Also, it is usually desirable to have R1 = R2 and Rf = R3, which will reduce the input offset voltages. If the signal source resistances are smaller than the input resistances the input resistance difference will not cause a serious issue. The output equation of the difference amplifier V0, can be obtained by making the ratio R3/R2 the same as Rf/R1, instead of making R1 = R2 and Rf = R3. This difference in the input resistances results in one of the input signals to be more amplified than the other. The problem arises when selecting the difference amplifier resistors as R1 = R2 and Rf = R3 is that the input resistances of the inverting amplifier and non-inverting amplifier are not equal. Where AC is the common mode gain of the amplifier. Where AD is Differential amplifier gain and VIN+ and -VIN- are the input voltages.īut in practical conditions the differential gain is denoted as follows: The output of an ideal differential amplifier is denoted as follows: Therefore, we can conclude that the gain (AD) of the differential amplifier circuit which is made using Op-Amp is given by -(Rf/R1). V0 = V02 + V01 = -V1 * (Rf + R1) / R1 + (Rf / R1) * V2ĭifferential gain (AD) is the gain obtained at the output signal with respect to the difference in the input signal (V1 – V2) is applied. When both the input signals V1 and V2 are present, the output voltage is, If the input resistances R1 = R2 and Rf = R3, then V02 = * V2 Input voltage V2 is potentially divided across the resistors R2 and R3 to give VR3, and then VR3 is amplified by (Rf+R1)/R1. Differential Amplifier built using Op-Amp When the input terminal is connected to the ground the circuits operate as a non-inverting amplifier. When the non-inverting terminal is connected to the ground, the circuit operates as an inverting amplifier then the input voltage signal V1 is amplified by the gain of -(Rf/R1). The differential amplifier using op-amp is a combination of both inverting and non-inverting amplifiers. There are mainly four configurations for the differential amplifiers. The differential amplification procedure can be implied by observing the outputs of the collectors of the two transistors Q1 and Q2. Therefore, this evidence supports the conclusion of the fluctuations in the input sinusoidal signal of the transistor Q2 is reflected as the same through the collector terminal of transistor and appear with a phase difference of 180 degrees through the collector of the transistor Q1. The above process leads to less amount of collector current(IC2) in transistor Q2 which reduces the voltage drop through the collector terminal resistor (RC2) of transistor Q2 and increases in the voltage output. Therefore, this shows that the emitter terminals of two transistors Q1 and Q2 are moving to the positive that in turn indicates a more negative base terminal at the transistor Q2. Due to the same effect, even IE1 increases which increases the common emitter current (IE1) resulting in an increase of voltage drop across emitter resistor (RE). Differential Amplifier built using BJTĬonsidering the differential amplifier built using BJTs, if the input voltage V1 at transistor Q1 is sinusoidal, then as V1 goes on increasing, the transistor Q1 starts conduction which results in a large collector current in Q1 increasing the voltage drop across Rc1, causing a decrease in output voltage V01. In the differential amplifier made using BJTs, input signals (V1 and V2) are applied to the base terminal of the transistors and the outputs are collected from the collector terminal of the transistors. Among these, the commonly used differential amplifier is the amplifier made using Op-Amps because they are suitably configured to result in a much practical differential amplifier. There are mainly two types of differential amplimers ones made using Op-Amps and ones made using transistors (BJTs or FETs). It is an electronic amplifier that has two inputs and amplifies the voltage difference between those inputs. The differential amplifier is one of the important circuits in analog systems and circuit designs. Differential Amplifier – Tasks for students.Wheatstone bridge differential amplifier.Characteristics of a Differential Amplifier.
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