The concept of connecting devices in a differential manner has found a lot of use in circuit configurations that have a wide range of applications. The wide variety of circuit functions is contributed by a number of factors such as the signal input, the output port location and the amplitude of the signal. Some of the examples of circuit functions that employ a differential connection of devices include amplification, multiplication, logic, frequency shifting, phase detection, signal ended conversion and comparison. One of the commonly used devices that employ the principle of differential connection is the differential amplifier. In differential amplifiers, a liner part of the transfer characteristic is used in the first stage of signal conditioning. Signal conditioning follows a signal source sensor or output as a preliminary signal conditioning circuit. An example of this special type of amplifiers is the universal operational amplifiers that are multi-stage amplifiers associated with high gain.
This laboratory exercise uses the CRO in the X-Y mode to fully display the transfer characteristics for both differential and common mode signals. This laboratory exercise also highlights the change of small signal differential gain with circuit balance together with the relative magnitude of common mode and differential gain enabling common signal ejection. The exercise further highlights the common mode signal range in which common signal rejection occurs. The differential amplifier used in this experiment is a simple long tailed pair with current source tail and resistance loads.
This laboratory experiment had three major objectives that were supposed to be met at the end of the exercise. To begin with, the experiment was to display and measure the differential transfer characteristics of a bipolar long-tailed pair differential amplifier. The second objective of this laboratory experiment was to display and measure the common mode characteristics of a bipolar long-tailed pair differential amplifier. The third and final objective was to investigate the common mode range of a bipolar long- tailed pair differential amplifier.
In conclusion, there are a number of a number of things learnt in relation to the main objective of this experiment. From the experiment, we have been able to learn how to use the CRO in the X-Y mode to display the transfer characteristics for differential and common mode signals. From that we have been able to highlight the change of small signal differential gain with circuit unbalance together with the relative magnitudes of common mode and differential gain enabling common signal rejection. Through the experiment we have also been able to determine the limited common mode signal range in which rejection occurs. This experiment has also helped us to know how to measure and calculate the characteristics of amplifier for the differential transfer characteristics of a bipolar long-tailed pair, common mode transfer characteristics of a bipolar long tailed pair and the common mode range of a bipolar long tailed pair differential amplifier. This experiment has been a great success since it has enabled us to understand how devices with circuits of a differential connection behave in different scenarios and the findings can be useful in modifying the amplifier to function better of develops other devices. The transfer characteristics for differential and common mode signals are a major determinant factor in determining the efficiency and versatility of a differential amplifier.