Digital temperature compensation method of crystal oscillator

Abstract

The invention discloses a digital temperature compensation method of a crystal oscillator, wherein a closed-loop feedback compensation framework is adopted. According to the method, a binary coding B0i corresponding to a target frequency f0 is determined and stored in a microprocessor. When the temperature changes, the microprocessor conducts real-time measurement on the output frequency of a VCXO to generate a binary code B1i. Meanwhile, the microprocessor compares with the above binary code B1i with a binary code corresponding to the target frequency to obtain a binary code of the needed compensation information. Finally, the binary code of the needed compensation information is converted into a compensation voltage through a digital-to-analog converter to be input to a voltage-controlled adjusting end of the VCXO. Therefore, the target frequency is output, and the temperature compensation is achieved. Compared with a digital temperature compensation method of an existing crystal oscillator, the above digital temperature compensation method does not need any temperature sensor. Meanwhile, the frequency deviation related to the temperature in real time is directly converted into a binary code which is in one-to-one correspondence with the temperature. Moreover, the binary code is converted into a corresponding compensation voltage for temperature compensation. Therefore, the temperature hysteresis problem caused by the fact that the temperature change of a temperature sensor and the temperature change of a crystal resonator are not synchronous in an existing temperature compensation crystal oscillator (TCX0) is overcome.

Description

technical field [0001] The invention belongs to the technical field of crystal oscillators, and more specifically, relates to a crystal oscillator. Background technique [0002] Temperature Compensated Crystal Oscillator (TCXO, Temperature Compensate Xtal (crystal) Oscillator) is a kind of crystal oscillator that can work in a wide temperature range and maintain the output frequency of the crystal oscillator within a certain accuracy range (10 -6 ~10 -7 order of magnitude) crystal oscillator. It has the characteristics of low power, can work immediately after starting up, and has high stability. It is widely used in various communications, navigation, radar, satellite positioning systems, mobile communications, program-controlled telephone exchanges, and various electronic measuring instruments. [0003] The existing temperature-compensated crystal oscillator is essentially a voltage-controlled crystal oscillator (Voltage Controlled Xtal (crystal) Oscillator, VCXO) with a ...

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Problems solved by technology

This method has advantages in phase noise characteristics when realizing high-frequency temperature-compensated crystal oscillators (TCXO), but the composition is relatively complicated and has not been widely used yet.

[0016] In summary, the existing temperature compensation methods for crystal oscillators all adopt an open-loop compensation framework, and a temperature sensor is used. The temperature sensor is as close as possible to the crystal resonator on the circuit, and the resonator chip of the crystal resonator It is packaged separately in a closed space, which inevitably produces a temperature hysteresis between the temperature sensor and the resonant chip, resulting in a failure to achieve a breakthrough in the frequency-temperature characteristics of the temperature-compensated crystal oscillator, that is, the TCXO.

Especially for crystal oscillators whose output signals are high frequency, this temperature hysteresis problem is more serious, and the compensation accuracy is limited

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