Digital-to-analog Converter - DAC Figures of Merit

DAC Figures of Merit

• Static performance:
  • Differential nonlinearity (DNL) shows how much two adjacent code analog values deviate from the ideal 1 LSB step.
  • Integral nonlinearity (INL) shows how much the DAC transfer characteristic deviates from an ideal one. That is, the ideal characteristic is usually a straight line; INL shows how much the actual voltage at a given code value differs from that line, in LSBs (1 LSB steps).
  • Gain
  • Offset
  • Noise is ultimately limited by the thermal noise generated by passive components such as resistors. For audio applications and in room temperatures, such noise is usually a little less than 1 μV (microvolt) of white noise. This limits performance to less than 20~21 bits even in 24-bit DACs.
• Frequency domain performance
  • Spurious-free dynamic range (SFDR) indicates in dB the ratio between the powers of the converted main signal and the greatest undesired spur.
  • Signal-to-noise and distortion ratio (SNDR) indicates in dB the ratio between the powers of the converted main signal and the sum of the noise and the generated harmonic spurs
  • i-th harmonic distortion (HDi) indicates the power of the i-th harmonic of the converted main signal
  • Total harmonic distortion (THD) is the sum of the powers of all HDi
  • If the maximum DNL error is less than 1 LSB, then the D/A converter is guaranteed to be monotonic. However, many monotonic converters may have a maximum DNL greater than 1 LSB.
• Time domain performance:
  • Glitch impulse area (glitch energy)
  • Response uncertainty
  • Time nonlinearity (TNL)