MICRF219 datasheet(12/24 Pages) MICREL

12 / 24 page

Micrel

MICRF219

January 2009

M9999-011509

(408) 944-0800

Application Information

219BP

n Exam

, 433.92 MH

R21

ures

CB pictures. The QR219BPF is a good s

point for the prototyping of most applications. Current

options: A wire anten

lso

icatio

mov

ante

Front-End Band Pass Filter

Components L1 and C8 form the band-pass filter at

front of the receiver. Its purpose is to attenuate

undesired outside band noise that degrades the

receiver performance. It is calculated by the parallel

resonance

equation:

f = 1/(2×PI×(SQRT L1×C8)).

Table 2 shows the component values for most

often used frequencies.

Figure 4. QR

Antenna and RF Port Connections

Figure 4 shows the schematic of the Q

configured for 433.29 MHz operation. Fig

are P

F Applicatio

ple

9BPF

19-23

tarting

design offers two antenna

na or

SMA antenna. The SMA connection a

an RF signal to be injected for test or verif

use an antenna such as a 50

Ω whip, re

SMA and solder the whip antenna in the hole

PCB instead. A wire of 22AWG with 167mm (6.

allows

n. To

e the

on the

-inch)

nna is

can be used as a substitution if low cost

needed.

Freq (MHz)

C8 (pF)

L1(nH)

315.0

6.8

390.0

6.8

418.0

6.0

433.92

5.6

ilter values for various

emoved if the outside

blem. The MICRF219

rs which improve the

e band noise.

Low-Noise Amplifier Input Matching

Capacitor C3 and inductor L2 form the “L” shape input

matching network. The capacitor provides additional

attenuation for low-frequency outside band noise.

The inductor provides additional ESD protection for

the antenna pin. Two methods can be used to find

these values that best matched near 50Ω. One

method is done by calculating the values using the

equations below and the other is using a Smith chart

utility. The latter is made easier via a software plot

where components are added on. In this way, the user

Table 2. Front Band-Pass F

frequencie

This band-pass filter can be r

band noise does not cause a pro

has built-in image reject mixe

selectivity significantly and reject outsid

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