辅导案例-ELEC2133
1 THE UNIVERSITY OF NEW SOUTH WALES School of Electrical Engineering and Telecommunication Assignment I 2020 ELEC2133 Analogue Electronics This assignment contributes to 5% of the total assessment of this course The due date is on Friday June 19, 2020 mid-day. Assignments are to be submitted on Moodle before the due date and time. Any submission after the due date will attract a penalty of 5% per day. The assignment contains one problem and will be marked out of 100%. 2 QUESTION 1 [ 100 marks] The circuit in figure 1 is a modified version of the differential amplifier where a resistor RG is inserted. RG serves as a means of adjusting the gain of the amplifier. a) Assuming an ideal operational amplifier, obtain an expression for the gain (Vo/Vid) of the amplifier. [20 Marks] Figure 1 {Hint: The virtual short circuit at the op-amp input causes the current through the R1 resistors to be (vid/2R1)} b) Design the operational amplifier to provide gains of -60 and -200 when RG is disconnected and connected, respectively. The input resistance seen by the input source is to be 10k. [10 marks] c) In the non-ideal case, the op-amp has the following DC imperfections Input bias current: IB = 80nA at room temperature Input offset current: Iio = ±4nA at room temperature Input offset voltage: Vio = ±2mV at room temperature Calculate the worst-case output offset voltage at room temperature by first calculating the output offset voltage due to Vio and then the output offset voltage due to Iio. [25 Marks] 3 Vin R1 =1KΩ R2 =10KΩ Vo + - R3 =10KΩ Figure 2 d) In reference to figure 2, the op-amp configured as the inverting amplifier has large signal limitations and other characteristics as provided in table 1. Large signal limitations Output voltage saturation ±13V Output current limits ±20mA Slew rate 0.5V/µs Other characteristics Internal compensation capacitor 30pF Open loop voltage gain 100dB Open loop bandwidth 6Hz Table 1: The non-ideal op-amp characteristics i. Estimate the bandwidth of the amplifier assuming that the internal compensation capacitor creates the dominant pole in the frequency response of the op-amp? [15 marks] ii. With Vin = VAcos(ωt) and VA=1V, will there be a frequency at which the output (Vo) will be distorted? If so, what is that frequency? [15 marks] iii. With Vin = VAcos(2π1000t) where VA=1V and assuming that a resistive load is connected at the output between node Vo and ground, what is the constrain on the resistive load if the output is to be undistorted? [15 marks]