LTC2366_15 Datasheet, PDF (12/24 Pages) Linear Technology – 1Msps/3Msps, 12-Bit Serial Sampling ADCs in TSOT

LTC2365/LTC2366
Applications Information
Signal-to-Noise Plus Distortion Ratio
The signal-to-noise plus distortion ratio (SINAD) is the
ratio between the RMS amplitude of the fundamental input
frequency to the RMS amplitude of all other frequency
components at the A/D output. The output is band limited
to frequencies from above DC and below half the sampling
frequency. Figure 6 shows a typical FFT with a 3MHz sam-
pling rate and a 1MHz input. The dynamic performance
is excellent for input frequencies up to and beyond the
Nyquist frequency of 1.5MHz.
Effective Number of Bits
The effective number of bits (ENOB) is a measurement
of the resolution of an ADC and is directly related to
SINAD by the equation:
ENOB = (SINAD – 1.76)/6.02
where ENOB is the effective number of bits of resolu-
tion and SINAD is expressed in dB. At the maximum
sampling rate of 3MHz, the LTC2366 maintains ENOB
above 11 bits up to the Nyquist input frequency of 1.5MHz
(refer to Figure 7).
Total Harmonic Distortion
The 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
band between DC and half the sampling frequency. THD
is expressed as:
THD = 20log
V₂₂ + V₃₂ + V₄₂ + ...V_n2
V₁
where V₁ is the RMS amplitude of the fundamental
frequency and V₂ through V_n are the amplitudes of the
second through nth harmonics. THD versus Input Fre-
quency is shown in Figure 8. The LTC2366 has excellent
distortion performance up to the Nyquist frequency and
beyond.
73.0
V_DD = 3.6V
72.5
72.0 ^VDD ^{= 2.35V}
71.5
V_DD = 3V
11.83
11.67
71.0
11.50
70.5
70.0
100
11.34
1000 1500
INPUT FREQUENCY (kHz)
23656 F07
Figure 7. LTC2366 ENOB and SINAD vs Input Frequency
–72 _{RIN = 10Ω}
–74
–76
–78
–80
V_DD = 3.6V
–82
–84
–86
–88
100
V_DD = 2.35V
V_DD = 3V
1000 1500
INPUT FREQUENCY (kHz)
23656 F08
Figure 8. LTC2366 Distortion vs Input Frequency
12
For more information www.linear.com/LTC2365
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