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dc1826afa

DEMO MANUAL DC1826A

the 50Ω terminator (R6) be removed. Slow rising edges

may compromise the SNR of the converter in the presence

of high amplitude higher frequency input signals.

Data Output

Parallel data output from this board (0V to 3.3V default),

if not connected to the DC718, can be acquired by a logic

analyzer, and subsequently imported into a spreadsheet, or

mathematical package depending on what form of digital

signal processing is desired. Alternatively, the data can be

fed directly into an application circuit. Use Pin 3 of J4 to

latch the data. The data can be latched using either edge

of this signal. The data output signal levels at J4 can also

be reduced to 0V to 2.5V if the application circuit cannot

tolerate the higher voltage. This is accomplished by mov-

ing JP4 to the 2.5V position.

Reference

The default reference is the LTC2389-18’s internal 4.096V

reference.Ifanexternalreferenceisdesiredusetheon-board

LTC6655-4.096 reference. It is enabled by stuffing 0Ω

resistors R7, R9 and R10 and removing 0Ω resistor R8.

Analog Input

The default driver for the analog inputs of the LTC2389-18

on the DC1826A is shown in Figure 2. This circuit converts

into a differential signal with a swing of ±4.096V between

the +IN and –IN inputs of the ADC. In addition, this circuit

band limits the input frequencies to approximately 16MHz.

It is also possible to drive the LTC2389-18 pseudo differ-

entially both with unipolar and bipolar outputs. The circuit

of Figure 3 shows the pseudo-differential unipolar driver.

This is connected on the DC1826A by removing R27 and

placing 0Ω resistors in the R31 and R42 positions.

Figure 4 shows the pseudo-differential bipolar driver circuit.

This is connected on the DC1826A by removing R29, R30,

C25 and C26 and placing 0Ω in the R30 position.

Alternatively, if your application circuit produces a differ-

ential signal which can drive the ADC, the circuit shown in

Figure 5 can be used. This is connected in the DC1826A

by removing R29, R30, R37, C23, C25 and C26 and by

adding a 0Ω resistor for R30 and R25. At this point it will

Figure 2. Default Driver Circuit

Figure 3. Pseudo-Differential Unipolar Driver

Figure 4. Pseudo-Differential Bipolar Driver

Figure 5. Fully Differential Driver

DC1826A SETUP