Define operational amplifier (op-amp) characteristics (input impedance, gain).
1 Answer
An operational amplifier, commonly referred to as an op-amp, is a highly versatile and widely used electronic component in analog circuits. It is a differential input, high-gain voltage amplifier with a wide range of applications, such as signal conditioning, filtering, amplification, and more. Op-amps have two input terminals (inverting and non-inverting) and one output terminal.
Input Impedance:
Input impedance refers to the electrical impedance seen at the input terminals of an op-amp. In an ideal op-amp, the input impedance is considered to be infinite, meaning that no current flows into the input terminals. Consequently, an ideal op-amp draws no current from the input signal source, ensuring minimal loading and accurate signal representation.
In practical op-amps, the input impedance is typically very high, often in the range of megaohms to teraohms, which allows them to have minimal impact on the connected circuit and maintain a high input signal voltage.
Gain:
The gain of an op-amp, often denoted as "A" or "Av," represents the amplification factor of the output voltage concerning the voltage difference between its input terminals. Ideally, the gain of an op-amp is infinite, which means it can amplify signals by an arbitrarily large factor.
In reality, the open-loop gain of most op-amps is very high, often in the range of tens of thousands to hundreds of thousands (dB), but not infinite. Manufacturers typically specify the open-loop gain in the datasheet.
To create practical and stable circuits, op-amps are often used in feedback configurations, where a portion of the output is fed back to the input to control the overall gain. In a closed-loop configuration, the actual gain is determined by the feedback network (resistors, capacitors, etc.) around the op-amp. This way, precise and controllable gain values can be achieved.
Keep in mind that op-amps have other essential characteristics, such as output impedance, bandwidth, slew rate, and common-mode rejection ratio (CMRR), which also play crucial roles in determining their performance and behavior in specific applications.
Input Impedance:
Input impedance refers to the electrical impedance seen at the input terminals of an op-amp. In an ideal op-amp, the input impedance is considered to be infinite, meaning that no current flows into the input terminals. Consequently, an ideal op-amp draws no current from the input signal source, ensuring minimal loading and accurate signal representation.
In practical op-amps, the input impedance is typically very high, often in the range of megaohms to teraohms, which allows them to have minimal impact on the connected circuit and maintain a high input signal voltage.
Gain:
The gain of an op-amp, often denoted as "A" or "Av," represents the amplification factor of the output voltage concerning the voltage difference between its input terminals. Ideally, the gain of an op-amp is infinite, which means it can amplify signals by an arbitrarily large factor.
In reality, the open-loop gain of most op-amps is very high, often in the range of tens of thousands to hundreds of thousands (dB), but not infinite. Manufacturers typically specify the open-loop gain in the datasheet.
To create practical and stable circuits, op-amps are often used in feedback configurations, where a portion of the output is fed back to the input to control the overall gain. In a closed-loop configuration, the actual gain is determined by the feedback network (resistors, capacitors, etc.) around the op-amp. This way, precise and controllable gain values can be achieved.
Keep in mind that op-amps have other essential characteristics, such as output impedance, bandwidth, slew rate, and common-mode rejection ratio (CMRR), which also play crucial roles in determining their performance and behavior in specific applications.