Datasheet AD7729 (Analog Devices) - 9

AD7729 TERMINOLOGY Output Rate Absolute Group Delay
This is the rate at which data words are made available Absolute group delay is the rate of change of phase versus fre- (270.833 kHz). quency, dø/df. It is expressed in microseconds.
Offset Error Differential Nonlinearity
This is the amount of offset, wrt VREF in the auxiliary DAC and This is the difference between the measured and the ideal is expressed in mVs. 1 LSB change between any two adjacent codes in the DAC or
Output Signal Span
ADC. This is the output signal range for the auxiliary DAC section.
Dynamic Range Sampling Rate
Dynamic Range is the ratio of the maximum output signal to the This is the rate at which the modulators on the receive channels smallest output signal the converter can produce (1 LSB), ex- sample the analog input. pressed logarithmically, in decibels (dB = 201og10 (ratio)). For an N-bit converter, the ratio is theoretically very nearly equal to
Settling Time
2N (in dB, 20Nlog10(2) = 6.02N). However, this theoretical This is the digital filter settling time in the AD7729 receive value is degraded by converter noise and inaccuracies in the section. On initial power-up or after returning from the power- LSB weight. down mode, it is necessary to wait this amount of time to get useful data.
Gain Error
This is a measure of the output error between an ideal DAC and
Signal Input Span
the actual device output with all 1s loaded after offset error has The input signal range for the I and Q channels is biased about been adjusted out. In the AD7729, gain error is specified for the VREF. auxiliary section.
Signal to (Noise + Distortion) Ratio
This is the measured ratio of signal to (noise + distortion) at the
Gain Matching Between Channels
This is the gain matching between the IRx and QRx channel output of the receive channel. The signal is the rms amplitude of and is expressed in dBs. the fundamental. Noise is the rms sum of all nonfundamental signals up to half the sampling frequency (fS/2), excluding dc.
Group Delay Between Channels
The ratio is dependent upon the number of quantization levels This is the difference between the group delay of the I and Q in the digitization process; the more levels, the smaller the quan- channels and is a measure of the phase matching characteristics tization noise. The theoretical signal to (noise + distortion) ratio of the two. for a sine wave is given by:
Integral Nonlinearity
Signal to (Noise + Distortion) = (6.02N + 1.76) dB This is the maximum deviation from a straight line passing through the endpoints of the auxiliary DAC transfer function. –8– REV. 0