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AD8351 - Gain Calculation for ADC Driving Application

I would like to use the AD8351 as a variable gain amplifier for a differential signal to an ADC with a differential input. The data sheet gives an equation for the voltage gain, Av, based on Rg and Rl. However, the example circuits for driving an ADC do not show Rl anywhere in the circuit (where there is Rl shown in Figure 34, but not in Figure 40). Is there a different equation that I should use to calculate the voltage gain when driving an ADC? Or is there a value that I should use for Rl when driving an ADC like Figure 40 in the datasheet?

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  • Hello,

    to my knowledge RL is the load which the AD8351 has to drive. Description for figure 40 states a 1kOhm input impedance of the AD6645. The gain diagrams (over frequency and over RG)  have this value as additional parameter, hence you should have all necessary values at hand, shouldn't you?

    Please check the ADC datasheet for the specified differential input impedance.

    kind regards

    Markus

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  • Hello,

    to my knowledge RL is the load which the AD8351 has to drive. Description for figure 40 states a 1kOhm input impedance of the AD6645. The gain diagrams (over frequency and over RG)  have this value as additional parameter, hence you should have all necessary values at hand, shouldn't you?

    Please check the ADC datasheet for the specified differential input impedance.

    kind regards

    Markus

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