ADS5500IPAPR datasheet(10/29 Pages) TI

10 / 29 page

ADS5500

SBAS303C − DECEMBER 2003 − REVISED MARCH 2004

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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 3dB.

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 1

LSB apart. DNL is the deviation of any single LSB

transition at the digital output from an ideal 1 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 3dB 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 1s in the digital code.

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

full-scale range (%FSR).

Integral Nonlinearity (INL)

INL is the deviation of the transfer function from a

reference line measured in fractions of 1 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

This is 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

Offset error is the deviation of output code from

mid-code when both inputs are tied to common-mode.

Propagation Delay

This is 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, then the SNR in dB is given by the formula:

SNR

+ 20Log

(10)

This is the ratio of the RMS signal amplitude, VS (set 1dB

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

spectral components, VN, excluding harmonics and DC.

ADS5500IPAPR Datasheet(PDF) 10 Page - Texas Instruments

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