MICRF219 datasheet(7/24 Pages) MICREL

7 / 24 page

Micrel

MICRF219

January 2009

M9999-011509

(408) 944-0800

ice

l oscill or

32 times the crystal reference frequency via a

ith a fully integr

re-down

IF signal then passes

er band

ss filter. The IF center fre

W is 330kHz @ 33.92M

IF@433.92 MHz ×

suppression of the image frequency at tw

frequency below the wanted signal. The loca

is set to

the IF

phase-locked loop synthesizer w

ated

loop filter.

Image-Reject Filter and Band-Pass Filter

The IF ports of the mixer produce quadratu

converted IF signals. These IF signals ar

filtered to remove higher frequency products

image reject filter where they are combined t

image frequencies. The

low-pass

rior to the

reject the

through a

quency is

third ord

1.2MHz. The IF B

Hz. This

W can be

varies with RF operating frequency. The IF

calculated via direct scaling:

BWIF = BW

⎟

⎞

⎠

⎜

⎝

433.92

)

RF 9.

fier s ages

the IF signal to its proper level

carrier from the IF signal. Post detection, the signal

formation. The prog mmable

seband

e low-pass

z, 13000Hz

W will vary

ted by direct

for filter BW calculation:

BWOperating Freq = BW@433.92MHz*

⎛

(MH

Freq

Operating

These filters are fully integrated inside the MIC

After filtering, four active gain controlled ampli

enhance

for

demodulation.

OOK Demodulator

The demodulator section is comprised of

programmable low pass filter, slicer, a

comparator.

Detector and Programmable Low-Pass Filt

The demodulation starts with the detector re

detector,

nd AGC

oving the

becomes base band in

low-pass

filter

further

enhances

the

information.

There are four programmabl

filter BW settings: 1625Hz, 3250Hz, 6500H

for 433.92MHz operation. Low pass filter B

with RF Operating Frequency. Filter BW val

easily calcula

ues can be

scaling. See equation below

⎟

⎠

⎞

⎜

⎝

⎛

433.92

(MHz)

Freq

Operating

It is very important to choose filter setting that fits best

the intended data rate to minimize data distortion.

Demod BW is set at 13000Hz @ 433.92MHz as default

(assuming both SEL0 and SEL1 pins are floating). The

low pass filter can be hardware set by external pins

SEL0 and SEL1.

SEL1

Demod BW (@ 434MHz)

SEL0

1625Hz

3250Hz

6500Hz

00Hz

- default

130

Table 1. Demodulation BW Selection

till AM. The data slicer

s and zeros based on

the threshold voltage built up in the CTH capacitor.

fter

the signal is ASK or OOK digital data.

d is default at 50%. The slicing

res

set via serial programming through

Slicing Level

Slicer and Slicing Level

The signal, prior to the slicer, is s

converts the AM signal into one

the slicer,

slicing threshol

hold can be

regi ter D5 and D6.

Slice Level 30%

Slice Level 40%

Slice Level 50%

- default

Slice Level 60%

AGC Comparator

The AGC comparator monitors the signal amplitude

from the output of the programmable low-pass filter.

When the output signal is less than 750mV thresh-hold,

1.5µA current is sourced into the external CAGC

capacitor. When the output signal is greater than

750mV, a 15µA current sink discharges the CAGC

capacitor.

The voltage developed on the CAGC

capacitor acts to adjust the gain of the mixer and the IF

amplifier to compensate for RF input signal level

variation.

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