Part # Application Notes Access Control Accessories Adapters Audio Broadcast Computer Power Supply Corded Terminals Cordless Terminal D datasheet

Part Manufacturer: ST Microelectronics

ST Microelectronics

Part Description: STM32F10xxx LCD glass driver firmware


Part Details:

AN2668 Application note Improving STM32F101xx and STM32F103xx ADC resolution by oversampling Introduction The STMicroelectronics Medium- and High-density STM32F101xx and STM32F103xx CortexTM-M3 based microcontrollers come with 12-bit enhanced ADC sampling with a rate up to Msamples/s. In most applications, this resolution is sufficient, but in some cases where higher accuracy is required, the concept of oversampling and decimating the input signal can be implemented to save the use of an external ADC solution and to reduce the application consumption. This application note gives two methods to improve ADC resolution. These techniques are based on the same principle: oversampling the input signal with the maximum 1 MHz ADC capability and decimating the input signal to enhance its resolution. The method and the firmware given within this application note apply to both Medium- and High-density STM32F10xxx products. Some specific hints are given at the end of the application note to take advantage of the Medium- and High-density STM32F103xx performance line devices and of the High-density STM32F101xx access line devices. This application note is split into two main parts: the first one describes how oversampling increases the ADC-specified resolution while the second describes the guidelines to implement the different methods available and gives the firmware flowchart of their implementation on the STM32F101xx and STM32F103xx devices. July 2008 Rev 1 1/21 www.st.com Contents AN2668 Contents 1 Definition of ADC signal-to-noise ratio . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2 Nyquist theorem and oversampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3 Oversampling using white noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1 SNR of oversampled signal with white input noise . . . . . . . . . . . . . . . . . . . 6 3.2 Decimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.3 When is this method efficient? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.4 Method implementation on the STM32F10xxx devices . . . . . . . . . . . . . . . 8 3.4.1 Oversampling using a white noise firmware flowchart . . . . . . . . . . . . . . . 9 3.4.2 Oversampling using white noise result evaluation . . . . . . . . . . . . . . . . . 10 4 Oversampling using triangular dither . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.1 When does this method work? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.2 Method implementation on STM32F10xxx devices . . . . . . . . . . . . . . . . . 13 5 Comparing the first and second methods . . . . . . . . . . . . . . . . . . . . . . 15 6 Hints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 6.1 What is the maximum number of bits that can be added tothe on-chip ADC resolution? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 6.2 Taking advantage of High-density STM32F10xxx devices . . . . . . . . . . . . 16 6.3 Taking advantage of the Medium- and High-density performance line (STM32F103xx) devices 17 Appendix A Quantization error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 2/21


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