Development of offset frequency generator based on programmable modulus DDS

Abstract

A novel offset frequency generator is designed and implemented in this paper, which is usually an essential component in a Dual Mixer Time Difference (DMTD) measurement system. The key element of the offset frequency generator is a Direct Digital Synthesizer (DDS) with programmable modulus, which is a modification of the typical accumulator-based DDS architecture and a guarantee of exactly frequency synthesizing. Microcontroller, reconstruction filter and driver amplifier are then implemented to generate the exact output offset frequency. If a Crystal Oscillator MV200 is used as a fixed frequency reference the generator, the relative error of its output frequency is less than 2.0×10−12. And the concise and reasonable circuit designs contribute to the offset frequency generator short term fractional frequency stability at a level of 3.32×10−12 at 1s averaging time. The circuit design and performance of the offset frequency generator proposed in this paper may be taken as technical references for the planning and designing of a low cost, miniaturization, and high accuracy DMTD system.