MICRF219 datasheet(7/23 Pages) MICREL

7 / 23 page

Micrel

MICRF219

June 2011

M9999-060811

(408) 944-0800

iagram, shown in Figure 1,

cture of the MICRF219 receiver.

ub-blocks:

tor

(

ditional five components

nce; a power supply d

omponents for the matching

nts: LNA,

and Synthesizer

n by quadra re

lock.

place

l to a ow

the IF

scillat

e cy via a

er with a fully integrated

loop filter.

Image-Reject Filter and Band-Pass Filter

ports of the mixer produce quadrature-down

converted IF signals. These IF signals are low-pass

filtered to remove higher frequency products prior to the

image reject filter where they are combined to reject the

image frequencies. The IF signal then passes through a

third order band pass filter. The IF center frequency is

1.2MHz. The IF BW is 330kHz @ 433.92MHz. This

varies with RF operating frequency.

The IF BW can be calculated via direct scaling:

BWIF

IF@433.92 MHz ×

Functional Description

The simplified block d

illustrates the basic stru

It is made up of four s

•

UHF Down-converter

•

OOK Demodula

•

Reference and Control logic

•

Auto-poll circuitry

Outside the device, the MICRF219 receiver re

three components to operate: two capacitors

CAGC) and the reference frequency device

quires just

CTH, and

(usually a

quartz crystal). An ad

to improve performa

are used

ecoupling

network,

and-pass

capacitor, two c

and two components for the pre-selector

filter.

Receiver Operation

UHF Downconverter

The UHF down-converter has six compone

mixers, synthesizer, image reject filter, ban pass filter

and IF amp.

LNA

The RF input signal is AC-coupled into the ga

the grounded source LNA input stage. The

Cascoded NMOS amplifier. The amplified R

then fed to the RF ports of two double balanc

Mixers

e circuit of

LNA is a

signal is

d mixers.

The LO ports of the Mixers are drive

local oscillator outputs from the synthesizer b

local oscillator signal from the synthesizer is

the low side of the desired RF signa

suppression of the image frequency at tw

frequency below the wanted signal. The loc

is set to 32 times the crystal reference frequ

phase-locked loop synthesiz

d on

l o

The IF

= BW

⎟

⎞

⎜

⎛

(MHz)

Freq

Operating

These filters

side the MICRF219.

r filt

rolled amplifier stages

ts proper level for

mprised of detector,

, slicer, and AGC

-Pass Filter

detector removing the

t detection, the signal

. The programmable

filter

further

enhances

the

baseband

information.

There are four programmable low-pass

ttings: 1625Hz, 3250Hz, 6500Hz, 13000Hz

for 433.92MHz operation. Low pass filter BW will vary

with RF Operating Frequency. Filter BW values can be

. See equation below

WOperating Freq = BW@433.92MHz*

⎠

⎝

433.92

are fully integrated in

ering, four active gain cont

Afte

enhance the IF signal to i

demodulation.

OOK Demodulator

The demodulator section is co

programmable low pass filter

comparator.

Detector and Programmable Low

The demodulation starts with the

carrier from the IF signal. Pos

becomes base band information

low-pa

filter BW se

easily calculated by direct scaling

for filter BW calculation:

⎟

⎠

⎞

⎜

⎝

⎛ O

433.92

(MHz)

Freq

perating

very important to choose filter setting that fits best

e in

data rate to minimize data distortion.

3000Hz @ 433.92MHz as default

nd SEL1 pins are floating). The

hardware set by external pins

SEL0 and SEL1.

SEL0

SEL1

Demod BW (@ 434MHz)

It is

tended

(assu

od BW is set at 1

ming both SEL0 a

low pass filter can be

1625Hz

3250Hz

6500Hz

13000Hz

- default

Table 1. Demodulation BW Selection

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