Method and apparatus for calibrating a sampling circuit

An apparatus for calibrating a first sampling circuit with a second sampling circuit, each sampling circuit having a signal input for receiving a signal to be sampled and a trigger input for receiving a trigger pulse that opens a switching circuit in that sampling circuit, said second sampling circuit including a sample and hold circuit that provides an output indicative of the potential at said sampling circuit input of said second sampling circuit at a time determined by a signal at said trigger pulse input of said second sampling circuit, said signal inputs of said first and second sampling circuits being connected by a signal conductor, said first sampling circuit generating a pulse indicative of the impulse response of said first sampling circuit on said signal input of said first sampling circuit, said apparatus comprising:

• a trigger pulse generating circuit that generates a sequence of trigger pulse pairs, each trigger pulse pair comprising a first pulse that is delayed relative to a second pulse;
• a connecting circuit that applies said first pulse to said trigger input of said first sampling circuit and for applying said second pulse to said trigger input of said second sampling circuit;
• and
• a controller that sets said delay between said first and second pulses and for measuring said output of said sample and hold circuit in said second sampling circuit.