Digitally tuned analog VLSI controllers

Digital controllers have historically enjoyed many advantages over those synthesized by analog electronics, but there are still some drawbacks to discrete-time implementations of controllers and signal processing algorithms: costly conversion of analog signals to digital and back, quantization errors, digital noise, time discretization, computation of signals by one CPU, and relatively large circuitry with limited processing speed. The key disadvantage of digitals systems is the signal latency due to A/D and D/A conversion time and relatively slow signal processing. The key disadvantages of analog signal processing are: limited accuracy due to limited tolerances of transistors and limited flexibility for adaptation. When digitally tuned analog controllers are used, then both disadvantages can be eliminated. Limited tolerances of circuit elements can be also compensated by digital tuning. Furthermore, this approach gives the possibility to reconfigure the system. Digitally controlled analog circuits have the following advantages: lower cost, high speed and small signal latency, parallel processing, direct implementation of continuous time designs, and smaller system noise important for a precision control.