AD7729 Просмотр технического описания (PDF) - Analog Devices

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AD7729

Dual Sigma-Delta ADC with Auxiliary DAC

Analog Devices 

AD7729

TERMINOLOGY

Absolute Group Delay

Absolute group delay is the rate of change of phase versus fre-

quency, dø/df. It is expressed in microseconds.

Differential Nonlinearity

This is the difference between the measured and the ideal

1 LSB change between any two adjacent codes in the DAC or

ADC.

Dynamic Range

Dynamic Range is the ratio of the maximum output signal to the

smallest output signal the converter can produce (1 LSB), ex-

pressed logarithmically, in decibels (dB = 201og10 (ratio)). For

an N-bit converter, the ratio is theoretically very nearly equal to

2N (in dB, 20Nlog10(2) = 6.02N). However, this theoretical

value is degraded by converter noise and inaccuracies in the

LSB weight.

Gain Error

This is 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. In the AD7729, gain error is specified for the

auxiliary section.

Gain Matching Between Channels

This is the gain matching between the IRx and QRx channel

and is expressed in dBs.

Group Delay Between Channels

This is the difference between the group delay of the I and Q

channels and is a measure of the phase matching characteristics

of the two.

Integral Nonlinearity

This is the maximum deviation from a straight line passing

through the endpoints of the auxiliary DAC transfer function.

Output Rate

This is the rate at which data words are made available

(270.833 kHz).

Offset Error

This is the amount of offset, wrt VREF in the auxiliary DAC and

is expressed in mVs.

Output Signal Span

This is the output signal range for the auxiliary DAC section.

Sampling Rate

This is the rate at which the modulators on the receive channels

sample the analog input.

Settling Time

This is the digital filter settling time in the AD7729 receive

section. On initial power-up or after returning from the power-

down mode, it is necessary to wait this amount of time to get

useful data.

Signal Input Span

The input signal range for the I and Q channels is biased about

VREF.

Signal to (Noise + Distortion) Ratio

This is the measured ratio of signal to (noise + distortion) at the

output of the receive channel. The signal is the rms amplitude of

the fundamental. Noise is the rms sum of all nonfundamental

signals up to half the sampling frequency (fS/2), excluding dc.

The ratio is dependent upon the number of quantization levels

in the digitization process; the more levels, the smaller the quan-

tization noise. The theoretical signal to (noise + distortion) ratio

for a sine wave is given by:

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

–8–

REV. 0

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