I am planning to use HMC661 and a high speed ADC to capture a ultra narrow pulse (BW>10GHz). I notice that in a document for a similar device (http://www.analog.com/media/en/technical-documentation/technical-articles/track-n-hold_0411.pdf ), a variable delay line is suggested to set phase between the clock to the track-and-hold amplifier and the ADC so the ADC samples the hold-mode portion of the signal. Can anyone suggest a suitable variable delay line? The sampling rate we plan to use is 2GSPS or 2.5GSPS. Your help is appreciated, thanks!