Datasheet AD7829-1 (Analog Devices) - 9

AD7829-1 TERMINOLOGY
As a result, the second and third order terms are specified
Signal-to-(Noise + Distortion) Ratio
separately. The calculation of the intermodulation distortion is The measured ratio of signal-to-(noise + distortion) at the as per the THD specification, where it is the ratio of the rms output of the A/D converter. The signal is the rms amplitude of sum of the individual distortion products to the rms amplitude the fundamental. Noise is the rms sum of all nonfundamental of the fundamental expressed in decibels (dB). signals up to half the sampling frequency (fS/2), excluding dc. The ratio is dependent upon the number of quantization levels
Channel-to-Channel Isolation
in the digitization process; the more levels, the smaller the A measure of the level of crosstalk between channels. It is quantization noise. The theoretical signal-to-(noise + measured by applying a full-scale 20 kHz sine wave signal to distortion) ratio for an ideal N-bit converter with a sine wave one input channel and determining how much that signal is input is given by attenuated in each of the other channels. The figure given is Signal-to-(Noise + Distortion) = (6.02N + 1.76) dB the worst case across all eight channels of the AD7829-1. Thus, for an 8-bit converter, this is 50 dB.
Relative Accuracy or Endpoint Nonlinearity
The maximum deviation from a straight line passing through
Total Harmonic Distortion (THD)
the endpoints of the ADC transfer function. The ratio of the rms sum of harmonics to the fundamental. For the AD7829-1 it is defined as
Differential Nonlinearity
2 2 2 2 2 The difference between the measured and the ideal 1 LSB V + V + V + V + V 2 3 4 5 6 THD dB ( ) = 20 log change between any two adjacent codes in the ADC. V1
Offset Error
where V1 is the rms amplitude of the fundamental, and V2, V3, V The deviation of the 128th code transition (01111111) to 4, V5, and V6 are the rms amplitudes of the second through the sixth harmonics. (10000000) from the ideal, that is, VMID.
Offset Error Match Peak Harmonic or Spurious Noise
The difference in offset error between any two channels. The ratio of the rms value of the next largest component in the ADC output spectrum (up to fS/2 and excluding dc) to the rms
Zero-Scale Error
value of the fundamental. Normally, the value of this specifica- The deviation of the first code transition (00000000) to tion is determined by the largest harmonic in the spectrum, (00000001) from the ideal; that is, VMID − 1.25 V + 1 LSB (VDD = but for parts where the harmonics are buried in the noise floor, 5 V ± 10%), or VMID − 1.0 V + 1 LSB (VDD = 3 V ± 10%). it will be a noise peak.
Full-Scale Error Intermodulation Distortion
The deviation of the last code transition (11111110) to With inputs consisting of sine waves at two frequencies, fa and (11111111) from the ideal; that is, VMID + 1.25 V − 1 LSB (VDD = fb, any active device with nonlinearities creates distortion 5 V ± 10%), or VMID + 1.0 V − 1 LSB (VDD = 3 V ± 10%). products at sum and difference frequencies of mfa ± nfb, where m, n = 0, 1, 2, 3… . Intermodulation terms are those for which
Gain Error
neither m nor n is equal to zero. For example, the second order The deviation of the last code transition (1111 . 110) to terms include (fa + fb) and (fa − fb), while the third order terms (1111 . 111) from the ideal; that is, VREF − 1 LSB, after the include (2fa + fb), (2fa − fb), (fa + 2fb), and (fa − 2fb). The offset error has been adjusted out. AD7829-1 is tested using the CCIF standard, where two input frequencies near the top end of the input bandwidth are used.
Gain Error Match
In this case, the second and third order terms are of different The difference in gain error between any two channels. significance. The second order terms are usually distanced in frequency from the original sine waves, while the third order terms are usually at a frequency close to the input frequencies. Rev. 0 | Page 8 of 20 Document Outline FEATURES APPLICATIONS GENERAL DESCRIPTION FUNCTIONAL BLOCK DIAGRAM PRODUCT HIGHLIGHTS TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS TIMING CHARACTERISTICS TIMING DIAGRAM ABSOLUTE MAXIMUM RATINGS ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TERMINOLOGY CIRCUIT INFORMATION CIRCUIT DESCRIPTION TYPICAL CONNECTION DIAGRAM ADC TRANSFER FUNCTION ANALOG INPUT POWER-UP TIMES POWER VS. THROUGHPUT OPERATING MODES PARALLEL INTERFACE MICROPROCESSOR INTERFACING AD7829-1 TO 8051 AD7829-1 TO PIC16C6x/PIC16C7x AD7829-1 TO ADSP-21xx INTERFACING MULTIPLEXER ADDRESS INPUTS OUTLINE DIMENSIONS ORDERING GUIDE