Single ended differential amplifier gain
The operational amplifier or OP-AMP is a direct coupled, high gain amplifier used to perform a wide variety of mathematical operation used to perform like summation, subtraction, multiplication, differentiation and integration etc. In analog computers it is often referred to as the basic linear or analog integrated circuit IC. The operational amplifier works in different modes depending on the nature of its job. These modes are explained below. In Figure a input signal is applied to terminal 1 and terminal 2 is ground. Figure shows that an amplified and inverted output signal is obtained at V01 but an equally amplified and in phase signal appears at V02 which is terminal 4.
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Content:
- Understanding the Transistor Differential Amplifier
- Electronic Devices - Operational Amplifiers
- Differential Amplifier Basics, Usage and Differences
- Audio buffer amplifier
- What is the difference between single ended and differential signaling?
- Multiple Choice Questions and Answers on Op-Amp ( Operational Amplifier )
- Analysis of the CMOS differential amplifier with active load and single-ended output
- Single-ended amplifier gain vs Fully differential amplifier gain
- Operational Amplifiers
Understanding the Transistor Differential Amplifier
This article reviews the basics of fully-differential amplifiers FDA , important specifications and what they mean, and how to interface to the signal chain using an FDA for balun-type functionality with additional performance. These ADCs are used in a wide variety of applications ranging from, but not limited to, communications wireless infrastructure and backhaul to test and measurement oscilloscopes and spectrum analyzers.
To support this input architecture, engineers must design the signal chain to interface to the ADC differentially. It is easy to assume that one must use a balun in the signal chain for best performance, despite coupling issues in some applications.
This is not always the case, however, especially in test and measurements where the DC component is needed. Fully differential amplifiers FDA are versatile tools to use in place of or along with baluns and offer a variety of benefits.
Fully differential signal processing provided by FDAs gives the circuit design increased immunity to external noise, twice the dynamic range and reduced even-order harmonics versus traditional amplifiers with single-ended outputs. To establish the proper external gain, eight resistors are needed.
With half the resistor count and only one IC, an FDA can provide both a single-ended-to-differential-interface and a differential-to-differential interface to the ADC. This also eliminates the need for a balun and allows DC components to pass; a balun provides DC isolation. This is important in many applications that need a superior response at low frequencies down to DC. An FDA is two amplifiers in one, a main differential amplifier from V in to V out composed of multiple feedback paths and the V ocm error amplifier better known as the common-mode output amplifier.
This V ocm setting on the V ocm pin can impact the overall output swing as discussed later. This is different than in a traditional op amp with a single-ended output, where the output common-mode voltage and single-ended output are inherently the same signal, impacting the dynamic range. When analyzing this amplifier it is best to think of it as including two inverting feedback paths.
One consists of an inverting input to non-inverting output, and the other is a non-inverting input to an inverting output see Figure 1. For the FDA to function properly, both paths must be closed.
To maintain balance, the feedback paths are best kept equal. Analysis of these two paths can become very complicated. The analysis is simplified in this discussion to introduce FDA basics and illustrate how they can assist design. FDA input and output voltages are defined in Figure 1. Figure 2 Basic FDA gain configuration, differential input-to-differential output. In Figure 2 external resistors are added to the basic FDA diagram to set the gain.
Equation 3 shows that if the feedback terms are not equal, the differential output voltage depends on V ocm. This is important, because the feedback terms should be equal or as close to each other as possible, because the V ocm term introduces both an offset and noise. Inherent in its differential architecture, the FDA improves noise immunity and system dynamic range. System noise can accumulate and impact dynamic range when signals travel across a printed circuit board PCB , cables and wiring, and through signal and ground paths.
The FDA enables coupled noise to be rejected at the inputs. This includes noise from power supplies and signals that appear as a common-mode in a typical op amp. Single-ended components cannot reject ground noise as each part has a different reference point. Despite diligent design efforts to control high-frequency ground currents, issues may arise where differential signaling can improve performance.
Noise accumulation in a typical op amp may degrade signal-to-noise ratio SNR , compromising system design. Along with greater noise immunity due to common-mode rejection by the FDA, the phase difference between the outputs enables the output voltage swing to be twice that 6 dB of a single-ended output see Figure 3.
A further advantage of FDAs and differential signal chains is inherent cancellation of even-order harmonics. Using a power series expansion, given a sine wave input and ignoring the DC component, Figure 4 illustrates second-order harmonic cancellation in nonlinear differential devices such as amplifiers FDA.
While full cancellation cannot be achieved in real devices, these products see a benefit from a balanced design over a single-ended configuration see Figure 5. Phase and amplitude components of the signal into the ADC are ideally matched for best performance. When there is unbalance in either or both the amplitude and phase, this is seen as a common-mode component on the output, producing SNR degradation.
Since the internal common-mode feedback circuitry forces the output common mode to equal the applied common mode at the V ocm , the balance error, Equation 5, is minimal.
Of the specifications that may be of particular interest in high-speed system designs, linearity should be well understood; items that may need to be reviewed are common-mode voltage, noise and stability.
It may seem obvious how specifying the common mode voltage range impacts performance; however, a review of this topic is helpful since this is what makes the FDA so powerful.
For AC-coupled signals, Vocm alignment with the ADC is not much of a concern as long as the input and output range are within specifications and are supplied as needed. Usually, one can default to mid supply of the amplifier to achieve best performance. An important consideration is Vpp out to meet maximum signal swing of the ADC. For an optimal system design, including margin to accommodate loss in the anti-aliasing filter is good design practice.
For example, if the full scale ADC input is 1. In a DC-coupled design, knowing both the required V ocm and voltage swing is paramount. Use Equations 6 and 7 to check that the amplifier can meet the desired output swing around V ocm.
With a DC-coupled signal, the performance and common-mode specifications at the desired V ocm must be verified. Typically in an FDA datasheet, V icm and V ocm specifications are noted with minimum and maximum values. Additionally, graphs are provided to show the linearity impact and optimal range for the FDA common-mode voltage.
Depending upon the FDA, power supplies may sometimes be aligned to maintain a V ocm just outside an optimal range for alignment with the ADC. Once verified that the required swing can be accommodated and that these supplies meet datasheet specifications, there should be no issue in using them to satisfy output common mode voltage needs. Noise gain NG is essential to determining output noise and stability. Different from signal gain, noise gain is the reciprocal of the attenuation from the output of an amplifier or any feedback loop to the input and is equal to.
For simplicity, we assume purely resistive feedback. Capacitors added to the feedback and input can impact stability and NG, making the NG expression with complex impedance equal to. Note the difference in the noise gain, Equation 8, and the signal gain, Equation 4.
Their independence allows noise gain to be manipulated with signal gain held constant. For simplicity, only resistive feedback is considered in the following example. Adding Rt adjusts the noise gain for stability. By manipulating the noise gain with Rt, the amplifier is stabilized without impacting the signal gain or signal bandwidth.
With increased NG, however, the system should be evaluated to determine if its impact on SNR and increased sensitivity to input offset voltage can be tolerated. What is its impact on noise? To calculate the FDA output noise, first reduce the circuit under evaluation to its simplest form see Figure 7.
Assume that the resistors are balanced and match as close as possible on each side. Also assume that the total differential noise is the root sum of the squares RSS of the individual contributors see Equation Having determined the output noise, will this work in the system? This means that the system noise bandwidth is 1. From here we use Equations to check compatibility:. If this is comparable, it is time to build an evaluation board to verify the calculation and assumptions.
What if you have a single-ended input and need to convert for a differential ADC? Most would say this is exactly what baluns were made to do. However, these devices cannot provide a power gain, are susceptible to coupling by design, over temperature specifications are typically not well maintained, can be very big and costly if wideband signals are needed, and do not preserve the DC component.
In a high speed system such as a communications receiver chain used in a test and measurement spectrum analyzer or oscilloscope, preserving the DC component while enabling GHz frequency capability may be necessary.
In this case, an FDA can be a very useful tool. If the design is DC-coupled, ensure both sides of the input circuit are configured to retain balance. The non-signal input side typically has an Rg component biased to the midrange of the expected source. This mid-scale reference point should give a balanced differential swing around V ocm at the output.
This is generally grounded if the source swings around ground. Configuring the FDA gain with external resistors provides design flexibility. Selected feedback resistors should be equal. Additionally, the impedances on each side from the summing junctions back to both the signal source and ground or bias voltage, non-signal side should be equal.
While this article covers only the basics of fully differential amplifiers, hopefully the information will help influence your choice of amplifier by informing you of options. Before reaching for the balun, ask yourself if an FDA is more appropriate.
We use cookies to provide you with a better experience. By continuing to browse the site you are agreeing to our use of cookies in accordance with our Privacy Policy. No Comments. What is an FDA? Figure 1 Diagram of a typical fully-differential amplifier. Figure 3 Dynamic range increase in FDAs.
Figure 4 Fully differential amplifier configuration. Figure 5 Single-ended amplifier configuration. Figure 6 FDA with additional Rt to adjust noise gain. Figure 7 FDA noise analysis simplified.
Figure 8 DC-coupled, single-ended input, differential output. Jump to Page:. Report Abusive Comment Thank you for helping us to improve our forums. Is this comment offensive?
Electronic Devices - Operational Amplifiers
There can be four different classifications of operational amplifier gain:. The differential amplifier has a unique feature that is, it amplifies the voltage difference between two input signals unlike the single-ended which amplify a single input signal. A principle application is to eliminate the noise common-mode fluctuating voltage. It may be also configurated to operate as a single-ended amplifier by grounding one of the inputs.
Differential Amplifier Basics, Usage and Differences
Year of fee payment : 4. Year of fee payment : 8. Year of fee payment : A differential to single-ended signal transfer circuit that allows increased gain and improved AC performance while reducing power supply voltage requirements. The transfer circuit includes a first operational transconductance amplifier OTA , a second operational amplifier OPA , first and second controlled current sources, a third current source, and first and second bipolar junction transistors. The inverting and non-inverting inputs of the transfer circuit are provided at the inverting input and the non-inverting input, respectively, of the OTA, which is coupled to the first and second controlled current sources to form a current mirror with tracking feedback. The output voltage of the transfer circuit is provided at the emitter of the first transistor, the base of which is connected to the non-inverting input INp. The first transistor is coupled to the third current source in an emitter follower configuration to provide both current gain and impedance matching.
Audio buffer amplifier
The operational amplifier is a direct-coupled high gain amplifier usable from 0 to over 1MH Z to which feedback is added to control its overall response characteristic i. The op-amp exhibits the gain down to zero frequency. Such direct coupled dc amplifiers do not use blocking coupling and by pass capacitors since these would reduce the amplification to zero at zero frequency. Large by pass capacitors may be used but it is not possible to fabricate large capacitors on a IC chip. The capacitors fabricated are usually less than 20 pf.
What is the difference between single ended and differential signaling?
Note: Please be cautious and check with your supplier if this product is for virus protection purposes and if the coronavirus COVID will affect your order. Module power supply: 5VV can be, but it depends on the baby's voltage output if the customer requires 5V voltage output, then the AD62X series chip is about 3. Module input signal type: single-ended signal or differential signal. The maximum magnification of the module: more than times measured , due to the gain of the assembly caused by the fluctuation of the waveform band, it is recommended to use multi-stage amplification for high gain. Modular Features : The AD is a low cost, high precision instrumentation amplifier that requires only one external resistor to set the gain from 1 to 10,
Multiple Choice Questions and Answers on Op-Amp ( Operational Amplifier )
The circuit will run from 6 to 15 vdc and give about 20 dB of gain. What is the application? The functions of an audio amplifier can be split into two sectors or components. The input impedance is determined by the value of R1 and is 1M as shown in this example. The second amplifier inverts the input and adds a reference voltage to generate Vout-. The standy control module is powered with a low-voltage power supply unit. A buffer is a unity-gain amplifier that has an extremely high input resistance and an extremely low output resistance.
Analysis of the CMOS differential amplifier with active load and single-ended output
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.
Single-ended amplifier gain vs Fully differential amplifier gain
RELATED VIDEO: Lecture 70 : Single - ended Vs. Differential Signaling and Basic Model of a Differential AmplifierProsig P systems use differential inputs, but what are they and why are they so special? This subject is not always fully understood and, therefore, the focus of this article is to try to make the difference clearer and explain why differential inputs are the obvious choice in a high quality, high precision system like the Prosig P First, we need to understand what we mean by single ended and differential inputs. To that end we should start with amplifiers. The difference between single ended and differential ended inputs is the difference between the types of amplifiers used.
Operational Amplifiers
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Effective date : Year of fee payment : 4. A fully differential line driver circuit 25 includes an input differential amplifier 26 and double-ended differential amplifiers 27,
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