AFS090 datasheet(118/334 Pages) MICROSEMI

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Device Architecture

2- 10 2

R e v isio n 2

ADC Terminology

Conversion Time

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.

DNL – Differential Non-Linearity

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 2-81).

ENOB – Effective Number of Bits

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 EQ 12.

EQ 12

FS Error – Full-Scale Error

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.

Figure 2-81 • Differential Non-Linearity (DNL)

Input Voltage to Prescaler

Error = –0.5 LSB

Error = +1 LSB

Ideal Output

Actual Output

ENOB

SINAD

1.76

–

6.02

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