A Design Of Programmable Oscillator

The crystal oscillator, which generally works at fixed frequency, is famous for its high stability. And different kinds of crystal oscillators fulfill the different engineering. The major characteristic of the programmable crystal oscillator is to set a series frequencies of high stability at short notice. Then several hundred kinds of fixed crystal oscillators in stock are substituted by a multi-purpose programmable crystal oscillator. It is flexible for designers, factories and companies, moreover it's convenience for integration will bring the latent frugal effects.Based on the phase-locked loop and the crystal oscillator as the source, a programmable oscillator is designed. Although it brings certain negative influence on the high stability of the crystal oscillator in this way, it is enough for general industry requirement. Moreover, it is advantageous for the frequency control.First, the basic principle of frequency synthetic technology is introduced in detailed in this paper. Second, the discussion and improvement of the design of the Voltage Controlled Oscillator (VCO), which is simulated by ADS, is presented; and another component loop passed filter (LPF), which is the core of PLL, is designed. Finally, a total solution and the coding are given at the end of this paper. There are has many merits in the design, such as wide rang frequencies, high resolution ratio, high stability, programming. And, as its strong practicability and economy, it is easy to make it popular.We use the phase locked loop chip LMX2306 in this design. In its peripheral circuits, we calculated the components of LPF directly, and choosed the better VCO after comparing the performances between Seiler common collector VCO and MAX2606. At last, the programmable date which is used to set dividing frequency sequence is loaded by codeloader. The output of this device is between 70MHz and 150MHz according to the VCO's inductor, and the minimum step can achieves 5kHz, the power is -10dBm.