ltc1411 Linear Technology Corporation, ltc1411 Datasheet - Page 9

• Manufacturer Part Number: ltc1411
• Description: Single Supply 14-bit 2.5msps Adc
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
Effective Number of Bits
The effective number of bits (ENOBs) is a measurement of
the resolution of an ADC and is directly related to the
S/(N + D) by the equation:
where S/(N + D) is expressed in dB. At the maximum
sampling rate of 2.5MHz the LTC1411 maintains good
ENOBs up to the Nyquist input frequency of 1.25MHz.
Refer to Figure 3.
Total Harmonic Distortion
Total harmonic distortion (THD) is the ratio of the RMS
sum of all harmonics of the input signal to the fundamental
ENOB
Figure 2a. LTC1411 Nonaveraged, 4096 Point FFT,
Input Frequency = 100kHz
S
–100
–120
–140
–100
–140
–120
–60
–80
–20
–40
–60
–80
–20
–40
= [S/(N + D) – 1.76]/6.02
0
0
Figure 2b. LTC1411 4096 Point FFT,
Input Frequency = 1MHz
0
0
SINAD = 75dB
SFDR = 81dB
f
f
SAMPLE
IN
= 1MHz
250
250
U
= 2.5MHz
INPUT FREQUENCY (kHz)
FREQUENCY (kHz)
500
500
U
750
750
SINAD = 78.8dB
SFDR = 95dB
f
f
SAMPLE
IN
= 100kHz
W
1000
1000
= 2.5MHz
1411 G15
1411 G14
1250
1250
U
itself. The out-of-band harmonics alias into the frequency
band between DC and half the sampling frequency. THD is
expressed as:
where V
quency and V
second through Nth harmonics. THD vs input frequency is
shown in Figure 4. The LTC1411 has good distortion
performance up to the Nyquist frequency and beyond.
THD
Figure 3. Effective Bits and Signal/(Noise + Distortion)
vs Input Frequency
1
–100
–110
–40
–50
–60
–70
–80
–90
–10
–20
–30
is the RMS amplitude of the fundamental fre-
20
86
80
74
68
62
56
50
44
38
32
26
20
14
0
Figure 4. Distortion vs Input Frequency
10
10
log
2
through V
2ND
V
INPUT FREQUENCY (kHz)
2
INPUT FREQUENCY (kHz)
2
100
100
THD
V
3
3RD
2
N
V
are the amplitudes of the
1
1000
V
1000
4
2
1411 G03
1411 TA02
V
10000
10000
LTC1411
N
2
10
14
13
12
11
9
1411f