MICRF102

Micrel

MICRF102

6

December 2006

Functional Description

The block diagram illustrates the basic structure of the

MICRF102. Identified in the figure are the principal functional

blocks of the IC, namely the (1, 2, 3, 4, 5) UHF Synthesizer,

(6a/b) Buffer, (7) Antenna tuner, (8) Power amplifier, (9) TX

bias control, (10) Reference bias and, (11) Process tuner.

The UHF synthesizer generates the carrier frequency with

quadrature outputs. The in-phase signal (I) is used to drive

the PA and the quadrature signal (Q) is used to compare the

antenna signal phase for antenna tuning purposes.

The Antenna tuner block senses the phase of the transmit

signal at the antenna port and controls the varactor capacitor

to tune the antenna.

The Power control unit senses the antenna signal and con-

trols the PA bias current to regulate the antenna signal to

the transmit power.

Block Diagram

TX

Bias

Control

Varactor

Device

Antenna

Tuning

Control

Power

Amp

Buffer

VSS

ANTM

ANTP

ASK

Buffer

Prescaler

Divide

by 32

REF.OSC

PC

VDD

VDD

(10)

(5)

(2)

Reference

Oscillator (1)

VCO (4)

(3)

(9)

(8)

(7)

(11)

(6a)

(6b)

STBY

Reference

Bias

Phase

Detector

The Process tune circuit generates process independent bias

currents for different blocks.

A PCB antenna loop coupled with a resonator and a resistor

divider network are all the components required to construct

a complete UHF transmitter for remote actuation applications

such as automotive keyless entry.

Included within the IC is a differential varactor that serves

as the tuning element to insure that the transmit frequency

and antenna are aligned with the receiver over all supply and

temperature variations.