Datasheet LTC1400 (Analog Devices) - 9

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