afs600 Actel Corporation, afs600 Datasheet - Page 114

• Manufacturer Part Number: afs600
• Description: Actel Fusion Programmable System Chips Mixed-signal Family With Optional Arm Support
• Manufacturer: Actel Corporation

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
Figure 2-86 • Integral Non-Linearity (INL)
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 2
the converter’s resolution. For a 10-bit ADC with a
unipolar full-scale voltage of 2.56 V, 1 LSB = (2.56 V / 2
= 2.5 mV.
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 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 -1 0 0
Actel Fusion Programmable System Chips
INL – Integral Non-Linearity
LSB – Least Significant Bit
No Missing Codes
Offset Error
2-86).
2-87).
Input V oltage to P rescaler
Ideal Output
IN L = +0.5 LSB
Actual Output
IN L = +1 LSB
N
, where N is
A d v a n c e d v 1 . 4
10
)
Figure 2-87 • Offset Error
ADC resolution is the number of bits used to represent
an analog input signal. To more accurately replicate the
analog signal, resolution needs to be increased.
Sampling rate or sample frequency, specified in samples
per second (sps), is the rate at which an ADC acquires
(samples) the analog input.
SNR is the ratio of the amplitude of the desired signal to
the amplitude of the noise signals at a given point in
time. For a waveform perfectly reconstructed from
digital samples, the theoretical maximum SNR
is the ratio of the full-scale analog input (RMS value) to
the RMS quantization error (residual error). The ideal,
theoretical
quantization error only and results directly from the
ADC’s resolution (N bits):
Resolution
Sampling Rate
SNR – Signal-to-Noise Ratio
0...01
0...00
SNR
minimum
dB[MAX]
In p u t V o lta g e to P re sca le r
Offset Error = 1.5 LSB
=
Ideal Output
ADC
6.02
dB
×
noise
N
+
1.76
is
dB
Actual Output
caused
(EQ
EQ 2-21
2-21)
by