afs600 Actel Corporation, afs600 Datasheet - Page 113

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

Terminology
Conversion time is the interval between the release of
the hold state (imposed by the input circuitry of a
track-and-hold) and the instant at which the voltage on
the sampling capacitor settles to within one LSB of a new
input value.
For an ideal ADC, the analog-input levels that trigger any
two successive output codes should differ by one LSB
(DNL = 0). Any deviation from one LSB in defined as DNL
(Figure
Figure 2-84 • Differential Non-Linearity (DNL)
ENOB specifies the dynamic performance of an ADC at a
specific input frequency and sampling rate. An ideal
ADC’s error consists only of quantization of noise. As the
input frequency increases, the overall noise (particularly
in the distortion components) also increases, thereby
reducing the ENOB and SINAD (also see “Signal-to-Noise
and Distortion Ratio (SINAD)”.) ENOB for a full-scale,
sinusoidal input waveform is computed using
Conversion Time
DNL – Differential Non-Linearity
ENOB – Effective Number of Bits
2-84).
Error = –0.5 LSB
In p u t V o lta g e to P re sca le r
ENOB
=
Ideal Output
SINAD 1.76
---------------------------------- -
6.02
–
Error = +1 LSB
Actual Output
EQ
2-20.
EQ 2-20
A d v an c ed v1 . 4
Full-scale error is the difference between the actual value
that triggers that transition to full-scale and the ideal
analog full-scale transition value. Full-scale error equals
offset error plus gain error.
The gain error of an ADC indicates how well the slope of
an actual transfer function matches the slope of the ideal
transfer function. Gain error is usually expressed in LSB
or as a percent of full-scale (%FSR). Gain error is the
full-scale error minus the offset error
Figure 2-85 • Gain Error
Gain-error drift is the variation in gain error due to a
change in ambient temperature, typically expressed in
ppm/°C.
0...00
1...11
FS Error – Full-Scale Error
Gain Error
Gain Error Drift
Actel Fusion Programmable System Chips
In p u t V o lta g e to P re sca le r
Ideal Output
(Figure
Actual Output
Gain = 2 LSB
2-85).
2-99