Hi,

I want to change the Pintercept of AD8319. From the datasheet it says that I can use the formula

PINTERCEPT(dBm) = PINTERCEPT(dBV) − 10 × log10(Z0 × 1 mW/1 Vrms2 ) to get the new intercept.

Does it mean that I can just substitute my new Zo and get the new intercept from the formula? I wondering where the PINTERCEPT(dBV) =2 dBV comes from. Is this still 2dBV when my Zo is not 50 ohms?

Thanks heaps!

Since these parts are voltage responding and inherently high-input impedance, we at a 52.3 Ohm matching resistor across the inputs, so that the voltage delivered to the input (from the source) is into a 50 Ohm load. This allows us to specify the input power in dBm. Changing Zo does not really adjust the intercept; that is just a voltage to power relation. It will only change the intercept if your source voltage is dependent upon the load impedance it drives. If you have a source that supplies the same voltage whether it is delivering into 50 Ohm or 100 Ohms, the the intercept will not change.

If you would like to change the intercept, referencing Figure 28 in the datasheet, instead of grounding the bottom 10k Ohm resistor, you would apply a voltage, which would create a static offset in the loop of the output circuitry, and thus shift the intercept of the part's transfer function.