impedance matching for a log amplifier input
impedance matching for a log amplifier input
(OP)
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!
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!





RE: impedance matching for a log amplifier input
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.