LTC1400CS8 datasheet(9/20 Pages) LINER

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LTC1400

APPLICATIONS INFORMATION

in 200ns to small load current transient 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 AIN input include the LT

® 1360 and the LT1363

op amps.

LTC1400 comes with a built-in unipolar/bipolar detection

circuit. If VSS potential is forced below GND, the internal

circuitry will automatically switch to bipolar mode.

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 and

the LinearView

TM CD-ROM.

LT 1215/LT1216: Dual and quad 23MHz, 50V/

µs single

supply op amps. Single 5V to

±15V supplies, 6.6mA

specifications, 90ns settling to 0.5LSB.

LT1223: 100MHz video current feedback amplifier.

±5V

±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

±15V supplies, 10mA supply current. Lowest distor-

tion at frequencies above 400kHz. Low noise. Best for AC

applications.

LT1229/LT1230: Dual and quad 100MHz current feedback

amplifiers.

±2V to ±15V supplies, 6mA supply current

each amplifier. Low noise. Good AC specs.

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/

µs op amps. ±5V to ±15V sup-

plies. 6.3mA supply current. Good AC and DC specs. 60ns

settling to 0.5LSB.

LT1364/LT1365: Dual and quad 50MHz, 450V/

µsopamps.

±5V to ±15V supplies, 6.3mA supply current per ampli-

fier. 60ns settling to 0.5LSB.

Internal Reference

The LTC1400 has an on-chip, temperature compensated,

curvature corrected, bandgap reference, which is factory

Figure 5. Intermodulation Distortion Plot in Bipolar Mode

FREQUENCY (kHz)

80 100

140

180

120

160

200

LTC1400 • F05

–10

–20

–30

–40

–50

– 60

–70

–80

–90

–100

–110

–120

fSAMPLE = 400kHz

fa = 99.512kHz

fb = 102.441kHz

fa fb

3fa

2fb – fa

2fa + fb

2fa – fb

2fb + fa

2fa

3fb

fa + fb

2fb

fb – fa

Figure 5 shows the IMD performance at a 100kHz input.

Peak Harmonic or Spurious Noise

The peak harmonic or spurious noise is the largest spectral

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). 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 be-

yond Nyquist.

Driving the Analog Input

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 driving

the analog input must settle after the small current spike

before the next conversion starts. Any op amp that settles

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