May 13, 2004

1

M9999-051304

MICRF505

Micrel

MICRF505

868MHz and 915MHz ISM Band Transceiver

General Description

The MICRF505 is a true single chip, frequency shift keying

(FSK) transceiver intended for use in half-duplex, bidirec-

tional RF links. The multi-channeled FSK transceiver is

intended for UHF radio equipment in compliance with the

North American Federal Communications Commission (FCC)

part 15.247 and 249, as well as the European Telecommuni-

cation Standard Institute (ETSI) specification, EN300 220.

The transmitter consists of a PLL frequency synthesizer and

a power amplifier. The frequency synthesizer consists of a

voltage-controlled oscillator (VCO), a crystal oscillator, dual

modulus prescaler, programmable frequency dividers, and a

phase-detector. The loop-filter is external for flexibility and

can be a simple passive circuit. The output power of the

power amplifier can be programmed to seven levels. A lock-

detect circuit detects when the PLL is in lock. In receive mode,

the PLL synthesizer generates the local oscillator (LO) signal.

The N, M , and A values that give the LO frequency are stored

in the N0, M0, and A0 registers.

The receiver is a zero intermediate frequency (IF) type which

makes channel filtering possible with low-power, integrated

low-pass filters. The receiver consists of a low noise amplifier

(LNA) that drives a quadrature mixer pair. The mixer outputs

feed two identical signal channels in phase quadrature. Each

channel includes a pre-amplifier, a third order Sallen-Key RC

low-pass filter that protects the following switched-capacitor

filter from strong adjacent channel signals, and a limiter. The

main channel filter is a switched-capacitor implementation of

a six-pole elliptic low pass filter. The cut-off frequency of the

Sallen-Key RC filter can be programmed to four different

frequencies: 100kHz, 150kHz, 230kHz, and 340kHz. The I

and Q channel outputs are demodulated and produce a

digital data output. The demodulator detects the relative

phase of the I and the Q channel signal. If the I channel signal

lags behind the Q channel, the FSK tone frequency is above

the LO frequency (data ‘1’). If the I channel leads the Q

channel, the FSK tone is below the LO frequency (data ‘0’).

The output of the receiver is available on the DataIXO pin. A

receive signal strength indicator (RSSI) circuit indicates the

received signal level. All support documentation can be

found on Micrel’s web site at www.micrel.com.

Features

• True single chip transceiver

• Digital bit synchronizer

• Received signal strength indicator (RSSI)

• RX and TX power management

• Power down function

• Reference crystal tuning capabilities

• Baseband shaping

• Three-wire programmable serial interface

• Register read back function

Applications

• Telemetry

• Remote metering

• Wireless controller

• Remote data repeater

• Remote control systems

• Wireless modem

• Wireless security system

Ordering Information

Part Number

Junction Temp. Range

Package

MICRF505BML

–40

∞C to +85∞C

32-Pin MLF™

Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com