Datasheet

LTC2313-14
15
231314fa
For more information www.linear.com/LTC2313-14
applicaTions inForMaTion
At the maximum sampling rate of 2.5MHz, the LTC2313-14
maintains an ENOB above 12 bits up to the Nyquist input
frequency of 1.25MHz. (Figure 14)
Signal-to-Noise Ratio (SNR)
The signal-to-noise ratio (SNR) is the ratio between the
RMS amplitude of the fundamental input frequency and
the RMS amplitude of all other frequency components
except the first five harmonics and DC. Figure 13 shows
that the LTC2313-14 achieves a typical SNR of 77.5dB at
a 2.5MHz sampling rate with a 497kHz input frequency.
Total Harmonic Distortion (THD)
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 (f
SMPL
/2).
THD is expressed as:
THD=20log
V2
2
+ V3
2
+ V4
2
+ V
N
2
V1
where V1 is the RMS amplitude of the fundamental fre-
quency and
V2 through V
N
are the amplitudes of the second
through Nth harmonics. THD versus Input Frequency is
shown in the Typical Performance Characteristics section.
The LTC2313-14 has excellent distortion performance up
to the Nyquist frequency.
been digitized 16,384 times. The distribution is Gaussian
and the RMS code transition noise is 0.7LSB. This cor
-
responds to a noise level of 77.5dB relative to a full scale
voltage of 4.096V.
Dynamic Performance
The
LTC2313-14 has excellent high speed sampling
capability. Fast Fourier Transform (FFT) 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 applied fundamental. The
LTC2313-14 provides guaranteed tested limits for both
AC distortion and noise measurements.
Signal-to-Noise and Distortion Ratio (SINAD)
The signal-to-noise and distortion ratio (SINAD) is the ratio be
-
tween the
R
MS amplitude of the fundamental input frequency
and 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
14 shows the LTC2313-14 maintains a SINAD above 76dB
up to the Nyquist input frequency of 1.25MHz.
Effective Number of Bits (ENOB)
The effective number of bits (ENOB) is a measurement of
the resolution of an ADC and is directly related to SINAD
by the equation where ENOB is the effective number of
bits of resolution and SINAD is expressed in dB:
ENOB = (SINAD – 1.76)/6.02
Figure 13. 16k Point FFT of the LTC2313-14 at f
IN
= 497kHz Figure 14. LTC2313-14 ENOB/SINAD vs f
IN
231314 F13
INPUT FREQUENCY (kHz)
AMPLITUDE (dBFS)
0 1000
500250
750
0
–20
–40
–60
–80
–100
–120
–140
–160
V
DD
= 5V
SNR = 77.5dBFS
SINAD = 77dBFS
THD = –85dB
SFDR = 87dB
231314 F14
INPUT FREQUENCY (kHz)
SINAD (dBFS)
ENOB
0 1250
750500250
1000
78
77
76
75
74
73
72
71
12.50
12.33
12.17
12.00
11.83
11.67
11.50
V
DD
= 5V
V
DD
= 3V