Micrel
MICRF211
Functional Diagram
Figure 1. Simplified Block Diagram.
Functional Description
basic structure of the MICRF211. It is made of three
sub-blocks; Image Rejection UHF Down-converter, the
OOK Demodulator, and Reference and Control Logics.
Outside the device, the MICRF211 requires only three
components to operate: two capacitors (CTH, and
CAGC) and the reference frequency device, usually a
quartz crystal. An additional five components may be
used to improve performance. These are: power supply
decoupling capacitor, two components for the matching
network, and two components for the pre-selector band
pass filter.
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 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 passes through a
third order band pass filter. The IF center frequency is
1.2MHz. The IF BW is 330kHz @ 433.92MHz, and this
varies with RF operating frequency. The IF BW can be
calculated via direct scaling:
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
March 2007
6
BW
IF
= BW
IF@433.92 MHz
×
⎜
⎛
Operating Freq (MHz)
⎞
⎟
433.92
⎠
⎝
These filters are fully integrated inside the MICRF211.
After filtering, four active gain controlled amplifier stages
enhance the IF signal to proper level for demodulation.
OOK Demodulator
The demodulator section is comprised of detector,
programmable low pass filter, slicer, and AGC
comparator.
Detector and Programmable Low-Pass Filter
The demodulation starts with the detector removing the
M9999-030107
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MICREL [ MICREL SEMICONDUCTOR ]
