HP HP-Bench-Briefs-1990-04-06 free download

File name HP-Bench-Briefs-1990-04-06.pdf

HEWLETT PACKARD SERVICE INFORMATION FROM HEWLETT-PACKARD 2nd Quarter 1990 Operational Ampllifier Basics Introduction The op amp is, therefore, an ideal Ideal Op Amps With Negative building block for all kinds of analog Feedback It can be mathematically shown that tasks. In practice, no single charac- if an amplifier has: teristic listed above can be fully The most common op amp circuit con- I an infinite high gain, achieved. The values that can be prac- figuration uses two external compo- tically obtained are nevertheless such nents: 1) an input component and 2) I an infinite bandwidth, that the resulting performance is a feedback component (see Figure 3). I an infinite high input impedance, extremely useful. When the feedback component is be- and tween the op amp output and the I a zero output impedance, -input, the circuit is said to have negative feedback. When the feed- then its characteristics can be totally Op Amp Fundamentals determined by external components connected in feedback loops. Such an An op amp is a very high gain dc I amplifier and usually has voltage V+ "ideal" operational amplifier (op Power Supply amp) is shown in Figure 1. Since RIN gains in the range of 20,000 to is infinite, there is no current flow into 1,000,000. The detailed schematic symbol of an op amp is shown in n 1 Input " e ~ i n g ~ either input terminal and the differen- tial input voltage is zero. If there is Figure 2a with the simplified symbol an output voltage Eo present, it can shown in Figure 2b. Ioninverting output Input only be the result of an infinitesimal Power voltage at the input. These are