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AD7091

1 MSPS, Ultralow Power, 12-Bit ADC in 8-Lead LFCSP

Analog Devices 

Data Sheet

TERMINOLOGY

Integral Nonlinearity (INL)

INL is the maximum deviation from a straight line passing

through the endpoints of the ADC transfer function. For the

AD7091, the endpoints of the transfer function are zero scale

(a point 0.5 LSB below the first code transition) and full scale

(a point 0.5 LSB above the last code transition).

Differential Nonlinearity (DNL)

DNL is the difference between the measured and the ideal

1 LSB change between any two adjacent codes in the ADC.

Offset Error

Offset error is the deviation of the first code transition (00 … 000

to 00 … 001) from the ideal (such as GND + 0.5 LSB).

Gain Error

Gain error is the deviation of the last code transition (111 … 110

to 111 … 111) from the ideal (such as VDD − 1.5 LSB) after the

offset error has been adjusted out.

Track-and-Hold Acquisition Time

The track-and-hold amplifier returns to track mode after the

end of a conversion. The track-and-hold acquisition time is the

time required for the output of the track-and-hold amplifier to

reach its final value, within ±0.5 LSB, after a conversion.

Signal-to-Noise Ratio (SNR)

SNR is the measured ratio of signal to noise at the output of the

ADC. The signal is the rms amplitude of the fundamental. Noise

is the sum of all nonfundamental signals up to half the sampling

frequency (fSAMPLE/2), excluding dc.

The ratio is dependent on the number of quantization levels in the

digitization process: the more levels, the smaller the quantization

noise. The theoretical signal-to-noise ratio for an ideal N-bit

converter with a sine wave input is given by

Signal-to-Noise Ratio = (6.02N + 1.76) dB

Therefore, for a 12-bit converter, the SNR is 74 dB.

AD7091

Signal-to-Noise-and-Distortion Ratio (SINAD)

SINAD is the measured ratio of signal to noise and distortion

at the output of the ADC. The signal is the rms value of the sine

wave, and noise is the rms sum of all nonfundamental signals up

to half the sampling frequency (fSAMPLE/2), including harmonics,

but excluding dc.

Total Unadjusted Error (TUE)

TUE is a comprehensive specification that includes the gain,

linearity, and offset errors.

Total Harmonic Distortion (THD)

THD is the ratio of the rms sum of harmonics to the funda-

mental. For the AD7091, THD is defined as

THD (dB) = 20 log V22 + V32 + V42 + V52 + V62

V1

where:

V1 is the rms amplitude of the fundamental.

V2, V3, V4, V5, and V6 are the rms amplitudes of the second

through the sixth harmonics.

Spurious-Free Dynamic Range (SFDR)

SFDR, also known as peak harmonic or spurious noise, is defined

as the ratio of the rms value of the next largest component in the

ADC output spectrum (up to fSAMPLE/2 and excluding dc) to the

rms value of the fundamental.

Aperture Delay

Aperture delay is the measured interval between the leading edge of

the sampling clock and the point at which the ADC samples data.

Aperture Jitter

Aperture jitter is the sample-to-sample variation in the effective

point in time at which the data is sampled.

Full Power Bandwidth

Full power bandwidth is the input frequency at which the ampli-

tude of the reconstructed fundamental is reduced by 0.1 dB or

3 dB for a full-scale input.

Rev. B | Page 9 of 20

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