micrf218 Micrel Semiconductor, micrf218 Datasheet - Page 10

• Manufacturer Part Number: micrf218
• Description: Micrf218 3.3v, Qwikradio 300 Mhz To 450 Mhz Receiver
• Manufacturer: Micrel Semiconductor

September 2007
Micrel
Functional Description
Figure 1 illustrates the basic structure of the
MICRF218. It is composed of three sub-blocks; Image
Rejection UHF Down-converter with Switch-able Dual
IF Bandwidths, the OOK Demodulator, and Reference
and Control Logics.
Outside the device, the MICRF218 requires only three
components to operate: two capacitors (CTH, and
CAGC) and the reference frequency device, usually a
quartz crystal.
Additional five components may be used to improve
performance. These are: low cost linear regulator
decoupling
matching network, and two components for the pre-
selector band pass filter.
IF_BW
SHDN
VDD
VSS
SEL0
SEL1
ANT
capacitor,
Amp
RF
Reference and Control
f
c
two
SYNTHESIZER
f
LO
components
mixer
mixer
UHF Downconverter
Wide / Narrow
Figure 1 Simplified Block Diagram
RO1
IF_BW
REJECT
FILTER
IMAGE
for
OSCILLATOR
REFERENCE
CONTROL
-f
Crystal
LOGIC
i
the
f
RO2
10
DO
Amp
CONTROL
IF
LOGIC
Receiver Operation
LNA
The RF input signal is AC-coupled into the gate circuit
of the grounded source LNA input stage. The LNA is
a Cascoded NMOS.
Mixers and Synthesizer
The LO ports of the Mixers are driven by quadrature
local oscillator outputs from the synthesizer block.
The local oscillator signal from the synthesizer is
placed on the low side of the desired RF signal to
allow suppression of the image frequency at twice the
IF frequency below the wanted signal. The local
oscillator is set to 32 times the crystal reference
frequency via a phase-locked loop synthesizer with a
fully integrated loop filter.
Image Reject Filter and IF Band-Pass Filter
The IF ports of the mixer produce quadrature down
converted IF signals. These IF signals are low-pass
filtered to remove higher frequency products prior to
the image reject filter where they are combined to
reject the image frequencies. The IF signal then
Low Pass Filter
Programmable
Detector
CONTROL
LOGIC
Slicing
Level
SLICER
Demodulator
RSSI
AGC
OOK
[phone]
M9999-090607
CAGC
RSSI
DO
CTH
MICRF218