impedance matching for a log amplifier input 2

[mageta]

i am using the ad8302 phase/amplitude comparator with its inputs fed by a band-pass filter output. the reference circuit in the ad8302 datasheet shows a 52.3 ohm shunt to match a 50 ohm system (antenna connection). can the ideal 0 impedance output of the active band-pass filter output allow me to use a 1k ohm shunt in order to reduce power consumption without messing up the impedance requirements of the ad8302?

the ad8302 input equivalent circuit is:
frequency at or below 500 mhz = 3k||2pf

the frequency i am using is well below this, 400 khz to 2 mhz.

thanks ahead!

 

[Comcokid]

There is a rule-of-thumb of >1/20 of a wavelength as to how long a connection between circuits is before you need to use transmission line connections and impedance matching. For 2 MHz, this comes to around 7 meters. I would assume that your circuits will be located more like a few cm apart.

For what you've indicated you should connect the output of your active filter to the input of the log amp with a 3K Ohm resistor. Since it is an active filter, the typical output impedance will of an op-amp will be only a few ohms. A 3K Ohm series resistor will make the log amp happy, and the active filter will see a 6K ohm load.