In this chapter we will be examining some common uses of op amps. Where Chapter Three focused on the theory of negative feedback in a more abstract way, this chapter zeroes in on the practical results of using negative feedback with op amps. Now that you know what negative feedback is and how it works, you can reap the benefits. The main theme is in the design and analysis of simple, small-signal, linear amplifiers. We will also be looking at some convenient approximation methods of analysis that can prove quite efficient. By the end of the chapter, you should be able to design single and multistage voltage amplifiers, voltage followers, and even amplifiers that sense current and/or produce constant current output. The voltage amplifiers offer the possibilities of inverting or not inverting the signal. Simple differential amplifiers are examined too. The chapter wraps up with a section on using op amps with a single polarity power supply and how to increase the available output current.