MICRF219AYQS(2009) 데이터 시트보기 (PDF) - Micrel

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MICRF219AYQS
(Rev.:2009)

300MHz to 450MHz ASK Receiver with RSSI, Auto-Poll, Bit-Check and Squelch

Micrel 

Micrel

MICRF219

suppression of the image frequency at twice the IF

frequency below the wanted signal. The local oscillator

is set to 32 times the crystal reference frequency via a

phase-locked loop synthesizer with a fully integrated

loop filter.

Image-Reject Filter and Band-Pass Filter

The IF 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

=

BWIF@433.92 MHz ×

⎜⎛ Operating Freq (MHz) ⎟⎞

⎝

433.92

⎠

These filters are fully integrated inside the MICRF219.

After filtering, four active gain controlled amplifier stages

enhance the IF signal to its proper level for

demodulation.

OOK Demodulator

The demodulator section is comprised of detector,

programmable low pass filter, slicer, and AGC

comparator.

Detector and Programmable Low-Pass Filter

The demodulation starts with the detector removing the

carrier from the IF signal. Post detection, the signal

becomes base band information. The programmable

low-pass filter further enhances the baseband

information. There are four programmable low-pass

filter BW settings: 1625Hz, 3250Hz, 6500Hz, 13000Hz

for 433.92MHz operation. Low pass filter BW will vary

with RF Operating Frequency. Filter BW values can be

easily calculated by direct scaling. See equation below

for filter BW calculation:

BWOperating Freq = BW@433.92MHz*

⎜⎛ Operating Freq (MHz) ⎟⎞

⎝

433.92

⎠

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.

SEL0

0

1

0

1

SEL1

0

0

1

1

Demod BW (@ 434MHz)

1625Hz

3250Hz

6500Hz

13000Hz - default

Table 1. Demodulation BW Selection

Slicer and Slicing Level

The signal, prior to the slicer, is still AM. The data slicer

converts the AM signal into ones and zeros based on

the threshold voltage built up in the CTH capacitor.

After the slicer, the signal is ASK or OOK digital data.

The slicing threshold is default at 50%. The slicing

threshold can be set via serial programming through

register D5 and D6.

D5

D6

Slicing Level

1

0

Slice Level 30%

0

1

Slice Level 40%

1

1

Slice Level 50% - default

0

0

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.

January 2009

7

M9999-011509

(408) 944-0800

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