MICRF002_08 datasheet(11/17 Pages) MICREL

11 / 17 page

Micrel, Inc.

MICRF002/RF022

July 2008

M9999-070808

Additional Applications Information

In addition to the basic operation of the MICRF002 the

following enhancements can be made. In particular it is

strongly recommended that the antenna impedance is

matched to the input of the IC.

Antenna Impedance Matching

As shown in Table 4 the antenna pin input impedance is

frequency dependant. The ANT pin can be matched to 50Ω

with an L-type circuit. That is, a shunt inductor from the RF

input to ground and another in series from the RF input to

the antenna pin.

Inductor values may be different from table depending on

PCB material, PCB thickness, ground configuration, and

how long the traces are in the layout. Values shown were

characterized for a 0.031 thickness, FR4 board, solid

ground plane on bottom layer, and very short traces.

MuRata and Coilcraft wire wound 0603 or 0805 surface

mount inductors were tested, however any wire wound

inductor with high SRF (self resonance frequency) should

do the job.

Shutdown Function

Duty-cycled operation of the MICRF002 (often referred to

as polling) is achieved by turning the MICRF002 on and off

via the SHUT pin. The shutdown function is controlled by a

logic state applied to the SHUT pin. When VSHUT is high,

the device goes into low-power standby mode. This pin is

pulled high internally, it must be externally pulled low to

enable the receiver.

LSHUNT

LSERIES

j100

j25

∞

–j25

–j100

Frequency

(MHz)

ZIN

Z11

S11

LSHUNT(nH)

LSERIES(nH)

300

12-j166

0.803-j0.529

305

12-j165

0.800-j0.530

310

12-j163

0.796-j0.536

315

13-j162

0.791-j0.536

320

12-j160

0.789-j0.543

325

12-j157

0.782-j0.550

330

12-j155

0.778-j0.556

335

12-j152

0.770-j0.564

340

11-j150

0.767-j0.572

345

11-j148

0.762-j0.578

350

11-j145

0.753-j0.586

355

11-j143

0.748-j0.592

360

11-j141

0.742-j0.597

365

11-j139

0.735-j0.603

370

10-j137

0.732-j0.612

375

10-j135

0.725-j0.619

380

10-j133

0.718-j0.625

385

10-j131

0.711-j0.631

390

10-j130

0.707-j0.634

395

10-j128

0.700-j0.641

400

10-j126

0.692-j0.647

405

10-j124

0.684-j0.653

410

10-j122

0.675-j0.660

415

10-j120

0.667-j0.667

420

10-j118

0.658-j0.673

425

10-j117

0.653-j0.677

430

10-j115

0.643-j0.684

435

10-j114

0.638-j0.687

440

8-j112

0.635-j0.704

8.2

Table 4. Input Impedance vs. Frequency

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