Introduction to Operational Amplifiers
Open Loop Configuration
| Voltage Followers | Comparators |
Op-amps in open-loop configuration have no feedback from the output back to the input terminal. This configuration is not normally used except for as comparators and/or oscillators due to its extremely high open-loop gain.
There are three variations of the open-loop configuration.
Differential Amplifier
In this configuration, shown in Figure 1, both inputs of the op-amp have signals present on the pins. The difference between these signals is amplified by the gain (A) of the amp Vout = A(Vi1-Vi2). These signals can be either AC, DC, or both.
Figure 1: Differential Open Loop Op-Amp Configuration
Inverting Amplifier
In this configuration, shown in Figure 2, a signal is provided to the input of the inverting pin. The non-inverting pin is connected to ground. The output becomes Vout = -AVi, where A is the gain of the amp and the output 180º out of phase with the input.
Figure 2: Inverting Open Loop Op-Amp Configuration
Non-Inverting Amplifier
In this configuration, shown in Figure 3, a signal is provided to the non-inverting pin. The inverting pin is connected to ground, and the gain (A) of the amp is very large. Vout = AVi (for very small signals). The output in this configuration is easily driven to saturation, so that the output is driven to the positive supply rail for a positive input and the negative supply rail for a negative input.
Figure 3: Non-Inverting Open Loop Op-Amp Configuration