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AD8376 or AD83875 output bias current

Question asked by intec on Mar 22, 2017
Latest reply on Mar 23, 2017 by RReeder

Hello together,

 

at the moment we are busy designing a broad band receiver whith the follwowing input specifications:

fin: 4kHz - 35MHz with variable amplitude.

 

To adjust the receveier to the incomming signal we have decided to cascade ther stages of AD8376 to get a higher dynamic range before sampling data with a high speed ADC.

Please find the complete application attached as PDF.

 

Because of the fact that we want to use low frequency input signals as well as in put frequencies > 10MHz we have decide to use the resistor option to set collector current properly.

In our case we have a power supply of +13V avaibale so we calculated the proper load and pull up resistors using the equations given on page 15 of the datasheet.

For our application we caluclated: 200R as pullup resistor to match 13V power supply. But that means that without having a signal at the input a power consumptiont of 4x((13V-5V)^2/200R) = 1,28W !!!

We have double checked this but it is correct when appying the given equitions. Bus still we cannot believe that the result is correct.

That means resistors get really hot and our battery powered devices is empty within a short time. And power supply may go down if an input siganl ist at the input terminal of the Opamp.

 

What can we do to come along with low frequency signals without having so much of power consumption? Is there any chance to get rid of this high current?

 

We cannot imagine that this high current is acceptable for other applications as well?

 

So what do you suggest or is ther no chance to solve this problem?

 

Thanks in advance

 

Christian

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