Power converters and inverters are used to generate a desired power supply by converting or inverting supplied power. Power converters and inverters are often constructed using analog or mixed signal (digital and analog) components, which introduce control problems due to variations in or distortion of performance of analog components caused by variations in manufacturing, mismatched components and variations in temperature during operation. All of these control problems often necessitate additional control mechanisms, which consume even greater amounts of limited die sizes and available power.
It is common for converters and inverters to employ switches, which must be controlled to generate the desired power supply. Common techniques of controlling switches to generate desired power include controlling the frequency and/or pulse width of a high frequency signal created by a pulse generator. This generally focuses a significant amount of energy at a particular frequency, causing a spike in EMI at the switching frequency.
Thus, a problem introduced by inverters and converters relying on high frequency switching is generation of undesirable EMI, which can interfere with the operation of other components or devices. EMI is also regulated. Thus, for purposes of component and device operation as well as compliance with regulations, EMI must be mitigated.
Common EMI control techniques involve analog or mixed signal circuitry with associated control, die size and power consumption problems. One EMI control technique relies on a mixed signal circuit that generates a randomized analog or digital signal, a microcontroller integrates the random signal into switch control signal, which a DAC converts into a randomized control voltage that, in turn, causes a voltage controlled oscillator (VCO) to produce a randomized switching frequency. The randomized frequencies spread a switch control frequency across a broader range of the frequency spectrum to reduce the EMI intensity at a particular frequency. A second EMI control technique relies on a phase locked loop (PLL) in a mixed signal circuit to spread a control signal across a range of frequency spectrum. A third EMI control technique relies on an analog circuit to generate a SAW wave, which is used to vary the frequency of a switch control signal in accordance with the analog wave. Each of these EMI control techniques involve analog or mixed signal circuitry with associated control, die size and power consumption problems.
An additional problem introduced by randomization of control signals is the random nature of frequency changes in cycles of a switch control signal. The magnitude of difference or displacement in frequency between a first frequency of a first cycle and a second frequency of a second cycle can be significant, which can cause additional problems. Frequency displacement between cycles is often referred to as cycle-to-cycle jitter or phase noise. If displacement exceeds a threshold limit then logic may malfunction.
Therefore, there is a need to improve upon one or more of the numerous problems with mixed signal and analog switch control circuitry and randomization of control signals to mitigate EMI.