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LTC6228/LTC6229

Rev. B

For more information www.analog.com

TYPICAL APPLICATIONS

18-Bit High Speed ADC Driver

The ultralow noise and distortion performance of the

LTC6228 makes it an excellent candidate for driving high

speed high resolution ADCs with fast, large amplitude

signals. Figure 4 shows a pair of LTC6228s driven by a dif-

ferential input, driving an LTC2387-18, a 15Msps, 18-bit

ADC. Figure 5 shows an FFT obtained with a –1dBFS,

1MHz input signal. The obtained SNR is 93.4dB, better

than the LTC2387-18’s guaranteed SNR of 93dB, and

close to its typical value of 95.7dB. Spurious free dynamic

range is an excellent 95dB, close to the LTC2387-18’s

guaranteed SFDR of 97dB.

High Speed Low Voltage Low Noise Instrumentation

Amplifier

Figure 6 shows a three op amp instrumentation amplifier

with a gain of 41V/V which can operate on a wide range

of supply voltage. An RC snubber is used at the common

terminal of the 30Ω gain setting resistors to reduce the

effects of any board induced layout coupling from the

output of one amplifier to the negative input of the other.

Figure 7 shows the measured frequency response of the

instrumentation amplifier for a load of 1kΩ. Figure 8

shows the measured CMRR of the instrumentation

amplifier, and Figure 9 shows the transient response for

a 50mVP-P input square wave applied to the positive input,

with the negative input grounded. The total supply voltage

was 3.3V. The extremely low offset voltage and low 1/f

noise at the LTC6229 inputs allow for wide band instru-

mentation amplifier operation, down to DC. Note, the bias

currents of the LTC6229 are higher than might appear in

a traditional low speed instrumentation amplifier. High

speed instrumentation such as in Figure 6 assume a cor-

respondingly low enough impedance excitation.

–

0.1µF

LTC6228

IN–

IN+

VCM

CLK

82pF

4.096V

82pF

6228 F04

LTC2387-18

DCO

LVDS

INTERFACE

TWOLANES

TESTPAT

SAMPLE

CLOCK

CNV

REFB

–

LTC6228

7.5V

–2.5V

4.096V

Figure 4. High Speed Driver for 18-Bit ADC

Figure 5. Measured Performance of LTC6228 Based Driver Driving the LTC2387-18

8192 Point FFT, –1dBFS

fSMPL = 15Msps, fIN = 1MHz

7.3VP-P 1MHz INPUT SIGNAL

SNR = 93.4dB

SFDR = 95dB

THD = –93.8dB

FREQUENCY (MHz)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

–140

–120

–100

–80

–60

–40

–20

6228 F05

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