Multiple data rate filtered modulation system for digital data

Abstract

A multi-rate data modulation circuit includes a multi-rate data conversion circuit and a modulator such as a direct digital synthesis circuit. The multi-rate data conversion circuit receives digital data at varying data rates, receives a data rate input corresponding to the digital data and converts the digital data to a converted output based upon the data rate input. The direct digital synthesis circuit receives the converted output and synthesizes a modulated output signal based upon the converted output. The multi-rate data conversion circuit may include a multi-rate converter, a multi-rate digital data filter, an output scaler and an adder. The multi-rate converter receives the digital data, the data rate input and a clock signal and converts the digital data to converted digital data. The multi-rate digital data filter receives the converted digital data and produces a filtered digital output. The output scaler receives the filtered digital output and produces a scaled and filtered digital output. Finally, the adder combines the scaled and filtered digital output with a center frequency input and produces the converted output. The multi-rate digital data filter may include a look-up table that produces filter parameters based upon the converted digital data and that operates at multiple data rates. The multi-rate digital data filter may include a digital data filter look-up table, a data rate decode circuit and a plurality of multiplexors. In such case, the data rate decode circuit receives the data rate input and produces control signals therefrom. Each of the plurality of multiplexors receives a portion of the converted digital data and control signals from the data rate decode circuit such that the multiplexors selectively provide the converted digital data to the digital data filter look-up table to produce the filtered digital output.