AD7339

–11–

REV. 0

TERMINOLOGY

Differential Nonlinearity

The difference between the measured and the ideal 1 LSB change

between any two adjacent codes in the ADC or DACs. A speci-

fied Differential Nonlinearity of

±1 LSB max over the operating

temperature range ensures monotonicity.

Integral Nonlinearity

The maximum deviation of any code from a straight line passing

through the endpoints of the transfer function. The endpoints

of the transfer function are zero scale, a point 0.5 LSB below the

first code transition (000 . . . 00 to 000 . . . 01) and full scale, a

point 0.5 LSB above the last code transition (111 . . . 10 to

111 . . . 11). The error is expressed in LSBs.

Signal to (Noise + Distortion)

Signal to (Noise + Distortion) is measured signal-to-noise at the

output of the ADC. The signal is the rms magnitude of the

fundamental. Noise is the rms sum of all nonfundamental sig-

Signal to (Noise + Distortion) is dependent on the number of

quantization levels used in the digitization process; the more

levels, the smaller the quantization noise. The theoretical signal

to (Noise + Distortion) ratio for a sine wave signal is given by

Signal to (Noise + Distortion) = (6.02N + 1.76) dB

where N is the number of bits. Thus for an ideal 8-bit converter,

Signal to (Noise + Distortion) is 49.92 dB.

ADC

Effective Number of Bits (ENOB)

Signal to (Noise + Distortion) is expressed in dBs; rewriting the

Signal to (Noise + Distortion) formula, it is possible to get a

measure of performance expressed in effective number of bits.

The effective number of bits for a device can be calculated di-

rectly from its measured Signal to (Noise + Distortion) value.

ENOB = (SNR – 1.76)/6.02

where SNR is the Signal to (Noise + Distortion).

Zero Input Offset Error

This is the offset error in the ADC when the analog input is

zero. Ideally, the digital output should equal 100 . . . 00. The

offset error is the deviation from the ideal output code. The

offset error is expressed in LSBs.

Intermodulation Distortion

With inputs consisting of sine waves at two frequencies, fa and

fb, any active device with nonlinearities will create distortion

products, of order (m + n), at sum and difference frequencies

of mfa

± nfb, where m, n = 0, 1, 2, 3, . . .. Intermodulation

terms are those for which m or n is not equal to zero. For the

AD7339, the Intermodulation Distortion is the level to which

the second and third intermodulation terms are suppressed

below a full scale output signal level, the second order terms

being (fa + fb) and (fa – fb) while the third order terms are

(2fa + fb), (2fa – fb), (fa + 2fb) and (fa – 2fb).

Error Rate

The rate at which A-to-D conversion errors occur.

DACS

Bipolar Zero Offset Error

The deviation between the measured output voltage and the

bias voltage (VREFA or VREFB, depending on which DAC is

being tested) when the DAC is loaded with code 100 . . . 00

after gain error has been adjusted out.

Gain Error

A measure of the output error between an ideal DAC and the

actual device output with all 1s loaded after offset error has been

adjusted out.

Update Rate

The rate at which the DACs can be loaded with new data. The

parallel DACs have an update rate of 2.304 MHz while the

serial DACs have an update rate of 256/10 kHz maximum.

Gain Matching Between DACs

The matching between the analog output amplitudes of the

parallel DACs when the same digital word is written to each

DAC.

Crosstalk

The ratio of the amplitude of a full-scale signal appearing on

one channel to the amplitude of the same signal which couples

onto another channel. Crosstalk is expressed in dBs.

Output Harmonic Content

When the digital word is converted to analog form, harmonics

will also be generated. The Output Harmonic Content specifies

the amount by which these harmonics are attenuated relative to

the fundamental frequency. With the parallel DACs, a full sine

wave of frequency 0 kHz to 128 kHz is input. The resulting

analog output is evaluated and the amount by which the

harmonics in the frequency band 0 MHz to 1.1152 MHz are

attenuated is measured relative to the magnitude of the fun-

damental output signal.