LTC1401 Linear Technology, LTC1401 Datasheet - Page 9

• Manufacturer Part Number: LTC1401
• Description: Complete SO-8/ 12-Bit/ 200ksps ADC with Shutdown
• Manufacturer: Linear Technology

APPLICATIONS
Peak Harmonic or Spurious Noise
The peak harmonic or spurious noise is the largest spec-
tral component excluding the input signal and DC. This
value is expressed in decibels relative to the RMS value of
a full-scale input signal.
Full Power and Full Linear Bandwidth
The full power bandwidth is the input frequency at which
the amplitude of the reconstructed fundamental is reduced
by 3dB for a full-scale input signal.
The full linear bandwidth is the input frequency at which
the S/(N+D) has dropped to 68dB (11 effective bits).
ence frequencies of mfa nfb, where m and n = 0, 1, 2, 3,
etc. For example, the 2nd order IMD terms include (fa + fb)
and (fa – fb) while 3rd order IMD terms includes
(2fa + fb), (2fa – fb), (fa + 2fb) and (fa – 2fb). If the two input
sine waves are equal in magnitude, the value (in decibels)
of the 2nd order IMD products can be expressed by the
following formula.
Figure 5 shows the IMD performance at a 50kHz input.
IMD fa
–100
–110
–120
– 60
–10
–20
–30
–40
–50
–70
–80
–90
Figure 5. Intermodulation Distortion Plot
0
0
fb
f
fa = 49.853kHz
fb = 53.076kHz
T
SAMPLE
A
fb – fa
10
= 25 C
2fb + fa
20
2fa – fb
U
20log
= 200kHz
3fb
30
FREQUENCY (kHz)
40 50
INFORMATION
U
Amplitude at (
fa
Amplitude at fa
fb
60
2fb – fa
3fa
2fa + fb
70
fa + fb
W
2fb
80
LTC1401 • F05
2fa
90
fa
100
fb
U
)
Driving the Analog Input
The analog input of the LTC1401 is easy to drive. It draws
only one small current spike while charging the sample-
and-hold capacitor at the end of a conversion. During
conversion, the analog input draws only a small leakage
current. The only requirement is that the amplifier driving
the analog input must settle after the small current spike
before the next conversion starts. Any op amp that settles
in 315ns to small load current transients will allow maxi-
mum speed operation. If a slower op amp is used, more
settling time can be provided by increasing the time
between conversions. Suitable devices capable of driving
the ADC’s A
op amps.
The following list is a summary of the op amps that are
suitable for driving the LTC1401, more detailed informa-
tion is available in the Linear Technology databooks and
the LinearView
LT1215/LT1216: Dual and quad 23MHz, 50V/ s single
supply op amps. Single 5V to 15V supplies, 6.6mA
specifications, 90ns settling to 0.5LSB.
LT1229/LT1230: Dual and quad 100MHz current feedback
amplifiers. 2V to 15V supplies, 6mA supply current
each amplifier. Low noise. Good AC specs.
LT1498/LT1499: Dual or quad 10MHz, 6V/ s, single
2.2V to 15V supplies, 1.7mA supply current per ampli-
fier, input/output swings rail-to-rail. Excellent AC and DC
specs.
LT1630: Dual or quad 30MHz, 10V/ s, single 2.7V to 15V
supplies, 3.5mA supply current per amplifier, input/output
swings rail-to-rail. Good AC and DC specs.
Internal Reference
The LTC1401 has an on-chip, temperature compensated,
curvature corrected, bandgap reference, which is factory
trimmed to 1.20V. It is internally connected to the DAC and
LinearView is a trademark of Linear Technology Corporation.
IN
input include the LT
TM
CD-ROM.
®
1498 and the LT1630
LTC1401
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