For a general-purpose practical op-amp, the open-loop voltage gain is about what?

For a general-purpose practical op-amp, the open-loop voltage gain is about what?

• A. 20
• B. 2,000
• C. 2,000,000
• D. 200,000

Answer: (D)

Open-loop voltage gain is the ratio of the output voltage to the input differential voltage with no feedback, Vout/(Vin+ − Vin−). In a general-purpose op-amp this gain is extremely large because the internal differential pair drives the output through high-gain stages, so even a tiny input difference pushes the output a lot. The typical open-loop gain for common general-purpose op-amps is on the order of 100,000 to 200,000, often quoted as about 2×10^5. In decibels, that’s roughly 100 dB. This immense gain is what lets negative feedback set a precise, predictable closed-loop gain by forcing the input difference to be very small. While the exact value varies with device and temperature, 200,000 is a representative, commonly cited figure.

Open-loop voltage gain is the ratio of the output voltage to the input differential voltage with no feedback, Vout/(Vin+ − Vin−). In a general-purpose op-amp this gain is extremely large because the internal differential pair drives the output through high-gain stages, so even a tiny input difference pushes the output a lot. The typical open-loop gain for common general-purpose op-amps is on the order of 100,000 to 200,000, often quoted as about 2×10^5. In decibels, that’s roughly 100 dB. This immense gain is what lets negative feedback set a precise, predictable closed-loop gain by forcing the input difference to be very small. While the exact value varies with device and temperature, 200,000 is a representative, commonly cited figure.