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ADA4930-1YCPZ-R2 数据表(PDF) 20 Page - Analog Devices |
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ADA4930-1YCPZ-R2 数据表(HTML) 20 Page - Analog Devices |
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20 / 25 page  ADA4930-1/ADA4930-2 Data Sheet Rev. D | Page 20 of 25 RS 50Ω VS 2V p-p RIN 401.333Ω ADA4930 RL VOUT, dm +VS –VS RG1 301Ω RG2 301Ω RF2 301Ω RF1 301Ω VOCM Figure 46. Single-Ended Input Impedance RIN 2. Add a termination resistor, RT. To match the 50 Ω source resistance, RT is added. Because RT||401.33 Ω = 50 Ω, RT = 57.116 Ω. ADA4930 RL VOUT, dm +VS –VS RS 50Ω RG1 301Ω RG2 301Ω RF2 301Ω RF1 301Ω VOCM VS 2V p-p RIN 50Ω RT 57.116 Ω Figure 47. Adding Termination Resistor RT 3. Replace the source-termination resistorcombination with its Thevenin equivalent. The Thevenin equivalent of the source resistanceRS and the termination resistance RT is RTH = RS||RT = 26.66 Ω. The Thevenin equivalent of the source voltage is VTH = VS T S T R R R + = 1.066 V p-p RS 50Ω VS 2V p-p RT 57.116 Ω RTH 26.661Ω VTH 1.066V p-p Figure 48. Thevenin Equivalent Circuit 4. Set RF1 = RF2 = RF to maintain a balanced system. Compensatethe imbalance causedby RTH. There are two methods available to compensate, which follow: • Add RTH to RG2 to maintain balanced gain resistances and increaseRF1and RF2toRF = TH S V V Gain(R G + RTH)to maintain the system gain. • Decrease RG2to RG2 = Gain V V R S TH F × × to maintain system gain and decrease RG1to (RG2 − RTH) to maintain balanced gain resistances. The first compensation methodis usedin the AnalogDevices DiffAmpCalc™tool.Using thesecondcompensation method, RG2= 160.498 Ω and RG1= 160.498 −26.66 = 133.837 Ω.The modified circuit is shown in Figure 49. ADA4930 RL VOUT, dm +VS –VS RTH 26.661Ω RG1 133.837Ω RG2 160.498Ω RF2 301Ω RF1 301Ω VOCM VTH 1.066V p-p Figure 49. Thevenin Equivalent with Matched Gain Resistors Figure 49 presentsan easily manageable circuit withmatched feedbackloops that can be easily evaluated. 5. The modifiedgain resistor, RG1, changes the input impedance. Repeat Step1 through Step 4 several times usingthemodified value of RG1 from the previousiteration until the value of RT does not change from the previous iteration. After three additional iterations, the changein RG1 is less than 0.1%. The final circuit is shown in Figure 50 with the closest 0.5% resistor values. ADA4930 RL VOUT, dm 1.990V p-p +VS –VS RS 50Ω RG 142Ω VP VN RG2 169Ω RF1 301Ω RF2 301Ω VOCM VS 2V p-p 0.998V p-p RT 64.2 Ω Figure 50. Terminated Single-Ended-to-Differential System with G = 1 |
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