MICRF102
Micrel
MICRF102
6
September 2002
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 purpose.
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.
Functional 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
Figure 2. MICRF102 Block Diagram
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.
