Switching amplifiers are widely used for processing input signals. Switching amplifiers receive a modulated signal, such as a pulse-width modulated digital signal. Most high efficiency switching amplifiers are based on the principle of Pulse Width Modulation (PWM), which is widely used in a variety of applications, which include digital audio amplifiers and control applications including motor controllers. Many of these applications convert a sampled digital signal to a digital PWM signal to achieve high efficiency and accuracy. The digital PWM signal is input to a switching amplifier that increases signal swing, to translate the digital PWM input signal to a PWM signal with significantly higher voltage levels. Undesirable spur components introduced in the switching amplifiers are associated with the frequency at which the PWM signal is switched. Undesired component exists at the switching frequency and the harmonics of the switching frequency. The components at the switching frequency and the harmonics of the switching frequency are typically in passband of the amplifier, allowing amplification of undesired off-channel signal components. Power devoted to generation of such off channel components reduces the efficiency of the amplifier. Hence, the switching frequency components in an input signal need to be eliminated.
There are several known methods for removing the signal component at the switching frequency and the odd harmonics thereof. One such method uses a four-pole filter to suppress the switching frequency. However, four-pole filters are generally bulky and require a lot of space, and are therefore not suitable for integration. Another method for removing switching frequency and the harmonics thereof suppresses the switching frequency by superimposing two components of an input signal. A first component is the original input signal and the other component is an inverted and delayed signal of the first component. The system uses two frequency components of the signal, which are overlapping, and which cancel each other thereby producing a three-stage signal. This signal after it is decoded, results in a signal, which is free from the switching frequency and the odd harmonics thereof. However, there are several computational overheads in such designs and the overall system becomes complex.
USPTO Backgrounds
USPTO Backgrounds