A certain op amp has an open-loop de gain of A001=200,000...

A certain op amp has an open-loop de gain of $A_{001}=200,000$ and an open-loop $3-d B$ bandwidth of $f_{B O L}=5 \mathrm{Hz}$ Sketch the Bode plot of the open-loop gain magnitude to scale. If this op amp is used in a noninverting amplifier having a closed-loop de gain of 100 , sketch the Bode plot of the closed-loop gain magnitude to scale, Repeat for a closed-loop de gain of 10

Key Concepts

Op-Amp Open-Loop Gain and Dominant Pole

The op-amp's open-loop gain is the intrinsic amplification provided by the device without any feedback applied. This gain typically decreases with frequency due to the presence of a dominant pole – a single frequency point after which the gain begins to roll off at a rate of about -20 dB/decade. Understanding this behavior is essential because it sets the baseline performance for any closed-loop configuration.

3-dB Bandwidth

The 3-dB bandwidth is the frequency at which the gain falls to 1/?2 of its maximum value, corresponding to a drop of approximately 3 decibels. It defines the frequency range over which the op-amp can amplify signals effectively. In op-amps with a dominant pole, this bandwidth is a key parameter that, in combination with the open-loop gain, influences the overall gain-bandwidth product.

Bode Plot

A Bode plot is a graphical representation of a system's frequency response, showing both magnitude and phase as functions of frequency on a logarithmic scale. For op-amps, the magnitude plot typically demonstrates a flat region at low frequencies followed by a slope, commonly -20 dB per decade after the dominant pole, which visually represents the roll-off of the open-loop gain.

Gain-Bandwidth Product

The gain-bandwidth product (GBW) is a constant for a given op-amp, representing the product of the open-loop gain and its 3-dB bandwidth. It is an important figure of merit because it provides insight into the achievable closed-loop bandwidth when the amplifier is configured for a specific closed-loop gain. This concept helps in understanding the trade-off between gain and bandwidth in op-amp circuits.

Non-Inverting Amplifier Configuration

The non-inverting amplifier is a configuration where the input signal is applied to the non-inverting input, and a portion of the output is fed back to the inverting input. The closed-loop gain is set by the resistive network in the feedback path. This configuration is widely used due to its high input impedance and ease of setting the gain, but its performance is ultimately limited by the op-amp's open-loop frequency response.

Closed-Loop Gain and Bandwidth

The closed-loop gain of an op-amp circuit, when feedback is applied, differs from the open-loop gain. Typically, as the closed-loop gain is specified, the effective bandwidth of the amplifier increases over that of the open-loop system, since the product of the closed-loop gain and the closed-loop bandwidth approximates the op-amp’s gain-bandwidth product. This means that lower closed-loop gains lead to wider bandwidths, a critical concept in amplifier design.

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