resistance, and zero output impedance. It is a perfect amplifier, a voltage-controlled voltage source (VCVS). SEC. 18-2 THE 741 OP AMP The 741 is a standard op amp that is widely used. It includes an internal compensating capacitor to prevent oscillations. With a large load resistance, the output signal can swing to within 1 or 2 V of either supply. With small load resistances, MPP is limited by the shortcircuit current. The slew rate is the maximum speed at which the output voltage can change when driven by a step input. The power bandwidth is directly proportional to slew rate and inversely proportional to the peak output voltage. SEC. 18-3 THE INVERTING AMPLIFIER The inverting amplifier is the most basic op-amp circuit. It uses negative feedback to stabilize the closed-loop voltage gain. The inverting input is a virtual ground because it is a short for voltage but an open for current. The closed-loop voltage gain equals the feedback resistance divided by the input resistance. The closed-loop bandwidth equals the unitygain frequency divided by the closed-loop voltage gain. SEC. 18-4 THE NONINVERTING AMPLIFIER The noninverting amplifier is another basic op-amp circuit. It uses negative feedback to stabilize the closed-loop voltage gain. A virtual short is between the noninverting input and the inverting input. The closed-loop voltage gain equals Rf/R1 . 1. The closed-loop bandwidth equals the unity-gain frequency divided by the closed-loop voltage gain. SEC. 18-5 TWO OP-AMP APPLICATIONS The summing amplifier has two or more inputs and one output. Each input is amplified by its channel gain. The output is the sum of the amplified inputs. If all channel gains equal unity, the output equals the sum of the inputs. In a mixer, a summing amplifier can amplify and combine audio signals. A voltage follower has a closed-loop voltage gain of unity and a bandwidth of funity. The circuit is useful as an interface between a high-impedance source and a lowimpedance load. SEC. 18-6 LINEAR ICS Op amps represent about a third of all linear ICs. A wide variety of op amps exists for almost any application. Some have very low input offsets, other have high bandwidths and slew rates, and others have low drifts. Dual and quad op amps are available. Even high-power op amps exist that can produce large load power. Other linear ICs include audio and video amplifiers, RF and IF amplifiers, and voltage regulators. |