Micrel

MICRF010

June 2005

11

M9999-063005

(408) 955-1690

Additional Applications Information

In addition to the basic operation of the MICRF010, 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

Figure 7. Antenna Pin Input Impedance

Figure 7 and Table 2 presents the antenna pin input

impedance. The Antenna pin can be matched to 50Ω with

a high pass circuit as shown in Figure 8. That is, a shunt

inductor from the ANT Pin to ground and a series capacitor

from ANT Pin to the antenna.

Figure 8. Antenna with Matching Network to ANT Pin

Inductor values may be different from Table 2, 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 inch 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.

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

L2

C3

ANT Pin

Table 2

Shutdown Function

Duty-cycled operation of the MICRF010 (often referred to

as polling) is achieved by turning the MICRF010 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.