The ADL5502 RF detector has some interesting functionality. It has two independent measurement blocks. The first block is a linear in volts-per-volt RMS responding detector with a measurement range of 35dB. The second block can detect the envelope or the peak of a signal. On the left hand side of the plot, it can be seen how the blue trace follows the envelope of the input signal with the device operating in envelope tracking mode. Taking the CNTL input pin low puts this detector into peak hold mode. This causes the output to hold the most recent peak of the input signal.