AD1876

REV. A

–4–

CLK

BUSY

CAL

Figure 1. AD1876 Calibration Timing

CLK

SAMPLE

BUSY

LSB

MSB

1

2

3

16

17

PREVIOUS LSB

X

Figure 2. Recommended AD1876 Conversion Timing

Definition of Specifications

NYQUIST FREQUENCY

An implication of the Nyquist sampling theorem, the “Nyquist

Frequency” of a converter is that input frequency which is one-

half the sampling frequency of the converter.

TOTAL HARMONIC DISTORTION

Total harmonic distortion (THD) is measured as the ratio of the

rms sum of the first nineteen harmonic components to the rms

value of a 1 kHz full-scale sine wave input signal and is ex-

pressed in percent (%) or decibels (dB). For input signals or

harmonics that are above the Nyquist frequency, the aliased

component is used.

SIGNAL-TO-NOISE PLUS DISTORTION RATIO

Signal-to-noise plus distortion (S/N+D) is defined to be the ra-

tio of the rms value of the measured input signal to the rms sum

of all other spectral components below the Nyquist frequency,

including harmonics but excluding dc.

D-RANGE DISTORTION

D-range distortion is the ratio of the distortion plus noise to the

signal at a signal amplitude of –60 dB. In this case, an A-weight

filter is used. The value specified for D-range performance is the

ratio measured plus 60 dB.

BANDWIDTH

The full power bandwidth is that input frequency at which the

amplitude of the reconstructed fundamental is reduced by 3 dB

for a full-scale input.

INTERMODULATION DISTORTION (IMD)

± nf

where m, n = 0, l, 2, 3. . . . Intermodulation terms are those for

which m or n is not equal to zero. For example, the second or-

are expressed as the decibel ratio of the rms sum of the mea-

sured input signals to the rms sum of the distortion terms. The

two signals applied to the converter are of equal amplitude, and

the peak value of their sum is –0.05 dB from full scale. The

IMD products are normalized to a 0 dB input signal.

APERTURE DELAY

Aperture delay is the time required after SAMPLE is taken

LOW for the internal sample-hold of the AD1876 to open, thus

APERTURE JITTER

Aperture jitter is the variation in the aperture delay from sample

to sample.