Ultrafast sampler with coaxial transition
An ultrafast sampler includes a series of Schottky diodes configured with a coplanar waveguide to form a nonlinear transmission line (NLTL) that compresses a local oscillator input to form a series of strobe pulses. Strobe pulses of opposite polarity are capacitively coupled to sampling diodes to obtain samples of a signal applied to a signal input. The samples are directed along an intermediate frequency waveguide to, for example, a signal processor such as an oscilloscope, for storage and analysis. The intermediate frequency waveguide is configured so that conductors of the intermediate frequency waveguide receive signal samples of a common polarity and strobe samples of opposite polarities so that portions of strobe pulses delivered to a signal processor are distinguished from signal samples. In an embodiment, the intermediate frequency waveguide and the strobe waveguide are symmetrically situated along a common axis, and conductors of the strobe waveguide are positioned between the axis and the conductors of the intermediate frequency waveguide. The sampling circuit is defined on a GaAs substrate and a coaxial-to-airline-to-substrate transition is configured to deliver signals from a coaxial cable to the sampling circuit. A signal output is configured to direct the signal back into a coaxial cable.
1. A transition for delivering an electrical signal propagating on a coaxial cable to a substrate, comprising:
a coaxial input configured to receive a coaxial input waveguide;
an airline defined by an airline conductor and an airline cavity;
an interconnect conductor situated in the airline cavity and configured to electrically couple a substrate to the airline conductor; and
a coaxial output configured to receive a coaxial output waveguide, wherein the airline conductor extends from the coaxial input to the coaxial output, and the airline is configured to have an impedance that substantially matches an impedance of at least one of the coaxial input waveguide and the coaxial output waveguide.
2. The transition of claim 1 , wherein the impedance of the airline is about 50 Ohms.
3. The transition of claim 1 , wherein the impedance of the airline is substantially defined by dimensions of the airline cavity and the airline conductor.
4. The transition of claim 1 , wherein the cavity is cylindrical.
5. The transition of claim 1 , wherein the interconnect includes a conductive puck.
6. The transition of claim 1 , wherein the substrate is retained by the housing.