19-06-2019, 05:35 PM
Looks nice and accurate. It's a quick way to prove that the DAC and output parts of a converter are working well.
Other useful test patterns are multiburst and ramps. Multiburst gives less information than a 2T pulse but can sometimes show anomalies that are hard to spot on 2T. Ramp tests are a sensitive check on the diferential linearity of the DAC. The ramp should be smooth. Integral linearity is less important in a video DAC. A slight overall curve is a minor problem but differential errors at major bit transitions can potentially be visible on real pictures. When you change (say) from 511 to 512 all 9 bits are switching at the same time, many DACs will show a visible glitch.
An especially evil test pattern is a single pixel of white against a black background. This will reveal the impulse response of the oversampling filter and any analogue filter after the DAC.
Other useful test patterns are multiburst and ramps. Multiburst gives less information than a 2T pulse but can sometimes show anomalies that are hard to spot on 2T. Ramp tests are a sensitive check on the diferential linearity of the DAC. The ramp should be smooth. Integral linearity is less important in a video DAC. A slight overall curve is a minor problem but differential errors at major bit transitions can potentially be visible on real pictures. When you change (say) from 511 to 512 all 9 bits are switching at the same time, many DACs will show a visible glitch.
An especially evil test pattern is a single pixel of white against a black background. This will reveal the impulse response of the oversampling filter and any analogue filter after the DAC.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
