Datasheet LTC1417 (Analog Devices) - 10

LTC1417
U U W U APPLICATIONS INFORMATION
0 f
Effective Number of Bits
SAMPLE = 400kHz fIN = 10.05859375kHz –20 SFDR = –97.44dB The effective number of bits (ENOBs) is a measurement of SINAD = 81.71dB the resolution of an ADC and is directly related to the –40 S/(N + D) by the equation: –60 ENOB (N) = [S/(N + D) – 1.76]/6.02 AMPLITUDE (dB) –80 where N is the effective number of bits of resolution and –100 S/(N + D) is expressed in dB. At the maximum sampling rate of 400kHz, the LTC1417 maintains near ideal ENOBs –120 0 50 100 150 200 up to the Nyquist input frequency of 200kHz (refer to FREQUENCY (kHz) Figure 4). 1417 G07 14 86
Figure 3a. LTC1417 Nonaveraged, 4096 Point FFT,
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Input Frequency = 10kHz
12 74 68 0 10 62 S/(N + D) (dB) fSAMPLE = 400kHz fIN = 197.949188kHz –20 SFDR = –98dB 8 SINAD = 81.1dB –40 EFFECTIVE BITS 6 –60 4 AMPLITUDE (dB) –80 2 1k 10k 100k 1M INPUT FREQUENCY (Hz) –100 1417 TA02 –120
Figure 4. Effective Bits and Signal/(Noise + Distortion)
0 50 100 150 200
vs Input Frequency
FREQUENCY (kHz) 1417 G08
Total Harmonic Distortion Figure 3b. LTC1417 Nonaveraged, 4096 Point FFT, Input Frequency = 200kHz
Total harmonic distortion (THD) is the ratio of the RMS sum of all harmonics of the input signal to the fundamental itself. The out-of-band harmonics alias into the frequency
Signal-to-Noise Ratio
band between DC and half the sampling frequency. THD is The signal-to-noise plus distortion ratio [S/(N + D)] is the expressed as: ratio between the RMS amplitude of the fundamental input 2 2 2 2 ... frequency to the RMS amplitude of all other frequency V2 V3 V4 Vn THD = + + + Log 20 components at the A/D output. The output is band limited V1 to frequencies from above DC and below half the sampling where V1 is the RMS amplitude of the fundamental fre- frequency. Figure 3b shows a typical spectral content with quency and V2 through Vn are the amplitudes of the a 400kHz sampling rate and a 200kHz input. The dynamic second through nth harmonics. THD vs Input Frequency is performance is excellent for input frequencies up to and shown in Figure 5. The LTC1417 has good distortion beyond the Nyquist limit of 200kHz. performance up to the Nyquist frequency and beyond. sn1417 1417fas 10