LTC1282AC datasheet(21/24 Pages) LINER

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LTC1282

APPLICATI

I FOR ATIO

Figure 25.

∆ Time Measurement with the LTC1282

MUXing with CD4051

The high input impedance of the LTC1282 provides an

easy, cheap, fast, and accurate way to multiplex many

channels of data through one converter. Figure 24 shows

a low cost CD4051, one of the most common multiplex-

ers connected to the LTC1282. The LTC1282’s input

draws no DC input current so it can be accurately driven

by the unbuffered MUX. The CD4520 counter increments

the MUX channel after each sample is taken.

100ps Resolution

∆Time Measurement with LTC1282

Figure 25 shows a circuit that precisely measures the

difference in time between two events. It has a 400ns full

scale and 100ps resolution. The start signal releases the

ramp generator made up of the PNP current source and

the 500pF capacitor. The circuit ramps until the stop

signal shuts off the current source. The final value of the

ramp represents the time between the start and stop

events. The LTC1282 digitizes this final value and out-

puts the digital data.

Figure 24. MUXing the LTC1282 with CD4051

VSS GND

AIN

REFOUT

VDD

LTC1282

RD BUSY

12-BIT

DATA

OUTPUT

µF

2N2369

20k

200k

250pF

POLYSTYRENE

430

Ω

2N5771

Ω

3.3V

74HC03

Ω

45.3

Ω

45.3

Ω

1N457

LM134

CLK

CLR

CLK

CLR

START

↑

STOP

↑

DATA

LATCH

SIGNAL

µF

100k

1N4148

0.001

µF

10k

1N457

74HC74

10pF

1N4148

100pF

10k

LTC1282 • F25

VSS

AB C

8 INPUT

CHANNELS

±1.25V

INPUT

VARIES

BUFFER

REQUIRED

D11

•

BUSY

LTC1282

AIN

µP

DSP

ENABLE

RESET

CD4520

COUNTER

LTC1282 • F24

–3V

CD4051

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