Exercise #3:
1. Identify the op-amp configuration in Figure 2.
2. Derive the expression for the closed-loop voltage gain Ay = vo/vr for the circuit shown in Figure 2. Assume an ideal op-amp.
3. Let R4 = 50k and R3 = 25k. Determine R1 and R2 such that A = 6, assuming the maximum resistor value is limited to 200k.
Figure 2:
Exercice #4:
Vg = -5V
RF = www
R = 20k
R = 40k WMM
R = 80k WMM
R = 160k
Figure 3:
A summing amplifier can be used as a digital-to-analog converter (DAC). An example of a 4-bit DAC is shown in Figure 3. When switch S3 is connected to the 5V supply, the most significant bit is a3 = 1; when S3 is connected to ground, the most significant bit is a = 0. The same condition applies to the other switches S2, S1, and So, corresponding to bits a2, a1, and a0, where a0 is the least significant bit.
a) Show that the output voltage is given by vo = 10 * (a3 * 2^3 + a2 * 2^2 + a1 * 2^1 + a0 * 2^0) / R, where R is in k.
b) Find the value of R such that vo = 2.5V when the digital input is a = 1000.
c) Using the results of part b, find vo for:
i) a = 0001
ii) a = 1111
