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LTC1419AIG

14-Bit, 800ksps Sampling A/D Converter with Shutdown

Linear Technology 

LTC1419

APPLICATIONS INFORMATION

that the amplifier driving the analog input(s) must settle

after the small current spike before the next conversion

starts (settling time must be 200ns for full throughput

rate).

10

1

0.1

0.01

0.01

0.1

1

10

SOURCE RESISTANCE (kΩ)

100

1419 F06

Figure 6. tACQ vs Source Resistance

Choosing an Input Amplifier

Choosing an input amplifier is easy if a few requirements

are taken into consideration. First, to limit the magnitude

of the voltage spike seen by the amplifier from charging

the sampling capacitor, choose an amplifier that has a

low output impedance (< 100Ω) at the closed-loop band-

width frequency. For example, if an amplifier is used in a

gain of +1 and has a unity-gain bandwidth of 50MHz, then

the output impedance at 50MHz should be less than

100Ω. The second requirement is that the closed-loop

bandwidth must be greater than 20MHz to ensure

adequate small-signal settling for full throughput rate. If

slower op amps are used, more settling time can be

provided by increasing the time between conversions.

The best choice for an op amp to drive the LTC1419 will

depend on the application. Generally applications fall into

two categories: AC applications where dynamic specifi-

cations are most critical and time domain applications

where DC accuracy and settling time are most critical.

The following list is a summary of the op amps that are

suitable for driving the LTC1419. More detailed informa-

tion is available in the Linear Technology databooks, the

LinearViewTM CD-ROM and on our web site at www.linear-

tech. com.

LinearView is a trademark of Linear Technology Corporation.

10

LT®1220: 30MHz unity-gain bandwidth voltage feedback

amplifier. ±5V to ±15V supplies. Excellent DC specifica-

tions.

LT1223: 100MHz video current feedback amplifier. ±5V

to ±15V supplies, 6mA supply current. Low distortion at

frequencies above 400kHz. Low noise. Good for AC

applications.

LT1227: 140MHz video current feedback amplifier. ±5V

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

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

applications.

LT1229/LT1230: Dual/quad 100MHz current feedback

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

each amplifier. Low noise. Good AC specs.

LT1360: 50MHz voltage feedback amplifier. ±5V to ±15V

supplies, 3.8mA supply current. Good AC and DC specs.

LT1363: 70MHz, 1000V/µs op amps, 6.3mA supply cur-

rent. Good AC and DC specs.

LT1364/LT1365: Dual and quad 70MHz, 1000V/µs op

amps. 6.3mA supply current per amplifier.

Input Filtering

The noise and the distortion of the input amplifier and

other circuitry must be considered since they will add to

the LTC1419 noise and distortion. The small-signal band-

width of the sample-and-hold circuit is 20MHz. Any noise

or distortion products that are present at the analog inputs

will be summed over this entire bandwidth. Noisy input

circuitry should be filtered prior to the analog inputs to

minimize noise. A simple 1-pole RC filter is sufficient for

50Ω

ANALOG INPUT

1000pF

1

+AIN

2

– AIN

LTC1419

3

VREF

10µF

4

REFCOMP

5

AGND

1419 F07

Figure 7. RC Input Filter

1419fb

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