Math Problem Statement

A differential amplifier has a typical common mode gain of 40dB and CMRR of 80dB. Find the output voltage Vo when the input voltages are 0.20mV and 0.25mV.

Solution

To find the output voltage VoV_o of a differential amplifier given the input voltages V1V_1 and V2V_2, the common-mode gain AcmA_{cm}, and the common-mode rejection ratio (CMRR), we can use the following steps:

  1. Convert dB values to linear scale:

    • Common-mode gain (AcmA_{cm}): Acm=104020=102=100A_{cm} = 10^{\frac{40}{20}} = 10^2 = 100
    • Common-mode rejection ratio (CMRR): CMRR=108020=104=10000\text{CMRR} = 10^{\frac{80}{20}} = 10^4 = 10000
  2. Calculate the differential gain AdA_d:

    • Differential gain (AdA_d) can be derived from the relationship: CMRR=AdAcm\text{CMRR} = \frac{A_d}{A_{cm}} Therefore: Ad=CMRR×Acm=10000×100=1000000A_d = \text{CMRR} \times A_{cm} = 10000 \times 100 = 1000000
  3. Calculate the common-mode voltage VcmV_{cm}: Vcm=V1+V22=0.20 mV+0.25 mV2=0.225 mVV_{cm} = \frac{V_1 + V_2}{2} = \frac{0.20\text{ mV} + 0.25\text{ mV}}{2} = 0.225\text{ mV}

  4. Calculate the differential input voltage VdV_d: Vd=V2V1=0.25 mV0.20 mV=0.05 mVV_d = V_2 - V_1 = 0.25\text{ mV} - 0.20\text{ mV} = 0.05\text{ mV}

  5. Calculate the output voltage VoV_o: The output voltage is the sum of the differential output and the common-mode output: Vo=Ad×Vd+Acm×VcmV_o = A_d \times V_d + A_{cm} \times V_{cm}

    Substituting the values: Vo=(1000000×0.05×103)+(100×0.225×103)V_o = (1000000 \times 0.05 \times 10^{-3}) + (100 \times 0.225 \times 10^{-3}) Vo=(1000000×0.00005)+(100×0.000225)V_o = (1000000 \times 0.00005) + (100 \times 0.000225) Vo=50+0.0225V_o = 50 + 0.0225 Vo=50.0225 mVV_o = 50.0225 \text{ mV}

Thus, the output voltage VoV_o is approximately 50.0225 mV50.0225 \text{ mV}.

Do you want further details or have any questions?

Here are 8 relative questions that expand on the above information:

  1. What is the significance of common-mode rejection ratio (CMRR) in differential amplifiers?
  2. How do you derive the differential gain from the given CMRR and common-mode gain?
  3. What are typical applications of differential amplifiers?
  4. How does the common-mode gain affect the performance of a differential amplifier?
  5. Can you explain how input voltages influence the output of a differential amplifier?
  6. What factors can affect the accuracy of a differential amplifier's output?
  7. How does noise influence the performance of a differential amplifier?
  8. What are the differences between a single-ended amplifier and a differential amplifier?

Tip: When dealing with dB (decibel) values, always remember to convert them to linear scale for accurate calculations in practical scenarios.

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Math Problem Analysis

Mathematical Concepts

Differential Amplifiers
Common-mode Gain
Common-mode Rejection Ratio (CMRR)
Differential Gain

Formulas

CMRR = 10^(CMRR dB / 20)
Differential gain = CMRR × Common-mode gain

Theorems

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Suitable Grade Level

Advanced