ADS5500MPAPREP datasheet(13/37 Pages) TI1

13 / 37 page

ADS5500-EP

SGLS286C − JUNE 2005 – REVISED SEPTEMBER 2008

www.ti.com

DEFINITION OF SPECIFICATIONS

Analog Bandwidth

The analog input frequency at which the spectral power of

the fundamental frequency (as determined by FFT

analysis) is reduced by 3 dB

Aperture Delay

The delay in time between the falling edge of the input

sampling clock and the actual time at which the sampling

occurs

Aperture Uncertainty (Jitter)

The sample-to-sample variation in aperture delay

Clock Pulse Width/Duty Cycle

A perfect differential sine−wave clock results in a 50%

clock duty cycle on the internal coversion clock. Pulse

width high is the minimum amount of time that the

ENCODE pulse should be left in logic 1 state to achieve

rated performance. Pulse width low is the minimum time

that the ENCODE pulse should be left in a low state (logic

0). At a given clock rate, these specifications define an

acceptable clock duty cycle.

Differential Nonlinearity (DNL)

An ideal ADC exhibits code transitions that are exactly one

LSB apart. DNL is the deviation of any single LSB

transition at the digital output from an ideal one LSB step

at the analog input. If a device claims to have no missing

codes, it means that all possible codes (for a 14-bit

converter, 16384 codes) are present over the full operating

range.

Effective Number of Bits (ENOB)

The effective number of bits for a sine−wave input at a

given input frequency can be calculated directly from its

measured SINAD using the following formula:

ENOB

+ SINAD * 1.76

6.02

If SINAD is not known, SNR can be used exceptionally to

calculate ENOB (ENOBSNR).

Effective Resolution Bandwidth

The highest input frequency where the SNR (dB) is

dropped by 3 dB for a full-scale input amplitude

Gain Error

The amount of deviation between the ideal transfer

function and the measured transfer function (with the offset

error removed) when a full-scale analog input voltage is

applied to the ADC, resulting in all ones in the digital code.

Gain error is usually given in LSB or as a percent of

full-scale range (%FSR).

Integral Nonlinearity (INL)

The deviation of the transfer function from a reference line

measured in fractions of one LSB using a best straight line

or best fit determined by a least square curve fit. INL is

independent from effects of offset, gain, or quantization

errors.

Maximum Conversion Rate

The encode rate at which parametric testing is performed.

This is the maximum sampling rate where certified

operation is given.

Minimum Conversion Rate

The minimum sampling rate where the ADC still works.

Nyquist Sampling

When the sampled frequencies of the analog input signal

are below fCLOCK/2, it is called Nyquist sampling. The

Nyquist frequency is fCLOCK/2, which can vary depending

on the sample rate (fCLOCK).

Offset Error

The deviation of output code from mid-code when both

inputs are tied to common-mode

Propagation Delay

The delay between the input clock rising edge and the time

when all data bits are within valid logic levels

Signal-to-Noise and Distortion (SINAD)

The RMS value of the sine wave fIN (input sine wave for an

ADC) to the RMS value of the noise of the converter from

DC to the Nyquist frequency, including harmonic content.

It is typically expressed in decibels (dB). SINAD includes

harmonics, but excludes DC.

SINAD

+ 20Log

(10)

Input(V

S )

Noise

) Harmonics

Signal-to-Noise Ratio (Without Harmonics)

SNR is a measure of signal strength relative to background

noise. The ratio is usually measured in dB. If the incoming

signal strength in

µV is VS, and the noise level (also in µV)

is VN, the SNR in dB is given by the formula:

SNR

+ 20Log

(10)

This is the ratio of the RMS signal amplitude, VS (set one

dB below full-scale), to the RMS value of the sum of all

other spectral components, VN, excluding harmonics and

dc.

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