 2015 Microchip Technology Inc.

Preliminary

DS50002416A-page 19

MICRF114

4.0

APPLICATION CIRCUIT

4.1

50-ohm Matching Example

Figure 4-1 shows the RF section of the MICRF114

application circuit. The VSS pin potential is the ground

reference for the whole circuit. The supply voltage

(1.8V to 3.6V) is connected to the VDD pin. Capacitors

C5 and C6 provide supply bypass (filtering). In every

application, the MICRF114 has to be controlled by an

MCU via the proprietary serial interface (SDI and SCK

pins). The quartz crystal (X1) connected to the OSC pin

determines the operating frequency which is 32 times

the crystal resonance frequency.

The matching network (L1, L2, C1, and C2) provides

optimum power transfer from the MICRF114 to the

antenna. The filter stage (L3, C3, and C4) removes the

unwanted

harmonics.

The

required

harmonic

suppression depends on the operating frequency,

antenna characteristics, and regional regulations. This

means the order of the filter (the number of

components) may be different in an actual application

with an integrated antenna.

Table 4-1 shows the values of the frequency-

dependent components for the two most popular

frequencies. Except for L1, it is recommended to use

0402 SMD components in the matching and filter

network.

FIGURE 4-1:

SCHEMATIC DIAGRAM

TABLE 4-1:

COMPONENT VALUES

Component

Frequency

315 MHz

433 MHz

X1

9.84375 MHz

13.56 MHz

L2

39 nH

22 nH

C1

9.1 pF

6.8 pF

C2

9.1 pF

5.6 pF

C3

12 pF

8.2 pF

L3

27 nH

18 nH

C4

12 pF

8.2 pF

Note:

This is a suggested schematic diagram only. Component values for C1 to C4 and L2 to L3 vary according

to operating frequency, antenna characteristics, and regional regulations. Certain components can be

removed.

OSC

SCK

SDI

VDD

RFO

VSS

From MCU

Filtering

Matching

C5

4.7 nF

C6

470 pF

L1

L2

C2

C1

Supply

L3

C3

C4

50 ohm

RF Output

X1

220 nH