MICRF002_08 datasheet(7/17 Pages) MICREL

7 / 17 page

Micrel, Inc.

MICRF002/RF022

July 2008

M9999-070808

Functional Diagram

Peak

Detector

AGC

Control

2nd Order

Programmable

Low-Pass Filter

5th Order

Band-Pass Filter

Synthesizer

Control

Logic

RSC

Resettable

Counter

Reference

Oscillator

Cystal

Ceramic

Resonator

CAGC

ANT

SEL0

VDD

VSS

SEL1

SWEN

REFOSC

430kHz

Switched-

Capacitor

Resistor

WAKEB

CTH

MICRF002

Amp

Compa-

rator

Wakeup

Reference and Control

UHF Downconverter

OOK Demodulator

fRX

fLO

fIF

SHUT

CAGC

CTH

Figure 1. MICRF002 Block Diagram

Application Information and Functional

Description

Refer to Figure 1 “MICRF002 Block Diagram”. Identified in

the block diagram are the four sections of the IC: UHF

Downconverter, OOK Demodulator, Reference and

Control, and Wakeup. Also shown in the figure are two

capacitors (CTH, CAGC) and one timing component,

usually a crystal or ceramic resonator. With the exception

of a supply decoupling capacitor, and antenna impedance

matching network, these are the only external components

needed by the MICRF002 to assemble a complete UHF

receiver.

For optimal performance is highly recommended that the

MICRF002 is impedance matched to the antenna, the

matching network will add an additional two or three

components.

Four control inputs are shown in the block diagram: SEL0,

SEL1, SWEN, and SHUT. Using these logic inputs, the

user can control the operating mode and selectable

features of the IC. These inputs are CMOS compatible, and

are internally pulled-up. IF Bandpass Filter Roll-off

response of the IF Filter is 5th order, while the demodulator

data filter exhibits a 2

nd order response.

Design Steps

The following steps are the basic design steps for using the

MICRF002 receiver:

1. Select the operating mode (sweep or fixed)

2. Select the reference oscillator

3. Select the CTH capacitor

4. Select the CAGC capacitor

5. Select the demodulator filter bandwidth

Step 1: Selecting the Operating Mode

Fixed-Mode Operation

For applications where the transmit frequency is accurately

set (that is, applications where a SAW or crystal-based

transmitter is used) the MICRF002 may be configured as a

standard superheterodyne receiver (fixed mode). In fixed-

mode operation the RF bandwidth is narrower making the

receiver less susceptible to interfering signals. Fixed mode

is selected by connecting SWEN to ground.

Sweep-Mode Operation

When used in conjunction with low-cost L-C transmitters

the MICRF002 should be configured in sweep-mode. In

sweep-mode, while the topology is still superheterodyne,

the LO (local oscillator) is swept over a range of

frequencies at rates greater than the data rate. This

technique effectively increases the RF bandwidth of the

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