Question

Review| Constants Part A DESIGN EXAMPLE: Your boss asks you to design an interface circuit that maps the -250mV to 250mV output v of a sensor (modeled as an ideal voltage source), to the OV to 8V input vo of an analog-to-digital (A/D) converter, as depicted below Confirm your bosses' observation by deriving an expression for v as a function of vi and 2 Express your answer in terms of v1, v2, Ri, R2, Rf. -4(금-2) nterface+A/D sensorcircuit converter Your boss observes that since the required mapping is v, = mul + b, with OV= m( 250mV) + b and 8V Correct n(250mV) +b, you ought to be able complete your design using an an op amp circuit of the following form, where ½-9 V and Rf- 72 kS2 Part B What R1 and R2 values do you choose to complete your design given that V2 9 Vand R -72 k2? Enter your answer as R1,R2 R2 0 R1,R2 Provide Feedback

Answer 1

Part A: - consifer ideal op - amp V^4 = V^- = OV by KCl at V^- node V^- + V_1/R-1 + V^- + V_2/R_2 + V^-V_0/R_f = 0 V_1/R-1 + V_2 /R_2 - V_0 /R_2 = 0 V_0 = R_f [V-1 /R_1 + V_2 /R_2] rightarrow 1 Part B: - from the given information if V-1 = -250 mV V_0 = 0 Volts V_1 = 250 mV V = 0 = 8 volts given V_2 = 9V R_f = 72 k ohm from equation 1 if V_1 = -250 mV V-2 = 9V V-0 = 0 Volts substitution V_0 = R_f [V_1/R_1 + V_2/R_2] 0 = R_f [- 250 times 10^-3/R_1 + 9/R_2] 0 = -0.25/R_1 + 9/R_2 9/R_2 = 0.25/R_1 R-2/R_1 = 9/0.25 R-2 = 36 R_1