8

Definitions

The "acquisition time" is the time required to get the input voltage. During this time, the hold capacitor is charged

by the input voltage.

The "aperture delay" is the time between the fourth falling edge of SCLK and the time when the input signal is

internally acquired or held for conversion.

Channel-to-channel isolation is the residual noise injected on the selected channel by other unselected channels.

The "conversion time" is the time required, after the input voltage is acquired, to convert the input voltage to a

digital word.

"Differential non-linearity" (DNL) is the maximum deviation from the ideal step size of 1 LSB.

Duty cycle is the ratio, for a periodic digital signal, of the high level duration divided by the total period.

Effective number of bits (ENOB) is a method of specifying signal-to-noise and distortion or SINAD. ENOB is

defined as (SINAD - 1.76) / 6.02 and says that the converter is equivalent to a perfect ADC of this (ENOB)

number of bits.

Full power bandwidth is a measure of the frequency at which the reconstructed output fundamental drops 3 dB

below its low frequency value for a full scale input.

Full scale error (single-ended input) is the deviation of the last code transition (111...110) to (111...111) from the

ideal (AVCC -1LSB), after offset error is fixed.

Positive full scale error (differential input) is the deviation of the last code transition (111...110) to (111...111) from

the ideal (AVCC -1LSB), after offset error is fixed.

Negative full scale error (differential input) is the deviation of the last code transition (111...110) to (111...111) from

the ideal (-AVCC +1LSB), after offset error is fixed.

Integral non-linearity (INL) is the deviation of each individual code from a line drawn from negative full scale

(½ LSB below the first code transition) through positive full scale (½ LSB above the last code transition). The

deviation of any given code from this straight line is measured from the center of that code value.

Intermodulation distortion (IMD) is the result of the product of two pure sinewaves at frequency fa and fb applied

to the ADC input. To avoid clipping when the sinewave is in phase, the level must be just below -6 dBFS.

Assuming that the level of the two tones is equal, IMD2 is the difference in dBc between level(fa or fb) and level(fa

± fb). IMD3 is is the difference in dBc between level(fa or fb) and level(2fa ± fb) or level(fa ± 2fb).

Missing codes are those output codes that never appear at the ADC outputs. The RH-AD128 is guaranteed not to

have any missing code.

Offset error (single-ended input) is the deviation of the first code transition (000...000) to (000...001) from the ideal

(i.e. GND +1 LSB).

Offset error (differential input) is the deviation of the mid-code transition (01…111) to (10…000) from the ideal (i.e.

AVCC/2 +1 LSB).

Signal-to-noise ratio (SNR) is the ratio, expressed in dB, of the rms value of the fundamental of input signal to

the rms value of the sum of all other spectral components below one-half the sampling frequency, not including

harmonics or DC-component.

Signal-to-noise plus distortion (S/N+D or SINAD) is the ratio of the rms value of the fundamental of input signal to

the rms value of all of the other spectral components below half the sampling frequency, including harmonics but

excluding DC-component.

Spurious free dynamic range (SFDR) is the difference, expressed in dB, between the desired signal amplitude of

fundamental to the amplitude of the peak spurious spectral component, where a spurious spectral component is

any signal present in the output spectrum that is not present at the input and may or may not be a harmonic.

Total harmonic distortion (THD) is the ratio, expressed in dBc, of the rms total of the first nine harmonic

components at the output to the rms level of fundamental of the input signal frequency as seen at the output. THD

is calculated as

THD=20log10[sqrt((Af2²+…+Af10²)/Af1²)] where Af1 is the RMS power of the fundamental at the output and Af2

to Af10 are the RMS power in the first nine harmonic frequencies.

Throughput time is the minimum time required between the start of two successive conversions. It is the

acquisition time plus the conversion time.

LEOAD128

Definitions

DS13668 - Rev 2

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