Signal conditioning I: adaptation and protection stages

Abstract

The analog-to-digital converter (ADC) is one fundamental block in modern engineering systems, since it interfaces the analog domain of the physical system involved with the digitized signal path used for processing, control and monitoring of the systems themselves. But actually, the ADC is the last block in a series of stages intended to adapt the magnitudes to measure to the logic values used by the processing units. When it comes to digital control of electronic power converters, the design of all stages prior to the ADC is critical. This ADC will generally be integrated into a digital signal processor (DSP) or a microcontroller, although it can be an independent integrated circuit (IC). Hence, we must ensure that input signals to the ADC do not exceed the full-scale input range, i.e., the largest signal amplitude that can be delivered to the converter before the signal is clipped in its digital output representation. In this article we will study how to adapt the main signals used to control an electronic converter (current and voltage waveforms) coming from the transducers to the extent that there is no signals in the analog input of the DSP whose amplitudes are higher or lower than the reference voltages of the ADC. For this purpose we will use a device known as operational amplifier. Different circuits are to be presented yielding diverse simulations. This article is not intended for an in-depth study of device architectures and particularities, but a practical guide to signal adaptation for a proper analog-to-digital conversion in power converters. Additionally, we will also see different ways to protect the ADC's inputs against spurious overvoltages that can damage the device.