LTC2366 Linear Technology, LTC2366 Datasheet - Page 11

• Manufacturer Part Number: LTC2366
• Description: (LTC2365 / LTC2366) 12-Bit Serial Sampling ADCs
• Manufacturer: Linear Technology

www.DataSheet.in
APPLICATIONS INFORMATION
DC PERFORMANCE
The noise of an ADC can be evaluated in two ways: signal-
to-noise ratio (SNR) in the frequency domain and histogram
in the time domain. The LTC2365/LTC2366 excel in both.
Figures 5 and 6 demonstrate that the LTC2365/LTC2366
have an SNR of over 72dB. The noise in the time domain
histogram is the transition noise associated with a 12-bit
resolution ADC which can be measured with a fi xed DC signal
applied to the input of the ADC. The resulting output codes
are collected over a large number of conversions. The
shape of the distribution of codes will give an indication
of the magnitude of the transition noise. In Figure 4, the
distribution of output codes is shown for a DC input that
has been digitized 16384 times. The distribution is Gaus-
sian and the RMS code transition is about 0.34LSB. This
corresponds to a noise level of 72.7dB relative to a full
scale of 3V.
10000
Figure 4. Histogram for 16384 Conversions
2000
8000
6000
4000
0
V
2045
DD
= 3V
2046
2047
CODE
2048
2049
2050
23656 F04
DYNAMIC PERFORMANCE
The LTC2365/LTC2366 have excellent high speed sampling
capability. Fast fourier transform (FFT) test techniques are
used to test the ADC’s frequency response, distortion and
noise at the rated throughput. By applying a low distortion
sine wave and analyzing the digital output using an FFT
algorithm, the ADC’s spectral content can be examined for
frequencies outside the fundamental. Figures 5 and 6 show
typical LTC2365 and LTC2366 FFT plots respectively.
–100
–120
–140
–100
–120
–140
–20
–40
–60
–80
–20
–40
–60
–80
0
0
0
0
V
f
f
SINAD = 72dB
THD = –80.3dB
V
f
f
SINAD = 72.8dB
THD = –86.1dB
Figure 5. LTC2365 FFT Plot
SMPL
IN
Figure 6. LTC2366 FFT Plot
SMPL
IN
DD
DD
= 994kHz
= 461kHz
250
= 3V
= 3V
LTC2365/LTC2366
= 3Msps
= 1Msps
100
INPUT FREQUENCY (kHz)
INPUT FREQUENCY (kHz)
500
200
750
300
1000
400
1250
23656 F06
23656 F05
1500
500
11
23656f