MICRF219 데이터 시트보기 (PDF) - Micrel

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MICRF219

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

Micrel 

Micrel

MICRF219

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.

Desense

Desense is a function designed to reduce the sensitivity

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.

The de-sense function is accessible only through serial

programming.

D0

D1

0

X

1

0

1

1

1

0

1

1

D2 MODE: Desense

X No Desense - default

0 6dB Desense

0 16dB Desense

1 30dB Desense

1 42dB Desense

Reference Control

There are 2 components in Reference and Control sub-

block: 1) Reference Oscillator and 2) Control Logic

through parallel Inputs: SEL0, SEL1, SHDN

Reference Oscillator

The reference oscillator in the MICRF219 (Figure 2)

uses a basic Pierce crystal oscillator configuration with

MOS transconductor to provide negative resistance.

Though the MICRF219 has build-in load capacitors for

the crystal oscillator, the external load capacitors are still

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

are external pins of the MICRF219 to connect the crystal

to the reference oscillator.

Reference oscillator crystal frequency can be calculated:

FREF OSC = FRF/(32 + 1.1/12)

For 433.92 MHz, FREF OSC = 13.52127 MHz.

To operate the MICRF219 with minimum offset, crystal

frequencies should be specified with 10pF loading

capacitance.

June 2011

8

M9999-060811

(408) 944-0800

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