DEFINITION OF SPECIFICATIONS

SNR + 10log10

P

S

P

N

(4)

SINAD + 10log10

P

S

P

N ) PD

(5)

THD + 10log10

P

S

P

D

(6)

ADS5463

ADS54RF63

SLAS515E – NOVEMBER 2006 – REVISED JULY 2009 ................................................................................................................................................... www.ti.com

PSRR is a measure of the ability to reject frequencies

present on the power supply. The injected frequency

Analog Bandwidth

level is translated into dBFS, the spur in the output

The analog input frequency at which the power of the

FFT is measured in dBFS, and the difference is the

fundamental is reduced by 3 dB with respect to the

PSRR in dB. The measurement calibrates out the

low-frequency value

benefit of the board supply decoupling capacitors.

Aperture Delay

Signal-to-Noise Ratio (SNR)

The delay in time between the rising edge of the input

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

sampling clock and the actual time at which the

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

sampling occurs

dc and in the first five harmonics.

Aperture Uncertainty (Jitter)

The sample-to-sample variation in aperture delay

Clock Pulse Duration/Duty Cycle

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

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

when the absolute power of the fundamental is used

the clock signal remains at a logic high (clock pulse

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

duration) to the period of the clock signal, expressed

power of the fundamental is extrapolated to the

as a percentage.

converter’s full-scale range.

Differential Nonlinearity (DNL)

Signal-to-Noise and Distortion (SINAD)

An ideal ADC exhibits code transitions at analog input

SINAD is the ratio of the power of the fundamental

values spaced exactly 1 LSB apart. DNL is the

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

deviation of any single step from this ideal value,

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

measured in units of LSB.

dc.

Common-Mode Rejection Ratio (CMRR)

CMRR measures the ability to reject signals that are

presented to both analog inputs simultaneously. The

injected common-mode frequency level is translated

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

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

when the absolute power of the fundamental is used

dBFS, and the difference is the CMRR in dB.

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

Effective Number of Bits (ENOB)

power of the fundamental is extrapolated to the

ENOB is a measure in units of bits of a converter's

converter’s full-scale range.

performance as compared to the theoretical limit

Temperature Drift

based on quantization noise

Temperature drift (with respect to gain error and

ENOB = (SINAD – 1.76)/6.02

offset error) specifies the change from the value at

the nominal temperature to the value at TMIN or TMAX.

Gain Error

It is computed as the maximum variation the

Gain error is the deviation of the ADC actual input

parameters over the whole temperature range divided

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

by TMIN – TMAX.

percentage of the ideal input full-scale range.

Total Harmonic Distortion (THD)

Integral Nonlinearity (INL)

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

INL is the deviation of the ADC transfer function from

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

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

LSB.

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

Offset Error

Two-Tone Intermodulation Distortion (IMD3)

Offset error is the deviation of output code from

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

mid-code

when

both

inputs

are

tied

to

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

common-mode.

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

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

Power-Supply Rejection Ratio (PSRR)

when the absolute power of the fundamental is used

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

power of the fundamental is extrapolated to the

converter’s full-scale range.

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