Here we will learn simulation of BJT differential amplifier using LT-SPICE sofftware .We will calculate CMRR . It is an with two inputs Vin By keeping in mind this discussion lets have a look at this below given circuitry. Differential amplifiers are used to amplify the differential output provided by resistance (strain gauge,thrmistor etc) bridges. When input signal Vin1 is applied to the transistor Q1, it’s amplified and inverted voltage gets generated at the collector of the transistor Q1. At the same time it’s amplified and non-inverted voltage gets generated at the collector of the transistor Q2 as shown in the above diagram. Depending on the changes it makes to the input signal, amplifiers are broadly classified into Current, […] In today’s post, we will have a detailed look at the amplifier circuit using BJT. 5.2) Basic BJT Differential Pair Figure 11.2: Basic BJT differential-pair using npn transistors. APPLICATION NOTE One Technology Way • P.O. See Figure below. As above only one input signal is given even though the output is taken from both collectors. Since two transistors are identical, same equations can be used for both. The output voltage is around 8 volts, with a 5 mA input which would make the gain about 1600. These operational amplifiers can be used for performing filtering, signal conditioning, and mathematical operations. \$\endgroup\$ – Sredni Vashtar Sep 26 at 0:45. So friends I hope you have understands all parameters and terms used in the amplifier circuit. The internal resistance of the transistor will have denoted by the lowercase having subscript. Also cascode might be useful. Understanding BJT Transistors and How to Practically Use Them in Your Designs. EEEB273 – Electronics Analysis & Design II Lecturer: Dr Jamaludin Bin Omar 7-3 1 7.2) Small-Signal Analysis of BJT Active Load • Figure 11.30 shows a differential amplifier with a 3-transistor active load circuit. For instance, internal ac emitter resistance is denoted as r’e, Circuit resistances exterior to the transistor itself use the italic capital. Differential amplifier is a basic circuit which used in all linear integrated circuit ... (BJT), so that have two separated inputs and outputs pins with common emitter pin as shown in figure 6.1 These BJT`s must be matching and have same types to be able to connect it in parallel with collector resistors 1 & 2. CIRCUIT BJT_DIFFAMP1.CIR Download the SPICE file. Differential amplifier using BJT - AC & DC analysis - YouTube by Glen Brisebois Download PDF. The formula for the gain is RC * gm. I could find the collector current of \$ Q_2 \$.But i need to find the current through \$ R_C \$ connected to \$ Q_2\$,to find \$ v_{O2}\$, which in turn would help me in analysing \$ Q_3\$(ie finding collector and emitter current of \$ Q_3\$ ). Thus the overall performance of the circuit is improved. How to solve MAX485 heating and stops working problem ? Based on the methods of providing input and taking output, differential amplifiers can have four different configurations as below. 1. 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. Differential amplifiers can be made using one opamp or two opamps. I could analyse the current mirror portion and the differential amplifier portion, but facing problem thereafter. We might replace the collector load resistors with a current mirror, but the emitter current mirror is almost certain to be included. Introduction . The effective resistance measured at output terminal with respect to ground. In the former case it is called dual input otherwise it is single input. So, friends, it is a complete post about BJT as an amplifier. It may have either one output or a pair of outputs where the signal of interest is the voltage difference between the two outputs. When we think of a differential amplifier, we typically think of a circuit like the one shown to the left. Chapter 13 Small-Signal Modeling and Linear Amplification 2. To investigate the simple differential amplifier using NPN transistors. BJT has a low thermal stability. Those with mounting studs or heat sinks are usually power transistors. So if you use the same amount of power at the input for both a BJT and FET transistor, the BJT transistor will produce more gain. As the name indicates Differential Amplifier is a dc-coupled amplifier that amplifies the difference between two input signals. You can see the proof of this in the AC Analysis section. A differential amplifier is a type of electronic amplifier that amplifies the difference between two input voltages but suppresses any voltage common to the two inputs. 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