How do I terminate my signal source into an ADC driver?

How do I terminate my signal source into an ADC driver? I'm using a single ended source to generate a differential output signal used to drive an ADC.

  • Good question, to terminate a single ended source, you first need to know what the input impedance is of the differential amplifier is. This impedance in parallel with the termination resistor will provide the proper system termination. The input impedance of a differential amplifier is not very high as is the case with a traditional op amp. It is largely determined by the input resistor RG. There is an equation (EQ1) that you can use as shown below

    Rin= RG/1-RF/2*(RG+RF) EQ1

    to calcualte the input impedance for a single ended input application. RF is the feedback resistor. Analog Devices has a very good applicagtion note     AN-1026 that goes over this and many other facts about how to use differential amplifiers.

    There's an even better way to calculate the termination resistor, that is to use our Differential Amplifier Calculator, we call it DiffAmpCalc and let it do the work for you. Its free and downloadable and you can find it at www.analog.com/diffampcalc. Its a very versitile tool and will performance all the differential amplifier calcualtions that you need for you. Noise, SNR, gain, power dissipation and much more, check it out and let me know what you think.

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