Device Architecture
INL – Integral Non-Linearity
INL is the deviation of an actual transfer function from a straight line. After nullifying offset and
gain errors, the straight line is either a best-fit straight line or a line drawn between the end points
of the transfer function (Figure 2-86).
INL = +0.5 LSB
Ideal Output
Actual Output
INL = +1 LSB
Input Voltage to Prescaler
Figure 2-86 • Integral Non-Linearity (INL)
LSB – Least Significant Bit
In a binary number, the LSB is the least weighted bit in the group. Typically, the LSB is the furthest
right bit. For an ADC, the weight of an LSB equals the full-scale voltage range of the converter
divided by 2N, where N is the converter’s resolution. For a 10-bit ADC with a unipolar full-scale
voltage of 2.56 V, 1 LSB = (2.56 V / 210) = 2.5 mV.
No Missing Codes
An ADC has no missing codes if it produces all possible digital codes in response to a ramp signal
applied to the analog input.
Offset Error
Offset error indicates how well the actual transfer function matches the ideal transfer function at a
single point. For an ideal ADC, the first transition occurs at 0.5 LSB above zero. The offset voltage is
measured by applying an analog input such that the ADC outputs all zeroes and increases until the
first transition occurs (Figure 2-87).
2-112
Preliminary v1.7
ACTEL [ Actel Corporation ]
