| 摘要 |
A low cost, high quality converter for generating an amplitude modulated signal in response to a sequence of digital words representing a modulation signal, such as a video image. The converter receives the sequence of digital words at an input rate. The input sequence of digital words is combined with a sequence of factors at a sample rate to generate a second sequence of digital words at the sample rate representing the amplitude modulated signal. The second sequence of digital words is then converted to the amplitude modulated signal. The sequence of factors is a sequence of cosines of the carrier frequency at the carrier phase angle of 45, 135, 225 and 315 degrees. The value of these cosines are +0.707, -0.707, -0.707, +0.707 respectively. These values are normalized to 1 so that they become a sequence of +1, -1, -1, and +1. Multiplication by the sequence of factors is thus carried out by alternately inverting the input sequence of digital words at one-half the sample rate. |
