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LTC2345-18

234518f

For more information www.linear.com/LTC2345-18

Buffering Single-Ended Analog Input Signals

While the circuit shown in Figure 6a is capable of buffering

single-ended input signals, the circuit shown in Figure 10

is preferable when the single-ended signal reference level

is inherently low impedance and doesn't require buffering.

This circuit eliminates one driver and lowpass filter, reduc-

ing part count, power dissipation, and SNR degradation

due to driver noise. Using the recommended driver and

filter combinations in Table 2, the performance of this

circuit with single-ended input signals is on par with the

performance of the circuit in Figure 6a.

ADC REFERENCE

AsshownpreviouslyinTable1b,theLTC2345-18 supports

three reference configurations. The first uses both the in-

ternalbandgapreferenceandreferencebuffer.Thesecond

externally overdrives the internal reference but retains the

internal buffer, which isolates the external reference from

ADC conversion transients. This configuration is ideal

for sharing a single precision external reference across

multiple ADCs. The third disables the internal buffer and

overdrives the REFBUF pin externally.

Internal Reference with Internal Buffer

The LTC2345-18 has an on-chip, low noise, low drift

(20ppm/°C maximum), temperature compensated band-

gap reference that is factory trimmed to 2.048V. The

reference output connects through a 20kΩ resistor to

applicaTions inForMaTion

Figure 9b. CMRR vs Input Frequency. Circuit Shown in Figure 9a

Figure 9a. Digitize Differential Signals with High CMRR

Figure 10. Buffering Single-Ended Input Signals. See Table 2 For Recommended

Amplifier and Filter Combinations

IN+ = IN– = 5Vpp SINE

±4.096V RANGE

FREQUENCY (Hz)

100

10k

100k

100

110

120

130

140

150

234518 F09b

–2V

LTC2345-18

234518 F09a

ONLY CHANNEL 0 SHOWN FOR CLARITY

–

0.1µF

47µF

IN0+

IN0–

½ LT6237

REFIN

REFBUF

LOWPASS FILTERS

BW ~ 4MHz

1nF

40.2

549

IN+

IN–

2.49k

LTC2345-18

234518 F10

ONLY CHANNEL 0 SHOWN FOR CLARITY

–

0.1µF

47µF

IN0+

IN0–

AMPLIFIER

REFIN

REFBUF

OPTIONAL

LOWPASS FILTER

CFILT

RFILT

–2V

IN+

IN–

UNIPOLAR

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