MICRF219AYQS TR【PDF 8/23 页】IC RECEIVER QWIKRADIO 16QSOP

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Sheet目录477

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Micrel

Slicer and Slicing Level

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

MICRF219

The de-sense function is accessible only through serial

programming.

converts the AM signal into ones and ze ros based on

the threshold voltage built up in the CTH cap ac itor.

After the slicer, the signal is ASK or OOK digi tal da ta .

The slicing threshold is default at 50%. The slic ing

threshold ca n b e set via serial programming through

D 6

Slicing Level

D 0

MODE: Desense

No Desense - default

6dB Desense

16dB Desense

30dB Desense

42dB Desense

Slice Leve l 30%

Slice Level 40%

Reference Control

There are 2 components in Referen ce and Control sub-

Slice Level 50%

Slice Level 60%

- default

block: 1) Reference Oscillator and 2) Control Logic

through parallel Inputs: SEL0, SEL 1, SHDN

AGC Comparator

The AGC comparator monitors the signal amplitude

from the output of the programmable low -p ass filter.

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

1.5μA current is sourced into the external CAGC

capaci tor. When the output signal is greater th an

750mV, a 15μA current sink discharges th e CAGC

capacitor. The voltage developed on t he CA GC

capacitor acts to adjust the gain of the mixer a nd the IF

amplifier to compensate for RF input s ig nal level

variation.

Desense

Desense is a function designed to reduce the se nsitivity

of the MICRF219 receiver to a maximum of 45dB for

training the MICRF219 receiver. This is done in order to

recognize an intended transmitter. Very often, a receiver

needs to learn how to recognize a particular transmitter.

It is important for the receiver not to learn the signal of a

stray transmitter near by. The simplest solution is to turn

down the receiver gain, so the receiver only recognizes

the transmitter at close range.

Reference Oscillator

The reference oscillator in the MICRF219 (Figure 2)

uses a b asic Pierce crystal oscillator configuration with

MOS transconductor to provide negative resistance.

Though the MICRF219 has build-in load capacitors for

the crystal oscill ator, the external load capacitors are still

required for tuning it to the right frequency. R01 and R02

are external pins of the MICRF 219 to connect the crystal

to the reference oscillator.

Reference oscillator crystal freque ncy can be calculated:

F REF OSC = F RF /(32 + 1.1/12)

For 433.92 MHz, F REF OSC = 13.52127 MHz.

To operate the MICRF219 with minimum offset, crystal

frequencies should be specified with 10pF loading

capacitance.

June 2011

M9999-060811

(408) 944-0800

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