LTC2362 Linear Technology, LTC2362 Datasheet - Page 11

• Manufacturer Part Number: LTC2362
• Description: (LTC2360 - LTC2362) 12-Bit Serial ADCs
• Manufacturer: Linear Technology

DC PERFORMANCE
The noise of an ADC can be evaluated in two ways: sig-
nal-to-noise ratio (SNR) in the frequency domain and
histogram in the time domain. The LTC2360/LTC2361/
LTC2362 excel in both. Figure 5 demonstrates that the
LTC2360/LTC2361/LTC2362 have an SNR of over 73dB.
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 distribu-
tion 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 Gaussian and the RMS
code transition is about 0.32LSB. This corresponds to a
noise level of 73dB relative to a full scale of 3V.
APPLICATIONS INFORMATION
–100
–120
–140
–20
–40
–60
–80
0
0
V
f
f
SINAD = 73dB
THD = –84dB
SMPL
IN
DD
= 124kHz
Figure 5. LTC2361 FFT Plot
= 3V
= 250ksps
25
INPUT FREQUENCY (kHz)
50
75
100
10000
8000
6000
4000
2000
236012 F05
Figure 4. Histogram for 16384 Conversions
125
0
V
2045
DD
= 3V
2046
2047
CODE
2048
DYNAMIC PERFORMANCE
The LTC2360/LTC2361/LTC2362 have excellent high speed
sampling capability. Fast fourier transform (FFT) test
techniques are used to test the ADCs’ 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 ADCs’ spectral content can
be examined for frequencies outside the fundamental.
Figures 5 and 6 show typical LTC2361 and LTC2362 FFT
plots respectively.
LTC2360/LTC2361/LTC2362
2049
2050
236012 F04
–100
–120
–140
–20
–40
–60
–80
0
0
V
f
f
SINAD = 73dB
THD = –81dB
SMPL
IN
DD
= 248kHz
Figure 6. LTC2362 FFT Plot
= 3V
= 500ksps
50
INPUT FREQUENCY (kHz)
100
150
200
236012 F06
250
11
236012f