|Section Index||Owatonna Steele County Amateur Radio||20-Jul-2007|
Operational amplifiers (Op-Amps) were used to solve mathematical equations utilizing analog computers. Based on the configuration, op-amps could add, multiply, integrate, or perform other operations on signals.
The earliest op-amps were constructed with vacuum tubes. Solid state electronics, of course, allowed circuits to be more compact. Ultimately, circuits such as that shown at right, were developed into integrated circuits. Like most integrated circuits, this greatly simplifies the process of understanding and op-amps.
Common characteristics of op-amps are:
Op-amps have two inputs and one output. In a steady state, the inputs must be balanced because the gain of the op-amp is acting solely on the voltage differential between the two inputs.
The capacitors (C1 and C2) are used to keep the power bus clean and help prevent feedback paths that might cause the op-amp to oscillate. They are often referred to as the bypass capacitors. In order to simplify the diagrams below, the power connections and capacitors are not illustrated.
Symbols and Terms
The value of Rf and R can be calculated, once a gain is selected. Using a gain of 2:
Feedback continues to be achieved by the use of resitors Rf and R. The input signal is applied to the inverting input of the op-amp, through R. The non-inverting input is connected to ground. Since the two inputs must be balanced, Vi must also be at ground potential. Since Vi is at ground potential, no current flows into it, meaning:
Selecting a gain of -4 and R = 1 kΩ results in:
Based on Hands-On Radio from Apr-2003 QST