AnsweredAssumed Answered

AD8318 input ac coupling cap placement

Question asked by zach.horn on Apr 28, 2015
Latest reply on Apr 29, 2015 by jdobler

The AD8318 log detector datasheet shows two input ac coupling capacitor arrangements. Please refer to the two attached pictures from that datasheet.


Figure 47 shows the ac coupling capacitors on the far side of the input matching resistor; the input matching resistor is connected directly from INHI to INLO. Figure 48 shows the ac coupling capacitors right at the AD8318 input pins; the input matching resistor is not connected directly to INHI and INLO.


We have found that using the arrangement in Figure 47 results in some loss of dynamic range on the low end (due perhaps to noise from the resistor?). Is this expected behavior and are both ac coupling cap arrangements valid? Note that other similar log detector datasheets only show the arrangement in Figure 48.