1. Terms DAC

Aperature delay or sampling delay

The time after the (active) edge of the clock to when the input signal is aquired or held for conversion.

Aperature jitter

The variation in aperature delay from sample to sample. Aperature jitter will increase the noise level.

(conversion) Latency or pipeline delay

The number of clock cycles between initiating a conversion and when the data of the first conversion is present on the output. The data for every sample is available after the pipline delay plus the output delay after the sample is taken.

Conversion time

The time required to do one conversion. The conversion does not include acquisition time, setup time for a multiplexer, or other elements. So the conversion time may be less than the "throughput time".

End Point and Best Fitting line

See also ADC parameter calculations

DC common-mode error

A specification for A/D conversion with a differential input. The change in ouput code when the input on both inputs are changed with the same voltage.

Differential gain error

Difference in output level (%) when a (high) frequency sine wave with a given amplitude is applied, with different DC input levels.

Differential non linearity error (DNL/DNLE)

The maximium deviation of the ideal 1 lsb step.

DNL indicates the deviation from the ideal 1 LSB step size of the analog input signal corresponding to a code-to-code increment. DNL, a static specification, relates to SNR, a dynamic specification. However, noise performance can not be predicted from DNL performance, except to say that SNR tends to become worse as DNL departs from zero. See also AD converter parameter calculations - DNL error

Differential phase error

The difference in the output phase of a reconstructed small signal sine wave at two different dc input levels.

Full scale error

The full scale error is the error of the last transition point (or trippoint) from the ideal transition point. It is equal to the sum of the gain error and offset error. See also AD converter parameter calculations - Full scale error

Gain error

The gain error is equal to the Full scale error with the offset error subtracted. It is the deviation (of the end point or best fit reference line) from the ideal slope of the transfer characteristic. The slope can be found in the "a" of the reference line y = ax + b. The gain error can be calculated with the equation (N-1)/a - (N-1). Where N is the number of trip-points and N-1 the number of steps between the trip-points. See also ADC parameter calculations - Gain error

Integral non linearity error (INL/INLE)

Integral non linearity error describes the departure from a reference line. This reference can be an end point line or best fitting line. INL does not include quantization errors, offset error, or gain error. It is a measure of the straightness of the transfer function and can be greater than the differential non-linearity. The size and distribution of the DNL errors will determine the integral linearity of the converter.

INL is a static specification and relates to THD (a dynamic specification). However, distortion performance can not be predicted from the INL specification, except to say that THD tends to become worse as INL departs from zero. See also ADC parameter calculations - INL error

Missing codes

Non-monotonicity

Offset error

The offset error is the error of the first transition point (or trip-point) from the ideal transition point (end point calculation).
For the best fitting line calculation the offset error is the offset of the best fitting reference line (related to the ideal transfer line). See also AD converter parameter calculations - Offset error

Quantization_error

The output of an A/D converter will stay constant for 1 lsb. So with and input voltage that ramps up for the beginning of an A/D converter step to to the next A/D converter step, the error will increase from 0 to 1 lsb.

For A/D converters with a halve lsb offset shift the error will be -1/2 lsb to +1/2lsb.

Signal to noise and distortion (SINAD)

The signal to noise and distortion is the ratio signal (or carrier) and all other spectrum bins (excluding dc) below half the sample frequency. See also Dynamic parameter calculations - SINAD

Signal to noise ratio (SNR)

Signal-to-Noise Ratio (SNR) is the ratio of the output signal amplitude to the output noise level, not including harmonics or DC.

SNR usually degrades as frequency increases because the accuracy of the comparator(s) within the ADC degrades at higher input slew rates. This loss of accuracy shows up as noise at the ADC output. In an A/D converter, noise comes from four main sources: (1) quantization noise, (2) noise generated by the converter itself, (3) application circuit noise and (4) jitter.

Quantization noise results from the quantization process, the process of assigning an output code to a range of input values. The amplitude of the quantization noise decreases as resolution increases because the size of an LSB is smaller at higher resolutions, which reduces the maximum quantization error. The theoretical maximum signal-to-noise ratio for an ADC with a full-scale sine-wave input derives from quantization noise and is defined as 20 * log(2^(n-1) x sqrt(6) ), or about 6.02n + 1.76 dB. With a perfectly linear but noisy system SINAD and SNR are interchangeable. Application circuit noise is that noise seen by the converter as a result of the way the circuit is designed and laid out. SNR increases with increasing input amplitude until the input gets close to full scale. The SNR increases at the same rate as the input signal until the input signal approaches full scale. That is, increasing the input signal amplitude by 1 dB will cause a 1 dB in increase in SNR. This is because the step size becomes a smaller part of the total signal amplitude as the the signal amplitude increases. When the input amplitude starts approaching full scale, however, the rate of increase of SNR vs. input signal decreases. SNR performance decreases at higher frequencies because the effects of jitter get worse.

Spurious free dynamic range (SFDR)

The spurious free dynamic range is the difference in dB between the signal and the any other signal (spurious) in the spectrum with the highest peak. See also Dynamic parameter calculations - SFDR

Total harmonic distortion (THD)

The total harmonic distortion is the ratio signal (or carrier) and the harmonics spectrum bins (multiples of the carrier). The number of harmonics for the ATX7006 is (default) seven, but adjustable. See also Dynamic parameter calculations - THD

Total unadjusted error (TUE)

Total Unadjusted Error is a specification that includes linearity errors, gain error, and offset error. It is the worst-case deviation from the ideal device performance. See also AD converter parameter calculations - TUE