MICRF218_11 MICREL [Micrel Semiconductor], MICRF218_11 Datasheet - Page 9

• Manufacturer Part Number: MICRF218_11
• Description: 3.3V, 315/433MHz Wide-IF Bandwidth ASK Receiver
• Manufacturer: MICREL [Micrel Semiconductor]

November 2011
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.
capacitor,
two
components
Figure 1 Simplified Block Diagram
for
the
9
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
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