# Differential Amplifier - Large Input Signal

A differential amplifier is a type of electronic amplifier that amplifies the difference between two input voltages only. The differential amplifier two inputs are the inverting input and non-inverting input. Its output signal is 180° out of phase with inverting input signal and in phase with non-inverting input signal.

The different modes of operation of the differential amplifier are:

• Common mode input signal vCM. Both inputs are connected together to the input signal.
• Large differential input signal.
• Small differential input signal vi<2vT

The circuit below shows the differential amplifier with a large differential input signal. When an Operational Amplifier (OPAMP) is used in this configuration it is also called a comparator.

Notes:

• When both V1 and V2 are 2.5V, see the small signal input circuit DC analysis for calculating the voltages.
• When V2-2vT < V1 < V2+2vT, the small signal input circuit AC analysis applies.
• When V1>V2+2vT, Q1 is on and Q2 is off.
V_1 = V_{R1} + V_{BE}
Ignoring IB, thus IC = IE
\label{1} V_{R2} = {(V_1 - V_{BE})R2 \over R1}
• When V1<V2-2vT, Q1 is off and Q2 is on.
V_2 = V_{R1} + V_{BE}
\label{2} V_{R3} = {(V_2 - V_{BE})R3 \over R1}
• Move the knob to see the effects of V1 on the inverting and non-inverting outputs.

Thank you for learning from electronics-course.com

We do not have a paywall as our mission is to provide everyone from Albania to Zimbabwe, rich or poor, a quality foundational electronics education. With advertising revenues falling despite increasing numbers of learners, we need your help to maintain and improve the course, which takes time, money and hard work.

If everyone who benefits from this course gives as little as \$2 via Paypal, we can continue to achieve our mission. Thanks!