Datasheet AD7927 (Analog Devices) - 10

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Data Sheet AD7927 Signal-to-(Noise + Distortion) Ratio (SINAD) Total Harmonic Distortion (THD)
This is the measured ratio of signal-to-(noise + distortion) at THD is the ratio of the rms sum of harmonics to the the output of the ADC. The signal is the rms amplitude of the fundamental. For the AD7927, it is defined as: fundamental. Noise is the sum of all nonfundamental signals 2 2 2 2 2 V  V  V  V  V 2 3 4 5 6 up to half the sampling frequency (f  S/2), excluding dc. The ratio THD( ) dB 20log V is dependent on the number of quantization levels in the digiti- 1 zation process; the more levels, the smaller the quantization where: noise. The theoretical signal-to-(noise + distortion) ratio for V1 is the rms amplitude of the fundamental. an ideal N-bit converter with a sine wave input is given by V2, V3, V4, V5, and V6 are the rms amplitudes of the second Signal-to-(Noise + Distortion) = (6.02N + 1.76)dB through the sixth harmonics. Thus, for a 12-bit converter, this is 74 dB. Figure 5 shows the Figure 7 shows a graph of total harmonic distortion vs. analog signal-to-(noise + distortion) ratio performance vs. input fre- input frequency for various supply voltages, and Figure 8 shows quency for various supply voltages while sampling at 200 kSPS a graph of total harmonic distortion vs. analog input frequency with an SCLK of 20 MHz. for various source impedances (see the Analog Input section). Rev. D | Page 9 of 28 Document Outline Features General Description Functional Block Diagram Product Highlights Revision History Specifications Timing Specifications Absolute Maximum Ratings ESD Caution Pin Configuration and Function Descriptions Terminology Typical Performance Characteristics Control Register Sequencer Operation Shadow Register Circuit Information Converter Operation Analog Input ADC Transfer Function Handling Bipolar Input Signals Typical Connection Diagram Analog Input Selection Digital Inputs VDRIVE The Reference Modes of Operation Normal Mode (PM1 = PM0 = 1) Full Shutdown (PM1 = 1, PM0 = 0) Auto Shutdown (PM1 = 0, PM0 = 1) Powering Up the AD7927 Power vs. Throughput Rate Serial Interface Writing Between Conversions Microprocessor Interfacing AD7927 to TMS320C541 AD7927 to ADSP-21xx AD7927 to DSP563xx Application Hints Grounding and Layout Outline Dimensions Ordering Guide Automotive Products