格林雷TCXO的工作原理

Understanding TCXO Compensation

All uncompensated quartz crystal oscillators will experience drift according to the characteristics of their quartz crystal. The amount of drift in the frequency reference is usually in the range of ±10 to ±50ppm, depending upon individual crystal characteristics. Temperature compensated crystal oscillators, or "TCXOs", are often selected for applications that require a more stable frequency reference and usually offer a resolution better than a standard, uncompensated quartz crystal oscillator.

TCXOs are compensated over the customer's required temperature range to a specific frequency stability needed for the particular application. TCXOs can, for example, be compensated to <1ppm over the industrial operating temperature range of -40°C to +85°C.

Temperature Compensated Crystal Oscillators - Methods

Various compensation methods have been used over the years, including:

Thermistor/Resistor Network Compensation - Thermistor/resistor compensation utilizes a correction voltage generated by a network of one or more thermistors to cancel the frequency vs. temperature variation. As early as 1961, compensation ratios of greater than 100-to-1 were being achieved, i.e., a crystal with a peak-to-peak deviation of 50ppm over temperature could be compensated to a level of 0.5ppm. Thermistor/resistor compensated TCXOs have been a mainstay in the industry for over 50 years.

Digital Temperature Compensation - By the late 1970s, advances in IC technology made it practical to devise compensation systems using analog-to-digital conversions and solid-state memory. Although crude by today's standards, digital TCXOs achieving better than 0.1ppm performance were produced by several manufacturers, including Rockwell Collins and Greenray Industries.

Over the years, other digital compensation implementations have been developed, many with embedded computing power as a means of facilitating calibration and system operation. Others utilized elaborate temperature measurement schemes, such as dual-mode crystal, self temp-sensing, to achieve temperature stabilities of 0.05ppm or better.

Analog Integration - The expanding capabilities of large-scale integration made it possible to include more of the functions required for temperature compensation into a single IC. This has led to development of the current generation of ASICs that allow construction of precision analog TCXOs with just two components - the ASIC and the quartz crystal. These ICs use analog multipliers to generate a smooth curve which fits a 5th order polynomial to the crystal to be compensated. Stabilities of better than ±0.2ppm can be achieved over temp ranges as wide as -40°C to +85°C.

Although first-generation fabrications often resulted in relatively large die, reductions in geometries and smaller ICs now enable precision TCXOs to be housed in packages as small as 2mm x 2.5mm.

While Greenray Industries manufactures temperature compensated crystal oscillators using each of these compensation methods, analog ASIC-type TCXOs outnumber all the other types, combined.

了解TCXO补偿

所有未补偿的石英晶体振荡器都会经历根据其石英晶体的特性进行漂移。频率基准的漂移量通常在10至50ppm范围内，具体取决于各晶体的特性。温度补偿石英晶体振荡器、或“TCXOs”通常用于需要更稳定频率基准的应用，其分辨率通常优于标准的无补偿石英晶体振荡器。

TCXOs在客户要求的温度范围内得到补偿，达到特定应用所需的特定频率稳定性。例如，在-40°C至+85°C的工业工作温度范围内，TCXOs可以补偿至小于1ppm贴片晶振。

温度补偿晶体振荡器.方法

多年来使用了各种补偿方法，包括：

热敏电阻/电阻网络补偿-热敏电阻/电阻补偿利用一个或多个热敏电阻网络产生的校正电压来抵消频率和温度的变化。早在1961年，就已经实现了大于100:1的补偿比，即在整个温度范围内峰峰值偏差为50ppm的晶体可以被补偿到0.5ppm的水平。50多年来，热敏电阻/电阻补偿型TCXO石英晶振一直是业界的主流。

数字温度补偿-到20世纪70年代末，IC技术的进步使得利用模数转换和固态存储器设计补偿系统变得切实可行。虽然以今天的标准来看，数字TCXOs还很粗糙，但性能优于0.1ppm的数字TCXOs已由多家制造商生产，包括Rockwell Collins和Greenray Industries。

多年来，已经开发出了其它数字补偿方案，其中许多具有嵌入式计算能力，作为一种促进校准和系统操作的手段。其他的利用复杂的温度测量方案，例如双模式晶体、自温度感应，以实现0.05ppm或更好的温度稳定性。

模拟积分大规模集成电路不断扩展的功能使得在单个IC中集成更多温度补偿所需的功能成为可能。这导致了当前一代ASIC的发展，允许仅用两个元件ASIC和石英晶体——来构建精密模拟TCXOs石英晶体振荡器。这些IC使用模拟乘法器来产生符合5的平滑曲线泰国(Thailand)要补偿的晶体的阶多项式。在-40°C至+85°C的宽温度范围内，稳定性优于0.2ppm。

尽管第一代制造工艺通常会导致相对较大的芯片，但随着几何尺寸和IC尺寸的减小，精密TCXOs现在可以封装在2mm x 2.5mm的封装中。

虽然Greenray Industries使用上述每种补偿方法制造温度补偿晶体振荡器，但模拟ASIC型TCXOs的数量超过了所有其他类型的总和。