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ADSD-1420S

Dual 14-Bit, 20MSPS Sampling A/D Converter

Murata Power Solutions 

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TECHNICAL NOTES

1. Rated performance requires using good high-frequency cir-

cuit board layout techniques. Connect the digital and

analog grounds to one point, the analog ground plane

beneath the converter. Due to the inductance and resis-

tance of the power supply return paths, return the analog

and digital ground separately to the power supplies.

CALIBRATION PROCEDURE

1. Connect the converter per Figure 3. Apply a pulse of 50

nanoseconds typical to START CONVERT (pin 11) at a rate

of 2MHz. This rate is chosen to reduce flicker if LED's are

used on the outputs for calibration purposes.

2. Zero (Offset) Adjustments

Apply a precision voltage reference source between

ANALOG INPUT A (pin 1) and SIGNAL GROUND (pin 3),

then adjust the reference source output per Table 2. Adjust

trimpot R1 until the code flickers equally between 10 0000

0000 0000 and 10 0000 0000 0001.

3. Repeat above step for Analog Input B (Pin 40). Use trimpot

R2 for the zero (Offset) adjustment .

Table 2. Offset Adjustment

Input

Range

Offset Adjust

+1/2 LSB

±2.5V

+0.000153V

Table 3. Output Coding

OUTPUT CODING

MSB

LSB

INPUT RANGE

±2.5V

11 1111 1111 1111

11 1000 0000 0000

11 0000 0000 0000

10 0000 0000 0000

01 0000 0000 0000

00 1000 0000 0000

00 0000 0000 0001

00 0000 0000 0000

+2.499695

+1.875000

+1.250000

±0.000000

–1.250000

–1.875000

–2.499695

–2.500000

BIPOLAR

SCALE

+FS – 1LSB

+3/4FS

+1/2FS

0

–1/2FS

–3/4FS

–FS+1LSB

–FS

4. To confirm proper operation of the device, vary the precision

reference voltage source to obtain the output coding listed

in Table 3.

34!24

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N3EC

N3EC

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N3ECPERDIVISION

N3EC

N3EC

Figure 2. ADSD-1420S Timing Diagram

.

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