MICRF213 datasheet(8/16 Pages) MICREL

8 / 16 page

Micrel, Inc.

MICRF213

May 2007

M9999-052307-A

(408) 944-0800

Application Information

+3.3V

1.8pF

ANT2

0.47µF

9.81563MHz

6.8pF

U1 MICRFAYQS

RO1

GNDRF

ANT

GNDRF

VDD

SEL0

SHDN

GND

SEL1

CTH

CAGC

RSSI

RO2

(np)SMA

68nH 5%

RSSI

4.7µF

(np)

+3.3V

(np)

JR2

short

JP3

open

JP1

short

0.1µF

ANT1

Helical PCB Antenna Pattern

39nH 5%

RSSI

GND

+3.3V

RSSI

75nH 2%

Figure 3. QR213HE1 Application Example, 315MHz

The MICRF213 can be fully tested by using one of the

many evaluation boards designed by Micrel and

intended for use with this device. As an entry level,

the QR213HE1 (reference Figure 3) offers a good

start for most applications. It has a helical PCB

antenna with its matching network, a band-pass-filter

front-end as a pre-selector filter, matching network

and the minimum components required to make the

device work. The minimum components are a crystal,

Cagc, and Cth capacitors. By removing the matching

network of the helical PCB antenna (C9 and L3), a

whip antenna (ANT2) or a RF connector (J2) can be

used instead. Figure 3 shows the entire schematic for

315MHz. Other frequencies can be used and the

values needed are listed in the tables below.

Capacitor C9 and inductor L3 are the passive

elements for the helical PCB matching network. It is

recommended that a tight tolerance be used for these

devices; such as 2% for the inductor and 0.1pF for the

capacitor. PCB variations may require different values

and optimization. Table 2 shows the matching

elements

for

the

device

frequency

range.

For

additional information, reference the: Small PCB

Antennas for Micrel RF Products application note.

Freq (MHz)

C9 (pF)

L3 (nH)

303.825

1.2

315

1.2

345

1.2

Table 2. Matching Values for the Helical PCB Antenna

To use another antenna, such as the whip kind, remove

C9 and place the whip antenna in the hole provided in

the PCB. Also, a RF signal can be injected there.

L1 and C8 form the pass-band-filter front-end. Its

purpose is to attenuate undesired outside band noise

which

reduces

the

receiver

performance.

calculated

the

parallel

resonance

equation

f = 1/(2*PI*(SQRT(L1*C8)). Table 3 shows the most

used frequency values.

Freq (MHz)

C8 (pF)

L1 (nH)

303.825

6.8

315

6.8

345

5.6

Table 3. Band-Pass-Filter Front-End Values

There is no need for the band-pass-filter front-end for

applications where it is proven the outside band noise

does not cause a problem. The MICRF213 has image

reject mixers which improve significantly the selectivity

and rejection of outside band noise.

Capacitor C3 and inductor L2 form the L-shape

matching network. The capacitor provides additional

attenuation for low frequency outside band noise and

the inductor provides additional ESD protection for the

antenna pin. Two ways can be used to find these

values, which are matched close to 50

Ω. One method

is done by calculating the values using the equations

below and another by using a Smith chart. The latter

is made easier by using software that plots the values

of the components C8 and L1, like WinSmith by Noble

Publishing.

To calculate the matching values, one needs to know

the input impedance of the device. Table 4 shows the

input impedance of the MICRF213 and the suggested

matching values used for the most frequencies.

MICRF213 Datasheet(PDF) 8 Page - Micrel Semiconductor

MICRF213 Datasheet(HTML) 8 Page - Micrel Semiconductor

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Datasheet Download

Link URL