Arcetri Observatory, together with MECSA, have developed a sample/hold curcuit and a demultiplexer for the ALMA sampler unit. ... The S/H circuit requires a 4 GHz sinusoidal clock (0 dBm nominal), and has an internal clipping circuit to protect the input from signal spikes. ... A custom chip has therefore to be designed. ... The chip requires two sinusoidal clocks, at 4 and 0.5 GHz. ... G. Collodi, G. Comoretto: A MMIC sampler for ALMA - Design report - Arcetri technical report n. 2/2001 . ...