1、英文资料及中文翻译 Modulating Direct Digital Synthesizer in a QuickLogic FPGA DDS Overview: In the pursuit of more complex phase continuous modulation techniques, the control of the output waveform becomes increasingly more difficult with analog circuitry. In these designs, using a non-linear digital design
2、eliminates the need for circuit board adjustments over yield and temperature. A digital design that meets these goals is a Direct Digital Synthesizer DDS. A DDS system simply takes a constant reference clock input and divides it down a to a specified output frequency digitally quantized or sampled a
3、t the reference clock frequency. This form of frequency control makes DDS systems ideal for systems that require precise frequency sweeps such as radar chirps or fast frequency hoppers. With control of the frequency output derived from the digital input word, DDS systems can be used as a PLL allowin
4、g precise frequency changes phase continuously. As will be shown, DDS systems can also be designed to control the phase of the output carrier using a digital phase word input. With digital control over the carrier phase, a high spectral density phase modulated carrier can easily be generated. This a
5、rticle is intended to give the reader a basic understanding of a DDS design, and an understanding of the spurious output response. This article will also present a sample design running at 45MHz in a high speed field programmable gate array from QuickLogic. A basic DDS system consists of a numerical
6、ly controlled oscillator (NCO) used to generate the output carrier wave, and a digital to analog converter (DAC) used to take the digital sinusoidal word from the NCO and generate a sampled analog carrier. Since the DAC output is sampled at the reference clock frequency, a wave form smoothing low pass filter is typically used to eliminate alias components. Figure 1 is a basic block diagram of a typical DDS system design.The generation of the output carrier from the reference sample clock input
