A high frequency phase reference

Abstract

Magnetic Induction Tomography (MIT) requires signal measurements with a very high degree of phase precision. To enable the development and characterisation of input amplifiers, signal distribution and signal measurement system for MIT, a high precision phase reference capable of operating over the frequency range DC - 50 MHz is being developed. The phase reference consists of two Direct Digital Synthesizers (DDS) which are supplied with a common clock and control bus. The synthesizers are programmable, allowing 14-bit resolution (20 m°) of the phase offset between the channels and 12-bit control of the output amplitude (8Vpp max). The phase reference is controlled by a PC via a USB interface. Details of the design of the phase reference and the results of measurements of the phase noise, phase drift and phase skew performance of the system is given.