LTC1401CS8 Linear Technology, LTC1401CS8 Datasheet - Page 8

• Manufacturer Part Number: LTC1401CS8
• Description: IC A/D CONV 12BIT W/SHTDN 8-SOIC
• Manufacturer: Linear Technology

Specifications of LTC1401CS8

• Number Of Bits: 12
• Sampling Rate (per Second): 200k
• Data Interface: MICROWIRE™, Serial, SPI™
• Number Of Converters: 1
• Power Dissipation (max): 30mW
• Voltage Supply Source: Single Supply
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

LTC1401
Effective Number of Bits
The effective number of bits (ENOBs) is a measurement of
the effective resolution of an ADC and is directly related to
the S/(N + D) by the equation:
where N is the effective number of bits of resolution and
S/(N + D) is expressed in dB. Figure 3 shows ENOBs vs
Input Frequency.
APPLICATIONS
8
N
=
Figure 2b. LTC1401 Nonaveraged, 4096 Point FFT
Plot with 100kHz Input Frequency
S N D
Figure 3. Effective Bits and Signal-to-Noise +
Distortion vs Input Frequency
–100
–110
–120
/
– 60
(
–10
–20
–30
–40
–50
–70
–80
–90
12
11
10
0
9
8
7
6
5
4
3
2
1
0
10k
+
0
6 02
f
f
SINAD = 65dB
THD = –66dB
V
T
T
f
SAMPLE
IN
SAMPLE
.
CC
A
A
10
= 99.072266kHz
= 25°C
= 25°C
)
= 3V
– .
20
U
= 200kHz
1 76
= 200kHz
INPUT FREQUENCY (Hz)
30
FREQUENCY (kHz)
40 50
INFORMATION
U
100k
60
70
W
80
LTC1400 • F02b
LTC1401 • F03
90
100
1M
74
68
62
56
50
U
Total Harmonic Distortion
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 of the sampling frequency. THD
is expressed as:
Where V1 is the RMS amplitude of the fundamental
frequency and V2 through Vn are the amplitudes of the
second through nth harmonics. THD vs input frequency is
shown in Figure 4. The LTC1401 has good distortion
performance up to the Nyquist frequency and beyond.
Intermodulation Distortion
If the ADC input signal consists of more than one spectral
component, the ADC transfer function nonlinearity can
produce intermodulation distortion (IMD) in addition to
THD. IMD is the change in one sinusoidal input caused by
the presence of another sinusoidal input at a different
frequency.
If two pure sine waves of frequencies fa and fb are applied
to the ADC input, nonlinearities in the ADC transfer
function can create distortion products at sum and differ-
THD = 20log
–100
–10
–20
–30
–40
–50
–60
–70
–80
–90
Figure 4. Distortion vs Input Frequency
0
10k
T
f
2ND HARMONIC
SAMPLE
A
= 25°C
√
V2
= 200kHz
INPUT FREQUENCY (Hz)
2
+ V3
V1
100k
2
3RD HARMONIC
+ ...Vn
THD
2
LTC1401 • F04
1M
1401fa