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OPA860: Calculation Gain of OPA860 as a Forward Amplifier (Fig.48 in datasheet)

Prodigy 90 points

Replies: 4

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Part Number: OPA860

Hi all 

I am going to use OPA860 as a Forward amplifier (Common E configuration). However, I am not clear about its calculation (in Figure 48 in data sheet). In fact, I am using Oscilloscope for obtaining the Vo waveform, and Oscilloscope have 50Ohm input as indicated in bellow figure. 

So, the RL = RC//RIN = 500//50 = 45.45 Ohm 

So, gm = 1/(102*10^-3) = 9.8Ohm 

Consequently, Gain = 45.45/(9.8+78) = 0.52. 

But in the above figure, Gain = 5. I am really not clear about how it can be 5. 

Could anyone please give me an explanation for this difference ? 

Thank you.