# 11.10 Problems

## Review Questions

- Define gain-bandwidth product. What is its use?
- How do you determine 𝑓
_{2}and 𝑓_{1}for a multi-stage circuit? - What happens if two or more stages share the same break frequency?
- What is slew rate?
- How is power bandwidth determined?
- How do power bandwidth and small-signal bandwidth differ?
- What are the advantages and disadvantages of noncompensated op amps?
- What are decompensated op amps?
- What causes DC offset voltage?
- What causes DC drift voltage?
- What is CMRR?
- What is PSRR?
- What parameters describe an op amps noise performance?
- What is S/N?

## Problems

### Analysis Problems

- Determine 𝑓
_{2}for the circuit in Figure 5.3.3 if a 411 op amp is used. - Determine 𝑓
_{2}for the circuit of Figure 5.3.5 if a 318 op amp is used. Note: 𝑓𝑢𝑛𝑖𝑡𝑦 = 15 MHz for a 318. - What is the minimum acceptable 𝑓𝑢𝑛𝑖𝑡𝑦 for the op amp in Figure 5.3.3 if the desired 𝑓
_{2}is 250 kHz? - What is the minimum acceptable 𝑓𝑢𝑛𝑖𝑡𝑦 for the op amp in Figure 5.3.5 if the desired 𝑓
_{2}is 20 kHz? - Determine the power bandwidth for Problem 5.1. Assume 𝑉𝑝 = 10 V.
- 6. Determine the power bandwidth for Problem 5.3. Assume 𝑉𝑝 = 12 V.
- What is the minimum acceptable slew rate for the circuit of Figure 5.3.3 if the desired power bandwidth is 20 kHz with a 𝑉𝑝 of 10 V?
- What is the minimum acceptable slew rate for the circuit of Figure 5.3.5 if the desired power bandwidth is 40 kHz with a 𝑉𝑝 of 5 V?
- A circuit has the following specifications: ± 15 V power supply, voltage gain equals 26 dB, desired power bandwidth equals 80 kHz at clipping. Determine the minimum acceptable slew rate for the op amp.
- Determine the system 𝑓
_{2}in Figure 5.3.6 if all three devices are 318s. - Determine the system slew rate for Figure 5.3.7. The first device is a 741 and the second unit is a 411.
- Find the output offset voltage for Figure 5.3.3.
- If 𝑅𝑠=𝑅𝑓=100Ω in Figure 5.5.2, find the output offset voltage using a 318 op amp.
- Assume that the circuit of Figure 5.5.3 is nulled at 25 ∘ C and that an optimum value for 𝑅𝑜𝑓𝑓 is used. Determine the drift at 75 ∘ C.
- Assuming that the 120 Hz power supply ripple in Figure 5.10.1 is 50 mV, how large is its contribution to the output?

- Utilizing a 5534 op amp, what is the approximate input noise voltage for a source resistance of 1 k Ω and a bandwidth from 10 Hz to 20 kHz?
- Assuming that the op amp of Problem 5.16 is connected like Figure 5.10.1 , what is the approximate output noise voltage? What is the approximate input referred noise voltage?
- Assume that 𝑅𝑠=0Ω , 𝑅𝑖=500Ω , and 𝑅𝑓=10𝑘Ω in Figure 5.8.2. Find the input noise voltage if the op amp is a 411.
- For a nominal output voltage of 2 V RMS, determine the signal-to-noise ratio for Problem 5.18. Assume that the input to Figure 5.5.2 is a 5 V peak 50 kHz square wave. Draw the output waveform if a 741 is used.
- Repeat Problem 5.20 using a 10 V peak, 100 kHz sine wave.

### Design Problems

- Determine an optimum value for 𝑅𝑜𝑓𝑓 in Figure 5.3.3 and determine the resulting offset voltage.
- Determine the optimum value for 𝑅𝑜𝑓𝑓 in Figure 5.10.1 . Assuming that the circuit has been nulled at 25 ∘ C, find the drift at 60 ∘ C.
- Determine a new value for the 100 k Ω resistor in Figure 5.3.8 in order to minimize the output offset.
- Using the optimum resistor found in Problem 5.24, determine a new value for the input capacitor that will maintain the original 𝑓
_{1}. - Design a circuit with a gain of 32 dB and an 𝑓
_{2}of at least 100 kHz. You may use any of the following: 741, 411, 318. - Design a circuit with a gain of 50 and an 𝑓𝑚𝑎𝑥 of at least 50 kHz, given a maximum output swing of 10 V peak. You may use any of the following: 741, 411, 318.
- Design a circuit with a gain of 12 dB, a small-signal bandwidth of at least 100 kHz, and an 𝑓𝑚𝑎𝑥 of at least 100 kHz for a peak output swing of 12 V.
- Utilizing two or more stages, design a circuit with a gain of 150 and a small signal bandwidth of at least 600 kHz.

### Challenge Problems

- Determine the system 𝑓
_{2}in Figure 5.4.10. - Determine the input noise voltage for the circuit of Figure 5.10.1 . Assume 𝑅𝑜𝑓𝑓 = 950 Ω .
- Determine the output noise voltage and the input-referred noise voltage for Problem 5.31.
- Assuming that driving source resistance in Figure 5.3.7 is 0 Ω , how much offset voltage is produced at the output of the circuit? Assume that both devices are 411’s.
- Assume that you have one each of: 411, 741, 318. Determine the combination that will yield the highest system slew rate in Figure 5.10.2 .

- Repeat Problem 5.34 in order to produce the highest system 𝑓
_{2}. - Assuming that the driving source resistance is 0 Ω in Figure 5.3.7. Determine the output noise voltage if both devices are 411’s.
- Derive Equation 5.3.9 from the text.

### Computer Simulation Problems

- Use a simulator to create a Bode plot for Problem 5.10. If a macro model for the LM318 is not available, use the 741 instead.
- Create a time domain representation of the output voltage of Problem 5.20 using a simulator.
- Create a time domain representation of the output voltage of Problem 5.21 using a simulator. Repeat the simulation using an LM318 op amp in place of the 741. What do the results indicate?
- Simulate the circuit designed in Problem 5.26. Verify 𝑓
_{2}and 𝐴𝑣 through a Bode plot. - Generate a Bode plot using a simulator and verify 𝑓
_{2}and 𝐴𝑣 for the circuit designed in Problem 5.29. - Generate a Bode plot using a simulator and verify 𝑓
_{2}for the circuit designed in Problem 5.35.