Static and dynamic errors in DAC

DAC errors are of two kinds: static errors, which exist when the digital input is steady, and dynamic errors, which appear when the input changes.

Static errors

1. Offset error: output is not zero for input code 0; the whole characteristic is shifted. Trimmed by an offset adjustment.
2. Gain (full-scale) error: deviation of the slope from the ideal; full-scale output is wrong. Trimmed by adjusting the reference.
3. Integral nonlinearity (INL): maximum deviation of the actual output from the ideal straight line.
4. Differential nonlinearity (DNL): deviation of each step from 1 LSB. DNL < -1 LSB makes the DAC non-monotonic.
5. Monotonicity error: the output decreases when the code increases.
6. Drift: change of offset and gain with temperature and time; supply sensitivity (PSRR). Causes: resistor mismatch in R-2R ladder, switch resistance, reference and op-amp errors.

Dynamic errors

1. Settling time: time needed for the output to reach and stay within +/-1/2 LSB of the final value after a code change. It is limited by the op-amp bandwidth and capacitances.
2. Slew rate limit: large steps produce a slew-limited, not exponential, response.
3. Glitches: spikes at major carry changes (0111 1111 to 1000 0000) because switches change at different times; the glitch energy is measured in nV-s. Reduced by a deglitching sample-and-hold or by segmented DACs.
4. Overshoot and ringing of the output amplifier.
5. Feedthrough of the digital signals to the analog output.
6. Clock jitter and harmonic distortion (THD), SNR, SFDR in high-speed DACs.

 Output
   ^        ___ overshoot
   |      /    \____ settling band +/- 1/2 LSB
   |     /           ------------ final value
   |  __/  <- slew
   +----|------------|--------------> time
      code change   settling time

Static errors determine accuracy of DC output; dynamic errors limit the speed and signal quality for waveform generation.