Chapter Questions
How do you recognize when positive feedback is present in the schematic of an op amp circuit?
In Fig. P4-2, $R_1=25 \mathrm{k} \Omega$ and $R_2=5 \mathrm{k} \Omega$. Assume for simplicity that $\pm V_{\text {sat }}= \pm 15 \mathrm{~V}$. Calculate (a) $V_{U T}$; (b) $V_{L T}$; (c) $V_H$.
For the values given in Problem 4-2, plot (a) $E_i$ vs. $t$; (b) $V_o$ vs. $t$; (c) $V_o$ vs. $E_i$. Let $E_i$ be a $100-\mathrm{Hz}$ triangular wave with peak values of $\pm 10 \mathrm{~V}$.
Label $V_{U T}, V_{L T}$, and $V_H$ on your sketches from Problem 4-3.
Given the waveshapes of $E_i$ vs. $t$ and $V_o$ vs. $t$ in Fig. P4-5, identify (a) the frequency of $E_i$; (b) the peak amplitude of $E_i$; (c) the value of $V_{U T}$; (d) the value of $V_{L T}$; (e) $V_H$.
Use Fig. 4-7 and Design Example 4-4 for guidance. Design a noninverting voltage-level detector with $V_{U T}=2.0 \mathrm{~V}$ and $V_{L T}=0.5 \mathrm{~V}$.
To see how negative threshold voltages are handled, redesign the voltage-level detector of Problem 4-6 for $V_{U T}=-0.5 \mathrm{~V}$ and $V_{L T}=-2.0 \mathrm{~V}$. (Note that $V_H=1.5 \mathrm{~V}$ in both problems.)
Refer to Fig. 4-8 and Design Example 4-5 for guidance. Design (a) a circuit whose output is at (+) $V_{\text {sat }}$ when its input is below $V_{L T}=0.5 \mathrm{~V}$; (b) a circuit whose output is at (-) $V_{\text {sat }}$ when its input is above $V_{U T}=2.0 \mathrm{~V}$.
Redesign the circuit of Fig. 4-9 for $V_{U T}=2.0 \mathrm{~V}$ and $V_{L T}=0.5 \mathrm{~V}$ (see Design Example 4-6).
For the circuit of Fig. P4-10 calculate (a) $V_{\text {curi }}$ (b) $V_H$; (c) $V_{U T}$; (d) $V_{L T}$. Assume that $\pm V_{\text {sat }}=$ $\pm 15 \mathrm{~V}$.
If $E_i$ is grounded in Fig. 4-14, calculate $V_o$.
Refer to the 311 circuit in Fig. 4-14. The strobe terminal is wired to $+15 \mathrm{~V}$. Find the value of $V_o$ when (a) $E_i=1 \mathrm{~V}$; (b) $E_i=-1 \mathrm{~V}$.
Repeat Problem 4-12 but with the strobe terminal wired to ground via a 10-k $\Omega$ resistor.
Design a window detector circuit whose output is high when the input voltage is between +2 and $+0.5 \mathrm{~V}$.
Which comparator has a faster response time, the 311 or the 301 ?