Datasheet

ADC78H90

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SNAS227D –NOVEMBER 2003–REVISED MARCH 2013

Figure 5. SCLK and CS Timing Parameters

Specification Definitions

ACQUISITION TIME is the time required to acquire the input voltage. That is, it is time required for the hold

capacitor to charge up to the input voltage.

APERTURE DELAY is the time between the fourth falling SCLK edge of a conversion and the time when the

input signal is acquired or held for conversion.

CONVERSION TIME is the time required, after the input voltage is acquired, for the ADC to convert the input

voltage to a digital word.

CROSSTALK is the coupling of energy from one channel into the other channel, or the amount of signal energy

from one analog input that appears at the measured analog input.

DIFFERENTIAL NON-LINEARITY (DNL) is the measure of the maximum deviation from the ideal step size of 1

LSB.

DUTY CYCLE is the ratio of the time that a repetitive digital waveform is high to the total time of one period. The

specification here refers to the SCLK.

EFFECTIVE NUMBER OF BITS (ENOB, or EFFECTIVE BITS) is another 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.

GAIN ERROR is the deviation of the last code transition (111...110) to (111...111) from the ideal (V

REF

- 1.5

LSB), after adjusting for offset error.

INTEGRAL NON-LINEARITY (INL) is a measure of 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 creation of additional spectral components as a result of two

sinusoidal frequencies being applied to the ADC input at the same time. It is defined as the ratio of the

power in the second and third order intermodulation products to the sum of the power in both of the

original frequencies. IMD is usually expressed in dB.

MISSING CODES are those output codes that will never appear at the ADC outputs. The ADC78H90 is ensured

not to have any missing codes.

OFFSET ERROR is the deviation of the first code transition (000...000) to (000...001) from the ideal (i.e. GND +

0.5 LSB).

SIGNAL TO NOISE RATIO (SNR) is the ratio, expressed in dB, of the rms value of the input signal to the rms

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

harmonics or d.c.

SIGNAL TO NOISE PLUS DISTORTION (S/N+D or SINAD) Is the ratio, expressed in dB, of the rms value of

the input signal to the rms value of all of the other spectral components below half the clock frequency,

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