March 2003

11

MICRF002/RF022

MICRF002/RF022

Micrel

Additional Applications Information

In addition to the basic operation of the MICRF002 the

following enhancements can be made. In particilar 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 50 Ohms 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 charac-

terized 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 V

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

high internally, it must be externally pulled low to enable the

receiver.

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6

1

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2

5

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0

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0

8

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5

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6

1

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2

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3

5

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0

j

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0

0

8

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05

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7

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6

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16

3

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0

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6

9

7

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1

9

7

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05

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7

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5

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5

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0

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8

4

7

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02

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0

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4

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1

13

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0

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5

3

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1

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3

7

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02

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1

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1

6

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0

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2

7

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02

17

4

0

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3

1

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15

2

6

.

0

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8

1

7

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00

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4

5

8

31

3

1

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11

3

6

.

0

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1

1

7

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17

4

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30

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1

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14

3

6

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0

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7

0

7

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00

13

4

5

9

38

2

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11

4

6

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0

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0

7

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13

4

0

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1

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4

6

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2

9

6

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00

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5

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13

5

6

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0

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–

4

8

6

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00

19

3

0

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42

2

1

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–

0

10

6

6

.

0

j

–

5

7

6

.

00

19

3

5

1

40

2

1

j

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0

17

6

6

.

0

j

–

7

6

6

.

00

19

3

0

2

48

1

1

j

–

0

13

7

6

.

0

j

–

8

5

6

.

00

16

3

5

2

47

1

1

j

–

0

17

7

6

.

0

j

–

3

5

6

.

00

16

3

0

3

45

1

1

j

–

0

14

8

6

.

0

j

–

3

4

6

.

00

13

3

5

3

44

1

1

j

–

0

17

8

6

.

0

j

–

8

3

6

.

00

13

3

0

4

42

1

1

j

–

84

0

7

.

0

j

–

5

3

6

.

02

.

83

3

j100

j25

∞

50

0

–j25

–j100

Table 4. Input Impedance Versus Frequency