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]