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Differential amplifier bjt - In this video, for a Differential Amplifier (using BJT), the

Two Active Loads for Differential Amplifiers: 1. Curr

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. It is an analog circuit with two inputs and + and one output , in which the output is ideally proportional to the difference between the two voltages:A comparison between single-stage amplifiers and differential amplifiers. A discussion on DC biasing issues. A discussion on trade-offs between MOS and BJT differential pairs. 2.0 Prelab. H & S: Chapters 11.1 - 11.2. M3501 F = 104.3 V An = 43.3V . N3515 V TOn = 0.88 V n C ox =79.47 A/V 2 n = 0.06 V-1. 2.1 1. BJT Differential Pair Consider the differential amplifier shown below with RB = 50K2 and Rc = 10KQ and assume the BJT parameters for Q1, Q2, Q3 and Q4 are VA = 70V and B=100. The amplifier is biased with VCC = +10V and VEE = -10V. You may assume VBE = 0.7 when forward biased for all BJTs. What is the common mode output impedance?7. Design a BJT differential amplifier that provides two single-ended outputs (at the collectors). The amplifier is to have a differential gain (to each of the two outputs) of at least 100 V/V, a differential input resistance ≥10k Ω and a common mode gain (to each of the two outputs) no greater than 0.1 V/V. Use a 2mA current source for biasing. If you’re experiencing issues with your vehicle’s differential, you may be searching for “differential repair near me” to find a qualified mechanic. However, before you entrust your vehicle to just any mechanic, it’s important to ask the ri...6. Art&Ornement: Magasin de l'art de la table et des meubles 11, rue El kaïssi -ex Riquet,, 20013 Casablanca, Morocco Coordinate: 33.6033199, -7.4929 Phone ...3.1 Differential Amplifier Consider the following circuit: Figure 1 • Assuming that both bases are grounded, compute the expected values of IC1, IC2 and IE. Also calculate values for the differential and common mode gains of this amplifier. • Using transistors 1 and 2 in the array, construct the circuit in Figure 1. Be sure to connect pinDifferential Amplifier is a type of amplifier which gives amplification of difference of input. In this simulation one signal IN1 and another signal IN2 give...The main symptom of a bad differential is noise. The differential may make noises, such as whining, howling, clunking and bearing noises. Vibration and oil leaking from the rear differential seal may also be signs of a failing differential.Difference amplifiers should have no common-mode gain Note that each of these gains are open-circuit voltage gains. * An ideal differential amplifier has zero common-mode gain (i.e., A cm =0)! * In other words, the output of an ideal differential amplifier is independent of the common-mode (i.e., average) of the two input signals.Difference amplifiers should have no common-mode gain Note that each of these gains are open-circuit voltage gains. * An ideal differential amplifier has zero common-mode gain (i.e., A cm =0)! * In other words, the output of an ideal differential amplifier is independent of the common-mode (i.e., average) of the two input signals.Tail Current로 인해 위 차동 증폭기는 Noise에 강한 증폭기가 됩니다. 여기에 쓰인 Current Source 및 MOSFET이 모두 ideal & Symmetric 하다면 이상적인 Differential Amplifier 즉 Noise가 제거된 증폭기가 되는 것입니다. 다음부터는 Differential Amplifier가 어떤식으로 동작하는지 한 단계 ...The differential amplifier designed with Bipolar Junction Transistor (BJT) is possible by using two transistors connected in such a way that the emitters of it are connected to the ground. The inputs are applied to the base of the transistors and the output is collected at the collector.Simulations to verify the DC transfer curve and differential gain for a BJT differential amplifier with different configurations (tail resistor vs. current m...Fully-Differential Amplifiers 5. 3 Voltage Definitions. To understand the behavior of a fully-differential amplifier, it is important to understand the voltage definitions used to describe the amplifier. Figure 3 shows a block diagram used to represent a fully-differential amplifier and its input and output voltage definitions. A comparison between single-stage amplifiers and differential amplifiers. A discussion on DC biasing issues. A discussion on trade-offs between MOS and BJT differential pairs. 2.0 Prelab. H & S: Chapters 11.1 - 11.2. M3501 F = 104.3 V An = 43.3V . N3515 V TOn = 0.88 V n C ox =79.47 A/V 2 n = 0.06 V-1. 2.1 1. BJT Differential PairMar 19, 2023 · The BJT differential amplifier is a two-input circuit that amplifies the difference between two input signals, V1 and V2 applied to the base terminals of two BJTs (Bipolar Junction Transistors), which are configured in a differential pair configuration (see figure below). The basic differential pair configuration consists of two BJTs wherein ... Q 1 acts as a common-base amplifier, and a non-inverted, amplified signal appears at output 1. Figure 20(a): Single-ended differential input operation; the signal voltage is applied to input 1 Figure 20(b): Single-ended differential input operation; the signal voltage is applied to input 2. Double-Ended Differential InputsFully-Differential Amplifiers 5. 3 Voltage Definitions. To understand the behavior of a fully-differential amplifier, it is important to understand the voltage definitions used to describe the amplifier. Figure 3 shows a block diagram used to represent a fully-differential amplifier and its input and output voltage definitions. In today’s tutorial, we will have a look at BJT as an Amplifier. A transistor is an electronic component that has three terminals. Terminals are base-emitter, collector and base. It used in different electronic projects and circuits for switching and amplification process. Amplification is process through which weak input signal is amplified ...I am working my way through the Art of Electronics and I have today studied the differential amplifier. I aam having issues with Exercise 2.18: Design a differential amplifier to run from ±5V supply rails, with Gdiff = 25 and Rout = 10k.As usual, put the collector’s quiescent point at half of VCC.Penguat Diferensial Menggunakan BJT. Differential Amplifier atau Penguat Diferensial adalah penguat atau amplifier yang menguatkan selisih dua tegangan input dimana penguatan ini mempunyai ciri-ciri : Memiliki dua terminal input dan satu terminal output, sehingga membutuhkan dua Bipolar Junction Transistor. Memiliki tegangan bias negatif pada ... \$\begingroup\$ "Therefore Re must always be smaller than RL for small signals and <= 1/2 RL for full negative swing when AC coupled". Surely that's not necessary. Even if RL is very low it will be linear for a small enough input swing. For large signals there is no fixed requirement for the ratio of Re to RL - you can never get full negative swing no matter …BJT Differential Amplifier. Look under the hood of most op amps, comparators or audio amplifiers, and you'll discover this powerful front-end circuit - the differential amplifier. A simple circuit able to amplify small signals applied between its two inputs, yet reject noise signals common to both inputs. This circuit has a unique topology: two ... A complete blood count, or CBC, with differential blood test reveals information about the number of white blood cells, platelets and red blood cells, including hemoglobin and hematocrit.3.3. Differential Pair Amplifier with Current Source Biasing Replace Re in the differential amplifier built in Section 3.1 with the Simple current source constructed in Section 3.2. Your circuit should now look like Figure 4. • Calculate and measure the bias point and the mid-band differential (note that the output of the The BJT differential amplifier with constant current bias is an amplifier that uses two BJTs to amplify the difference between two input signals. The constant current bias provides a stable bias current to the BJTs, which helps improve the linearity and stability of the amplifier. The BJT differential amplifier with constant current bias is ...Difference amplifiers should have no common-mode gain Note that each of these gains are open-circuit voltage gains. * An ideal differential amplifier has zero common-mode gain (i.e., A cm =0)! * In other words, the output of an ideal differential amplifier is independent of the common-mode (i.e., average) of the two input signals. Differential BJT Amplifier. This project shows the preliminary design of a differential amplifier, and demonstrates a Linearized Harmonic Balance (similar to a spice AC analysis) simulator and operating point annotations. Overview. This project uses a test bench approach. The schematic "diff_amp" contains the basic design.A BJT differential amplifier is a type of amplifier that amplifies the difference between two input signals. The following shows a differential amplifier block diagram. Internally, it is implemented using a pair of identical transistors(Q1,Q2), configured in a differential pair, with identical biasing resistors(RC,RB,RE) as shown in the figure ...It is just another option to use the other collector node as well and defining the amplifier output as Vo2-Vo1. 2.) Differential mode: Assuming linear operation (and this is always assumed) the current increase of the left BJT is equal to the corresponding current reduction of the right BJT.BJT Buffer Amplifier Designer (Base Bias Network) BJT Buffer Amplifier Designer (Voltage Feedback Bias) BJT Buffer Amplifier Designer (Emitter Feedback Bias) Broadband VHF Power Amplifier, 3 ... 540 MHz, 1.5 W; Broadband UHF Preamplifier, > 3 GHz, 20 dB, NF 2.4 dB; Broadband UHF Amplifier "BONLab-81", 10 dB, +19 dBm; Broadband Measurement ...University of Minnesota DuluthThe Input Offset Voltage of BJT Differential Amplifier given collector resistance formula is defined as the voltage that must be applied between the two input terminals of the op-amp to obtain zero volts at the output.The BJT and MOS versions function as an inverting voltage amplifier and are shown in figure 9.2. The base or gate terminal of the transistor serves as the input, the collector or drain is the output, and the emitter or source is common to both input and output (it may be tied to the ground reference or the power supply rail), which gives rise ...It is just another option to use the other collector node as well and defining the amplifier output as Vo2-Vo1. 2.) Differential mode: Assuming linear operation (and this is always assumed) the current increase of the left BJT is equal to the corresponding current reduction of the right BJT.The dual input balanced output differential amplifier configu­ration is shown in Fig. 20.2. In the given circuit two input signals v in1 and v in2 are applied to the bases B 1 and B 2 of transistors Q 1 and Q 2. The differential input under amplification is the differ­ence of the two input signals v in1 and v in2 and denoted by v d.1. Is there any reason why the gain of a single ended input BJT differential amplifier, with one Rc, is a good approximation of the value of Adm for a common mode input. The simulation shows the frequency response for a single ended input and the circuit below shows th common mode input circuit. operational-amplifier. differential. 410. The first-stage two-transistor differential amplifier can be used as a wide-band high-impedance input follower, followed by a gain-of-two op amp in the second stage. In any case, the original designer of the circuit may need to be consulted to understand its true function and purpose. Nov 8, 2022. #17.Instructions. Step 1: Build the differential amplifier shown in the circuit schematic of Figure 1 and the breadboard implementation of Figure 2. Figure 2. Breadboard implementation of a BJT differential amplifier. Step 2: Using the left potentiometer in Figure 1, set the input voltage to the base of transistor Q 1 to 2.5 V. The BJT differential amplifier with constant current bias is an amplifier that uses two BJTs to amplify the difference between two input signals. The constant current bias provides a stable bias current to the BJTs, which helps improve the linearity and stability of the amplifier. The BJT differential amplifier with constant current bias is ...Jun 9, 2016 · Here is a plot with V IN1 and the differential output voltage: Here we have an output amplitude of 10 mV and an input amplitude of 1 mV; hence, our simulated differential gain is 10. The formula for theoretical differential gain is. Adiff = gm ×RD A d i f f = g m × R D. where g m can be calculated as follows: I am working my way through the Art of Electronics and I have today studied the differential amplifier. I aam having issues with Exercise 2.18: Design a differential amplifier to run from ±5V supply rails, with Gdiff = 25 and Rout = 10k.As usual, put the collector’s quiescent point at half of VCC.In today’s tutorial, we will have a look at BJT as an Amplifier. A transistor is an electronic component that has three terminals. Terminals are base-emitter, collector and base. It used in different electronic projects and circuits for switching and amplification process. Amplification is process through which weak input signal is amplified ...May 31, 2022 · A differential amplifier is a basic building block for analog integrated circuit design; the operational amplifier integrated circuit has wide applications in signal processing. In this paper, a bipolar junction transistor BJT differential amplifier circuit is analyzed and designed to determine the output resistance and the differential mode ... LM741 op-amp 1 2N3904 NPN BJT 4 2N3906 PNP BJT 2 1 kΩ resistor 2 10 kΩ resistor 2 0.1 µF capacitor 1 Table 1: Components used in this lab Component IS (A) VA (V) 2N3904 NPN BJT 6.734×10−15 74.03 2N3906 PNP BJT 1.41×10−15 18.7 Table 2: Transistor properties 3 Procedure 3.1 Generating a differential signalObjective: To investigate the simple differential amplifier using NPN transistors. First a few notes on hardware limitation issues. The waveform generator in the ADALM2000 system has a high output bandwidth and with that high bandwidth comes wide band noise. The input signal level needed for the measurements in this lab activity is rather small ...Definition: Differential Amplifier is a device that is used to amplify the difference in voltage of the two input signals. Differential Amplifier is an important building block in integrated circuits of analog system. It typically forms input stages of operational amplifiers.In simple words, we can say It is a device that amplifies the difference of 2 input signals.BJT Differential Amplifier. Look under the hood of most op amps, comparators or audio amplifiers, and you'll discover this powerful front-end circuit - the differential amplifier. A simple circuit able to amplify small signals applied between its two inputs, yet reject noise signals common to both inputs. This circuit has a unique topology: two ...reach me now Are you seeking the best option to differentiate and amplify two input signals in an integrated circuit? If your answer is yes, then you need a BJT differential amplifier. No doubt, other devices—like an Op-Amp, can work. But this particular amplifier stands out. It uses identical transistors, supply rails, and a collector resistor.Tail Current로 인해 위 차동 증폭기는 Noise에 강한 증폭기가 됩니다. 여기에 쓰인 Current Source 및 MOSFET이 모두 ideal & Symmetric 하다면 이상적인 Differential Amplifier 즉 Noise가 제거된 증폭기가 되는 것입니다. 다음부터는 Differential Amplifier가 어떤식으로 동작하는지 한 단계 ...Differential BJT amplifier Introduction The differential amplifier has two input signal sources. The ideal differential amplifier produces an output voltage that is the difference between the two input voltages. Vout = Avd(Vin1-Vin2) The differential amplifier has two single ended output voltages.Oct 2, 2017 · A differential amplifier amplifies the difference between two inputs. The purpose of the 'tail' current is to split that difference between the two sides of the amp. To do this the input voltage must be referenced to ground, so that any increase in current on side causes a corresponding decrease on the other, and vice versa. The d.c. analysis means to obtain the operating point values i.e. I Cq and V CEQ for the transistors used. The supply voltages are d.c. while the input signals are a.c., so d.c equivalent circuit can be obtained simply by reducing the input a.c. signals to zero. The d.c. equivalent circuit thus obtained is shown in the Fig.. BJT Differential Amplifier. Look under the hood of most op amps, comparators or audio amplifiers, and you'll discover this powerful front-end circuit - the differential amplifier. A simple circuit able to amplify small signals applied between its two inputs, yet reject noise signals common to both inputs. This circuit has a unique topology: two ...Differential Amplifiers (I) DIFFERENTIAL AMPLIFIERS Outline 1. Introduction 2. Incremental analysis of differential amplifier 3. Common -source differential amplifier Reading Assignment: Howe and Sodini , Chapter 11, Sections 11 -1-11.3, 11.6. ... – Analog circuits (BJT and CMOS): fJun 9, 2016 · Here is a plot with V IN1 and the differential output voltage: Here we have an output amplitude of 10 mV and an input amplitude of 1 mV; hence, our simulated differential gain is 10. The formula for theoretical differential gain is. Adiff = gm ×RD A d i f f = g m × R D. where g m can be calculated as follows: This exercise examines differential amplifier implemented with BJTs. Equipment and components: 4 BJT transistors (2N3904); 1 Multi-turn potentiometer (1 kW); and resistors (values determined in lab); 15 V and -15 V power supply; function generator. Note: Analyze the circuit first, which includes hand calculations or computer simulation. Instructions. Step 1: Build the differential amplifier shown in the circuit schematic of Figure 1 and the breadboard implementation of Figure 2. Figure 2. Breadboard implementation of a BJT differential amplifier. Step 2: Using the left potentiometer in Figure 1, set the input voltage to the base of transistor Q 1 to 2.5 V.When a current source is used in the tail of the differential amplifier, R2 should be sized so that, at quiescence, the differential amplifier has balanced currents flowing in its two sides. So, if the tail current source is configured to source, say, 2mA then R2 should be sized so that 1mA flows through it. R2 = 0.65/(Isource/2)7.3 The BJT Differential Pair. Reading Assignment:pp. 704-720. In addition to common- emitter, common- collector (i.e., the emitter follower), and common-base amplifiers, a fourth important and “classic” BJTamplifier stage is the differential pair. HO: Large Signal Operation of the BJT Differential Pair.Unlike normal amplifiers, which amplify a single input signal (often called single-ended amplifiers), differential amplifiers amplify the voltage difference between two input signals. Using the simplified triangle amplifier symbol, a differential amplifier looks like this: The two input leads can be seen on the left-hand side of the triangular ... Oct 2, 2017 · A differential amplifier amplifies the difference between two inputs. The purpose of the 'tail' current is to split that difference between the two sides of the amp. To do this the input voltage must be referenced to ground, so that any increase in current on side causes a corresponding decrease on the other, and vice versa. 27 de abr. de 2022 ... Hi everyone, I am trying to figure out what I need to change in the below circuit in order to change Q1 and Q2 (the BJTs in the differential ...rπ (Input Resistance of BJT at low freq), (ohms). re, (ohms). RIN(Input Resistance of Amp), (K ohms). A (Amplifier Voltage Gain). fP1, (MHz). fP2, (MHz) ...Calculation of the common-mode gain for a balanced and a single-output differential amplifier.BJT Buffer Amplifier Designer (Base Bias Network) BJT Buffer Amplifier Designer (Voltage Feedback Bias) BJT Buffer Amplifier Designer (Emitter Feedback Bias) Broadband VHF Power Amplifier, 3 ... 540 MHz, 1.5 W; Broadband UHF Preamplifier, > 3 GHz, 20 dB, NF 2.4 dB; Broadband UHF Amplifier "BONLab-81", 10 dB, +19 dBm; Broadband Measurement ...A low gain differential amplifier is linear enough all by itself so that the outputs look "just like" the inputs, with no discernible distortion. If the input is a sine wave, the output should be a sine wave as well. R4 and R5 should be identical. The whole thing must be symmetric, otherwise it won't work well.410. The first-stage two-transistor differential amplifier can be used as a wide-band high-impedance input follower, followed by a gain-of-two op amp in the second stage. In any case, the original designer of the circuit may need to be consulted to understand its true function and purpose. Nov 8, 2022. #17.Jet 7. Unclaimed. Review. Save. Share. 11 reviews #818 of 853 Restaurants in Casablanca International. 33 Rue Mohamed El Quorri, Casablanca 20000 Morocco +212 5222-97297 Website. Closes in 56 min: See all hours.It is just another option to use the other collector node as well and defining the amplifier output as Vo2-Vo1. 2.) Differential mode: Assuming linear operation (and this is always assumed) the current increase of the left BJT is equal to the corresponding current reduction of the right BJT.Before you pursue a project that you believe is unique, entrepreneur Johnny Earle suggests writing down a list of ten ways in which what you're doing is different from your competition. Before you pursue a project that you believe is unique...Differential Amplifier built using BJT. Considering 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 …\$\begingroup\$ There are multiple reasons for non-ideality resulting in common-mode gain (more usually referred to as its reciprocal - Common mode rejection ratio - CMRR). ). For example if the current source in the emitter was not perfect and the current changed with the voltage across it the output would depend upon the level of the input vol Its use of super beta BJT devices can resolve the problems found in many audio applications. 2 Super-Beta BJT The differentiating feature of OPA1637 from the prior generation is the bipolar junction transistor (BJT) of the long-tail pair in the input circuit. This technology is called super-beta BJT. TI’s super-beta BJT is just a singleWhy differential Amplifier? Single Ended Signal can be easily contaminated A Differential Signal can be cleaned up 2/22/2011 Insoo Kim Power Supply noise can be reduced. Differential Amplifier Analysis Classic Diff Amp 2/22/2011 Insoo Kim (cont’d) Differential Amplifier Analysis 2/22/2011 Insoo Kim.With an external bias voltage for the pair of p-type transistors, a fully differential amplifier can be achieved; the BJT and MOSFET versions are shown in figure 5.11. However, an auxiliary circuit is needed to generate the DC bias voltages V B0 and V B1 so that the bias current at the bottom is equal to twice the current in each branch. The FET differential amplifiers considered had a double-ended output ECE 315 –Spring 2007 –Farhan Rana –Cornell University Differential Amplifier: Conversion to Single-Ended Output +-vi1 vi2 vo1 vo2 RL Suppose one tries to connect a load to one of the outputs: 1 2 2 id vc ic vd id out o vd v A v A v v v A We have lost half of the voltage May 22, 2022 · An amplifier with sufficiently high CMRR can be used to separate the desired signal from the interfering noise. The analysis of Section 7.3.2 indicates that the common-mode rejection ratio of a differential amplifier with the output taken between collectors should be infinite. Differential BJT Amplifier This project shows the preliminary design of a differential amplifier, and demonstrates a Linearized Harmonic Balance (similar to a spice AC analysis) simulator and operating point annotations. Overview This project uses a test bench approach. The schematic "diff_amp" contains the basic design.Here's the approach. Starting at the collector of Q 2, we can say at the voltage there is 20 V − I C 2 ⋅ R C 2. We now subtract from this V B E 3 ≈ 700 mV to get to the emitter of Q 3. Then apply the voltage divider there to get the base voltage of Q 2 as: V B 2 = ( 20 V − I C 2 ⋅ R C 2 − V B E 3) ⋅ R 5 R 4 + R 5.Nov 3, 2015 · It is just another option to use the other collector node as well and defining the amplifier output as Vo2-Vo1. 2.) Differential mode: Assuming linear operation (and this is always assumed) the current increase of the left BJT is equal to the corresponding current reduction of the right BJT. The Input Offset Voltage of BJT Differential Amplifier given collector resistance formula is defined as the voltage that must be applied between the two input terminals of the op-amp to obtain zero volts at the output.op-amps, video amplifiers, high-speed comparators, and many other analog-based circuits. MOSFET differential amplifiers are used in integrated circuits, such as operational amplifiers, they provide a high input impedance for the input terminals. A properly designed differential amplifier with its current-mirrorBJT Differential Amplifier. Look under the hood of most op amps, comparators or audio amplifiers, and you'll discover this powerful front-end circuit - the differential amplifier. A simple circuit able to amplify small signals applied between its two inputs, yet reject noise signals common to both inputs. This circuit has a unique topology: two ... 3.1 Differential Amplifier Consider the following circuit: Figure 1 • Assuming that both bases are grounded, compute the expected values of IC1, IC2 and IE. Also calculate values for the differential and common mode gains of this amplifier. • Using transistors 1 and 2 in the array, construct the circuit in Figure 1. Be sure to connect pinJun 6, 2021 · In short, a differential amplifier suppresses in phase signals while simultaneously boosting out of phase signals. This can be a very useful attribute, particularly in the area of noise reduction. Figure 7.5.9: Input-output waveforms for common mode. Figure 7.5.9: (continued) Input-output waveforms for common mode. In short, a differential amplifier suppresses in phase signals while simultaneously boosting out of phase signals. This can be a very useful attribute, particularly in the area of noise reduction. Figure 7.5.9: Input-output waveforms for common mode. Figure 7.5.9: (continued) Input-output waveforms for common mode.Here is a plot with V IN1 and the differential output voltage: Here we have an output amplitude of 10 mV and an input amplitude of 1 mV; hence, our simulated differential gain is 10. The formula for theoretical differential gain is. Adiff = gm ×RD A d i f f = g m × R D. where g m can be calculated as follows:Learn how to calculate the Differential Output Resistance of BJT Differential Amplifier. We are ignoring Early Effect.The Lecture has been recorded by Hamza ...How does a BJT differential amplifier amplify? Ask Question Asked 1 year,, process of design and analysis of a differential amplifier b) to verify the dif, 3.3. Differential Pair Amplifier with Current Source B, THE 10 BEST BBQ Restaurants in Casablanca (Updated 2023) Africa. Morocco. Casablanca-Set, Its use of super beta BJT devices can resolve the problems found in , The differential input impedance is 400 Ω. That's the short answer. And, t, The BJT differential amplifier with constant current bias is an amplifier th, The following circuit diagram show an amplitude modulator co, Here's the approach. Starting at the collector of Q 2, we can say , Mar 21, 2023 · The basic BJT and MOSFET-based differenti, Differential amplifier is a closed loop amplifier circu, Build the NPN differential pair test circuit shown in f, Problem 5.2 - Increased Gain Common Source JFET Amplif, Instructions. Step 1: Build the differential amplifier shown in , Feb 9, 2021 · Differential Amplifier built using BJT. Con, The overall single-ended to differential gain (GAIN) m, The circuit can be rearranged to combine signal grounds at, How does a BJT differential amplifier amplify? Ask Ques.