Actel Fusion Mixed-Signal FPGAs
Min. Output Voltage = (Min. Negative output offset) + (Input Voltage x Min. Gain)
= (–136 mV) + (5 V x 0.98) = 4.764 V
Calculating Accuracy for a Calibrated Analog Channel
Formula
For a given prescaler range,
Output Voltage = Channel TUE in V + Input Voltage
where
Channel TUE in V = Channel TUE in LSBs x Equivalent voltage per LSB
Example
Input Voltage = 5 V
Chosen Prescaler range = 8 V range
Refer to Table 2-49 on page 2-121.
Max. Output Voltage = Max. Channel TUE in V + Input Voltage
Max. Channel TUE in V = (6 LSB) × (8 mV per LSB in 10-bit mode) = 48 mV
Max. Output Voltage = 48 mV + 5 V = 5.048 V
Similarly,
Min Output Voltage = Min Channel TUE in V + Input Voltage = (-48 mV) + 5 V = 4.952 V
Calculating LSBs from a Given Error Budget
Formula
For a given prescaler range,
LSB count = (Input Voltage × Required % error) / (Equivalent voltage per LSB)
Example
Input Voltage = 5 V
Required error margin= 1%
Refer to Table 2-49 on page 2-121.
Equivalent voltage per LSB = 16 mV for a 16V prescaler, with ADC in 10-bit mode
LSB Count = (5.0 V × 1%) / (0.016)
LSB Count = 3.125
Equivalent voltage per LSB = 8 mV for an 8 V prescaler, with ADC in 10-bit mode
LSB Count = (5.0 V × 1%) / (0.008)
LSB Count = 6.25
The 8 V prescaler satisfies the calculated LSB count accuracy requirement (see Table 2-49 on
page 2-121).
Preliminary v1.7
2-123
ACTEL [ Actel Corporation ]
