Datasheet LTC1411 (Analog Devices) - 9

LTC1411
U U W U APPLICATIO S I FOR ATIO
0 86 14 SINAD = 78.8dB 80 13 SFDR = 95dB –20 fSAMPLE = 2.5MHz 74 12 fIN = 100kHz 68 11 –40 EFFECTIVE BITS 62 10 –60 56 50 –80 44 S/(N + D) (dB) AMPLITUDE (dB) 38 –100 32 –120 26 20 –140 14 0 250 500 750 1000 1250 10 100 1000 10000 INPUT FREQUENCY (kHz) INPUT FREQUENCY (kHz) 1411 G14 1411 TA02
Figure 2a. LTC1411 Nonaveraged, 4096 Point FFT, Figure 3. Effective Bits and Signal/(Noise + Distortion) Input Frequency = 100kHz vs Input Frequency
0 0 SINAD = 75dB –10 SFDR = 81dB –20 fSAMPLE = 2.5MHz –20 fIN = 1MHz –30 –40 –40 –60 –50 –60 –80 –70 AMPLITUDE (dB) DISTORTION (dB) –100 –80 THD 2ND –90 –120 3RD –100 –140 –110 0 250 500 750 1000 1250 10 100 1000 10000 FREQUENCY (kHz) INPUT FREQUENCY (kHz) 1411 G03 1411 G15
Figure 2b. LTC1411 4096 Point FFT, Figure 4. Distortion vs Input Frequency Input Frequency = 1MHz Effective Number of Bits
itself. The out-of-band harmonics alias into the frequency band between DC and half the sampling frequency. THD is The effective number of bits (ENOBs) is a measurement of expressed as: the resolution of an ADC and is directly related to the S/(N + D) by the equation: 2 2 2 2 ENOB V + V3 + V4 +…V S = [S/(N + D) – 1.76]/6.02 THD N = 20 2 log where S/(N + D) is expressed in dB. At the maximum V1 sampling rate of 2.5MHz the LTC1411 maintains good where V ENOBs up to the Nyquist input frequency of 1.25MHz. 1 is the RMS amplitude of the fundamental fre- quency and V Refer to Figure␣ 3. 2 through VN are the amplitudes of the second through Nth harmonics. THD vs input frequency is shown in Figure 4. The LTC1411 has good distortion
Total Harmonic Distortion
performance up to the Nyquist frequency and beyond. Total harmonic distortion (THD) is the ratio of the RMS sum of all harmonics of the input signal to the fundamental 1411f 9