Datasheet LTC1406 (Analog Devices) - 8
| Manufacturer | Analog Devices |
| Description | Low Power, 8-Bit, 20Msps, Sampling A/D Converter |
| Pages / Page | 16 / 8 — APPLICATIONS INFORMATION. Figure 2a. Nonaveraged, 4096 Point FFT. Input … |
| File Format / Size | PDF / 381 Kb |
| Document Language | English |
APPLICATIONS INFORMATION. Figure 2a. Nonaveraged, 4096 Point FFT. Input Frequency = 1MHz
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LTC1406
U U W U APPLICATIONS INFORMATION
0 f where ENOB is the effective number of bits and S/(N + D) SAMPLE = 20MHz –10 fIN1 = 1.000977MHz is expressed in dB. At the maximum sampling rate of 20MHz –20 SFDR = 64.8dB SINAD = 48.6dB the LTC1406 maintains near ideal ENOBs up to and be- –30 yond the Nyquist input frequency of 10MHz (see Figure 3). –40 –50 8 50 –60 AMPLITUDE (dB) –70 7 44 –80 6 38 –90 S/(N + D) (dB) 5 32 –100 0 1 2 3 4 5 6 7 8 9 10 4 FREQUENCY (Hz) 3 1406 F02a EFFECTIVE BITS
Figure 2a. Nonaveraged, 4096 Point FFT
2
Input Frequency = 1MHz
1 0 100k 1M 10M 100M 0 INPUT FREQUENCY (Hz) fSAMPLE = 20MHz –10 1406 TA02 fIN1 = 28.99902MHz –20 SFDR = 54.9dB
Figure 3. Effective Bits and Signal-to-(Noise + Distortion)
SINAD = 47.0dB –30
vs Input Frequency
–40 –50
Total Harmonic Distortion
–60 AMPLITUDE (dB) –70 Total harmonic distortion is the ratio of the RMS sum of all –80 harmonics of the input signal to the fundamental itself. The –90 out-of-band harmonics alias into the frequency band –100 0 1 2 3 4 5 6 7 8 9 10 between DC and half the sampling frequency. THD is FREQUENCY (Hz) expressed as: 1406 F02b
Figure 2b. Nonaveraged, 4096 Point FFT
2 2 2 2
Input Frequency = 30MHz
V2 + V + V4 + . .V THD = 20 3 log n V1 where V
Signal-to-Noise Ratio
1 is the RMS amplitude of the fundamental fre- quency and V2 through Vn are the amplitudes of the sec- The signal-to-noise plus distortion ratio [S/(N + D)] is the ond through nth harmonics. THD vs Input Frequency is ratio between the RMS amplitude of the fundamental input shown in Figure 4. The LTC1406 has good distortion per- frequency and the RMS amplitude of all other frequency formance up to the Nyquist frequency and beyond. components at the ADC output. The output is band limited to frequencies above DC to below half the sampling fre-
Intermodulation Distortion
quency. The effective number of bits (ENOBs) is a mea- If the ADC input signal consists of more than one spectral surement of the resolution of an ADC and is directly related component, the ADC transfer function nonlinearity can to the S/(N + D) by the equation: produce intermodulation distortion (IMD) in addition to ENOB = [S/(N + D) – 1.76]/6.02 THD. IMD is the change in one sinusoidal input caused by the presence of another sinusoidal input at a different fre- quency (see Figure 5). 8
U U W U APPLICATIONS INFORMATION
0 f where ENOB is the effective number of bits and S/(N + D) SAMPLE = 20MHz –10 fIN1 = 1.000977MHz is expressed in dB. At the maximum sampling rate of 20MHz –20 SFDR = 64.8dB SINAD = 48.6dB the LTC1406 maintains near ideal ENOBs up to and be- –30 yond the Nyquist input frequency of 10MHz (see Figure 3). –40 –50 8 50 –60 AMPLITUDE (dB) –70 7 44 –80 6 38 –90 S/(N + D) (dB) 5 32 –100 0 1 2 3 4 5 6 7 8 9 10 4 FREQUENCY (Hz) 3 1406 F02a EFFECTIVE BITS
Figure 2a. Nonaveraged, 4096 Point FFT
2
Input Frequency = 1MHz
1 0 100k 1M 10M 100M 0 INPUT FREQUENCY (Hz) fSAMPLE = 20MHz –10 1406 TA02 fIN1 = 28.99902MHz –20 SFDR = 54.9dB
Figure 3. Effective Bits and Signal-to-(Noise + Distortion)
SINAD = 47.0dB –30
vs Input Frequency
–40 –50
Total Harmonic Distortion
–60 AMPLITUDE (dB) –70 Total harmonic distortion is the ratio of the RMS sum of all –80 harmonics of the input signal to the fundamental itself. The –90 out-of-band harmonics alias into the frequency band –100 0 1 2 3 4 5 6 7 8 9 10 between DC and half the sampling frequency. THD is FREQUENCY (Hz) expressed as: 1406 F02b
Figure 2b. Nonaveraged, 4096 Point FFT
2 2 2 2
Input Frequency = 30MHz
V2 + V + V4 + . .V THD = 20 3 log n V1 where V
Signal-to-Noise Ratio
1 is the RMS amplitude of the fundamental fre- quency and V2 through Vn are the amplitudes of the sec- The signal-to-noise plus distortion ratio [S/(N + D)] is the ond through nth harmonics. THD vs Input Frequency is ratio between the RMS amplitude of the fundamental input shown in Figure 4. The LTC1406 has good distortion per- frequency and the RMS amplitude of all other frequency formance up to the Nyquist frequency and beyond. components at the ADC output. The output is band limited to frequencies above DC to below half the sampling fre-
Intermodulation Distortion
quency. The effective number of bits (ENOBs) is a mea- If the ADC input signal consists of more than one spectral surement of the resolution of an ADC and is directly related component, the ADC transfer function nonlinearity can to the S/(N + D) by the equation: produce intermodulation distortion (IMD) in addition to ENOB = [S/(N + D) – 1.76]/6.02 THD. IMD is the change in one sinusoidal input caused by the presence of another sinusoidal input at a different fre- quency (see Figure 5). 8
