Datasheet LTC1414 (Analog Devices) - 8
| Manufacturer | Analog Devices |
| Description | 14-Bit, 2.2 Msps, Sampling A/D Converter |
| Pages / Page | 20 / 8 — APPLICATIONS INFORMATION. Figure 3. Effective Bits and Signal/(Noise + … |
| File Format / Size | PDF / 296 Kb |
| Document Language | English |
APPLICATIONS INFORMATION. Figure 3. Effective Bits and Signal/(Noise + Distortion). Figure 2b. LTC1414 2048 Point FFT,
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LTC1414
U U W U APPLICATIONS INFORMATION
14 0 86 SINAD = 78dB 13 80 12 –20 SFDR = 84dB 74 fSAMPLE = 2.2MHz 11 68 f 10 S/(N + D) (dB) –40 IN = 997.949kHz 9 –60 8 7 EFFECTIVE BITS AMPLITUDE (dB) –80 6 5 –100 4 3 fSAMPLE = 2.2MHz –120 2 0 200 400 600 800 1000 1k 10k 100k 1M 10M FREQUENCY (kHz) INPUT FREQUENCY (Hz) 1414 TA02 1414 F02b
Figure 3. Effective Bits and Signal/(Noise + Distortion) Figure 2b. LTC1414 2048 Point FFT, vs Input Frequency Input Frequency = 1MHz
0 –10
Effective Number of Bits
–20 The effective number of bits (ENOBs) is a measurement of –30 the resolution of an ADC and is directly related to the –40 S/(N + D) by the equation: –50 THD –60 ENOBS = [S/(N + D) – 1.76]/6.02 DISTORTION (dB) –70 where S/(N + D) is expressed in dB. At the maximum –80 2nd –90 sampling rate of 2.2MHz the LTC1414 maintains near ideal 3rd –100 ENOBs up to the Nyquist input frequency of 1.1MHz. Refer 1 10k 100k 1M 10M to Figure␣ 3. INPUT FREQUENCY (Hz) 1414 F04
Figure 4. Distortion vs Input Frequency Total Harmonic Distortion
Total harmonic distortion (THD) is the ratio of the RMS
Intermodulation Distortion
sum of all harmonics of the input signal to the fundamental If the ADC input signal consists of more than one spectral itself. The out-of-band harmonics alias into the frequency component, the ADC transfer function nonlinearity can band between DC and half the sampling frequency. THD is produce intermodulation distortion (IMD) in addition to expressed as: the THD. IMD is the change in one sinusoidal input caused by the presence of another sinusoidal input at a different 2 2 2 2 frequency. V + V3 + V4 +…V THD N = 20 2 log If two pure sine waves of frequencies f V a and fb are applied 1 to the ADC input, nonlinearities in the ADC transfer func- where V tion can create distortion products at the sum and differ- 1 is the RMS amplitude of the fundamental fre- quency and V ence frequencies of mf 2 through VN are the amplitudes of the a ± nfb, where m and n = 0, 1, 2, 3 second through Nth harmonics. THD vs input frequency is etc. For example, the 2nd order IMD terms include (fa ± fb). shown in Figure 4. The LTC1414 has good distortion If the two input sine waves are equal in magnitude, the performance up to the Nyquist frequency and beyond. value (in dB) of the 2nd order IMD products can be expressed by the following formula: 8
U U W U APPLICATIONS INFORMATION
14 0 86 SINAD = 78dB 13 80 12 –20 SFDR = 84dB 74 fSAMPLE = 2.2MHz 11 68 f 10 S/(N + D) (dB) –40 IN = 997.949kHz 9 –60 8 7 EFFECTIVE BITS AMPLITUDE (dB) –80 6 5 –100 4 3 fSAMPLE = 2.2MHz –120 2 0 200 400 600 800 1000 1k 10k 100k 1M 10M FREQUENCY (kHz) INPUT FREQUENCY (Hz) 1414 TA02 1414 F02b
Figure 3. Effective Bits and Signal/(Noise + Distortion) Figure 2b. LTC1414 2048 Point FFT, vs Input Frequency Input Frequency = 1MHz
0 –10
Effective Number of Bits
–20 The effective number of bits (ENOBs) is a measurement of –30 the resolution of an ADC and is directly related to the –40 S/(N + D) by the equation: –50 THD –60 ENOBS = [S/(N + D) – 1.76]/6.02 DISTORTION (dB) –70 where S/(N + D) is expressed in dB. At the maximum –80 2nd –90 sampling rate of 2.2MHz the LTC1414 maintains near ideal 3rd –100 ENOBs up to the Nyquist input frequency of 1.1MHz. Refer 1 10k 100k 1M 10M to Figure␣ 3. INPUT FREQUENCY (Hz) 1414 F04
Figure 4. Distortion vs Input Frequency Total Harmonic Distortion
Total harmonic distortion (THD) is the ratio of the RMS
Intermodulation Distortion
sum of all harmonics of the input signal to the fundamental If the ADC input signal consists of more than one spectral itself. The out-of-band harmonics alias into the frequency component, the ADC transfer function nonlinearity can band between DC and half the sampling frequency. THD is produce intermodulation distortion (IMD) in addition to expressed as: the THD. IMD is the change in one sinusoidal input caused by the presence of another sinusoidal input at a different 2 2 2 2 frequency. V + V3 + V4 +…V THD N = 20 2 log If two pure sine waves of frequencies f V a and fb are applied 1 to the ADC input, nonlinearities in the ADC transfer func- where V tion can create distortion products at the sum and differ- 1 is the RMS amplitude of the fundamental fre- quency and V ence frequencies of mf 2 through VN are the amplitudes of the a ± nfb, where m and n = 0, 1, 2, 3 second through Nth harmonics. THD vs input frequency is etc. For example, the 2nd order IMD terms include (fa ± fb). shown in Figure 4. The LTC1414 has good distortion If the two input sine waves are equal in magnitude, the performance up to the Nyquist frequency and beyond. value (in dB) of the 2nd order IMD products can be expressed by the following formula: 8
