ADR421ARMZ datasheet(17/24 Pages) AD

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ADR420/ADR421/ADR423/ADR425

Rev. I | Page 17 of 24

APPLICATIONS

OUTPUT ADJUSTMENT

The ADR42x trim terminal can be used to adjust the output

voltage over a ±0.5% range. This feature allows the system

designer to trim system errors out by setting the reference to

a voltage other than the nominal. This is also helpful if the

part is used in a system at temperature to trim out any error.

Adjustment of the output has a negligible effect on the

temperature performance of the device. To avoid degrading

temperature coefficients, both the trimming potentiometer

and the two resistors need to be low temperature coefficient

types, preferably <100 ppm/°C.

ADR420/

ADR421/

ADR423/

ADR425

VIN

INPUT

GND

TRIM

470kΩ

10kΩ

10kΩ (ADR420)

15kΩ (ADR421)

OUTPUT

VOUT = ±0.5%

VOUT

Figure 40. Output Trim Adjustment

REFERENCE FOR CONVERTERS IN OPTICAL

NETWORK CONTROL CIRCUITS

In the high capacity, all optical router network of Figure 41,

arrays of micromirrors direct and route optical signals from

fiber to fiber, without first converting them to electrical form,

which reduces the communication speed. The tiny micro-

mechanical mirrors are positioned so that each is illuminated

by a single wavelength that carries unique information and

can be passed to any desired input and output fiber. The mirrors

are tilted by the dual-axis actuators controlled by precision

analog-to-digital converters (ADCs) and digital-to-analog

converters (DACs) within the system. Due to the microscopic

movement of the mirrors, not only is the precision of the

converters important, but the noise associated with these

controlling converters is extremely critical, because total noise

within the system can be multiplied by the numbers of

converters used. Consequently, the exceptional low noise of the

ADR42x is necessary to maintain the stability of the control

loop for this application.

DAC

ADC

DSP

CONTROL

ELECTRONICS

ACTIVATOR

LEFT

LASER BEAM

SOURCE FIBER

GIMBAL + SENSOR

DESTINATION

FIBER

ACTIVATOR

RIGHT

MEMS MIRROR

AMPL

PREAMP

AMPL

ADR421

Figure 41. All Optical Router Network

HIGH VOLTAGE FLOATING CURRENT SOURCE

The circuit in Figure 42 can be used to generate a floating

current source with minimal self-heating. This particular

configuration can operate on high supply voltages determined

by the breakdown voltage of the N-channel JFET.

+VS

–VS

SST111

VISHAY

VIN

GND

VOUT

ADR420/

ADR421/

ADR423/

ADR425

2N3904

2.10kΩ

OP09

Figure 42. High Voltage Floating Current Source

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