ADS5474IPFPR datasheet(31/38 Pages) TI

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DEFINITION OF SPECIFICATIONS

SNR + 10log10

(4)

SINAD + 10log10

N ) PD

(5)

THD + 10log10

(6)

ADS5474

www.ti.com......................................................................................................................................................... SLAS525A – JULY 2007 – REVISED AUGUST 2008

The injected frequency level is translated into dBFS,

the spur in the output FFT is measured in dBFS, and

Analog Bandwidth

the difference is the PSRR in dB. The measurement

The analog input frequency at which the power of the

calibrates out the benefit of the board supply

fundamental is reduced by 3 dB with respect to the

decoupling capacitors.

low-frequency value.

Signal-to-Noise Ratio (SNR)

Aperture Delay

SNR is the ratio of the power of the fundamental (PS)

The delay in time between the rising edge of the input

to the noise floor power (PN), excluding the power at

sampling clock and the actual time at which the

dc and in the first five harmonics.

sampling occurs.

Aperture Uncertainty (Jitter)

The sample-to-sample variation in aperture delay.

SNR is either given in units of dBc (dB to carrier)

Clock Pulse Duration/Duty Cycle

when the absolute power of the fundamental is used

The duty cycle of a clock signal is the ratio of the time

as the reference, or dBFS (dB to full-scale) when the

the clock signal remains at a logic high (clock pulse

power of the fundamental is extrapolated to the

duration) to the period of the clock signal, expressed

converter full-scale range.

as a percentage.

Signal-to-Noise and Distortion (SINAD)

Differential Nonlinearity (DNL)

SINAD is the ratio of the power of the fundamental

An ideal ADC exhibits code transitions at analog input

(PS) to the power of all the other spectral components

values spaced exactly 1 LSB apart. DNL is the

including noise (PN) and distortion (PD), but excluding

deviation of any single step from this ideal value,

dc.

measured in units of LSB.

Common-Mode Rejection Ratio (CMRR)

CMRR measures the ability to reject signals that are

presented to both analog inputs simultaneously. The

SINAD is either given in units of dBc (dB to carrier)

injected common-mode frequency level is translated

when the absolute power of the fundamental is used

into dBFS, the spur in the output FFT is measured in

as the reference, or dBFS (dB to full-scale) when the

dBFS, and the difference is the CMRR in dB.

power of the fundamental is extrapolated to the

Effective Number of Bits (ENOB)

converter full-scale range.

ENOB is a measure in units of bits of converter

Temperature Drift

performance as compared to the theoretical limit

Temperature drift (with respect to gain error and

based on quantization noise:

offset error) specifies the change from the value at

ENOB = (SINAD – 1.76)/6.02

the nominal temperature to the value at TMIN or TMAX.

It is computed as the maximum variation the

Gain Error

parameters over the whole temperature range divided

Gain error is the deviation of the ADC actual input

by TMIN – TMAX.

full-scale range from its ideal value, given as a

percentage of the ideal input full-scale range.

Total Harmonic Distortion (THD)

THD is the ratio of the power of the fundamental (PS)

Integral Nonlinearity (INL)

to the power of the first five harmonics (PD).

INL is the deviation of the ADC transfer function from

a best-fit line determined by a least-squares curve fit

of that transfer function. The INL at each analog input

value is the difference between the actual transfer

function and this best-fit line, measured in units of

THD is typically given in units of dBc (dB to carrier).

LSB.

Two-Tone Intermodulation Distortion (IMD3)

Offset Error

IMD3 is the ratio of the power of the fundamental (at

Offset error is the deviation of output code from

frequencies f1, f2) to the power of the worst spectral

mid-code

when

both

inputs

are

tied

component at either frequency 2f1 – f2 or 2f2 – f1).

common-mode.

IMD3 is given in units of either dBc (dB to carrier)

when the absolute power of the fundamental is used

Power-Supply Rejection Ratio (PSRR)

as the reference, or dBFS (dB to full-scale) when the

PSRR is a measure of the ability to reject frequencies

power of the fundamental is extrapolated to the

present on the power supply.

converter full-scale range.

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