Micrel, Inc.
MICRF002/RF022
Functional Diagram
CAGC
C
AGC
5th Order
Band-Pass Filter
AGC
Control
2nd Order
Programmable
Low-Pass Filter
Switched-
Capacitor
Resistor
R
SC
Compa-
rator
DO
ANT
RF
Amp
f
RX
f
LO
f
IF
IF
Amp
430kHz
IF
Amp
Peak
Detector
VDD
VSS
Synthesizer
UHF Downconverter
SEL0
SEL1
SWEN
SHUT
f
T
REFOSC
Cystal
or
Ceramic
MICRF002
Resonator
Reference
Oscillator
Reference and Control
Wakeup
Control
Logic
Resettable
Counter
OOK Demodulator
CTH
C
TH
WAKEB
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 C
TH
capacitor
4. Select the C
AGC
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
7
M9999-070808
July 2008
MICREL [ MICREL SEMICONDUCTOR ]
