Micrel

MICRF009

January 18, 2005

12

M9999-011805

(408) 955-1690

Additional Applications Information

In addition to the basic operation of the MICRF009, 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 Figure 7, and Table 4, the antenna pin input

impedance is frequency dependent.

The ANT pin can be matched to 50Ω with an L-type circuit

as shown in Figure 3. That is, a shunt inductor from the

antenna input to ground and another in series from the

antenna input to the ANT pin.

Inductor values may be different from Table 4, 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 MICRF009 (often referred to

as polling) is achieved by turning the MICRF009 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, and it must be externally pulled low

to enable the receiver.

j100

j25

∞

50

0

–j25

–j100

Figure 7

Frequency

(Mhz)

S11

Mag, angle

Z11, ohms

C3, pF

L2, nH

300

0.944,-36.65

14.45-j150

2.2

47

305

0.940,-37.499

14.84-j145

2.2

47

310

0.942,-37.579

14.28-j145

2.2

47

315

0.945, -37.66

13.48-j145

2.2

47

320

0.943,-38.237

13.58-j143

2

47

325

0.942, -38.814

13.43-j140

1.8

47

330

0.94, -39.39

13.5-j138

1.8

47

335

0.938, -39.967

13.59-j136

1.8

43

340

0.937, -40.544

13.44-j134

1.8

43

345

0.935, -41.12

13.51-j132

1.8

43

350

0.933, -41.697

13.57-j130

2

39

355

0.931, -42.274

13.62-j123

2.2

36

360

0.93, 42.85

13.48-j126

2.2

36

365

0.928, -43.427

13.52-j124

2

36

370

0.926, -44.004

13.57-j122

1.8

36

375

0.925, -44.581

13.42-j120

2.2

33

380

0.923, -45.157

13.46-j118

2

33

385

0.921, -45.734

13.49-j117

1.8

33

390

0.92, -46.311

13.35-j115

1.8

33

395

0.917, -46.729

13.6-j114

1.8

33

400

0.914, -47.148

13.89-j113

2

30

405

0.912, -47.566

14.00-j112

1.8

30

410

0.909, -47.985

14.25-j110

1.8

30

415

0.907, -48.403

14.34-j109

2.2

27

420

0.906, -48.797

14.28-j108

2

27

425

0.909, -49.152

13.63-j107

2

27

430

0.911, -49.507

13.15-j107

1.8

27

435

0.911, -49.925

12.94-j106

1.8

27

440

0.904, -50.571

13.66-j104

1.8

27

Table 4