怎么在PSoC 1中校准放大器和ADC

在当今混合信号系统的世界中，许多应用需要模拟量，包括但不限于电压、电流、温度、压力、加速度、pH、流量和ECG来测量和处理。该领域的使用范围从实验室和医疗设备在受控环境中运行到工业设备在恶劣的运行条件下运行。要测量的模拟信号可以从ECG系统中的几微伏到发电厂中的几千伏。不幸的是，有没有这样的东西作为现实世界中一个理想的转换器，其中系统抗衡，引入系统和影响输出ADC的误差。最重要的误差是偏移和增益误差。参考下面的图表。这是一个阴谋的一系列+2.5 V的一个8位的ADC，X轴表示输入电压，Y轴表示ADC计数。蓝线是理想的ADC输出。红线是实际的ADC输出。注意，实际输出偏离理想状态。这种偏移称为偏移误差。所有的运算放大器在输入有限的偏移电压。该偏移电压被添加到输入信号，通过放大器在输出的增益放大和体现。除了放大器，ADC也有自己的偏移电压，增加了系统误差。偏移误差是一个附加误差，可以很容易地从系统中删除。下图是与+2.5V范围相同的8位ADC的情节。请注意，实际输出的斜率是现在不同于理想的输出斜率。这种斜率的变化称为增益误差。这些错误可能是由使用许多校准技术系统移除：
相关双采样双点校准增益校准使用外部参考。PSoC 1，以其灵活的模拟资源和路由可以实现上述所有的校准技术很容易。根据应用的不同，其中一个或一个以上的方法可以结合起来，以实现最大的精确度。在PSoC黑客上阅读完整的博客。



     以下为原文
  In today s world of mixed-signal systems, many applications require analog quantities including but not limited to voltage, current, temperature, pressure, acceleration, pH, flow, and ECG to be measured and processed. The field of uses ranges from lab and medical equipment operating in controlled environments to industrial equipment running under harsh operating conditions. The analog signals to be measured can range from a few micro-volts in ECG systems to thousands of volts in electricity generation plants.

Unfortunately, there is no such thing as an ideal converter in the real world, where systems have to contend with errors that are introduced into the system and affect the ADC s output. The most important errors are offset and gain errors.  

Refer graph below.  This is a plot of an 8 bit ADC with a range of +2.5V.  X axis denotes the input voltage and Y axis denotes the ADC counts.  The blue line is the ideal ADC output. The red line is the actual ADC output.  Notice the actual output is shifted from the ideal.  This shift is called the offset error.


  
All operational amplifiers have a finite offset voltage at the input.  This offset voltage gets added to the input signal, gets amplified by the amplifier s gain and manifests at the output.  Apart from the amplifier stage, the ADC also has its own offset voltage which adds to the system error.  Offset error is an additive error and can be easily removed from the system.

Graph below is the plot of the same 8 bit ADC with the +2.5V range.  Note that the slope of the actual output is now different from the slope of the ideal output.  This shift in slope is called the gain error.


  
These errors may be removed from a system using many calibration techniques like:
   

     
• Correlated Double Sampling
• Two-point Calibration
• Gain calibration using external reference.
  

   
PSoC 1, with its flexible analog resources and routing makes it very easy to implement all of the above calibration techniques.  Depending upon the application, one or more of these methods can be combined to achieve maximum accuracy.

Read the full blog at the PSoC Hacker.