Voltage controlled differential amplifier design

Skip to Main Content. A not-for-profit organization, IEEE is the world's largest technical professional organization dedicated to advancing technology for the benefit of humanity. Use of this web site signifies your agreement to the terms and conditions. Design of integrated analog CMOS circuits-a multichannel telemetry transmitter [single-stage differential amplifier] Abstract: A single-stage differential amplifier, implemented in a standard metal-gate process, serves as a basis for consideration of specific characteristics of analog CMOS circuits.

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• EP0151532A2 - Voltage controlled diode attenuator - Google Patents
• What is a Differential Amplifier : Design & Its Applications
• PCB Design & Analysis
• Differential amplifier
• Differential Amplifier
• Voltage-controlled floating resistor using differential difference amplifier
• 8.2: Single-ended and Differential Amplifiers
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WATCH RELATED VIDEO: Amplifier with gain control

EP0151532A2 - Voltage controlled diode attenuator - Google Patents

The Differential Amplifier Circuit using Transistors is widely applied in integrated circuitry, because it has both good bias stability and good voltage gain without the use of large bypass capacitors.

Differential amplifiers can also be constructed as discrete component circuits. Figure a shows that a basic Differential Amplifier Circuit using Transistors consists of two voltage divider bias circuits with a single emitter resistor. Like the emitter current in a single-transistor voltage divider bias circuit, I E in the differential amplifier remains virtually constant regardless of the transistor h FE value.

So, the differential amplifier has the same excellent bias stability as a single-transistor voltage divider bias circuit. The circuit of a Differential Amplifier Circuit using Transistors using a plus-minus supply is shown in Fig. The base resistors R B1 and R B2 are included to bias the transistor bases to ground while offering an acceptable input resistance to a signal applied to one of the bases.

The transistor emitter currents I E1 and I E2 are exactly equal only if the devices are perfectly matched. To allow for some differences in transistor parameters, a small-value potentiometer R EE is sometimes included between the emitters, see Fig. Adjustment of R EE increases the resistance in series with the emitter of one transistor, and reduces the emitter resistance for the other transistor.

This reduces the I E for one transistor and increases it for the other, while the total emitter current remains constant. Consider what happens when the at input voltage v i at the base of Q 1 is positive-going, as illustrated in Fig. Q 1 emitter current I E1 increases. So, the ac output voltage at Q 1 collector is in anti-phase to v i at Q 1 base, and the output at Q 2 collector is in phase with v i.

The voltage gain of a single-stage amplifier with an unbypassed emitter resistor and no external load is given by. Referring to Fig. Neglecting R E because it is very much larger than h ib , the voltage gain from the base of Q 1 to its collector is,. Equation gives the voltage gain from one input terminal to one output of a differential amplifier.

It is seen to be half the voltage gain of a similar single-transistor CE amplifier with R E bypassed; but note that the differential amplifier requires no bypass capacitor. This is an important advantage, because bypass capacitors are usually large and expensive.

Another way to contemplate the operation of the Differential Amplifier Circuit using Transistors is to think of the input voltage being equally divided between Q 1 base-emitter and Q 2 base-emitter. This is illustrated in Fig. Thus, for v i at Q 1B , transistor Q 1 behaves as a common-emitter circuit, and because Q 2 receives the input at its emitter, Q 2 behaves as a common-base circuit.

The input impedance at the base of a CE circuit with an unbypassed emitter resistor is,. The input resistance at Q 1B is,. Note that there are usually bias resistors in parallel with Z b , so that the circuit input impedance is. As in the case of CE and CB circuits, the output impedance at the transistor collector terminals is given by. When one transistor base is grounded in a Differential Amplifier Circuit using Transistors, and an input is applied to the other one, as already discussed, v i is amplified to produce the outputs at the collector terminals.

In this case v i is the voltage difference between the two base terminals. Figure shows a differential amplifier with dc input voltages V i1 and V i2 applied to the transistor bases.

If the voltage, gain from the base to the collector is A v , the dc voltage changes at the collectors are;. It is seen that the differential amplifier can be employed as a direct-coupled amplifier, or dc amplifier. The term difference amplifier is also used for this circuit. Design procedures for a Differential Amplifier Circuit using Transistors are similar to those for voltage divider bias circuits.

Because there is no bypass capacitor in a differential amplifier, one of the coupling capacitors determines the circuit lower cutoff frequency f 1. The capacitor with the smallest resistance in series with it is normally the largest capacitor, and in the case of a differential amplifier this is usually the input coupling capacitor. So, the input coupling capacitor determines the circuit lower cut-off frequency.

Consider the capacitor-coupled differential amplifier in Fig. The circuit uses a plus-minus supply , and a single collector resistor R C. No output is taken from Q 1 collector, so there is no need for a collector resistor. The collector-emitter voltage should be a minimum of 3 V, as always.

As discussed, capacitor C 1 sets the lower cutoff frequency. Skip to content.

What is a Differential Amplifier : Design & Its Applications

A gain control circuit includes at least a first T1, T2 and a second T3, T4 transistor differential amplifier the input circuits of which are connected in parallel to a signal voltage source. The gain control is performed by distributing a constant current Is between these differential amplifiers as a function of a control quantity Uc for setting the transconductance of the stages in a complementary way. The two differential amplifiers are provided with negative feed back F, R1, R2, R3 but with different feed back factors. As the transistors in As the transistors in the differential amplifiers carrying signals of the same phase are interconnected the output signal from the automatic gain control circuit will consist of a superposition of the output signals of the two differential amplifiers.

PCB Design & Analysis

The differential amplifier is a basic operational amplifier that consists of three basic terminals. Among those, two are of input that is inverting and the non-inverting terminals. Hence, these amplifiers are the circuits that can perform various operations mainly it is the difference between the two applied input signals. The most important factor gain is applicable here for both the applied input signals. Hence this concept of application leads to the elimination of the noise quantity from the input signals. The concept of DC offset and the way it performs subtraction over the applied signals makes it the best in the area of IC designing. These are the circuits with negative feedback which is proven beneficial in terms of performing various operations. These differential amplifiers can be designed with transistor s or the Op-amps and are simple to analyze.

Differential amplifier

JavaScript seems to be disabled in your browser. For the best experience on our site, be sure to turn on Javascript in your browser. A Plus account is required to perform this action. Get valuable resources straight to your inbox - sent out once per month. An operational amplifier op amp is an analog circuit block that takes a differential voltage input and produces a single-ended voltage output.

Differential Amplifier

The Differential Amplifier Circuit using Transistors is widely applied in integrated circuitry, because it has both good bias stability and good voltage gain without the use of large bypass capacitors. Differential amplifiers can also be constructed as discrete component circuits. Figure a shows that a basic Differential Amplifier Circuit using Transistors consists of two voltage divider bias circuits with a single emitter resistor. Like the emitter current in a single-transistor voltage divider bias circuit, I E in the differential amplifier remains virtually constant regardless of the transistor h FE value. So, the differential amplifier has the same excellent bias stability as a single-transistor voltage divider bias circuit.

Voltage-controlled floating resistor using differential difference amplifier

Differential Voltage Current Controlled Current Feedback Operational Amplifier is an attractive active element for realizing resistorless filters with a minimum active component count. This is verified through a design example, where a 3rd-order leapfrog filter has been realized using the AMS 0. The performance of the Differential Voltage Current Controlled Current Feedback Operational Amplifier filter is evaluated and compared with that obtained by the corresponding filter, where Differential Voltage Current Controlled Current Conveyors have been employed. The Current Feedback Operational Amplifier CFOA is a four terminal active element which offers particularly higher speed, higher slew rate, and better bandwidth than those achieved by the conventional voltage-mode op amps [ 1 , 2 ]. A number of CFOA topologies with terminals of single type have been already introduced in the literature [ 3 — 6 ]. The realization of time-constants in filters, where the aforementioned types of CFOAs are utilized, is achieved by employing passive resistors. This is a drawback with respect to the nowadays analog filter realization trend, where resistorless filter structures with electronic tuning capability are preferred. As a solution, active resistors could be employed, but the performance of the resulted filter configurations in terms of linearity is worsened in this case.

8.2: Single-ended and Differential Amplifiers

In work and life, many of us strive for a constant or a routine. Moreover, if you are a perfectionist and a planner like myself, a routine is a must. Furthermore, discovering a routine for anyone is a path to a norm, and I dare say a more efficient day to day life. However, as it is in math and science, life is also filled with the events and circumstances that are the polar opposite of constant, the ever-present variable.

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RELATED VIDEO: Transistor-Based Voltage Controlled Amplifier (VCA)

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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. Single amplifiers are usually implemented by either adding the appropriate feedback resistors to a standard op-amp , or with a dedicated integrated circuit containing internal feedback resistors. It is also a common sub-component of larger integrated circuits handling analog signals. In practice, however, the gain is not quite equal for the two inputs. A more realistic expression for the output of a differential amplifier thus includes a second term:. As differential amplifiers are often used to null out noise or bias voltages that appear at both inputs, a low common-mode gain is usually desired. The common-mode rejection ratio CMRR , usually defined as the ratio between differential-mode gain and common-mode gain, indicates the ability of the amplifier to accurately cancel voltages that are common to both inputs.

In this tutorial, we will learn about one of the important circuits in analog circuit design: A Differential Amplifier. It is essentially an electronic amplifier, which has two inputs and amplifies the difference between those two inputs. We will see the working of a Differential Amplifier, calculate its gain and CMRR, list out some important characteristics and also see an example and an application. The Differential Pair or Differential Amplifier configuration is one of the most widely used building blocks in analog integrated-circuit design.