Question 7.5: Determine the bandwidth of each of the amplifiers in Figure ...
Determine the bandwidth of each of the amplifiers in Figure 7–9 . Both op-amps have an open-loop gain of 100 dB and a unity-gain bandwidth of 3 MHz.
(a) For the noninverting amplifier in Figure 7–9 (a), the closed-loop gain is
A_{c l(\mathrm{NI})}=\frac{R_f}{R_i}+1=\frac{220 ~\mathrm{k} \Omega}{3.3 ~\mathrm{k} \Omega}+1=67.7
Use Equation (7–6) and solve for f_{c(c l)}\left(\text { where } f_{c(c l)}=B W_{c l}\right).
A_{c l} f_{c(c l)}=\text { unity-gain bandwidth } (7-6)
f_{c(c l)}=B W_{c l}=\frac{\text { unity-gain } B W}{A_{c l}}
B W_{c l}=\frac{3 ~\mathrm{MHz}}{67.7}=44.3 ~\mathrm{kHz}
(b) For the inverting amplifier in Figure 7–9 (b), the closed-loop gain is
A_{c l(\mathrm{I})}=-\frac{R_f}{R_i}=-\frac{47 ~\mathrm{k} \Omega}{1.0 ~\mathrm{k} \Omega}=-47
Using the absolute value of A_{c l(\mathrm{I})}, the closed-loop bandwidth is
B W_{c l}=\frac{3 ~\mathrm{MHz}}{47}=63.8 ~\mathrm{kHz}
P R A C T I C E EXERCISE
Determine the bandwidth of each of the amplifiers in Figure 7–9 . Both op-amps have an A_{o l}^{\prime} of 90 dB and a unity-gain bandwidth of 2 MHz.