Common mode gain of differential amplifier

This feedback reduces the common mode gain of differential amplifier. While the two signals causes in phase signal voltages of equal magnitude to appear across the two collectors of Q 1 and Q2. Now the output voltage is the difference between the two collector voltages, which are equal and also same in phase,

This applies also to the common mode - however, in the gain formula you must replace Re with 2Re. 5.) Finally, an important comment: You have defined the diff. mode as V1=Vd/2 and V2=-Vd/2. This is OK. However, please note that in the first part of your question the expression for Ad does NOT apply to your definition.lower than the differential mode UGF.) 4. Report the DC gain, GBW, UGF and phase margin and output swing range of both common-mode and differential signal paths. In conclusion, the designed amplifier should have the following characteristics, 1. The output common-mode voltage can be determined by the reference voltage (theCommon mode rejection is a key aspect of the differential amplifier. CMR can be measured by connecting the base of both transistors M 1 and M 2 to the same input source. The plot below shows the differential output for both the resistively biased and current source biased differential pair as the common mode voltage from W1 is swept from …For common mode gain, raise each input 1 V and analyze what happens to the output. The change in output divided by the change in input (1 V in this example) is the common mode gain. Similarly, starting with the previously analyzed case of both inputs at 0, raise the positive input 1 mV and see what you get. The differential mode gain is then ...A common-mode feedback loop must be used: Circuit must operate on the common-mode signals only! BASIC IDEA: CMFB is a circuit with very small impedance for the commonmode signals - but transparent for the differential signals. Use a common-mode detector (eliminates the effect of differential signals and detect common-mode signals)

The INA851 integrates a two-amplifier input gain stage and a differential amplifier output stage into a one-chip solution. The INA851 redefines the instrumentation amplifier landscape by offering an integrated design within ... common mode range and differential output based on user inputs. The calculator also provides a visual graphical ...The differential input signal is 10 mV peak at 1 kHz. The low-frequency common-mode noise is 10 times greater in amplitude. Figure 5 provides the input and output waveforms as monitored by the oscilloscope. The amplifier provides a voltage gain of 10, meaning the output will be 100 mV peak or 200 mV peak-to-peak. Figure 5.Feb 11, 2022 · • Intro Differential Amplifiers - Differential and Common Mode Gain, Derivation, Formulas, Simplifications IFE - TU Graz 5.9K subscribers Subscribe 5.7K views 1 year ago Operational... Mar 20, 2023 · The output voltage, vout, is given by the following equation: Vout = Acm(Vcm) V o u t = A c m ( V c m) where Acm A c m is the common-mode gain of the amplifier. where the common mode Vcm V c m is defined as, Vcm = V1+V2 2 V c m = V 1 + V 2 2. Common mode operation is useful for applications such as sensing the level of a signal relative to ... The differential input signal is 10 mV peak at 1 kHz. The low-frequency common-mode noise is 10 times greater in amplitude. Figure 5 provides the input and output waveforms as monitored by the oscilloscope. The amplifier provides a voltage gain of 10, meaning the output will be 100 mV peak or 200 mV peak-to-peak. Figure 5.The two non-inverting amplifiers form a differential input stage acting as buffer amplifiers with a gain of 1 + 2R2/R1 for differential input signals and unity gain for common mode input signals. Since amplifiers A1 and A2 are closed loop negative feedback amplifiers, we can expect the voltage at Va to be equal to the input voltage V1.Figure 1. As we saw in MasteringElectronicsDesign.com: The Differential Amplifier Transfer Function, the signal at the amplifier output is as follows: (2) If we arrange this equation differently, as in (3), (3) one can see that, in the unique case in which. (4) the circuit amplifies the difference of the input signals, V1-V2.To find the common-mode gain, both inputs of the differential amplifier will be injected with the same signal. Figure 14 shows the output signal, which is unchanged for the frequency spectrum as shown in Table 1, where a 4 mV pk output can be seen. Thus, the common-mode gain:

Amplifier specifications: Gain, Gain-Bandwidth Product, Common-Mode Rejection ... common mode to differential mode gain. Thus CMRR will be a negative number ...5/11/2011 Differential Mode Small Signal Analysis of BJT Diff Pair 9/21 We then turn off the two common-mode sources, and analyze the circuit with only the two (equal but opposite valued) differential-mode sources. d From this analysis, we can determine things like the differential mode gain and input resistance! Q: This still looks very difficult!amplifier (gain 10,000) System output [-10 points if both sensors see the same signal- differential amplification will then yield zero] [-10 points if one sensor is blocked from both light and interference] 3b Differential gain G± = 10V/1 mV = 10,000. Common mode gain Gc < 0.1 V/10 mV = 10 at 0 to 0.1 Hz Common mode gain Gc < 0.1 V/1 mV = 100 ... Difference-Mode Gain: Avd Common-Mode Gain: Avc One always wants the difference-mode gain to be much muchlarger than the common-mode gain (ideally one would want the common mode gain to be zero!) vi1 vi2 Common-Mode Rejection Ratio (CMRR): vc vd A A CMRR ECE 315 –Spring 2007 –Farhan Rana –Cornell University٦ رجب ١٤٢٨ هـ ... Most differential signals are measured using an instrumentation amplifier or difference amplifier. This article will discuss how these ...

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This feature is described by saying that the amplifier rejects a common- mode signal or by saying that the common-mode gain is zero. On the other hand, when a difference develops between ∆V 1 and ∆V 2, this difference is amplified. For this reason the circuit is often referred to as a differential amplifier.Summary:: Differential amplifier common mode gain derivation of forumlas I'm having a hard time deriving for equations 10-8 -10-9.٦ رجب ١٤٢٨ هـ ... Most differential signals are measured using an instrumentation amplifier or difference amplifier. This article will discuss how these ...Common mode gain — A perfect operational amplifier amplifies only the voltage difference between its two inputs, completely rejecting all voltages that are common to both. However, the differential input stage of an FDA is never perfect, leading to the amplification of these identical voltages to some degree.Difference-Mode Gain: Avd Common-Mode Gain: Avc One always wants the difference-mode gain to be much muchlarger than the common-mode gain (ideally one would want the common mode gain to be zero!) vi1 vi2 Common-Mode Rejection Ratio (CMRR): vc vd A A CMRR ECE 315 –Spring 2007 –Farhan Rana –Cornell UniversityJan 11, 2021 · A well-designed differential amplifier typically has a high differential gain and low common mode gain, resulting in a high CMRR. The CMRR is often expressed in decibels (dB) as A CMRR of 10,000 (80dB) means that if the amplitudes of the differential input signal and the common-mode noise are equal, the desired signal will appear on the output ...

The common-mode input to differential-output gain is zero since does not change in response to a common-mode input signal. While the gain of the differential amplifier has been calculated only for two specific types of input signals, any input can be decomposed into a sum of differential and common-mode signals.a common-mode gain of 1/1000 and a 10 V common-mode voltage at its inputs will exhibit a 10 mV output change. The differential or normal mode gain (A D) is the gain between input and output for voltages applied differentially (or across) the two inputs. The common-mode rejection ratio (cMrr) is simply the ratio of the differential gain, A D, to ...CMMR: CMMR stands for Common Mode Rejection Ratio, it is given as the ratio of differential mode gain to the common mode gain. In dB, For an ideal amplifier CMMR should be practically infinite but in actual practice, it is not so and has a finite value. It is defined as the ratio of the desired signal to the undesired signal. The larger the ...AIM:-Measurement of operational Amplifier Parameters – Common Mode Gain, Differential Mode Gain, CMRR, Slew Rate. EQUIPMENT REQUIRED: S no. Particulars Specification/Range Quantity Make/Model No. 1. Trainer kit 1 2. Connecting wires 3. multimeter 1 4. CRO 1 THEORY: 1. Common Mode Gain: When the same input voltage is applied to both input ...Aug 29, 2015 · Add a comment. 1. The common mode voltage reaching the input of a differential amplifier is (as mentioned) the unneeded part of the input referenced to some specified circuit ground (common). The reason it is an issue and specified as a maximum is usually due to limitations of the amplifier input circuits voltage range. common-mode voltage that is present on the inputs (the common-mode voltage will pass through at unity gain regardless of the differential gain). Therefore, if a 10 mV differential signal is applied to the amplifier inputs, amplifier A1’s output will equal +5 V, plus the common-mode voltage, and A2’s output will be –5 V,A well-designed differential amplifier typically has a high differential gain and low common mode gain, resulting in a high CMRR. The CMRR is often expressed in decibels (dB) as A CMRR of 10,000 (80dB) means that if the amplitudes of the differential input signal and the common-mode noise are equal, the desired signal will appear on …It is because a differential amplifier amplifies the difference between the two signals between (v1-v2) and for common-mode signals, this differences zero. Note ...This feedback reduces the common mode gain of differential amplifier. While the two signals causes in phase signal voltages of equal magnitude to appear across the two collectors of Q 1 and Q2. Now the output voltage is the difference between the two collector voltages, which are equal and also same in phase,May 22, 2022 · The common-mode input to differential-output gain is zero since does not change in response to a common-mode input signal. While the gain of the differential amplifier has been calculated only for two specific types of input signals, any input can be decomposed into a sum of differential and common-mode signals.

Not all architectures are created equal. Just like you wouldn’t pick a single tool to build a house you shouldn’t assume all instrumentation amplifiers (INA) operate optimally in all applications.. Common mode rejection ratio (CMRR) and common mode rejection (CMR) measure the ability of a differential input amplifier, such as an op amp or an …

The input voltage represented by common-mode voltage and differential voltage is shown in Fig. 11.2. Figure 11.2: Small differential and common-mode inputs of a differential amplifier Let V out1 be the output voltage due to input voltage V in1 and V out2 be the output voltage due to V in2. The differential-mode output voltage V out(d) be defined asThe Lee active load provides a typically high differential-mode gain and an unusually small common-mode gain. The conventional differential amplifier with a current-source load will have a common-mode gain of order unity, whereas the Lee Load yields a common-mode gain one to two orders of magnitude smaller [as much asrejected the common mode gain must be zero. When this happens it can be shown that O cm vdm R R v v 1 =0 + 2. (10) This relationship shows that any common mode voltage will be disregarded. Likewise any differential mode voltage will be amplified by 1 2 R R. The relationship in (10) holds true only for an ideal difference amplifier. In The common mode rejection is a feature of differential amplifiers. Op-amps are amplifiers with differential input; so common mode rejection applies to ...The important aspects of the Frequency Response of Common Mode Gain of Differential Amplifier can be calculated with some approximations. Consider the time constant=R T C T, where R T and C T are the equivalent output resistance and capacitance of the tail current source and R T is usually greater than or equal to output resistance of a transistor.Where Ad = differential gain. V in1, V in2 = input voltages. When V in1 = V in2, obviously the output will be zero. ie, differential amplifier suppresses common mode signals. For effective operation, components on either sides should be match properly. Input signals are applied at base of each transistor and output is taken from both collector ...1 kΩ, the differential gain is equal to 11. We can see from Equation 3 that a pro-grammed gain of 1 is fundamentally not achievable. Common Mode Gain. The output volt-age that results from the presence of DC common mode voltage is given by: R2R4 V OUT = V cm 1 1– –––––2 (4) R1R3 Using Equation 1, the formula for theTo find the common-mode gain, both inputs of the differential amplifier will be injected with the same signal. Figure 14 shows the output signal, which is unchanged for the frequency spectrum as shown in Table 1, where a 4 mV pk output can be seen. Thus, the common-mode gain:Detailed Solution. Download Solution PDF. Concept: CMRR (Common mode rejection ratio) is defined as the ratio of differential-mode voltage gain (A d) and the common-mode voltage gain (A c ). Mathematically, in dB this is expressed as: C M R R = 20 log | A d A c m |. Generally, it can be expressed as. C M R R = A d A c.= Differential gain of the IA (V/V) G CM = Common-mode gain of the IA (V/V) See Figures 1A and 1B for V S and R S. Common-mode rejection ratio is the ratio of differential gain to common-mode gain. Adding gain ahead of the difference amplifier increases the CMR of the IA so long as the op amps in the gain stage have better CMR than the ...

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a common-mode gain of 1/1000 and a 10 V common-mode voltage at its inputs will exhibit a 10 mV output change. The differential or normal mode gain (A D) is the gain between input and output for voltages applied differentially (or across) the two inputs. The common-mode rejection ratio (cMrr) is simply the ratio of the differential gain, A D, to ...Differential Mode Gain (Ad) : Common Mode Gain (Acm) : OUTPUT CMRR (Numerical) : CMRR (dB) : EXAMPLE: Op Amp CMRR Calculator 1: INPUTS: A D = 2, A CM = 10000 OUTPUTS: CMRR (Numerical) = A D /A CM = 0.0002 CMRR (dB) = 20*Log 10 ...The Common mode gain of differential amplifier formula is defined as the amplification given to signals that appear on both inputs relative to the common (typically ground). This means the output is unaffected by voltages that are common to both inputs is calculated using Common Mode Gain = -( Load Resistance /(2* Internal Small Signal ...though the obvious use of a fully differential amplifier is with symmetrical feedback, the gain can be controlled with only one feedback path. Using matched resistors R1 = R3 and R2 = R4 in the analysis circuit of Figure 1 balances the feedback paths so that β1 = β2 = β, and the transfer function is The common-mode voltages at the input and ...In normal operation, an op-amp has extremely high gain, but if you go outside of common mode voltage range, then the gain will start degrading/decreasing rapidly. ... The "common mode" of a differential amplifier is the average ground-referenced voltage of …Differential Amplifier, Differential Mode and Common Mode Gain of an amplifier is defined as V OUT /V IN . For the special case of a differential amplifier, the input V IN is the difference between its two input terminals, which is equal to (V 1 -V 2 ) as shown in the following diagram.Ideal Differential Amplifiers An ideal differential amplifier amplifies the difference signal between two inputs: +-Avd vi1 vi2 vi1 vi2 The need for differential amplifiers: Differential amplifiers are used to remove unwanted signals tha t are common to both input signals. For example, in many cases useful informati on is carried by the The common-mode gain has been analyzed for the DG MOSFET differential amplifier designed. The common-mode gain has been simulated for the differential signals listed as V in+ in Tables 3 and 4. A maximum value of 84.65 μV has been measured.Hence, the common mode gain expression is: Acm=A=-gm * Rc/(1+gm * 2re). This expression shows that the common mode gain will be zero for an ideal current source (re approachung infinite) only. Note: The above (rough) calculation is accurate enough to demonstrate the systematic common mode effect caused by the a finite re. ….

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.• MOSFET Differential Amplifiers • Reading: Chapter 10.3‐10.6. EE105 Spring 2008 Lecture 24, Slide 2Prof. Wu ... common‐mode output voltage cannot fall below V CM ...Common mode rejection is a key aspect of the differential amplifier. CMR can be measured by connecting the base of both transistors M 1 and M 2 to the same input source. The plot below shows the differential output for both the resistively biased and current source biased differential pair as the common mode voltage from W1 is swept from …• Differential amplifier amplifies the difference between two voltages but rejects “ common mode ” signals – ⇒ Improved noise immunity • Using “ half -circuit ” technique, small -signal operation of differential amplifiers is analyzed by breaking the problem into two simpler ones – Differential mode problem – Common mode problem Feb 24, 2012 · A differential amplifier (also known as a difference amplifier or op-amp subtractor) is a type of electronic amplifier that amplifies the difference between two input voltages but suppresses any voltage common to the two inputs. A differential amplifier is an analog circuit with two inputs (V 1 and V 2) and one output (V 0) in which the output ... The amplifi er’s common mode rejection ratio (CMRR) is the ratio of the differential mode gain to the common mode gain. For these calculations, only common mode and differential mode gain is considered for amplifi ers. Thus, an amplifi er’s output can be determined as: VOUT = (VCM • ACM) + (VDIFF • ADIFF) – + VCM AMP VOUT dn1023 ...This feature is described by saying that the amplifier rejects a common- mode signal or by saying that the common-mode gain is zero. On the other hand, when a difference develops between ∆V 1 and ∆V 2, this difference is amplified. For this reason the circuit is often referred to as a differential amplifier. ٢٧ جمادى الأولى ١٤٤٢ هـ ... The Common-Mode Rejection Ratio (CMRR) indicates the ability of a differential amplifier to suppress signals common to the two inputs.The "common mode" of a differential amplifier is the average ground-referenced voltage of the two input signals. Let's take a typical load cell as an example. These devices are made of variable-resistance strain gauges in a bridge configuration. Common mode gain of differential amplifier, Ideal Differential Amplifiers An ideal differential amplifier amplifies the difference signal between two inputs: +-Avd vi1 vi2 vi1 vi2 The need for differential amplifiers: Differential amplifiers are used to remove unwanted signals tha t are common to both input signals. For example, in many cases useful informati on is carried by the , If Vin1=Vin2 (i.e. common mode input) rises, then, textbooks say that the Vout1 and Vout2 both rise by equal amounts and that this is how common mode signals are removed (if we take Vout1-Vout2). But if Iss is fixed by the current source and M1 and M2 are at identical states ( Vin1=Vin2, R1=R2 ), then I believe I can assume that Id1=Id2=Iss/2 ., A Designer’s Guide to Instrumentation Amplifiers, 3rd Edition ... in, amplifier (gain 10,000) System output [-10 points if both sensors see the same signal- differential amplification will then yield zero] [-10 points if one sensor is blocked from both light and interference] 3b Differential gain G± = 10V/1 mV = 10,000. Common mode gain Gc < 0.1 V/10 mV = 10 at 0 to 0.1 Hz Common mode gain Gc < 0.1 V/1 mV = 100 ... , Common mode rejection is a key aspect of the differential amplifier. CMR can be measured by connecting the base of both transistors Q 1 and Q 2 to the same input source. The plot below shows the differential output for both the resistively biased and current source biased differential pair as the common mode voltage from W1 is swept from …, M.B. Patil, IIT Bombay 2 the di erential ampli er is given by, Vo = AdVid + AcVic; (2) where Ad is the di erential gain, and Ac is the common-mode gain. A good di erential ampli er should reject Vic entirely, i.e., it should have Ac =0. In …, So even if the driving differential amplifier produces a differential output current and has zero common mode current, there could still be a common mode voltage. This is important as transistors operate as voltage-controlled current sources and many differential amplifiers are actually transconductance amplifiers as this gives the widest ..., Problem 5.2 - Increased Gain Common Source JFET Amplifier-Large Drain Resistor. The gain of the circuit in 5.1 is not high. A naïve application of the gain formula [Eq. (1)] would imply that the gain should increase substantially if the drain resistor is changed to 18kΩ, as shown at right. Build this circuit., Let Vc be a common mode signal. This signal will be applied to both inputs. Let Vd and -Vd be differential signals applied to the inputs. To one input we apply Vc + Vd and to the other we apply Vc + (-Vd) The differential signal seen by the amplifier is the difference between these two, namely (Vc + Vd) - (Vc - Vd) = 2Vd., The differential mode gain implies the amplification produced due to the difference of signals on the terminals. An ideal Op Amp has an infinite differential gain. The common mode gain implies the amplification produced due to the signal common to both terminals. An ideal Op Amp has zero common mode gain. In Figure 1, V1 and V2 can …, The differential input signal is 10 mV peak at 1 kHz. The low-frequency common-mode noise is 10 times greater in amplitude. Figure 5 provides the input and output waveforms as monitored by the oscilloscope. The amplifier provides a voltage gain of 10, meaning the output will be 100 mV peak or 200 mV peak-to-peak. Figure 5., The ratio of output power to input power is interpreted differently depending on the context. The ratio is referred to as gain when referring to amplifiers, and when referring to machines, it is known as efficiency., Feb 3, 2021 · The common-mode gain is defined by the matching of the two stages and the “stiffness” of the resistor or current source at the emitter of the two transistors. Achieving really good common-mode rejection usually requires the resistor be replaced by an active current source of some kind. References: “Alan Blumlein.” , Let Vc be a common mode signal. This signal will be applied to both inputs. Let Vd and -Vd be differential signals applied to the inputs. To one input we apply Vc + Vd and to the other we apply Vc + (-Vd) The differential signal seen by the amplifier is the difference between these two, namely (Vc + Vd) - (Vc - Vd) = 2Vd., Common mode gain — A perfect operational amplifier amplifies only the voltage difference between its two inputs, completely rejecting all voltages that are common to both. …, The ideal common-mode gain of an instrumentation amplifier is zero. In the circuit shown, common-mode gain is caused by mismatch in the resistor ratios / and by the mismatch in common-mode gains of the two input op-amps. Obtaining very closely matched resistors is a significant difficulty in fabricating these circuits, as is optimizing the ..., 1-4 Figure 1-3b shows a 3-op amp in-amp operating under the same conditions. note that, just like the op amp circuit, the input buffer amplifiers of the in-amp pass the common-mode signal through at unity gain. In contrast, the signal is amplified by both buffers., An ideal differential amplifier has zero common-mode gain (i.e., Acm =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. We refer to this characteristic as common-mode suppression. , Jun 17, 2020 · I'm going to write up a simplified starting point for just the first part of the question (the slightly easier part.) You are supposed to be able to perform the addition indicated in 18-5 and find this simplified form: , Common mode analysis: In common mode Vs1 = Vs2 = Vs/2 V s 1 = V s 2 = V s / 2. Vd = Vs1 − Vs2 = 0 V d = V s 1 − V s 2 = 0. VC = Vs1+Vs2 2 = Vs 2 V C = V s 1 + V s 2 2 = V s 2. Due to Vs1 ac emitter current, Ie1 passes through emitter terminal of T1 and Ie2 due to Vs2. But Ie1 and Ie2 both are same in amplitude and same in phase., Ideally, the differential amplifier should affect the difference-mode signal only. However, the common-mode signal is also amplified to some extent. The common-mode rejection ratio (CMRR) is defined as the ratio of the difference signal voltage gain to the common-mode signal voltage gain., A common-mode feedback loop must be used: Circuit must operate on the common-mode signals only! BASIC IDEA: CMFB is a circuit with very small impedance for the commonmode signals - but transparent for the differential signals. Use a common-mode detector (eliminates the effect of differential signals and detect common-mode signals), Apr 2, 2014 · Fundamentally, the term common mode implies that the signal at the two input terminals of a differential amplifier is identical in both magnitude and phase. When signals V1 and V2 are applied as input we can spilt them into a combination of common mode and differential mode signals in the following manner. V1 = (V1 + V2)/2 + (V1 - V2)/2 , What is common mode gain and differential gain in an amplifier and why are these important? What is the common mode rejection ratio?Aaron Danner is a profes..., is differential and the output common-mode voltage can be controlled independently of the differential voltage. The purpose of the Vocm input in the fully-differential amplifier is to set the output common-mode voltage. In a standard operational amplifier with single-ended output, the output common-mode voltage and the signal are the same thing., Differential amplifiers are one of the most common building blocks in analog circuit design. The front end of every op amp, for example, consists of a differential amplifier. Differential amplifiers are used whenever a desired signal is the difference between two signals, particularly when this difference is masked by common mode noise., Common mode gain — A perfect operational amplifier amplifies only the voltage difference between its two inputs, completely rejecting all voltages that are common to both. …, Indraprastha Institute of Information Technology Delhi ECE315/515 Common Mode Rejection Ratio (CMRR) (contd.) •What is the CMRR of an ideal differential input amplifier (e.g. op-amp)? •Recall that the ideal common-mode gain of a differential input amplifier is ZERO • Also recall that the differential gain of an ideal op-amp is some high value. …, ٢٩ شعبان ١٤٤٠ هـ ... Common-Mode Gain ... ) will yield zero. In practical circuits the differential output will always show some minute voltages due the transistors ..., ٣ صفر ١٤٣٩ هـ ... The ability of the amplifier to have a low common-mode gain, i.e., not amplify ... Differential Ampli ers. Common-Mode Rejection (Noise Rejection)., Problem 5.2 - Increased Gain Common Source JFET Amplifier-Large Drain Resistor. The gain of the circuit in 5.1 is not high. A naïve application of the gain formula [Eq. (1)] would imply that the gain should increase substantially if the drain resistor is changed to 18kΩ, as shown at right. Build this circuit., The Common mode gain of differential amplifier formula is defined as the amplification given to signals that appear on both inputs relative to the common (typically ground). This means the output is unaffected by voltages that are common to both inputs is calculated using Common Mode Gain = -( Load Resistance /(2* Internal Small Signal ..., The same can be said about the differential mode voltage V d, common-mode voltage V c and the common mode gain A c of the circuit. The V id is the differential voltage of the op-amp which can still be related to output voltage of the op-amp (same as th output voltage of the circuit) using the open loop gain of the op-amp.