Datasheet LTC1412 (Analog Devices) - 9
| Fabricante | Analog Devices |
| Descripción | 12-Bit, 3Msps, Sampling A/D Converter |
| Páginas / Página | 16 / 9 — APPLICATIONS INFORMATION. Figure 3. Effective Bits and Signal/(Noise + … |
| Formato / tamaño de archivo | PDF / 347 Kb |
| Idioma del documento | Inglés |
APPLICATIONS INFORMATION. Figure 3. Effective Bits and Signal/(Noise + Distortion). vs Input Frequency
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LTC1412
U U W U APPLICATIONS INFORMATION
12 74 68 produce intermodulation distortion (IMD) in addition to 10 62 THD. IMD is the change in one sinusoidal input caused by 56 the presence of another sinusoidal input at a different 8 S/(N + D) (dB) frequency. 6 If two pure sine waves of frequencies fa and fb are applied 4 to the ADC input, nonlinearities in the ADC transfer func- EFFECTIVE NUMBER OF BITS tion can create distortion products at the sum and differ- 2 ence frequencies of mfa ±nfb, where m and n = 0, 1, 2, 3, 0 etc. For example, the 2nd order IMD terms include 1k 10k 100k 1M 10M INPUT FREQUENCY (Hz) (fa + fb). If the two input sine waves are equal in magni- 1412 G01 tude, the value (in decibels) of the 2nd order IMD products
Figure 3. Effective Bits and Signal/(Noise + Distortion)
can be expressed by the following formula:
vs Input Frequency Total Harmonic Distortion
( Amplitude at fa ± f )b IMD f ( +f )= a b 20 log Amplitude at f Total Harmonic Distortion (THD) is the ratio of the RMS a sum of all harmonics of the input signal to the fundamental 0 itself. The out-of-band harmonics alias into the frequency fSMPL = 3MHz –10 fIN1 = 85.693359kHz band between DC and half the sampling frequency. THD is –20 fIN2 = 114.990234kHz expressed as: – 30 – 40 – 50 V2 2 2 + V2 + V 2 4 + . .V THD = 20 3 log n – 60 V – 70 1 AMPLITUDE (dB) – 80 where V1 is the RMS amplitude of the fundamental fre- – 90 quency and V2 through Vn are the amplitudes of the –100 second through Nth harmonics. THD vs input frequency is –110 0 200 400 600 800 1000 1200 1400 shown in Figure 4. The LTC1412 has good distortion FREQUENCY (kHz) performance up to the Nyquist frequency and beyond. 1412 G05
Figure 5. Intermodulation Distortion Plot
0 – 20
Peak Harmonic or Spurious Noise
– 40 The peak harmonic or spurious noise is the largest spec- tral component excluding the input signal and DC. This – 60 value is expressed in decibels relative to the RMS value of DISTORTION (dB) – 80 a full-scale input signal. THD –100 3RD
Full Power and Full Linear Bandwidth
2ND –120 The full power bandwidth is that input frequency at which 10 100 1k 10k INPUT FREQUENCY (Hz) the amplitude of the reconstructed fundamental is 1412 G03 reduced by 3dB for a full-scale input signal.
Figure 4. Distortion vs Input Frequency
The full linear bandwidth is the input frequency at which
Intermodulation Distortion
the S/(N + D) has dropped to 68dB (11 effective bits). The LTC1412 has been designed to optimize input bandwidth, If the ADC input signal consists of more than one spectral allowing the ADC to undersample input signals with fre- component, the ADC transfer function nonlinearity can 9
U U W U APPLICATIONS INFORMATION
12 74 68 produce intermodulation distortion (IMD) in addition to 10 62 THD. IMD is the change in one sinusoidal input caused by 56 the presence of another sinusoidal input at a different 8 S/(N + D) (dB) frequency. 6 If two pure sine waves of frequencies fa and fb are applied 4 to the ADC input, nonlinearities in the ADC transfer func- EFFECTIVE NUMBER OF BITS tion can create distortion products at the sum and differ- 2 ence frequencies of mfa ±nfb, where m and n = 0, 1, 2, 3, 0 etc. For example, the 2nd order IMD terms include 1k 10k 100k 1M 10M INPUT FREQUENCY (Hz) (fa + fb). If the two input sine waves are equal in magni- 1412 G01 tude, the value (in decibels) of the 2nd order IMD products
Figure 3. Effective Bits and Signal/(Noise + Distortion)
can be expressed by the following formula:
vs Input Frequency Total Harmonic Distortion
( Amplitude at fa ± f )b IMD f ( +f )= a b 20 log Amplitude at f Total Harmonic Distortion (THD) is the ratio of the RMS a sum of all harmonics of the input signal to the fundamental 0 itself. The out-of-band harmonics alias into the frequency fSMPL = 3MHz –10 fIN1 = 85.693359kHz band between DC and half the sampling frequency. THD is –20 fIN2 = 114.990234kHz expressed as: – 30 – 40 – 50 V2 2 2 + V2 + V 2 4 + . .V THD = 20 3 log n – 60 V – 70 1 AMPLITUDE (dB) – 80 where V1 is the RMS amplitude of the fundamental fre- – 90 quency and V2 through Vn are the amplitudes of the –100 second through Nth harmonics. THD vs input frequency is –110 0 200 400 600 800 1000 1200 1400 shown in Figure 4. The LTC1412 has good distortion FREQUENCY (kHz) performance up to the Nyquist frequency and beyond. 1412 G05
Figure 5. Intermodulation Distortion Plot
0 – 20
Peak Harmonic or Spurious Noise
– 40 The peak harmonic or spurious noise is the largest spec- tral component excluding the input signal and DC. This – 60 value is expressed in decibels relative to the RMS value of DISTORTION (dB) – 80 a full-scale input signal. THD –100 3RD
Full Power and Full Linear Bandwidth
2ND –120 The full power bandwidth is that input frequency at which 10 100 1k 10k INPUT FREQUENCY (Hz) the amplitude of the reconstructed fundamental is 1412 G03 reduced by 3dB for a full-scale input signal.
Figure 4. Distortion vs Input Frequency
The full linear bandwidth is the input frequency at which
Intermodulation Distortion
the S/(N + D) has dropped to 68dB (11 effective bits). The LTC1412 has been designed to optimize input bandwidth, If the ADC input signal consists of more than one spectral allowing the ADC to undersample input signals with fre- component, the ADC transfer function nonlinearity can 9