Design For A Low Phase Noise Overtone TCXO

This paper relates to a novel 121.4 MHz overtone TCXO with low phase noise. It differs from conventional approaches, and adding series inductances and frequency multiplication are not applied in it. It makes the frequency of a 100 MHz 5th overtone crystal oscillator mixed with that of a 21.4 MHz fundamental mode voltage controlled crystal oscillator(VCXO). The product is filtered and amplified to produce a 121.4 MHz signal. In this design, the microprocessor AT89S52 is used to control frequency of 21.4 MHz VCXO to implement the compensation. Experimental results are presented in this paper. The frequency-temperature stability of the prototype 121.4 MHz TCXO has achieved plusmn3times10^-7 within the temperature range from -40 to 85degC. A phase noise level of -140 dBc/Hz at 1 kHz offset has been realized. The approach presented in this paper can provide a high stability and low phase noise level requirement of overtone TCXO. In fact, it is also available for a higher frequency.