LTC1400
U U
W U
APPLICATIO S I FOR ATIO
0
settles in 200ns to small load current transient will allow
maximum 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
f
= 400kHz
SAMPLE
–10
–20
fa = 99.512kHz
fb = 102.441kHz
fa fb
–30
–40
–50
3fa
2fb – fa
the ADC’s A input include the LT®1360 and the LT1363
2fa
IN
–60
–70
2fa + fb
op amps.
2fa – fb
fa + fb
2fb
2fb + fa
–80
fb – fa
3fb
LTC1400 comes with a built-in unipolar/bipolar detection
–90
–100
–110
–120
circuit. If V potential is forced below GND, the internal
SS
circuitry will automatically switch to bipolar mode.
0
20 40 60 80 100 120 140 160 180 200
FREQUENCY (kHz)
The following list is a summary of the op amps that are
suitable for driving the LTC1400, more detailed informa-
tion is available in the Linear Technology databooks or the
Linear Technology Website.
1400 F05
Figure 5. Intermodulation Distortion Plot in Bipolar Mode
Figure 5 shows the IMD performance at a 100kHz input.
Peak Harmonic or Spurious Noise
LT1215/LT1216: Dual and quad 23MHz, 50V/μs single
supply op amps. Single 5V to ±15V supplies, 6.6mA
specifications, 90ns settling to 0.5LSB.
Thepeakharmonicorspuriousnoiseisthelargestspectral
component excluding the input signal and DC. This value
is expressed in decibels relative to the RMS value of a
full-scale input signal.
LT1223: 100MHz video current feedback amplifier. ±5V
to ±15V supplies, 6mA supply current. Low distortion up
to and above 400kHz. Low noise. Good for AC applica-
tions.
LT1227: 140MHz video current feedback amplifier. ±5V to
±15V supplies, 10mA supply current. Lowest distortion
at frequencies above 400kHz. Low noise. Best for AC
applications.
Full Power and Full Linear Bandwidth
The full power bandwidth is the input frequency at which
theamplitudeofthereconstructedfundamentalisreduced
by 3dB for a full-scale input signal.
LT1229/LT1230: Dual and quad 100MHz current feedback
amplifiers.±2Vto±15Vsupplies,6mAsupplycurrenteach
amplifier. Low noise. Good AC specs.
The full linear bandwidth is the input frequency at which
the S/(N + D) has dropped to 68dB (11 effective bits). The
LTC1400 has been designed to optimize input bandwidth,
allowing the ADC to undersample input signals with fre-
quencies above the converter’s Nyquist Frequency. The
noise floor stays very low at high frequencies; S/(N +
D) becomes dominated by distortion at frequencies far
beyond Nyquist.
LT1360: 37MHz voltage feedback amplifier. ±5V to ±15V
supplies. 3.8mA supply current. Good AC and DC specs.
70ns settling to 0.5LSB.
LT1363:50MHz, 450V/μsopamps. ±5Vto±15Vsupplies.
6.3mA supply current. Good AC and DC specs. 60ns
settling to 0.5LSB.
Driving the Analog Input
LT1364/LT1365:Dualandquad50MHz,450V/μsopamps.
±5V to ±15V supplies, 6.3mA supply current per amplifier.
60ns settling to 0.5LSB.
The analog input of the LTC1400 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 driv-
ing the analog input must settle after the small current
spike before the next conversion starts. Any op amp that
Internal Reference
The LTC1400 has an on-chip, temperature compensated,
curvature corrected, bandgap reference, which is factory
1400fa
9
Linear [ Linear ]
