Common Mode Rejection Ratio MCQ [Free PDF] – Objective Question Answer for Common Mode Rejection Ratio Quiz

Although frequency response and bode plots indicate the effect of frequency variation on gain, the Bode plot is generally used for stability determination and network design.

Two types of plots can be obtained using the Bode plot. They are magnitude versus frequency and phase angle versus frequency plots.

When the operating frequency has increased the gain of the amplifier decrease. As it is linearly related to frequency, the phase shift is logarithmically related to frequency.

The change in function of frequency is attributed to the internally integrated capacitor as well as a stray capacitor. These capacitors are due to the physical characteristic of the semiconductor device.

Phase angle plots are not generally provided because phase shifts of later generation op-amp are less than 90^o even at cross-over frequency.

The gain of the op-amp remains essentially constant from 0 to the break frequency f_o and therefore rolls off at a constant rate of 20dB per decade. Thus, the open-loop bandwidth is the frequency band extending from 0Hz to f_o.

Whether the op-amp is inverting / non-inverting the gain will always roll off at a rate of 20dB/decade, using only resistive components regardless of the value of its closed-loop gain.

Op-amps using external components like resistor and capacitor to form the compensating network are sometimes called tailored frequency response op-amps because the user has to provide the compensation if it is needed to tailor the response.

The gain versus frequency curve of 709c decreases from the outermost compensated curve to the innermost.

For example, if C₁ =10pF, R₁ = 0Ω and C₂ = 3pF, the bandwidth ≅ 5kHz.

While if C₁ =5000pF, R₁ =1.5Ω and C₂= 200pF, the bandwidth will be 100Hz.

The uncompensated op-amps offer broader open-loop bandwidth whereas; the internally compensated op-amps have very small open-loop bandwidth.

The compensating networks are used to improve /modify the performance of an op-amp circuit over the desired frequency range by controlling its gain and phase shift.

Op-amp 709 is the first-generation op-amp. Generally, a first-generation op-amp is required for an external compensating network.

741c belongs to later generation op-amp and it has an internal compensating network. In an internally compensated op-amp, the compensating network is designed into the circuit to control the gain and phase shift of the op-amp and they are called compensating op-amp.