This slide will now look at the DAC output spectrum using a 10-bit DAC model. These plots are the result of modeling a DAC as though it were part of a DDS with an angle-to-amplitude converter (or map) with a 14-bit input bus and 10-bit output bus (that is, P equals 14 and D equals 10). With P equals 14 the map contains 2 to the 14 or 16,384 samples constituting one full cycle of a sinusoid. The input to the map is a linear ramp pattern that increments by one LSB per system clock period. Hence, the output of the map is a digital sinusoid comprised of a sequence of 16,384 10-bit codes. The digital sinusoid produced by the map drives the input of the DAC. All of the plots shown here span DC to Nyquist along the horizontal axis. The upper plot is the spectrum of an ideal DAC. Because the DAC is ideal, its spectrum is identical to the spectrum of the map. As such, it contains the fundamental signal and a host of quantization spurs associated with the 10-bit amplitude resolution of the map. The middle plot is for a DAC with a warped transfer function. That is, a transfer function similar to the red trace on the previous slide. Note the appearance of harmonics in the spectrum – the result of a nonlinear or warped transfer function. The lower plot uses the same warped transfer function as the middle plot, but includes random errors added to the DAC output samples. This models the effect of random errors introduced by the DAC on a sample-by-sample basis. Specifically, in this case, the random errors are such that no sample deviates by more than 3 LSB from its expected value. Because the errors added to the samples in the lower plot are random, it does not contribute to harmonic distortion, but instead results in an overall increase in the noise floor. Although not shown on these plots, sampled DACs can produce additional spurious components. This is because each new code that appears at the DAC input requires a different combination of internal switches to produce the proper output voltage or current corresponding to the input code. The activation and deactivation of these switches tends to produce spurious signals in the output spectrum.