MICRF221 datasheet(7/26 Pages) MICREL

7 / 26 page

Micrel Inc.

MICRF221

October 2008

M9999-100108

(408) 955-1690

Functional Diagram

SYNTHESIZER

CONTROL

LOGIC

IF AMP

LNA

MIXER

CONTROL

LOGIC

CONTROL

LOGIC

CONTROL

LOGIC

-f

IMAGE

REJECT

FILTER

DESENSE

DETECTOR

OOK

DEMODULATOR

UHF

DOWNCOVERTER

REFERENCE

AND CONTROL

AUTOPOLL

PROGRAMMABLE

FILTER

BITCHECK

WAKE-UP

SQUELCH

SLEEP

TIMER

SLEEP

OSCILLATOR

REFERENCE

OSCILLATOR

AGC

CONTROL

RSSI

CAGC

CTH

SLICE

LEVEL

SLICER

DO'

fLO

Figure 3. Simplified Block Diagram

Functional Description

The simplified block diagram, shown in Figure 3,

illustrates the basic structure of the MICRF221

receiver. It is made of four sub-blocks:

• UHF Down-converter

• OOK Demodulator

• Reference and Control logic

• Auto-poll circuitry.

Outside the device, the MICRF221 receiver requires

just three components to operate: two capacitors

(CTH, and CAGC) and the reference frequency device

(usually

quartz

crystal).

additional

five

components are used to improve performance: a

power supply decoupling capacitor, two components

for the matching network, and two components for the

pre-selector band-pass filter.

Receiver Operation

UHF Downconverter

The UHF down-converter has six components: LNA,

mixers, synthesizer, image reject filter, band pass filter

and IF amp.

LNA

The RF input signal is AC-coupled into the gate circuit

of the grounded source LNA input stage. The LNA is a

Cascoded NMOS amplifier. The amplified RF signal is

then fed to the RF ports of two double balanced

mixers.

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