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温度偿补晶体振荡器(TCXO)需要定期调整以修正老化漂移。对于内部补偿的振荡器,它是一种在工作温度范围内通过变容管调谐的振荡器,其老化调整是借助于改变振荡环路中电抗元件完成的。但是在老化调整后,继而使原有的频率对变容二极管偏压变化的灵敏度发生改变,因此,变容二极管相当于总负载电抗的差别部分。这种经过老化调整而改变的灵敏度干扰了原来的频率——温度特性,并且引起某一调谐偏离误差。为了充分发挥数字谐偏离误并满足某些新军用规程如SINGARS制定的调谐偏离误差规范要求,需要有一种方法来减小TCXO的调补偿的优点差。实现老化调整的另一种方法,是改变变容二极管的直流偏压。假如振荡器的频率与电压曲线完全是线性的,则电路对变容二极管偏压的灵敏度(PPm′v)就能保持恒定,在频率——温度特性曲线中不会引入附加的误差。对于串联与并联谐振两种振荡器的电压线性度要求,是与使用一个并联谐振晶体的TCXO的误差分析一道讨论的。本文给出了电容和变容二极管调谐的两种振荡器的比较数据。比较数据及误差分析两者表明:变容二极管调谐对于减小TCXO中调谐偏离误差是一种可行的技术。
Temperature Compensated Crystal Oscillators (TCXOs) require periodic adjustments to correct for aging drift. For internally compensated oscillators, it is an oscillator tunable through varactor over the operating temperature range and its aging adjustment is done by changing the reactance element in the oscillating loop. However, after aging adjustment, the sensitivity of the original frequency to the change of the bias voltage of the varactor diode is changed accordingly. Therefore, the varactor diode corresponds to the difference of the total load reactance. This change in sensitivity after aging adjustment interferes with the original frequency-temperature characteristics and causes some tuning deviation error. To take full advantage of the numerical harmonic misalignment and to meet some of the new military disciplines such as the tuning deviation error specification set forth by SINGARS, there is a need for a method to reduce the benefits of TCXO mismatch. Another way to adjust for aging is to change the DC bias of the varactor. If the oscillator’s frequency and voltage curve are completely linear, the sensitivity of the circuit to the varactor biasing voltage (PPm’v) can be kept constant without introducing any additional error in the frequency-temperature characteristic. The voltage linearity requirements for both series and parallel resonant oscillators are discussed in conjunction with the error analysis of a TCXO using a parallel resonant crystal. This article gives a comparison of capacitance and varactor tuning of two oscillators. Both the comparative data and the error analysis show that varactor tuning is a viable technique to reduce the tuning deviation error in the TCXO.