Digital controllers for electrical engineering (microcontrollers, DSP, FPGA): main peripherals

Abstract

Listen

Translate article

The control circuits used in power equipment are usually based on mixed (analog & digital) circuits. For instance, in the case of the DC/DC converters used in power conversion, the control circuits generate digital signals (square waveforms) based on analog values (converter output voltage). Usual control schemes require square waveforms, in which the duty cycle and frequency can be modified according to a given algorithm that takes the output voltage/current, the reference, etc. as inputs. It is possible to implement not very simple control schemes using Voltage Controlled Oscillators (VCOs) and operational amplifiers (OpAmps). The regulator in these DC/DC converters is usually implemented as a proportional-integral-derivative controller (PID). In this way, the control circuits have evolved in such a way that it is possible to find all the necessary blocks to implement the control schemes in only one IC. But, as digital electronic components and topologies become more and more complex, the control circuit is also requested to implement control algorithms that are, in turn, more complex, more than just one feedback loop. In this way, digital control becomes a powerful solution. Microcontrollers offer a good solution, since they include a CPU and many different blocks such as timers, input/output ports, etc. in a single chip. Over the years, the microcontroller's CPU was not powerful enough, but lately CPU speed has experienced a huge increment: from the 4MHz of the initial units to 50MHz of the modern DSCs. In parallel, the costs have reduced, making these devices a very attractive solution for control systems. However, this is not the last step: designers require more and more control capabilities, and most of the times the previous circuits offer many blocks that are not necessary. On the other hand, designers tend to personalize their designs more and more, in such a way that designers can define their own control circuit, with a specific control circuitry, etc. In other words, they can select a given CPU, or implement a control circuit using state-machine. Although full-custom technologies are out of the reach for the majority of the designers, semicustom technologies constitute a good deal. Just like microcontrollers and DSCs, FPGAs and CPLDs have reduced their costs, the cost of the debugging systems needed for custom technologies has also dropped. Nowadays, there is a wide range of possibilities and the selection process is a far from being an easy task.