Power-amplifier-inserted transversal filter for application to pulse-density-modulation switching-mode transmitters

A power-amplifier filter architecture is described in which a switching-mode power amplifier with pulse density modulation is inserted in each path of a transversal filter. This filter suppresses the quantization noise that remains at the output of the component power amplifiers as well as amplifies the signal with high efficiency. The center frequency and pass bandwidth of the filter can be varied widely by changing the delay difference between adjacent paths and changing the number of paths in the filter. Computer simulation of the output powers of the desired signal and the undesired signal (due mainly to quantization noise) reveals that use of this architecture greatly reduced the power of the undesired signal while maintaining the power of the desired signal, even when the number of paths is increased. Evaluation of the signal constellation and error vector magnitude after quadrature detection shows that the demodulated signals are not degraded even when the number of paths is increased.