Datasheet LTC1401 (Analog Devices) - 9

LTC1401
U U W U APPLICATIONS INFORMATION
ence frequencies of mfa ±nfb, where m and n = 0, 1, 2, 3,
Driving the Analog Input
etc. For example, the 2nd order IMD terms include (fa + fb) The analog input of the LTC1401 is easy to drive. It draws and (fa – fb) while 3rd order IMD terms includes only one small current spike while charging the sample- (2fa + fb), (2fa – fb), (fa + 2fb) and (fa – 2fb). If the two input and-hold capacitor at the end of a conversion. During sine waves are equal in magnitude, the value (in decibels) conversion, the analog input draws only a small leakage of the 2nd order IMD products can be expressed by the current. The only requirement is that the amplifier driving following formula. the analog input must settle after the small current spike before the next conversion starts. Any op amp that settles fa Amplitude at ( fb) IMD(fa ± fb) = ± 20log in 315ns to small load current transients will allow maxi- Amplitude at fa mum speed operation. If a slower op amp is used, more settling time can be provided by increasing the time Figure 5 shows the IMD performance at a 50kHz input. between conversions. Suitable devices capable of driving 0 the ADC’s AIN input include the LT ®1498 and the LT1630 f –10 SAMPLE = 200kHz fa = 49.853kHz op amps. –20 fb = 53.076kHz –30 TA = 25°C fa fb 2fa + fb The following list is a summary of the op amps that are –40 3fa 2fa suitable for driving the LTC1401, more detailed informa- –50 2fa – fb fa + fb tion is available in the Linear Technology databooks or the – 60 2fb + fa 2fb 3fb –70 2fb – fa Linear Technology Web site. AMPLITUDE (dB) –80 fb – fa –90
LT1215/LT1216:
Dual and quad 23MHz, 50V/µs single –100 supply op amps. Single 5V to ±15V supplies, 6.6mA –110 specifications, 90ns settling to 0.5LSB. –120 0 10 20 30 40 50 60 70 80 90 100
LT1229/LT1230:
Dual and quad 100MHz current feedback FREQUENCY (kHz) LTC1401 • F05 amplifiers. ±2V to ±15V supplies, 6mA supply current each amplifier. Low noise. Good AC specs.
Figure 5. Intermodulation Distortion Plot LT1498/LT1499:
Dual or quad 10MHz, 6V/µs, single
Peak Harmonic or Spurious Noise
2.2V to ±15V supplies, 1.7mA supply current per ampli- fier, input/output swings rail-to-rail. Excellent AC and DC The peak harmonic or spurious noise is the largest spec- specs. tral component excluding the input signal and DC. This value is expressed in decibels relative to the RMS value of
LT1630:
Dual or quad 30MHz, 10V/µs, single 2.7V to ±15V a full-scale input signal. supplies, 3.5mA supply current per amplifier, input/output swings rail-to-rail. Good AC and DC specs.
Full Power and Full Linear Bandwidth Internal Reference
The full power bandwidth is the input frequency at which the amplitude of the reconstructed fundamental is reduced The LTC1401 has an on-chip, temperature compensated, by 3dB for a full-scale input signal. curvature corrected, bandgap reference, which is factory trimmed to 1.20V. It is internally connected to the DAC and The full linear bandwidth is the input frequency at which the S/(N+D) has dropped to 68dB (11 effective bits). LinearView is a trademark of Linear Technology Corporation. 1401fa 9