RFRXD0420T-I/LQ Microchip Technology, RFRXD0420T-I/LQ Datasheet - Page 11

• Manufacturer Part Number: RFRXD0420T-I/LQ
• Description: IC RCVR 315/433MHZ ASK/FSK32LQFP
• Manufacturer: Microchip Technology

Specifications of RFRXD0420T-I/LQ

• Frequency: 300MHz ~ 450MHz
• Sensitivity: -106dBm
• Data Rate - Maximum: 80 kbps
• Modulation Or Protocol: ASK, FM, FSK
• Applications: Home Automation, Remote Sensing, RKE
• Current - Receiving: 9.2mA
• Data Interface: PCB, Surface Mount
• Antenna Connector: PCB, Surface Mount
• Voltage - Supply: 2.5 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 32-LQFP
• For Use With: DV164102 - KIT DEV RFPICKIT KIT 1
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Features: -
• Memory Size: -

3.1.3
An external PLL loop filter is connected to pin LF
(Pin 29). The loop filter controls the dynamic behavior
of the PLL, primarily lock time and spur levels. Gener-
ally, the PLL lock time is a small fraction of the overall
receiver start-up time (see Electrical Characteristics
Section). The crystal oscillator is the largest contributor
to start-up time. Thus, for the majority of applications,
design loop filter values for a wide loop bandwidth to
suppress noise. Figure 3-4 illustrates an example filter
circuit for a wide frequency range suitable for a majority
of applications.
FIGURE 3-4:
3.1.4
Receiver performance is heavily influenced by the
preselector (also known as the front-end filter). The
purpose of the preselector is to filter unwanted signals
and noise from entering the receiver.
The most important unwanted signal is the image
frequency (f
image frequency calculated in Figure 3-3 as this will be
the frequency that needs to be filtered out by the
preselector.
The preselector can be designed using a simple LC
filter or a Surface Acoustic Wave (SAW) filter. A simple
LC filter provides a low cost solution but will have the
least effect filtering the image frequency. A SAW filter
can effectively filter the image frequency with a
minimum of 40 dB attenuation.
FIGURE 3-5:
 2003 Microchip Technology Inc.
PLL LOOP FILTER
PRESELECTOR
OPTIONAL
rf-image
PLL LOOP FILTER EXAMPLE
CIRCUIT
SAW FILTER EXAMPLE CIRCUIT
). Pay particular attention to the
C2
Antenna
Note:
29
R1
10 kΩ
C1
1000 pF
Refer to SAW filter manufacturer’s data sheet for pin outs
and values for impedance matching components.
C1
L1
2
1
Preliminary
Input
Input Gnd
F1
3
4
Case Gnd
SAW Filter
Output Gnd
7
Output
8
The SAW filter has the added advantage of filtering
wide-band noise and improving the signal-to-noise
ratio (SNR) of the receiver.
SAW filters require impedance matching. Refer to the
manufacturers' data sheet and application notes for
SAW filter pinouts, specified impedances and recom-
mended matching circuits. Figure 3-5 shows a SAW
filter example circuit.
A secondary purpose of the preselector is to provide
impedance matching between the antenna and LNA
(Pin 31).
3.1.5
Receiver performance and device packaging influence
antenna selection. There are many third-party anten-
nas to choose from. Third-party antennas typically
have an impedance of 50 Ω. The preselector compo-
nents should be chosen to match the impedance of the
antenna to the LNA
26 Ω || 2 pF.
The designer can chose to use a simple wire antenna.
The length of the wire should be one-quarter the wave-
length (λ) of the receive frequency. For example, the
wavelength of 433.92 MHz is:
therefore
Finally, the wire antenna should be impedance
matched to the preselector. The typical impedance of a
one-quarter wavelength wire antenna is 36 Ω.
3.1.6
For a majority of applications, LNA
Vss (ground) enabling High Gain mode. If the applica-
tion requires short range communications, LNA
can be tied to V
More Information on LNA
in the Circuit Description section.
5
6
λ = c / f
λ = 3 x 10
λ = 0.69 m
0.25λ = 17.3 cm or 6.8 inches
ANTENNA
LNA GAIN
rfRXD0420/0920
L2
rf
DD
where c = 3 x 10
8
(pulled up) enabling Low Gain mode.
m/s / 433.92 x 10
C2
IN
LNA
GAIN
IN
(Pin 31) impedance of
operation can be found
8
m/s
GAIN
6
DS70090A-page 11
Hz
can be tied to
GAIN
IN