a question on the power detector circuit

[John Xu]

Dear all,
We want to use MAX3645 for our applications. When I reading the datasheet of the MAX3645. I have one question on the power detector.

Pls. refer page 7, the power detector and LOS indicator part.It calim that that "Power detection is accomplished by rectifying and lowpass filtering the data signal, then comparing it to the programmed threshold voltage." As my understanding, the power is defined as the average value of the squared input signal. So just rectified input signal and low pass filter it(it functions as average as my understanding) can gives the value of the power of input signal? Is ther any misunderstanding for me?

Can anyone give me some explainations?

Thanks
Regards
John

 

[flatulent]

You are correct.

This data sheet uses the word "power" very loosely. Its function is only to detect the presence of a signal above a certain voltage level. You use an external resistor to set the level you want.

 

[wylee]

LOS in MAXIM's LA is actually just voltage level comparator after rectifying the input voltage swing.

It compares the rectified input voltage with a pre-programmed voltage (using Rth at TH pin), if the input voltage swing is not large enough resulting th retified voltage is below the preset threshold voltage, the comparator will trigger LOS pin to HIGH (means signal lost

Attached is a simplified block diagram of how LOS works